JPS6221863B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to hot work tool steel, and more particularly to age hardening type austenitic hot work tool steel having excellent wear resistance and toughness at high temperatures. Conventional hot work tool steels include 5Cr hot work tool steels represented by JIS SKD61 and 62, and 0.35C of SKD7.
−3Cr−3Mo hot work tool steel and ASM6F4 0.2C
-3Ni-3Mo and 0.2C-3Cr-3Mo precipitation hardening hot work tool steels are known. Furthermore, it is also known that these tool steels are all made of martensite base or bainite base with precipitated carbides, and therefore their hardness rapidly decreases at around 550°C. On the other hand, the temperature of workpiece materials such as copper alloys is 700℃.
In case of high temperature as above, JIS SKD5, AISI
H19 is used, but these hot work tool steels are all martensitic and cannot avoid softening. Therefore, an austenitic hot work tool steel with high high temperature strength is required as a hot work tool steel for such work materials, and JIS SUH660 and the like are used for this purpose, but this has the disadvantage of being expensive. There is. In contrast, conventionally known age-hardening austenitic hot work tool steels, which are relatively inexpensive,
The drawback is that it has low toughness and is easily damaged during use. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an improved age-hardening austenitic hot work tool steel that eliminates these drawbacks of various conventionally known hot work tool steels. The present inventor conducted various studies to achieve this objective, and as a result found that age-hardening austenitic hot work tool steel having the following chemical components is optimal. That is, in the present invention, C0.35~0.60%, Si0.02
% or less, Mn14.0~20.0%, Cr2.0~8.0%, Ni1.5
The basic ingredients are ~3.5% and V0.5~3.5%, and
Mo0.01~4.0%, W0.01~4.0%, Ti0.001~0.5
%, Zr0.001~0.5%, Nb0.001~0.5% or more, and the balance is essentially Fe and trace impurities. It is something to do. Hereinafter, the present invention will be explained in detail based on examples thereof. First, the hot work tool steel according to the present invention is characterized by having the chemical composition as described above, and the reason for limiting the chemical composition and composition range of the steel according to the present invention will be explained here. C strengthens the austenite base of steel and combines with carbide constituent elements Cr, Mo, W, V, and Nb,
It is effective in causing age hardening, significantly hardening the steel, and improving wear resistance. In order to fully exhibit these effects, a C content of 0.35% or more is required, but if it is too large, the toughness will be impaired, so the content is limited to 0.35 to 0.60%. Since Si is an element that impairs toughness at high temperatures, the content should be reduced to 0.05% as much as possible for manufacturing reasons.
The creep characteristics are improved by limiting to the following. Mn is added to make the microstructure of the steel austenite, and this element provides a stable austenite base and high-temperature strength, so it plays an important role in the steel of the invention. . This stable austenite can also be obtained with 14% or less Mn, but if it is too low, the toughness will be insufficient, so it should be 14% or more, and if it is too high, it will reduce the maximum hardness of age hardening and Since the strength decreases, it is set at 20%. Cr combines with C to form a double carbide, contributes to wear resistance, and is added to solidly dissolve in the austenite matrix to increase high-temperature strength. In order to fully exhibit this result in balance with the toughness, the content is limited to a range of 2% to 8%. Although Ni tends to reduce age hardenability, it is extremely effective in improving toughness. but,
If Ni is less than 1.5%, the effect will be small, and if it is more than 4%, the decrease in aging hardness will be small, so Ni is limited to a range of 1.5 to 3.5%. V causes improvement in toughness by refining crystal grains and significant solid solution strengthening of austenite, and also causes age hardening due to carbide precipitation, improving wear resistance, and is added to maintain high-temperature strength. do. However, below 0.5%, the effect is small;
If it exceeds 3.5%, the toughness will decrease, so keep it below 3.5%. Mo combines with C to form carbides and strengthens the austenite base as a solid solution, thereby increasing wear resistance and high-temperature hardness. However, if the amount is too small, there will be no effect, and if the amount is too large, the toughness will decrease, so it is limited to a range of 0.01 to 4.0%. W exhibits the same effect as Mo, and is excellent in forming carbides and solid solution strengthening of the austenite base, and is limited to 0.01 to 4.0%. Ti, Zr, and Nb are effective in strongly deoxidizing molten metal.
In addition, C and M·C are fixed as carbides, forming very hard carbides and improving wear resistance. However, if it is contained in a large amount, it will have a negative effect on toughness, so it should be limited to 0.5% or less. The tool steel according to the present invention has the chemical composition and composition range as described above, and next, the present invention steel will be described with reference to Examples. Table 1 shows the JIS steel used in the experiment.
The chemical components of SKD5 and 62 and the experimental samples of the present invention are shown. Table 2 shows the hardness (Hv) of the samples shown in Table 1 when they were aged or tempered after being rapidly cooled from the standard solution temperature or quenching temperature. As can be seen from Table 2, in the case of the steel of the present invention,
It was confirmed that the hardness showed the highest hardness at 750℃ aging, and there was only a slight decrease in hardness even at higher aging temperatures. hardness decreases. As a result, when the operating temperature reaches 700°C or higher, plastic flow is more likely to occur due to insufficient hot strength, and wear is also more likely to occur.

【table】

【table】

[Table] Next, these samples were subjected to a high temperature tensile test, a Charpy impact test, and a creep rupture test (750℃, rupture time of 10Kgt/ ^mm2 ), and their high temperature strength, ductility, and toughness were compared. . The results are shown in Table 3. The results in Table 3 also show that the steel of the present invention is superior in tensile strength and creep rupture time at 700° C. and Charpy impact value at room temperature compared to martensitic JIS SKD5 and 61. As described above, the present invention has various mechanical strengths at high temperatures that are superior to conventionally known hot work tool steels, precipitation hardening hot work tool steels, martensitic hot work tool steels, etc. The present invention also provides an improved age-hardening austenitic hot work tool steel that is less expensive than austenitic hot work tool steels such as JIS SUH660.

Claims (1)

[Claims] 1 C0.35~0.60%, Si0.05% or less, Mn14.0~
20.0%, Cr2.0~8.0%, Ni1.5~3.5%, V0.5~3.5
% is the basic alloy component, Mo0.01~4.0%, W0.01
~4.0%, Ti0.001~0.5%, Zr0.001~0.5%,
An age-hardening austenitic hot work tool steel containing one or more of 0.001 to 0.5% of Nb, with the remainder consisting essentially of Fe and trace impurities.