AU2013205082B2

AU2013205082B2 - Steel product and method of producing the product

Info

Publication number: AU2013205082B2
Application number: AU2013205082A
Authority: AU
Inventors: Graeme Mcgregor
Original assignee: Infrabuild Construction Solutions Pty Ltd
Current assignee: Infrabuild Construction Solutions Pty Ltd
Priority date: 2013-04-13
Filing date: 2013-04-13
Publication date: 2017-04-27
Anticipated expiration: 2033-04-13
Also published as: KR102427244B1; AU2021202437A1; AU2014252700A1; CN110331346A; JP2019178424A; AU2013205082A1; AU2019201022B2; JP2022046474A; NZ712644A; CN105164282A; SG11201507872VA; US20180202014A1; AU2019201022A1; WO2014165934A1; BR112015025895A2; EP2984190A4; CN105164282B; EP2984190A1; CA2908922A1; US20160068925A1

Abstract

A method of producing a steel product includes heat treating a mechanically worked steel product and 5 increasing the ductility and maintaining or increasing the yield stress of the steel. 4255953_1 (GHMatters) P93465.AU 13/04/13

Description

2013205082 05 Apr 2017 1

STEEL PRODUCT AND METHOD OF PRODUCING THE PRODUCT

The present, invention relates to a steel product for use in the mining and construction industries. 5

The present invention also relates to a method of producing the steel product.

The steel may be any one of low carbon steel, 10 medium carbon steel and high strength low alloy steel (which is also described in the steel industry as a microalloy steel).

The term "low carbon steel" is understood herein 15 to mean steel having less than 0.3 wt.% C, other elements such as Si and Mn that are added as deliberate additions to the steel, residual/incidental impurities, and balance Fe. 20 The term "medium carbon steel" is understood herein to mean steel having 0.3-0.6 wt.% C, other elements such as Si and Mn that are added as deliberate additions to the steel, residual/incidental impurities, and Balance Fe. 25

The term "residual/incidental impurities" covers elements such as Cu, Sn, Mo, Al, Zn, Ni, and Cr that may be present in very small concentrations, not as a consequence of specific additions of these elements but as 30 a consequence of standard steelmaking practices. For example, the elements may be present as a consequence of the use of scrap steel to produce low carbon and medium carbon steels. 35 The term "high strength low alloy steel" is understood herein to mean steel of the following composition, in wt.%: 8919523J (GHMatters) P93465.AU 5/04/17 2 2013205082 05 Apr 2017 C: 0.07-0.30;

Si: 0.9 or less;

Mn: 2.0 or less;

Mo: 0.35 or less; 5 Ti: 0.1 or less; V: 0.1 or less;

Nb: 0.1 or less;

Cu: 0.1 or less; N: 0.02 or less; 10 S: 0.05 or less;

Al: 0.05 or less;

Residual/incidental impurities: 1.0 or less; and Fe: balance. 15 The term "residual/incidental impurities" in the context of high strength low alloy steels is understood as described above in relation to low and medium carbon steels. The concentrations of elements such as Cu and Mo in the table in the preceding paragraph are total 20 concentrations, i.e. the concentrations of these elements as a total of deliberate additions and residual/incidental impurities .

The steel product may be any suitable product. 25 The product may be wire, rod, bar, or strip. The steel product may be in the form of a steel product that is made from any one of wire, rod, bar, and strip. The steel product may include any product, including but not limited to reinforcement bar for concrete construction, 30 reinforcement mesh for the concrete construction and mining industries made by welding together spaced-apart parallel line wires and spaced-apart parallel cross-wires, pipe made from steel strip, couplers for coupling together any elongate products such as reinforcing bars, ligatures 35 for reinforcing cages for concrete columns and beams, rock bolts made from steel bar, and other steel products used in tensile or compression applications in the concrete 8919523.1 (GHMatters) P93465.AU 5/04/17 3 2013205082 05 Apr 2017 construction, construction, mining or manufacturing industries .

The present invention is based on a surprising 5 finding that it is possible to treat steel by heating the steel (hereinafter referred to as "heat treatment") that has been mechanically worked (e.g. cold formed) and: (a) increase the ductility (for example, measured as elongation and described in the specification in terms of 10 elongation and known by the term Agt (uniform elongation) when referring to reinforcing steels and often expressed as Agt(-o.5%)), (b) maintain and in many instances increase the yield stress (YS) (often expressed as Proof Stress (PS)for reinforcing steels) and (c) maintain and in many 15 instances increase the tensile strength (TS) of the steel. This is a surprising finding because, as far as the applicant is aware, long established metallurgy teaches that heat treatment of mechanically-worked steel results in an increase in ductility and a decrease in the yield 20 stress and the tensile strength of the steel.

In general terms, the applicant found that steel that had been mechanically worked to reduce the cross-sectional area of the steel by 5—30% and in some instances 25 up to 75% and then heat treated at a temperature in a range of 300-750°C for a time period of 5 minutes to 16 hours maintained and in many instances produced an increase in yield stress of at least 5% relative to that of the mechanically worked steel and an increase in 30 ductility of at least 5% relative to that of the mechanically worked steel. In general terms, the applicant found that mechanically worked steel could be heat treated at higher temperatures and for shorter times or at lower temperatures and for longer times to produce 35 increases in yield stress, tensile strength and ductility.

Typically, and without limiting the scope of the 8919523J (GHMatters) P93465.AU 5/04/17 4 2013205082 05 Apr 2017 present invention, specific steel chemistries and process routes and properties are summarised in the following table .

