JPS5944382B2 - Cast hot-work tool steel with excellent wear resistance - Google Patents

Description

Detailed Description of the Invention The present invention has particularly high wear resistance under severe friction conditions with the workpiece at high temperatures, and also has moderate strength, excellent toughness, and good thermal conductivity. This relates to cast hot-work tool steel that can withstand harsh repeated thermal shocks of rapid heating and cooling, and has a long life.The tool surface is not subjected to cutting after casting, and the cast skin is used as the tool surface. This is a prerequisite.

Casting here includes general casting methods such as general sand casting and various precision castings. Although the casting surface differs depending on the casting method, the formation of a strong casting surface on the surface is the same, and in either case, excellent surface characteristics are exhibited in relation to the material of the present invention. A piercer plug tool for manufacturing steel pipes in hot conditions causes severe abrasion with the high-temperature workpiece, and is subsequently subjected to a rapid cooling effect such as surface water cooling.

Conventional hot work tool steel S is used as a tool material for these applications.
KD62 cannot withstand severe abrasion, causing seizures, peeling, etc., and heat cracks develop under severe thermal stress conditions of repeated rapid heating and cooling, resulting in rough skin. As a result, the load on the tool increases, leading to early wear and tear and not necessarily providing a satisfactory service life. On the other hand, AI
Even if a high-strength hot work tool steel made of a high-alloy alloy such as SIHl9 (4Cr-4W-2V-4C0) is used, its thermal conductivity is relatively low, leading to excessive temperature rise on the tool surface and premature heat cracking. This often resulted in a shortened lifespan. The properties required for tool materials for severe applications such as those mentioned above are (1) moderate room temperature to high temperature strength that can withstand severe wear effects and working stress at high temperatures, and appropriate carbide content and its distribution form (2) high temperature. (3) Resistance to the occurrence and propagation of cracks under the action of thermal stress due to rapid temperature rise due to severe frictional contact with the workpiece, lubrication, and repeated rapid heating and rapid cooling due to rapid heating (3) High-temperature partner Characteristics of forming an oxide film that protects the tool surface under severe abrasion conditions between the material and the tool, provides a lubricating effect, suppresses heat generation from wear, and has an insulating effect (4) Minimizes temperature rise on the tool surface. It has good thermal conductivity to suppress and prevent the generation of a sudden temperature gradient, and the effect (3) is particularly large in the tool for this purpose.

In response to the above-mentioned required properties, currently used hot work tool steels such as the above-mentioned SKD62 have strength at high temperatures, but are insufficient in property (3), which is the most important factor.
In addition, (2) and (4) were also not sufficient, and there were cases in which a sufficient lifespan could not be obtained due to early seizure, settling, cracking, etc.

The present invention eliminates the above-mentioned drawbacks of conventional steels, and its most important feature is improved wear resistance due to the formation of a strong protective oxide film based on the cast oxidized skin, as well as appropriate strength and Provides a cast hot work tool steel with carbides, thermal conductivity, and toughness that significantly improves service life under severe wear conditions at high temperatures and thermal shock due to rapid heating and cooling. It is.

That is, the steel of the present invention has low to medium C, low Cr, and low MO (N
- CO-Ti is the basic component, and it has excellent oxide film properties (ease of formation, adhesion, and peeling resistance in the film layer), moderate high temperature strength, carbide amount and distribution, and good thermal conductivity. Cu, Ni, Si, and Mn are added to this to improve the properties of the oxide film, and S is also added to improve self-lubricating properties.This creates an extremely strong oxidized surface for casting, and is resistant to dirt before use. Furthermore, by applying an appropriate oxide film treatment or by the oxidation effect caused by the temperature rise of the tool surface during use, good adhesion and protection can be achieved.
A heat-insulating oxide film is formed early, and along with moderate strength and carbide distribution, it can withstand severe abrasion between the workpiece and the workpiece at high temperatures, and has a strong cast structure, moderate high-temperature strength and good properties. In combination with thermal conductivity, it does not cause wear due to sagging (plastic flow), and does not cause large cracks even under the repeated stress of rapid heating and cooling in relation to lubrication and cooling during use.
This invention relates to a cast hot work tool steel for use in cast skins, which is characterized by significantly improved service life compared to conventional hot work tool steels such as SKD62.

After casting, as a general rule, it is oxidized in various atmospheres such as air, air, or steam atmosphere depending on the purpose and application before use. It is also possible to utilize the oxide film itself and use it without prior oxide film treatment. Table 1 shows the chemical composition of the present invention steel and the conventional steel (SKD62) and the seizure critical load ratio in the high temperature seizure wear test.

