JP4696602B2 - Method for producing rolled H-section steel with excellent low-temperature toughness - Google Patents

Description

The present invention relates to a method of manufacturing a rolled H-shaped steel, in particular, be used in a structure or the platform that is used in a cold region, tangential peak - absorbing energy formate - low temperature toughness requirements more excellent 27J at -40 ℃ The present invention relates to a suitable manufacturing method for rolled H-section steel.

Recently, resource development shea base rear, shifts etc. cold regions Arctic Ocean, the path b-flop lines and offshore structures, the H-shaped steel which is applied to Howe di in g or the platform, and excellent low-temperature toughness steel Is required.

  Since these are assembled by welding, it is required that the weld heat affected zone (HAZ) has good toughness at low temperatures as well as the base material.

  TMCP using both controlled rolling and accelerated cooling is widely applied to toughen thick steel plates, and shape steel is also considered to be an extremely effective means from the viewpoint of material control. FIG. 2 schematically shows a method for manufacturing the H-section steel.

After reheating the steel material by a heating furnace, a hole-type rolling, rough uni bar - monkey rolling and finish uni bar - formed into a desired shape through a monkey rolling, accelerated cooling is mainly finishing Uni bar - after monkey rolled product The shape is applied after molding.

However, when TMCP is applied to shape rolling, there are the following problems, which are not widely used. That is,
When considering 1 formability, a heating temperature at a high temperature exceeding 1200 ° C. is required, and a waiting time for performing the controlled rolling is required, which impedes productivity.

For thickness of 2 web parts and flanges are different, if the accelerated cooling both, web blanking is easily subcooled, shape defects are likely to occur, such as web blanking buckling.

3 web Bed height, flange width, the web blanking thickness and flange thickness combination variety of sizes of H-shaped steel according to the, the great effort to produce a high efficiency while simultaneously the material control and shape control Cost.

Therefore, accelerated cooling is generally applied from the viewpoint of shape control as cooling from flange outer surface, web parts are cooled has become a principal. When applying accelerated cooling to material control, complex control is required to ensure strength and low temperature toughness on the premise of shape control.

  Accordingly, an object of the present invention is to provide a method for producing a rolled H-section steel having excellent low-temperature toughness with few production restrictions even when accelerated cooling is applied.

  The present inventors conducted various studies in order to alleviate manufacturing restrictions due to the application of accelerated cooling and to establish a manufacturing technology for highly efficient rolled H-section steel that achieves low temperature toughness of -40 ° C or lower. .

As a result, when high temperature heating is required as in the case of shape steel, (1) reduction of the amount of C and addition of no precipitation embrittlement element to improve low temperature toughness without performing controlled rolling Furthermore, it was found that (2) it is important to reduce the amount of dissolved N. The present invention, flange thickness tensile strength 490MPa or more intensity grayed les at 40mm below - to target de rolled H-shaped steel.

Based on the knowledge obtained, the present invention was further made in addition to optimizing rolling and cooling conditions and performing strength control.
1 C: 0.08 to 0.18 mass%, Si: 0.6 mass% or less, Mn: 1.2 to 1.8 mass%, P: 0.018 mass% or less, S: 0.005 mass% or less, Al: 0 0.010 to 0.050 mass%, Ti: 0.005 to 0.020 mass%, N: 0.0010 to 0.0050 mass%, a carbon equivalent of 0.44% or less, the balance Fe and an unavoidable impurity. after heating at 1100 to 1300 ° C., flange rolling end temperature 900 ° C. or higher, web parts are after rolling at Ar ₃ temperature or lower at a rolling 20% or more cumulative rolling reduction rolling end temperature 700 ° C. or higher, flange is, Ar after accelerated cooling at a _third temperature above the cooling rate of 1 ° C. / s or more, heating condensate below 450-700 ° C., web parts are solute N amount, characterized in that the cooling is less than 0.0030Mass% Method for producing a rolled H-shaped steel excellent in temperature toughness.