Steel Chemistry Process Route Cold Work HT Temp and Time YS (PS) - MPa Elongation (Agt) % Ratio TS : YS HSLA Cold work and HT Less than 20% -could be up to 35% 300-700°C and 5 mins -16 hrs Greater than 650 MPa Greater than 5% Low C Cold work and HT 20-25% -could be up to 45% 300-600°C and 5 mins-16 hrs Greater than 500 MPa Greater than 5% Sreater than 1.08:1 Medium C Cold work and HT 20-75% 300-700°C and 5 mins-16 hrs 750-1000 MPa Greater than 5% 5

The present invention is based on an extensive research and development program that has focused on testing a substantial number of samples of low carbon steels, medium carbon steels, and high strength low alloy 10 steels. The samples included samples that were mechanically worked under different conditions and heat treated at different temperatures and for different times. The research and development program is discussed in a later section of the specification in more detail. 15

The present invention provides a method of producing a steel product that includes heat treating a mechanically worked steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the 20 ductility and maintaining or increasing the yield stress of the steel.

The present invention also provides a method of producing a steel product that includes heat treating a 25 mechanically worked steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and maintaining or increasing the yield stress and tensile strength of the steel. 30 Elongation is a measure of ductility. 8919523_1 (GHMatters) P93465.AU 5/04/17 5 2013205082 05 Apr 2017

Elongation is expressed herein as Uniform Elongation - Agt. The term "Uniform Elongation" is understood herein to be a measure of the ability of steel to deform both elastically and plastically before reaching its maximum tensile 5 strength. The numerical amounts for elongation reported in the specification are the elongation of steel in percentage terms measured after the maximum tensile strength of the steel has been reached and dropped to 99.5% of the maximum tensile strength and expressed as Agt(-10 o.5%)· This method is used for reliability of measurement.

The increase in elongation of the heat treated steel relative to that of the mechanically worked steel may be greater than 5%. 15

The increase in elongation of the heat treated steel may be greater than 10%.

The increase in elongation of the heat treated 20 steel may be greater than 15%.

The increase in elongation of the heat treated steel may be greater than 20%. 25 The increase in elongation of the heat treated steel may be greater than 30%.

The increase in elongation of the heat treated steel may be greater than 50%. 30

The increase in elongation of the heat treated steel may be greater than 100%.

The increase in elongation of the heat treated 35 steel may be greater than 150%.

The increase in elongation of the heat treated 8919523.1 (GHMatters) P93465.AU 5/04/17 6 2013205082 05 Apr 2017 steel may be greater than 200%.

The increase in the yield stress of the heat treated steel relative to that of the mechanically worked 5 steel may be greater than 5%. 10 15 20

The increase in the yield stress of the heat treated steel may be greater than 10%. The increase in the yield stress of the heat treated steel may be greater than 15%. The increase in the yield stress of the heat treated steel may be greater than 20%. The increase in the yield stress of the heat treated steel may be greater than 30%. The increase in the yield stress of the heat treated steel may be greater than 40%. The heat treatment step may be carried out at any 25 30 suitable temperature. There are a number of factors that may have an impact on the selection of the heat treatment temperature in any given situation. One factor is heat treatment time. The applicant has also found that each heat treatment temperature has a time window within which the yield stress and ductility are increased to a level above a desired minimum. This window narrows as the heat treatment temperature increases. Another factor is the steel composition. Another factor is the target properties, such as ductility and yield stress.

The heat treatment step may be carried out at a 35 temperature below the austenitising temperature of the steel. 8919523.1 (GHMatters) P93465.AU 5/04/17 7 2013205082 05 Apr 2017

The heat, treatment step may be carried out at a temperature below 750°C.

The heat treatment step may be carried out at a 5 temperature below 700°C.

The heat treatment step may be carried out at a temperature below 600°C. 10 The heat treatment step may be carried out at a temperature below 550°C.

The heat treatment step may be carried out at a temperature below 500°C. 15

The heat treatment step may be carried out at a temperature below 450°C.

The heat treatment step may be carried out at a 20 temperature below 400°C.

The heat treatment step may be carried out at a temperature below 300°C. 25 The heat treatment step may be carried out at a temperature below 250°C.

The heat treatment step may be carried out at a temperature above the austenitising temperature of the 30 steel provided the heat treatment time is selected to be sufficiently short to produce an increase in yield stress and ductility.

The heat treatment step may be carried out for 35 any suitable time. There are a number of factors that may have an impact on the selection of the heat treatment time. As discussed above in relation to heat treatment 8919523J (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 8 temperature, these factors include heat treatment temperature and steel composition and target properties and productivity. 5 The heat treatment step may be carried out for less than 5 hours. 10 20 25 30

The heat treatment step may be carried out for less than 4 hours. The heat treatment step may be carried out for greater than 1 hour. The heat treatment step may be carried out for greater than 45 minutes. The heat treatment step may be carried out for greater than 30 minutes. The heat treatment step may be carried out for greater than 10 minutes. The heat treatment step may be carried out for greater than 5 minutes. The heat treatment step may be carried out for greater than 1 minute. The heat treatment step may be carried out for greater than 30 seconds. The heat treatment step may be carried out in any suitable atmosphere. The atmosphere may be an oxidising atmosphere or a reducing atmosphere. By way of particular example, the heat treatment step may be carried out in air. 8919523.1 (GHMatters) P93465.AU 5/04/17 9 2013205082 05 Apr 2017

The mechanically worked steel product may be any suitable form of product. The mechanically worked steel product may be in the form of any one of wire, rod, bar, or strip. 5

The steel product may be in the form of any one of wire, rod, bar, or strip.