In Table 1, sample materials A-Y are steels of the present invention (casting),
Sample Z is conventional steel (cast).

In addition, as a comparison material, the results of a simultaneous test of a forged->cut sample of the composition corresponding to the steel C of the present invention are also shown. The test piece used in this high-temperature baking wear test was a cylindrical test piece (the test end surface was a cast surface, and the comparison material was a cast → cut surface), which had been subjected to a surface oxide coating treatment at 700°C and then heated to a high temperature (950°C). The maximum load (critical load) at which seizure will not occur when the end face is pressed against a mating material while rotating at high speed and a frictional effect is applied.
is calculated, and the seizure critical load of the conventional material (SKD62) is calculated as 10
It is expressed as an index with 0 as the value. It can be seen that the material of the present invention clearly has a higher seizure critical load than the conventional material.

This is because the oxide film formed on the casting surface of the steel of the present invention is extremely strong and has a lubricating and protective effect, and even if the oxide film partially peels off during use, a strong oxide film is immediately regenerated. The effect of this is large, and the S-added ones have a strong cast structure that can withstand plastic flow on the surface, appropriate room temperature to high temperature strength, and improved high temperature seizing wear resistance due to the appropriate distribution of carbides. The wear life is improved by the lubrication effect caused by the formation of MnS-based inclusions.
Table 1 also lists the results of a forged and machined sample made from the components of the present invention subjected to a similar oxide coating treatment and subjected to an experiment. It can be seen that the wear resistance is clearly inferior. Cast samples of the steel of the present invention are excellent because of the combination of the strong oxide film formed at the time of cooling the casting and the subsequent oxide film treatment, which provide excellent adhesion and excellent protection with an appropriate thickness. This is because a chemical oxide film is formed, which is one of the major features of the steel of the present invention. Table 2 shows the heat crack resistance of the steel samples of the present invention and conventional steel (all cast materials).

A test piece of 18 mm φ x 25 mm was immersed in a heating bath at 900°C, rapidly heated, and then water-cooled to 200°C, which was repeated 1000 times.
This is the result of repeated application.

It can be seen that the steel of the present invention has better heat crack resistance than the conventional steel. This is because thermal conductivity, toughness, and ductility have great effects on heat crack resistance under severe thermal shock conditions of rapid heating and cooling. ,S
This is due to the relatively high thermal conductivity of the steel of the present invention, which has a medium to low alloy pace and has a lower amount of alloying elements such as i that reduce thermal conductivity than conventional steels, and also because it has excellent ductility. In addition, in contrast to forged products, in cast products such as the steel of the present invention, excessive plastic deformation is easily inhibited by thermal stress due to the fine and strong casting solidification crystal structure on the surface, resulting in a forged product. In contrast, it prevents the formation of deep cracks, and this point is also one of the features of the steel of the present invention. Next, the reason for limiting the composition range of the steel of the present invention will be described.

C prevents ferrite formation, Cr, MO(W), V, T
It is added to form carbides by combining with carbide-forming elements such as i, to improve seizure resistance against severe wear at high temperatures, and to impart appropriate strength at room temperature to high temperatures.

If it is too large, the amount of carbide becomes too large and coarse carbides tend to form, reducing toughness, so 0.601%
If the content is too low, the effect of the above content cannot be obtained, so the content should be 0.25% or more. Si has the effect of increasing oxidation resistance, and is added depending on the purpose and use in order to adjust the oxidation resistance of the steel of the present invention.

If it is too large, the formation and growth of the oxide film will be excessively small, reducing seizure resistance at high temperatures and thermal conductivity, so it should be 1.50 or less. Mn has the effect of promoting the formation and growth of an oxide film, and is added to adjust the oxidation resistance depending on the intended use.

In S-added steel, it is also added to form MnS. If it is too large, it lowers the A1 transformation point, increases annealing hardness, and reduces machinability, so it should be 1.50% or less. Ni is added to improve the adhesion of the oxide film and to increase the seizure resistance at high temperatures.

If it is too large, it will lower the A1 transformation point, increase the annealing hardness, and reduce machinability, so it should be 1.501% or less, and if it is too low, the effect of the above addition cannot be obtained, so 0.
20% or more. Cr is added in order to provide appropriate oxidation properties, combine with C to form carbide, improve seizure wear resistance, provide appropriate hardenability, and improve the A1 transformation point.