2. Further to the steel material, Ca: 0.0010-0.0050 mass%, REM: 0.005-0.020 mass% , Mg: 0.0005-0.0050 mass% , Zr: 0.001-0. 005 mass%, Hf: 0.001~0.005 mass %, B: 0.0005~0.0030 solute N amount of 1, wherein the addition of more mass% of one or two 0 A method for producing a rolled H-section steel having excellent low temperature toughness of .0030 mass% or less .

3. Further, one or two or more of Cu: 0.70 mass %, Ni: 1.0 mass % or less, Cr: 0.50 mass % or less is added to the steel material 1 or 2 The manufacturing method of the rolling H-section steel which is excellent in the low temperature toughness whose solid solution N amount of description is 0.0030 mass% or less .

4 when hot rolling, the web blanking the low temperature toughness of solute N amount is less 0.0030Mass% according to any one of 1 to 3, characterized in that is rolling at least once with water cooling for A method for producing excellent rolled H-section steel.

According to the present invention is extremely industrially can be manufactured with high productivity rolled H-beams of various sizes having excellent low-temperature toughness useful.

In the present invention, the component composition and production conditions of the steel material are specified. The percentage of the component composition is mass %.
[Ingredient composition]
C: 0.08 to 0.18%
C needs 0.08% or more for ensuring the strength of the base material. On the other hand, addition exceeding 0.18% not only lowers the base metal toughness, but also lowers the weldability. Therefore, the C content is set to a range of 0.08 to 0.18%.
Si: 0.6% or less Si dissolves in steel and increases the strength of the base metal, but addition exceeding 0.6% lowers the toughness of the weld heat affected zone (HAZ). 0.6%.
Mn: 1.2 to 1.8%
Mn, since the solid solution effect in web blanking, but in the flange requires 1.2% or more for improving hardenability, addition of more than 1.8% of reducing the weldability, 1 The range is 2 to 1.8%.
P: 0.018% or less P is unavoidably present in steel and is particularly harmful to the toughness of the solidified segregation part. For this reason, it is desirable that the amount be extremely low, but considering the economy, the content is made 0.018% or less.
S: 0.005% or less S is formed a MnS, elongation and Shall peak - to lower the ductility, such as - the absorption energy formic. Particularly, in the present invention that the low temperature toughness is required, it Shall peak - the upper shelf energy formate - it is necessary to increase the, therefore 0.005% or less.
Al: 0.010 to 0.050%
Al is added as a deoxidizing material in the steelmaking stage, and 0.010% or more is necessary to exert its effect. On the other hand, even if added over 0.050%, the effect is saturated, so the upper limit is made 0.050%.
N amount: 0.0010 to 0.0050%, Ti: 0.005 to 0.020%
In the present invention, the amount of solid solution N is 0.0030% or less after finish rolling and accelerated cooling, so the amount of N in the steel material after melting is 0.0010 to 0.0050%, Ti: 0.005. 0.020%. The reason for limiting the solid solution N amount to 0.0030% or less will be described.

  Fig. 1 shows a simulation of shape steel rolling of 0.14C-0.2Si-1.5Mn steel. After reheating to 1280 ° C, the rolling was finished by 950 ° C (without CR), and the plate thickness was 30 mm, followed by air cooling. The results of arranging the toughness of the base metal by the amount of solute N are shown for the case where the cooling is performed and the case where the cooling is accelerated.

  Toughness decreases due to an increase in the amount of solute N. In particular, when it exceeds 0.003%, embrittlement becomes prominent, and in order to ensure low temperature toughness at -40 ° C. without controlled rolling, the amount of solute N needs to be 0.0030% or less.

In order to make the solid solution N amount 0.0030% or less, it is desirable that the N amount in the steel is 0.0030% or less. However, stable to the N content in steel to 0.0030% or less complicates the steelmaking process, it is industrially difficult.

  On the other hand, as shown in FIG. 1, the addition of Nb and V is effective for fixing solute N, but forms carbonitride to promote precipitation embrittlement and offsets the toughness improvement effect. Therefore, in the present invention, the amounts of Nb and V are not added (inevitably up to 0.005% and 0.010%, respectively).