The steel product may be in the form of a steel 10 product that is made from any one of wire, rod, bar, and strip. A non-exclusive range of steel products is set out above. One particular steel product of interest to the applicant is reinforcement mesh for the concrete construction and mining industries made by welding 15 together spaced-apart parallel line wires and spaced-apart parallel cross-wires .

The mechanically worked steel product may be a cold rolled or drawn or any other suitable mechanically 20 worked product that has a reduced transverse cross- sectional area after it has been mechanically worked.

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 75% 25 of the cross-sectional area before the mechanical working step.

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 30 60%.

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 50%. 35

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 8919523J (GHMatters) P93465.AU 5/04/17 10 2013205082 05 Apr 2017 40%.

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 5 35%.

The reduced transverse cross-sectional area of the mechanically worked steel product may be less than 30%. 10

The reduced transverse cross-sectional area of the mechanically worked steel product may be greater than 2%. 15 The reduced transverse cross-sectional area of the mechanically worked steel product may be greater than 5%.

The reduced transverse cross-sectional area of 20 the mechanically worked steel product may be greater than 10%.

The reduced transverse cross-sectional area of the mechanically worked steel product may be greater than 25 15%.

The reduced transverse cross-sectional area of the mechanically worked steel product may be greater than 25%. 30

The method may include cooling the heat treated product from the heat treatment temperature at any suitable cooling rate. For example, the heat treated product may be quenched by being water-cooled. By way of 35 further example, the heat treated product may be cooled in ambient air. The applicant has found that, in general, the cooling rate does not have a significant impact on 8919523.1 (GHMatters) P93465.AU 5/04/17 11 2013205082 05 Apr 2017 properties, namely ductility, yield stress and tensile strength. However, the applicant has found that quenching the heat treated product may have a significant impact on the properties in some situations, such as when 5 quenching from heat treatment temperatures of at least 750°C after a particular time. In one example, after approximately 8 minutes at 750°C there was a sudden increase in tensile strength and a reduction in yield stress and Agt. This response is typical of a steel that 10 is heat treated at a temperature above the austenitising temperature. In this example, there was a heat treatment window of up to 8 minutes for which subsequent quenching had no impact on properties. 15 The steel may be a low carbon steel, as described above.

The steel may be a medium carbon steel, as described above. 20

The steel may be a high strength low alloy steel, as defined above.

The high strength low alloy steel may contain 25 greater than 0.040 wt.% V. The high strength low alloy steel may contain greater than 0.050 wt.% V. 30 The high strength low alloy steel may contain greater than 0.060 wt.% V. The high strength low alloy steel may contain greater than 0.005 wt.% N. 35 The high strength low alloy steel may contain greater than 0.015 wt.% N. 8919523.1 (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 5 10 12

The high strength low alloy steel may contain greater than 0.018 wt.% N.

The present invention provides a method of producing a steel product that includes: (a) mechanically working a feed steel, (b) heat treating the mechanically worked feed steel at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and yield stress of the steel; and (c) forming a steel product.

The present invention provides a method of producing a steel product that includes: 20 (a) mechanically working a steel product, and (b) heat treating the mechanically worked steel product at a temperature above 200°C and 25 below 800°C for up to 6 hours and increasing the ductility and yield stress of the steel.

The present invention provides a method of 3 0 producing a steel product that includes: (a) mechanically working a feed steel, (b) forming the steel product, and 35 (c) heat treating the steel product at a temperature above 200°C and below 800°C for 8919523J (GHMatters) P93465.AU 5/04/17 13 2013205082 05 Apr 2017 up to 6 hours and increasing the ductility and yield stress, of the steel product.

The present invention provides a method of 5 producing a steel product that includes: (a) mechanically working a feed steel, (b) forming the steel product, and 10 (c) heat treating the formed steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility, yield stress and tensile strength of the 15 steel product.

The increase in elongation of the heat treated steel may be greater than 5% relative to that of the mechanically worked feed steel. 20 25 30

The increase in elongation of the heat treated steel relative to that of the mechanically worked steel may be greater than 5%.

The increase in elongation of the heat treated steel may be greater than 10%.

The increase in elongation of the heat treated steel may be greater than 20%.

The increase in elongation of the heat treated steel may be greater than 30%.

The increase in elongation of the heat treated 35 steel may be greater than 50%.

The increase in elongation of the heat treated 8919523J (GHMatters) P93465.AU 5/04/17 14 2013205082 05 Apr 2017 steel may be greater than 100%.

The increase in elongation of the heat treated steel may be greater than 200%. 5

The increase in the yield stress of the heat treated steel may be greater than 10%.

The increase in the yield stress of the heat 10 treated steel may be greater than 20%.

The increase in the yield stress of the heat treated steel may be greater than 30%. 15 The increase in the yield stress of the heat treated steel may be greater than 40%.

The method may also include forming the steel product into another steel product. 20

The feed steel may be any one of low carbon steel, medium carbon steel, and high strength low allow steel. 25 The feed steel may be in any suitable form. The feed steel may be in the form of any one of wire, rod, bar, or strip.

It is noted that the mechanical working step 30 comprises reducing the transverse cross-sectional area, i.e. the diameter, of wire, rod and bar.

It is also noted that the mechanical working step comprises reducing the transverse cross-sectional area, 35 i.e. the thickness, of the strip.

The steel product may be any suitable form of 8919523.1 (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 product. 15

The other steel product may be in the form of a steel product that is made from any one of wire, rod, bar, 5 and strip.