If the amount is too high, the formation and growth of an oxide film will be excessively small, reducing seizure resistance at high temperatures, as well as decreasing thermal conductivity and thermal shock resistance. Therefore, the content should be 2.50% or less. Since this effect cannot be obtained, the content should be 0.301% or more. MO and W combine with C to form carbides, which improves seizure resistance at high temperatures, provides appropriate strength at room and high temperatures, refines grains, and improves the A1 transformation point. It is added singly or in combination for this purpose. In this case, the strength improving effect of W is relatively greater than that of MO, and the amounts of W and MO added are adjusted in consideration of the purpose and usage conditions. If it is too large, the thermal conductivity will decrease and the toughness will also decrease (ZW+MO) is 2.50.
V
is added to form a carbide with C to improve wear resistance, refine crystal grains, improve the A1 transformation point, and impart appropriate room temperature to high temperature strength. Too much will form coarse carbide,
It also reduces toughness and thermal conductivity, so 1.
If the content is too low, the effect of the above-mentioned content cannot be obtained, so the content should be 0.05% or more. CO is an indispensable and important additive element that enhances the adhesion of the oxide film, provides a lubricating effect and heat insulation effect by forming a strong oxide film, and provides excellent seizing and wear resistance at high temperatures.

If the content is too high, the toughness will deteriorate, so the content should be 5.00% or less. If the content is too low, the effect of the content cannot be obtained, so the content should be 0.20% or more. Cu is an important element that increases the fracture resistance and peeling resistance of the formed oxide film layer, and has the effect of improving the adhesion due to CO as well as the seizure wear resistance at high temperatures based on the formation of a strong oxide film on the steel of the present invention. It is an additive element. If it is too large, the hot plastic workability will be reduced, so the content should be 5.00S or less, and if it is too low, the effect of its inclusion will not be obtained, so the content should be 0.20% or more. Ti improves the adhesion, fracture resistance, and peelability of the oxide film of the steel of the present invention, and also forms a special carbide with high hardness that is difficult to dissolve in the matrix, greatly improving the seizing wear resistance at high temperatures. Along with CO, it is an essential and important additive element that forms the characteristics of the steel of the present invention.

It also has the effect of making the casting structure finer and stronger and improving crack resistance. Ti is added to obtain the above effect, but it is not necessary to add a large amount; if it is too large, it will form coarse carbides and reduce toughness, so it should be added to 150%.
If it is too low, the effect of containing it will not be obtained, so 0.
0.5% or more. S combines with Mn to form MnS, which provides a lubricating effect and improves seizure resistance at high temperatures.

In particular, the effect of maintaining seizure and wear resistance during the period between partial coating peeling and regeneration during use is significant. If the amount is too high, the toughness will deteriorate, so the content should be 0.30% or less. If the content is too low, the effect of addition cannot be obtained, so the content should be 0.03% or more. In addition, P
Containing lubricating inclusion-forming elements such as B, Ce, Se, Te, and Bi, singly or in combination, also brings about the same effect as S-containing. As described above, the present invention, in combination with a strong casting oxidation skin, produces an extremely dense and highly adhesive oxide film on the tool surface during oxide film treatment before use or when used as a tool, and maintains an appropriate carbide distribution and room temperature. ~A cast hot-work tool steel that has a balance of high-temperature strength, good thermal conductivity, and excellent toughness to withstand severe frictional effects at high temperatures and thermal shock caused by rapid heating and cooling, and has a long service life.It is intended for use with cast skins. It is.

Claims (1)

[Claims] 1 C 0.25-0.60%, Si 1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 1.00% Ti, 0.05-1.50% Ti, the balance Fe and normal impurities. 2 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, Cu0.20~
A cast hot work tool steel with excellent wear resistance, characterized by comprising 5.00% Fe and normal impurities. 3 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, S0.03~0
．． A cast hot work tool steel with excellent wear resistance, characterized by comprising 30% Fe and the balance Fe and normal impurities. 4 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, Cu0.20~
5.00% S, 0.03 to 0.30% S, and the balance Fe and normal impurities. 5 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05-1.50, Ni0.20-1
．． A cast hot work tool steel with excellent wear resistance characterized by comprising 50% Fe and the balance Fe and normal impurities. 6 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, Ni0.20~
1.50% V, 0.05-1.00% V, and the remainder Fe and normal impurities. Cast hot work tool steel with excellent wear resistance. 7 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, S0.03~0
．． 30% Ni, 0.20-1.50% Ni, the balance Fe and normal impurities. 8 C0.25-0.60%, Si1.50% or less, M
n1.50% or less, Cr0.30-2.50%, (1/
2W+Mo)0.30~2.50%, Co0.20~5
．． 00%, Ti0.05~1.50%, Cu0.20~
5.00%, S0.03~0.30%, Ni0.20~
1.50% V, 0.05-1.00% V, and the remainder Fe and normal impurities. Cast hot work tool steel with excellent wear resistance.