Ti forms TiN that is stable even at high temperatures, and is effective in reducing solid solution N. However, manufacturing processes of shaped steel, because it requires reheating at a high temperature exceeding 1200 ° C., fine TiN during reheating dissolves part, increasing the amount of dissolved N.

  Accordingly, in the present invention, in the steel material, the N content is 0.0010 to 0.0050% and Ti: 0.005 to 0.020%. The Ti amount is 3.0 or more in terms of the stoichiometric ratio of N amount, and if the upper limit exceeds 5.0, the solid solution Ti becomes TiC and embrittles. In the present invention, the amount of N is defined as the total amount of N (= the amount of solid solution N + the amount of N in the precipitate).

Carbon equivalent (Ceq): 0.44% or less Increasing the carbon equivalent is effective for increasing the strength of the base metal, but conversely reduces the base metal toughness, weldability, and HAZ toughness. 0.44%. In the present invention, the carbon equivalent is defined by the following formula.

Carbon equivalent (Ceq) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
The above is the basic component composition of the present invention. For the purpose of ensuring the HAZ toughness according to the welding conditions, Ca: 0.0010 to 0.0050 % , REM: 0.005 to 0.020 % , Mg: 0 .0005 to 0.0050 % , Zr: 0.001 to 0.005%, Hf: 0.001 to 0.005%, B: 0.0005 to 0.0030 % , or two or more kinds may be added. it can.

  Ca, REM, Mg, Zr, and Hf have the effect of improving the HAZ toughness by forming oxides or oxysulfides and refining the HAZ structure. it can.

  Further, one or more of Cu: 0.70% or less, Ni: 1.0% or less, and Cr: 0.50% or less can be added. These elements are added from the viewpoint of securing the strength as necessary when it is desired to keep the amount of C relatively low from the viewpoint of weldability.

  If Cu is added in excess of 0.7%, precipitation embrittlement occurs, so when it is added, the upper limit is made 0.7%.

Ni is a useful element that strengthens without reducing toughness, but is extremely expensive, so when added, the upper limit is made 1.0%.
When Cr is added in an amount exceeding 0.5%, surface flaws (scale flaws) are promoted. Therefore, when Cr is added, the upper limit is made 0.5%. Next, manufacturing conditions will be described.
[Production conditions]
Heating temperature: 1100-1300 ° C
From the viewpoint of reducing deformation resistance at the time of rolling, particularly at the time of punch rolling, the heating temperature needs to be 1100 ° C. or higher. On the other hand, when the temperature exceeds 1300 ° C., a part of fine TiN present in the raw material is dissolved, increasing the amount of dissolved N and lowering the base material toughness. Therefore, the heating temperature was set to a range of 1100 to 1300 ° C. Preferably, it is 1180-1280 degreeC.
Rolling conditions:
Flange: If you try rolling below the rolling end temperature 900 ° C. or higher flange of 900 ° C., it is necessary to wait during rolling, productivity is markedly inhibited. Therefore, the rolling finishing temperature of the flange was 900 ° C. or higher.
Web Bed: Ar ₃ temperature or less cumulative rolling reduction of 20% or more, the rolling end temperature 700 ° C. or higher the other hand, the web blanking, after rolling, is usually air cooling in terms of shape control, since it is necessary to secure strength Therefore, it is necessary to secure a cumulative reduction amount of 20% or more in the two-phase region in the middle of the ferrite transformation of Ar ₃ or less. However, if the finish rolling temperature is less than 700 ° C., buckling of the web blanking has a 700 ° C. The lower limit of the finish rolling temperature to occur. As for the web blanking performed so as not to affect the at least one or more shape control the water cooling to the rolling path way, since easily ensured when the forced cooling intensity desired.