The mechanical working step (a) may include cold rolling or drawing or any other suitable mechanical working step that reduces the transverse cross-sectional 10 area of the feed steel. 15 25 30 35

The reduced transverse cross-sectional area of the feed steel may be less than 75% of the cross-sectional area before the mechanical working step. The reduced transverse cross-sectional area of the feed steel may be less than 60%. The reduced transverse cross-sectional area of the feed steel may be less than 50%. The reduced transverse cross-sectional area of the feed steel may be less than 40%. The reduced transverse cross-sectional area of the feed steel may be less than 35%. The reduced transverse cross-sectional area of the feed steel may be less than 30%. The reduced transverse cross-sectional area of the feed steel may be greater than 2%. The reduced transverse cross-sectional area of the feed steel may be greater than 10%.

The reduced transverse cross-sectional area of 8919523.1 (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 5 10 16 the feed steel may be greater than 15%.

The reduced transverse cross-sectional area of the feed steel may be greater than 25%. The heat treatment step may be carried out at a temperature below the austenitising temperature of the steel.

The heat treatment step may be carried out at a temperature below 750°C.

The heat treatment step may be carried out at a temperature below 700°C. 15

The heat treatment step may be carried out at a temperature below 600°C.

The heat treatment step may be carried out at a 20 temperature below 550°C.

The heat treatment step may be carried out at a temperature below 500°C. 25 The heat treatment step may be carried out at a temperature below 450°C.

The heat treatment step may be carried out at a temperature below 400°C. 30

The heat treatment step may be carried out at a temperature below 300°C.

The heat treatment step may be carried out at a 35 temperature above 200°C.

The heat treatment step may be carried out for 8919523J (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 less than 5 hours. 17

The heat treatment less than 4 hours. 5 step may be carried out for The heat treatment greater than 1 hour. step may be carried out for The heat treatment 10 greater than 45 minutes. step may be carried out for The heat treatment greater than 30 minutes. step may be carried out for 15 The heat treatment greater than 10 minutes. step may be carried out for The heat treatment greater than 5 minutes. 20 step may be carried out for The heat treatment greater than 1 minute. step may be carried out for The heat treatment 25 greater than 30 seconds. step may be carried out for The heat treatment any suitable atmosphere. step (b) may be carried out in 30 The present, invention also provides a steel product made by the above method.

The present invention also provides a mechanically worked and heat treated high strength low 35 alloy steel product that has a steel composition, an elongation and a yield stress as described above. 8919523J (GHMatters) P93465.AU 5/04/17 18 2013205082 05 Apr 2017

The steel product may be in the form of a steel product that is made from any one of wire, rod, bar, and strip as described above. 5 The present invention is based on an extensive research and development program that focused on testing a substantial number of samples of low carbon steel, medium carbon steel and high strength low alloy. The samples included samples mechanically worked under different 10 conditions and heat treated at different temperatures and for different times. A key finding of the research and development program was that mechanical working of the steel samples was critical to obtaining improvements in elongation, yield stress, and tensile strength in heat 15 treatment of the samples.

The research and development program was carried out on steel wire suitable for use in the manufacture of reinforcing mesh and other reinforcement products for the 2 0 mining and construction industries. The steel wire was made from low carbon steel, medium carbon steel, and high strength low alloy steel. The steel wire was made by rolling a larger diameter steel rod to smaller diameters. 25 The following is a summary of the research and development program in relation to low carbon steel and high strength low alloy steel. • Steel compositions - High strength low alloy 3 0 steel and low carbon steel. Examples of the steel compositions are set out below.

High Strength Low Alloy c Mn Si P S Cu Ni Cr Mo V A1 Nb Ti CE . 17 1.10 .2 . 013 .040 .28 . 07 . 11 .01 .102 .002 . 001 .001 .42 . 18 1.06 .25 . 014 .046 .28 . 07 . 10 .01 .093 .002 . 001 .001 . 42 35 8919523.1 (GHMatters) P93465.AU 5/04/17 19

Low Carbon c P Mn Si S Ni Cr Mo Cu Al-T B .06 .006 .50 .15 .009 .006 .012 .001 .014 .002 .0003 .18 .010 .71 .20 .012 .005 .001 .008 .001 .0003 2013205082 05 Apr 2017 • Initial rod product - conventional AS 1442 5 rolling procedure in a rod mill to produce 10 mm and 8 mm rod - the rod was then cold rolled to smaller diameter wires to form test samples. The samples included (a) 10 mm diameter rod rolled to 9.5 mm wire, (b) 8 mm diameter rod rolled to 7.7 mm, 7.6 mm, 10 7.5 and 6.75 mm wire, (c) 10.5 mm rod rolled to 9.5 mm, and (d) 8.5 mm rod rolled to 6.75 mm. • Heat treatment furnace - a fan forced air furnace and a resistance heated furnace. 15 • Heat treatment temperatures - see Figures. • Heat treatment times - see Figures. 20 · Air cool for samples having test data reported in

Figures 1-21 and 26-28 and water quench for samples having test data reported in Figures 22-25. • Sample size - 300 mm long 25 • Testing procedures - tensile tests on Instron machine and elongation determined via an extensometer. The results in the Figures include graphs of proof stress (PS). Yield stress reported 30 as Proof stress. Elongation reported as Uniform

Elongation (Agt(_0.5%)) .

The results of the research work are summarised in part in Figures 1-28 of the specification which are 35 described and discussed below. It is noted that Figures 8919523.1 (GHMatters) P93465.AU 5/04/17 20 2013205082 05 Apr 2017 1-25 focus on work on high strength low alloy steel ("HSLA") samples and Figures 26-28 focus on low carbon steel samples . 5 The applicant carried out a similar program in relation to medium carbon steel samples and obtained comparable results .

