JPS6059052A - Hot working tool steel - Google Patents

Abstract

PURPOSE:To obtain a hot working tool steel having increased toughness and improved mechanical characteristics such as heat check resistance by adding a very small amount of Ca, Mg, Al, B or REM to an Mn-Ni-Cr-Cu tool steel and by reducing the amount of Si. CONSTITUTION:This hot working tool steel consists of, by weight, 0.15-0.80% C, <0.10% Si, <=3.0% Mn, one or more among <=4.0% Ni, <=10.0% Cr and <=3.0% Cu, one or more among <=5.0% Mo, <=5.0% W, <=3.0% V, <=1.0% Ti, <=1.0% Nb, <=1.0% Zr and <=5.0% Co, one or more among 0.0005-0.010% Ca, 0.001-0.50% Mg, 0.001-0.10% Al, 0.005-0.010% B and 0.0005-0.40% REM, and the balance Fe with inevitable impurities. To the steel may be added a very small amount of S, Se, Te, Bi or Pb. The shock resistance of the steel can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot work tool steel that has good toughness and excellent mechanical properties such as heat check resistance and impact resistance.

In recent years, hermetic forging without burr is becoming popular for the purpose of chipless processing that does not generate processing waste in press working and forging, but in such closed forging, the processing die is worn out. In many cases, they become unusable early due to cracking, cracking, or chipping, and improvements in these problems are strongly desired. On the other hand, there is a marked trend toward high-precision and high-speed forging in conventional burr pressing and forging processes, and with this, the life of the mold is significantly reduced due to wear, cracking, and chipping of the gold. There is a strong desire to improve this, but conventional hot work tool steels have poor wear resistance and temperature resistance.
It has not been possible to satisfactorily satisfy the conflicting characteristics of crackability and chipping resistance, and it has not been possible to meet these demands.

The inventors of the present invention have focused on these conventional problems and have investigated various types of problems, and have developed a method for preventing cracking and chipping, as well as reducing abrasion and the occurrence of heat checks caused by thermal shock. We have previously discovered that it is effective to improve the resistance to this disease and its propagation. In order to improve the resistance to the occurrence and propagation of heat check due to thermal shock, and to simultaneously improve the contradictory properties of wear resistance, cracking resistance, and #chipping resistance, it is necessary to significantly lower the SL and at the same time increase Ca, Mg, A sentence, B.

The present invention was completed by discovering that it is effective to add one or more types of REM.

In other words, this invention was made with a focus on the problems newly occurring in recent press working and forging work, and in particular significantly increases the resistance to the occurrence and propagation of heat checks due to thermal shock, making it possible to improve the performance of practical molds. The object of the present invention is to provide a hot work tool steel that has improved wear resistance, cracking resistance, and chipping resistance at the same time.

The hot work tool steel according to the present invention has C: 0.15 in weight %.
% or more and 0.80% or less, Si: less than 0.10%, Mn: 3.0% or less, and Ni: 4.0% or less, Cr: 10.0% or less, Cu: 3.0% or less One or more types of.

Furthermore, Mo: 5.0% or less, W: 5.0% or less.

V: 3.0% or less, Ti: l, 0% or less,
Nb: 1.0% or less, Zr: 1.0% or less, Co: 5
．． One or more of the following 0% or less, Zarani Ca:
0.0005% or more and 0.010% or less, Mg: 0.00
1% or more 0., 50% or less, Ai: 0.001% or more 0
．． Less than 10%.

B: 0.0005% or more and 0.010% or less.

REM (requires one or more rare earth elements): 0.0
0.005% or more and 0.40% or less, and if necessary, S: 0.03% or more and 0.20% or less, Se: 0.03% or more and 0.20% or less, Te: 0.
0.01% or more and 0.15% or less.

Bi: 0.02% or more and 0.15% or less, Pb: 0.03
% or more and 0.20% or less, and the balance is Fe and impurities.

By the way, in accordance with the above-mentioned purpose of the present invention, first, among the conventional hot work tool steels, JISSKT4.5KD61
．． Selecting 3N i-3Mo steels, the resistance to the occurrence and propagation of heat check due to the thermal shock of St contained in these steels was investigated. Each was evaluated by

For these tests, each of the above-mentioned test steels was melted in a 50Kgf high-frequency induction furnace, then forged into bars with a diameter of 20mm, and subjected to heat check resistance and impact resistance tests.