Cooling conditions <br/> flange: Ar ₃ temperature or higher performs the cooling rate 1 ° C. / s or more accelerated cooling after the temperature rolling 450-700 ° C. or less after recuperation, accelerated cooling start temperature is Ar ₃ lower than the temperature If the cooling rate is less than 1 ° C./s, sufficient strength cannot be obtained. Even when the recuperation temperature after cooling exceeds 700 ° C., sufficient strength cannot be obtained. On the other hand, if less than 450 ° C. is sufficient Serufuten Pas - effect can not be obtained toughness, reducing the ductility. Therefore, after rolling, accelerated cooling is performed at a cooling rate of 1 ° C./s or higher from the Ar ₃ temperature or higher, and the temperature after reheating is set to a cooling condition of 450 to 700 ° C. or lower.
Web Bed: after rolling the cooled web blanking, when accelerated cooling, since the shape control, such as warpage warpage becomes unstable, and allowed to cool.

  Steel materials having the chemical composition shown in Table 1 were melted, and H-shaped steel was produced by hot rolling. Tables 2 and 3 show the rolling conditions, the mechanical properties of the obtained H-section steel, and the solute N amount. The amount of solute N is obtained from the total nitrogen content in steel as the nitride nitrogen quantitative value. The total nitrogen content is derived based on JIS G 1228, and the nitride nitrogen quantitative value is derived based on the appendix of JIS A 5523. did.

Tensile specimens, the JIS1A No. full thickness tensile test piece, 1/4 parts of flange width for flanges, for web blanking collected from 1/4 parts web blanking width. Shall Pi - For impact test specimens (2 mm V notch), thickness 1/4 parts of the flange width 1/4 parts, each collection direction than the plate thickness 1/2 parts of the web blanking width 1/4 parts as the rolling direction Collected.

  In the inventive examples, the tensile strength is 490 MPa or more, the yield point is 325 MPa or more, and the toughness is 100 J or more at −40 ° C. On the other hand, steel with a solid solution N content of 0.0030% or more had reduced toughness and did not satisfy the target of 27J. Also, steel with high carbon and high carbon equivalent did not satisfy the target of base metal toughness.

  On the other hand, when the manufacturing method deviated from the scope of the present invention, the base material performance and shape did not satisfy the targets.

The figure which shows the influence of the amount of N in steel on low-temperature toughness. The figure explaining the H-section steel manufacturing procedure.

Claims (4)

C: 0.08 to 0.18 mass%, Si: 0.6 mass% or less, Mn: 1.2 to 1.8 mass%, P: 0.018 mass% or less, S: 0.005 mass% or less, Al: 0. A steel material consisting of 0.10 to 0.050 mass%, Ti: 0.005 to 0.020 mass%, N: 0.0010 to 0.0050 mass%, a carbon equivalent of 0.44% or less, the balance Fe and unavoidable impurities is 1100. after heating at to 1300 ° C., flange rolling end temperature 900 ° C. or higher, web parts are after rolling at Ar ₃ temperature or lower at a rolling 20% or more cumulative rolling reduction rolling end temperature 700 ° C. or higher, flange is, Ar ₃ after accelerated cooling at a cooling rate 1 ° C. / s or more from the above temperature, heated condensate below 450-700 ° C., web low amount of dissolved N, wherein the following 0.0030Mass% to cool Method for producing a rolled H-shaped steel excellent in toughness. Further to the steel material, Ca: 0.0010-0.0050 mass%, REM: 0.005-0.020 mass% , Mg: 0.0005-0.0050 mass% , Zr: 0.001-0.005 mass %, Hf: 0.001~0.005 mass%, B: 0.0005~0.0030 solute N amount of claim 1, wherein the addition of more mass% of one or two 0 A method for producing a rolled H-section steel having excellent low temperature toughness of .0030 mass% or less . The steel material is further added with one or more of Cu: 0.70 mass % or less, Ni: 1.0 mass % or less, and Cr: 0.50 mass % or less. The manufacturing method of the rolling H-section steel which is excellent in the low temperature toughness whose solid solution N amount of description is 0.0030 mass% or less . When hot rolling, the low temperature toughness of solute N amount is less 0.0030Mass% according to web blanking in any one of claims 1 to 3, characterized in that the rolling at least once with water cooling for A method for producing rolled H-section steel that excels in resistance.

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