Figure 1 is a graph of tensile strength (MPa) 10 versus heat treatment time (0-30 minutes) for samples heat treated at 300, 400, 500, 600, and 700°C, with the samples comprising 9.5 mm diameter HSLA wire samples mechanically worked by being cold rolled from 10 mm diameter rod in accordance with the invention. It is evident from the 15 figure that there was an increase in tensile strength of the cold rolled samples at short (less than 4 minutes) heat treatment times at each of the heat treatment temperatures. The tensile strength of the samples that were heat treated at the higher temperatures (e.g. 500, 20 600, and 700°C) decreased as the heat treatment times increased. However, there was no decrease in tensile strength with heat treatment time for the samples that were heat treated at lower temperatures (300 and 400°C).

In addition, the increase in tensile strength was achieved 25 with relatively short heat treatment times across the range of heat treatment temperatures. This is potentially significant in terms of processing times and costs.

Figure 2 includes a graph of elongation (measured 30 as Uniform Elongation — Agt) versus heat treatment time (0— 5 hours) for 9.5 mm diameter HSLA wire samples cold rolled from 10 mm diameter rod and heat treated at 300°C in accordance with the invention. This graph is described as the "N10PLUS" curve in the Figure. Figure 2 also includes 35 comparative data for 6.75 mm diameter low carbon steel wire samples cold rolled from 8.5 mm diameter rod and heat treated in the same way. This graph is described as the 8919523.1 (GHMatters) P93465.AU 5/04/17 21 2013205082 05 Apr 2017 "6.75EX8.5" curve in the Figure. Figure 2 illustrates increases in ductility that might be expected as a consequence of the heat treatment of either steel. 5 Figure 3 includes graphs of yield stress (reported as Proof Stress - MPa) versus heat treatment time (0-5 hours) for the Figure 2 samples (HSLA and low carbon steel) heat treated at 300°C. 10 Figure 4 includes graphs of tensile strength (MPa) versus heat treatment time (0-5 hours) for the Figure 2 samples (HSLA and low carbon steel) heat treated at 300°C. 15 It is evident from Figures 2-4 that there was an increase in each of ductility, tensile strength and yield stress of the N10PLUS HSLA samples whereas there was the conventional response of an increase in ductility and a decrease in tensile strength and yield stress of the 20 6.75EX8.5 low carbon steel samples. An interesting point in relation to the N10PLUS samples is that the results were achieved at a low heat treatment temperature of 300°C. 2 5 Figure 5 is a graph of elongation (Agt) versus heat treatment temperature (0-500°C) for HSLA samples heat treated for 4 hours, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The 30 samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 5 that there was an increase in ductility in the cold drawn samples at heat treatment temperature greater than 200°C and that the ductility increased as the heat 35 treatment temperature increased.

Figure 6 is a graph of elongation (Agt) versus 8919523.1 (GHMatters) P93465.AU 5/04/17 22 2013205082 05 Apr 2017 heat treatment, time (0-7 hours) for HSLA samples heat treated at 100°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod. The samples were cold rolled to different 5 extents, with the highest reduction being around 12%. It is evident from Figure 6 that there was a slight decrease in ductility in the cold drawn samples across the range of heat treatment times. Basically, the ductility change was conventional and the teaching is that the heat treatment 10 temperature of 100°C was too low. The ductility was higher for the samples having lower cold reductions.

Figure 7 is a graph of elongation (Agt) versus heat treatment time (0-16 hours) for HSLA samples heat 15 treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from 20 Figure 7 that after an initial decrease in ductility (which is conventional) there was a significant initial increase in ductility in a relatively short heat treatment time (up to 30 minutes) at 300°C for each of the samples and that the ductility tended to level out after around 3 25 hours of heat treatment at that temperature. The ductility was higher for the samples having lower cold reductions .

Figure 8 is a graph of elongation (Agt) versus 30 heat treatment time (0-30 minutes) for HSLA samples heat treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. These samples were cold rolled and heat treated under the same 35 conditions as the Figure 7 samples. This graph focuses on the first 30 minutes of heat treatment time highlighted in the discussion of Figure 7. It is evident from Figure 8 8919523.1 (GHMatters) P93465.AU 5/04/17 23 2013205082 05 Apr 2017 that, after an initial decrease in ductility (which is conventional) there was a steady increase in ductility with heat treatment time at 300°C for each of the samples, with the ductility being higher for the samples having 5 lower cold reductions .

Figure 9 is a graph of elongation (Agt) versus heat treatment time (0-30 minutes) for HSLA samples heat treated at 500°C, with the samples comprising 7.5 mm, 7.6 10 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 9 that after an initial decrease in ductility 15 (which is conventional) there was a steady increase in ductility with heat treatment time at 500°C for each of the samples, with the ductility being higher for the samples having lower cold reductions. 20 Figure 10 is a graph of yield stress (Proof

Stress MPa) versus heat treatment temperature (0-500°C) for HSLA samples heat treated for 4 hours, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in 25 accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 10 that the yield stress of each of the cold drawn samples initially increased and then decreased as the heat treatment 30 temperature increased. The yield stress was higher for the samples having higher cold reductions. The shapes of the graphs in Figure 10 indicate that there is a window of heat treatment temperatures, namely a window in the range of 150-400°C, in which there was a significant increase in 35 yield stress of the samples. 8919523.1 (GHMatters) P93465.AU 5/04/17 24 2013205082 05 Apr 2017

Figure 11 is a graph of yield stress (Proof Strength - MPa) versus heat treatment time (0-7 hours) for HSLA samples heat treated at 100°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire 5 samples cold drawn from 8 mm diameter rod in accordance with the invention. The samples were cold drawn to different extents, with the highest reduction being around 12%. It is evident from Figure 11 that there was an increase (albeit not substantial) in yield stress in the 10 cold drawn samples across the range of heat treatment times. The yield stress was higher for the samples having higher cold reductions.