Among these, the influence of St on heat check resistance was determined by using a test piece with a diameter of 15+ am and a thickness of 5 mm, and raising the temperature from room temperature to 750°C by high-frequency induction heating.
Next, the temperature is raised and lowered by cooling to room temperature by water cooling for 15 minutes.
This was determined by examining the maximum heat check depth that occurred in each test piece after 00 repetitions. The results were as shown in FIG.

Moreover, the influence of Si on impact resistance was determined by using a JIS No. 3 impact test piece and setting the test temperature to room temperature to determine the impact value of each test steel. The results were as shown in FIG.

As shown in Figures 1 and 2, the St content is approximately o, i
The impact value improves as the maximum heat check depth decreases at 0% by weight, and the Si contained in hot work tool steel increases.
By reducing the content to less than 0.10% by weight, the mechanical properties represented by heat check resistance and impact resistance of conventional hot work tool steels can be significantly improved, and the thermal shock resistance of hot work tool steels can be significantly improved. It has been found that resistance to the occurrence and propagation of heat checks due to heat checking can be significantly improved, and the contradictory properties of wear resistance, cracking resistance, and chipping resistance can be improved.

Subsequently, we further investigated the effects of additive elements on the toughness of the above-mentioned low-St hot work tool steel, and particularly
We decided to investigate the effects of M, B, and REM (rare earth elements).

Therefore, in this investigation, JIS hot work tool steel
5KD61 was selected and this steel was melted in a 50 kgf vacuum induction furnace to change the Si content in this steel, and each steel contained Ca, Mg, and AJI.

B, one or more elements selected from REM as the first
It was contained in the values shown in the table, and then it was made into ingots and forged into bars with a diameter of 20 mm. Next, impact test pieces based on JIS No. 3 test pieces were made from each bar and an impact test was conducted at room temperature. . The results are shown in FIG.

Table 1 (Weight %) As shown in Table 1 and Figure 3, when an appropriate amount of one or more of Ca, Mg, Ai, B, and REM is contained in low St hot work tool steel, have newly discovered that the impact resistance of low St hot work tool steel can be further improved.

Next, the composition range (weight %) of the hot work tool steel according to this invention
The reason for this limitation will be explained.

C: 0.15% or more and 0.80% or less C is an effective element for ensuring the hardness and wear resistance required for hot work tool steel, and in order to obtain such effects, 0.15% or more and 0.80% or less It is necessary to contain 15% or more. However, if it is too large, the toughness and workability will decrease, so 0.
It was set to 80% or less.

Si: Less than 0.10% St can significantly improve the resistance to the occurrence and propagation of heat check due to thermal shock in hot work tool steel by regulating this content as described above.
Wear-resistant and crack-resistant.

Since the contradictory properties of chipping resistance can be simultaneously satisfied, the Si content is set to less than 0.10%.

Mn: 3.0% or less Mn is an element that has a deoxidizing and desulfurizing effect during steel melting, and also contributes to improving hardenability, so it should be added as appropriate depending on the melting method etc. It's also good. However, if it is too large, the toughness and workability will deteriorate, so it is necessary to keep it at 3.0% or less.

Ni: 4.0% or less, Cr: 10.0% or less.

Cu: 3.0% or less of one or more Ni, Cr, and Cu all strengthen the matrix and increase the strength of hot work tool steel, especially high temperature strength, impact resistance, and heat check resistance. These elements are effective for achieving this effect, and one or more of these elements are added in order to obtain such effects. In addition, Ni and Cr contribute to improving hardenability, and C
r is an element that contributes to improving wear resistance by forming carbides, and Cu contributes to improving wear resistance by precipitation hardening. However, if added in large amounts, the toughness and workability will decrease, so Ni should be added at 4.0% or less, and Cr should be added at io
, o% or less, and Cu needs to be 3.0% or less.

Mo: 5.0% or less, W: 5.0% or less, V: 3.0
% or less, Ti: 1.0% or less, Nb (including cases where it is partially replaced with Ta): 1.0% or less.

One or more of the following: Zr: 1.0% or less, Co: 5.0% or less. Mo, W, V, Ti, Nb, Zr, and Co all form carbides and increase heat treatment hardness. In addition to the above, Nb, 'Ti, and Zr are also effective elements in refining crystal grains, ensuring toughness, and improving impact resistance. Therefore, one or more of these are added. However, if added in large amounts, the manufacturability will deteriorate, the toughness will decrease, and the surface will increase, so MO should be less than 5.0%, W should be less than 5.0%, and ■ should be less than 3.0%. Below, Ti
1.0 or less for Nb, 1.0% or less for Nb,
1.0% or less for Zr, 5.0% for Co
It is necessary to do the following.