Figure 12 is a graph of yield stress (Proof 15 Stress - MPa) versus heat treatment time (0-16 hours) for HSLA samples heat treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to 20 different extents, with the highest reduction being around 12%. It is evident from Figure 12 that there was a significant initial increase in yield stress in a relatively short heat treatment time (0-30 minutes) at 300°C for each of the samples and that the yield stress 25 tended to level out after around 30 minutes of heat treatment at that temperature. The yield stress was higher for the samples having higher cold reductions.

Figure 13 is a graph of yield stress (Proof 30 Stress - MPa) versus heat treatment time (0-30 minutes) for HSLA samples heat treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to 35 different extents, with the highest reduction being around 12%. These samples were cold rolled and heat treated under the same conditions as the Figure 12 samples. This graph 8919523J (GHMatters) P93465.AU 5/04/17 25 2013205082 05 Apr 2017 focuses on the first 30 minutes of heat treatment time highlighted in the discussion of Figure 12. It is evident from Figure 13 that there was a steady increase in yield stress with heat treatment time at 300°C for each of the 5 samples. The yield stress was higher for the samples having higher cold reductions.

Figure 14 is a graph of yield stress (Proof Stress - MPa) versus heat treatment time (0-30 minutes) 10 for HSLA samples heat treated at 500°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from S mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 15 12%. It is evident from Figure 14 that there was an initial increase in yield stress at the heat treatment temperature of 500°C for each of sample, with the yield stress of each sample reaching a maximum yield stress after 10 minutes. The yield stress of each sample 20 decreased with heat treatment times greater than 10 minutes. The yield stress was higher for the samples having higher cold reductions.

Figure 15 is a graph of tensile strength (MPa) 25 versus heat treatment temperature for HSLA samples heat treated for 4 hours, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the 30 highest reduction being around 12%. It is evident from Figure 15 that the tensile strength of each of the cold rolled samples initially increased and then decreased as the heat treatment temperature increased. The tensile strength was higher for the samples having higher cold 35 reductions. The shapes of the graphs in Figure 15 indicate that there was a window of heat treatment temperatures, namely a window in the range of 150-350°C, 8919523.1 (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 5 10 15 20 30 35 26 in which there was a significant increase in tensile strength of the samples.

Figure 16 is a graph of tensile strength (MPa) versus heat treatment time (0-7 hours) for HSLA samples heat treated at 100°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 16 that there was a slight change in tensile strength in the cold rolled samples across the range of heat treatment times. The tensile strength was higher for the samples having higher cold reductions. Figure 17 is a graph of tensile strength (MPa) versus heat treatment time (0-16 hours) for HSLA samples heat treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 17 that there was a significant initial increase in tensile strength in a relatively short heat treatment time (0-30 minutes) at 300°C for each of the samples and that the tensile strength tended to level out after around 30 minutes of heat treatment at that temperature. The tensile strength was higher for the samples having higher cold reductions . Figure 18 is a graph of tensile strength (MPa) versus heat treatment time (0-30 minutes) for HSLA samples heat treated at 300°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The samples were cold rolled to different extents, with the highest reduction being around 12%. These samples were 8919523.1 (GHMatters) P93465.AU 5/04/17 27 2013205082 05 Apr 2017 cold rolled and heat treated under the same conditions as the Figure 17 samples. This graph focuses on the first 30 minutes of heat treatment time highlighted In the discussion of Figure 17. It Is evident from Figure 17 that 5 there was a steady Increase In tensile strength with heat treatment time at 300°C for each of the samples. The tensile strength was higher for the samples having higher cold reductions . 10 Figure 19 is a graph of tensile strength (MPa) versus heat treatment time (0-30 minutes) for HSLA samples heat treated at 500°C, with the samples comprising 7.5 mm, 7.6 mm, and 7.7 mm diameter wire samples cold rolled from 8 mm diameter rod in accordance with the invention. The 15 samples were cold rolled to different extents, with the highest reduction being around 12%. It is evident from Figure 19 that there was an initial increase in tensile strength at the heat treatment temperature of 500°C for each sample, with the tensile strength of each sample 20 reaching a maximum tensile strength after 10 minutes, and the tensile strength of each sample decreasing with heat treatment times greater than 10 minutes. The tensile strength was higher for the samples having higher cold reductions. 25

Figure 20 is a graph of elongation (Agt) versus heat treatment time (0-30 minutes) for HSLA samples heat treated at 300, 400, 500, 600, and 700°C, with the samples comprising 9.5 mm diameter wire samples cold rolled from 30 10 mm diameter rod in accordance with the invention. It is evident from Figure 20 that the ductility of the samples increased with heat treatment time at each heat treatment temperature, with the rate of increase in ductility increasing with heat treatment temperature. 35

Figure 21 is a graph of yield stress (Proof Strength - MPa) versus heat treatment time (0-30 minutes) 8919523J (GHMatters) P93465.AU 5/04/17 28 2013205082 05 Apr 2017 for HSLA samples heat treated at 300, 400, 500, 600, and 700°C, with the samples comprising 9.5 mm diameter wire samples cold rolled from 10 mm diameter rod in accordance with the invention. It is evident from Figure 21 that 5 there was an increase in yield stress of the cold drawn samples at short heat treatment times at each of the heat treatment temperatures. The yield stress of the samples heat treated at the higher temperatures decreased (e.g. 500, 600, and 700°C) as the heat treatment times 10 increased. However, there was no decrease in yield stress with heat treatment time for the samples that were heat treated at lower temperatures (300 and 400°C). The increase in yield stress was achieved with relatively short heat treatment times across the range of heat 15 treatment temperatures. This is potentially significant in terms of processing times and costs.

Figure 22 is a graph of elongation (Agt) versus heat treatment time (0-20 minutes) for 6.75 mm diameter 20 HSLA wire samples cold rolled from 8 mm diameter rod and heat treated at 750°C and then water quenched in accordance with the invention. It is evident from Figure 22 that water quenching heat treated samples had no detrimental impact on the ductility at heat treatment 2 5 times between 2 and 8 minutes. It is evident from a comparison of the results in Figure 22 and the results in Figure 9 for 7.5, 7.6, 7.7 mm material cold rolled from 8 mm diameter rod and heat treated at 500°C that the ductility of the 6.75 mm material of Figure 22 was higher 30 than for the 7.5, 7.6, 7.7 mm material of Figure 9. This finding is contrary to the evidence for the 7.5, 7.6, 7.7 mm shown in Figure 9 where the ductility decreased with increasing cold reduction. This may be a consequence of the higher heat treatment temperature for the 6.75 mm 35 material generating greater ductility. 89I9523J (GHMatters) P93465.AU 5/04/17 29 2013205082 05 Apr 2017

Figure 23 is a graph of elongation (Agt) versus heat, treatment time (0-20 minutes) for 6.75 mm diameter HSLh wire samples cold rolled from 8 mm diameter rod and heat treated at 500°C and then water quenched in 5 accordance with the invention. It is evident from Figure 23 that water quenching heat treated samples had no detrimental impact on ductility at heat treatment times greater than 5 minutes. In addition, it is also evident that the higher heat treatment temperature of 750°C for 10 the samples referred to in the preceding paragraph

generated approximately 2% higher than for the samples heat treated at 500°C

Figure 24 is a graph of yield stress (Proof 15 Strength - MPa) and tensile strength (MPa) versus heat treatment time (0-20 minutes) for 6.75 mm diameter HSLA wire samples cold rolled from 8 mm diameter rod and heat treated at 750°C and then water quenched in accordance with the invention. It is evident from Figure 24 that 20 water quenching samples that were heat treated for up to 7 minutes and then quenched had an improvement in yield stress and tensile strength, albeit not substantial. Heat treatment times greater than 7 minutes followed by quenching resulted in a significant increase in tensile 25 strength and a significant reduction in yield stress. It is evident from Figure 24 that there was a heat treatment time window of up to 7 minutes at the heat treatment temperature in which there was an improvement in yield stress and tensile strength. 30

Figure 25 is a graph of yield stress (Proof Strength - MPa) and tensile strength (MPa) versus heat treatment time (0-20 minutes) for 6.75 mm diameter HSLh wire samples cold rolled from 8 mm diameter rod and heat 35 treated at 500°C and then water quenched in accordance with the invention. It is evident from Figure 25 that water quenching heat treated samples had substantially no 8919523.1 (GHMatters) P93465.AU 5/04/17 30 2013205082 05 Apr 2017 impact, on yield stress and tensile stress. In other words, at this heat treatment temperature there is no downside in water quenching treated steel. It is noted nevertheless that these heat treatment conditions produced 5 an increase in yield stress and tensile strength.

Figures 26-28 focus on the results of research and development work on low carbon steel samples. 10 Figure 26 is a graph of elongation (Agt) versus heat treatment time (0-30 minutes) for samples heat treated at 500°C, with the samples comprising 9.5 mm and 6.75 mm diameter low carbon steel wire samples cold rolled from 10 mm diameter and 8.5 mm rod respectively in 15 accordance with the invention. It is evident from Figure 26 that the ductility of the samples increased with heat treatment time.

Figure 27 is a graph of yield stress (Proof 20 Strength - MPa) versus heat treatment time (0-30 minutes) for samples heat treated at 500°C, with the samples comprising 9.5 mm and 6.75 mm diameter low carbon steel wire samples cold rolled from 10 mm diameter and 8.5 mm rod respectively in accordance with the invention. It is 25 evident from Figure 27 that the yield stress of the more heavily mechanically worked sample (i.e. the 6.75 mm sample) initially increased (up to 2 minutes heat treatment time) and then decreased with heat treatment time, with a period of 7 minutes treatment time passing 30 before the yield stress decreased to the initial start amount. The initial increase in yield stress is a surprising result and indicates that there is a heat treatment window in which it is possible to achieve an increase in yield stress. It is also evident from Figure 35 27 that the yield stress of the less heavily mechanically worked sample (i.e. the 9.5 mm sample) was not adversely affected by heat treatment for up to 8 minutes. When 8919523J (GHMatters) P93465.AU 5/04/17 31 2013205082 05 Apr 2017 considered in conjunction with Figure 26, the yield stress results reported in Figure 27 are a significant result because the results indicate that it is possible to heat treat such heavily worked steel and achieve the Figure 26 5 increase in ductility without a loss of yield stress.

Figure 28 is a graph of tensile strength (MPa) versus heat treatment time (0-30 minutes) for samples heat treated at 500°C, with the samples comprising 9.5 mm and 10 6.75 mm diameter low carbon steel wire samples cold rolled from 10 mm diameter and 8.5 mm rod respectively in accordance with the invention. It is evident from Figure 28 that the tensile strength of the less heavily mechanically worked sample (i.e. the 9.5 mm sample) 15 initially increased (up to 8 minutes heat treatment time) and then decreased with heat treatment time. The initial increase in tensile strength is a surprising result and indicates that there is a heat treatment window in which it is possible to achieve an increase in tensile strength. 20 When considered in conjunction with Figures 26 and 27, the Figure 28 result is a significant result because it indicates that it is possible to heat treat such heavily worked steel and achieve the Figure 26 increase in ductility and the Figure 27 increase in yield stress 25 without a loss of tensile strength.

In general terms, as illustrated by the results of the research work summarised in the Figures, the applicant found surprisingly that the ductility (measured 30 as elongation), the yield stress, and the tensile strength of the wire of high strength low alloy and low carbon steels could be increased as a consequence of a combination of mechanical working and heat treatment. The finding is a significant finding for the following 35 reasons: 8919523.1 (GHMatters) P93465.AU 5/04/17 32 2013205082 05 Apr 2017 • It is possible to significantly reduce the amount of steel required to manufacture products without a loss of force capacity of the steel in the products. The reduced amount of steel required for products 5 improves the economics of construction and reduces the carbon footprint. • There is an opportunity for higher strength and ductility products . 10 • There is a possibility of changing the design and resultant cost of composite products that are made from the steel products. One example is steel reinforced concrete products used in the construction 15 industry. The invention may make it possible to reduce the amount of steel and/or the amount of concrete used in these products or to increase the structural performance of these products for a given amount of steel. 20 • The method is inexpensive in that it can be carried out with low capital and operating costs. 25 35

The present invention can be used at different stages in the manufacture of end-use products and therefore provides considerable flexibility. For example, steel wire can be processed in accordance with the invention to increase the yield stress and ductility of the wire and then coiled.

The coiled product can be formed into end use products such as ligatures etc. Alternatively, standard wire can be produced and coiled and then processed to produce products such as mesh sheets and ligatures etc and these products can be processed in accordance with the invention to increase the yield stress and ductility of the products. 8919523J (GHMatters) P93465.AU 5/04/17 2013205082 05 Apr 2017 5 10 33

In addition to the above-described test work, the research and development program included test work on heat treated products at 100°C for at least 1 hour. These tests indicated that there is no loss of properties, such as ductility and yield stress, at this temperature. This is important from a practical viewpoint because it indicates that there will be no loss of properties when the steel is on site or in use. Many modifications may be made to the invention described above without departing from the spirit and scope of the invention. 15 By way of example, the research and development program reported above has focused on wire. However, the view of the applicant is that the results are found with wire should translate to rod, bar, and strip steel products . 89I9523J (GHMatters) P93465.AU 5/04/17

Claims

1. A method of producing a steel product includes heat treating a mechanically worked low carbon, medium carbon or high strength low alloy steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and maintaining or increasing the yield stress of the steel.

2. A method of producing a steel product includes heat treating a mechanically worked low carbon, medium carbon or high strength low alloy steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and maintaining or increasing the yield stress, and tensile strength of the steel.

3. The method defined in claim 1 or claim 2 wherein the increase in ductility, measured as elongation, of the heat treated steel relative to that of the mechanically worked steel is greater than 5%.

4. The method defined in any one of the preceding claims wherein the increase in the yield stress of the heat treated steel relative to that of the mechanically worked steel is greater than 5%.

5. The method defined in any one of the preceding claims wherein the mechanically worked steel product is a cold rolled or drawn product that has a reduced transverse cross-sectional area after it has been mechanically worked.

6. The method defined in claim 5 wherein the reduced transverse cross-sectional area of the mechanically worked steel product is less than 75% of the cross-sectional area before the mechanical working step.

7. A method of producing a steel product includes: (a) mechanically working a low carbon, medium carbon or high strength low alloy feed steel, and (b) heat treating the mechanically worked feed steel at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and yield stress of the steel; and (c) forming a steel product.

8. A method of producing a steel product includes: (a) mechanically working a low carbon, medium carbon or high strength low alloy steel product, and (b) heat treating the mechanically worked steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility, yield stress, and tensile strength of the steel.

9. A method of producing a steel product includes: (a) mechanically working a low carbon, medium carbon or high strength low alloy feed steel, (b) forming the steel product from the mechanically worked feed steel, and (c) heat treating the steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility and yield stress, of the steel product.

10. A method of producing a steel product includes: (a) mechanically working a low carbon, medium carbon or high strength low alloy feed steel, (b) forming the steel product product from the mechanically worked feed steel, and (c) heat treating the formed steel product at a temperature above 200°C and below 800°C for up to 6 hours and increasing the ductility, yield stress and tensile strength of the steel product.

11. The method defined in claim 9 or claim 10 wherein the mechanical working step (a) includes cold rolling or drawing that reduces the transverse cross-sectional area of the feed steel.

12. The method defined in claim 11 wherein the reduced transverse cross-sectional area of the feed steel is less than 75% of the cross-sectional area before the mechanical working step.

13. The method defined in any one of claims 1 to 6 and 8 to 12 wherein the heat treatment step is carried out at a temperature below 750°C.

14. The method defined in claim 13 wherein the heat treatment step is carried out at a temperature below 300°C.

15. The method defined in any one of claims 1 to 6 and 8 to 14 wherein the heat treatment step is carried out for a time greater than 30 seconds.

16. The method defined in in any one of claims 1 to 6 and 8 to 15 wherein the heat treatment step is carried out for less than 4 hours.

17. The method defined in claim 7 wherein the heat treatment step is carried out at a temperature below 750°C.

18. The method defined in claim 17 wherein the heat treatment step is carried out at a temperature below 300°C.

19. The method defined in claim 17 or claim 18 wherein the heat treatment step is carried out for a time less than 6 hours.

20. The method defined in any one of claims 17 to 19 wherein the heat treatment step is carried out for greater than 30 seconds.