Ca: 0.0005% or more and 0.010% or less.

Mg+0.001% or more - H0.50% or less.

Sentence A: 0.001% or more 0, 1'O% or less, B: 0
．． 0005% or more and 0.010% or less, REM: 0.00
As mentioned above, one or more of Ca, Mg, AM, B, REM (one or more rare earth elements) from 0.05% to 0.40% improves the toughness of low St hot work tool steel. One or more of these elements are added because they are effective elements for further increasing the impact resistance and, in particular, considerably improving the impact resistance. In this case, Ca, Mg, and REM increase the toughness of the steel by deoxidizing and controlling the morphology of inclusions in the steel, and AfL and B fix the N in the steel in the form of AIN and BN to eliminate the negative effects of N. In addition, A-texture has the effect of increasing the toughness of steel by contributing to deoxidation strengthening and prevention of grain coarsening. In order to obtain such an effect, Ca should be 0.0005% or more, Mg should be o,ooi% or more, An should be O,oO1% or more, B should be 0.0005% or more, REMhaO, OOO5. % or more is necessary. However, if it is contained in a large amount, it will deteriorate the toughness and workability of the steel, so the content of Ca should be o, oio% or less, M
o for g, 5o% or less, 0.1 for AJI
0% or less, B should be o, oio% or less, and REM should be 0.40% or less.

S: 0.03% or more and 0.20% or less, Se: 0.03%
0.20% or more, Te: 0.01% or more and 0.15%
Hereinafter, B i: 0, 0.02% or more and 0.15% or less, Pb: 0.03% or more and 0.20% or less, S, Se, Te, Bi, and Pb are all steel. It is an effective element for improving the machinability of metals, and one or more of these are added as necessary to improve the machinability when processing into the shape of a specified tool, mold, etc. It is good, but
In this case, in order to obtain the above effect, S must be 0.03
% or more, Se 0.03% or more, Te 0.02% or more, Bi 0.02% or more, and PB 0.03% or more. However, if added in a large amount, it will harm the toughness and reduce the workability, so the S content should be 0.2
0% or less, Se 0.20% or less, Te 0.15% or less, Bi 0.15% or less,
Pb needs to be 0.20% or less.

Examples of the present invention will be described below along with comparative examples.

First, steel having the chemical composition shown in Table 2 (odd numbered steels are comparison steels, even numbered steels are inventive steels) was melted and then ingot-formed. In addition, in Table 2, test steel No.

1.2 and No. 17.18 have basic components in JISSK
Compatible with T4 and low Si, No. 3
, 4, No. 11.12 and No.

23.24 has the basic components compatible with 5KD61 and has low S
i, No. 5, 6 and No. 1
3.14 has a basic composition corresponding to 5KD8 and has a low St, while No. 7.8° No. 15.16 and No. 19, 20 have a basic composition corresponding to 3Ni-3Mo steel and It has a low St, No. 9.10
and No. 21 and No. 22 have basic components corresponding to semi-high-speed steel used as high-strength hot work tool steel and low Si.

Next, for each steel ingot obtained above, a forging ratio of 6 to 7
After forging to a certain degree, quenching and tempering heat treatments were performed to examine the impact resistance, anisotropy, and heat check resistance of each sample steel. At this time, the quenching and tempering heat treatment was performed under the quenching (denoted by H) and tempering (denoted by T) conditions shown in Table 3, using test pieces having hardness also shown in Table 3. And the impact resistance test is JIS a
No. 1 test piece, and the test temperature was set to room temperature. The results are also shown in Table 3. On the other hand, the heat check resistance test was performed using a test piece with a diameter of 15 mu and a thickness of 5 fflI11, and was heated to 750'C by high-frequency induction heating at room temperature. Heating to room temperature and then water cooling to room temperature was repeated 150 times.
This was done by performing the test 0 times and measuring the maximum heat check depth. As shown in Section 37', the steels of the present invention all have higher impact values than the comparative steels, and the anisotropy of the impact values depending on the forging direction is also higher. It is clear that excellent results have been obtained. Furthermore, regarding heat check resistance, it is clear that the maximum heat check depth of the steels of the present invention is smaller than that of the comparative steels in all steels of the same type.

In this way, the steel of the present invention has better mechanical properties, including impact resistance and heat check resistance, than conventional hot work tool steels, and it is more resistant to heat checks due to thermal shock than hot work tool steels. It is possible to improve resistance to generation and propagation, and it is possible to simultaneously improve the conflicting properties of wear resistance, cracking resistance, and chipping resistance, and to extend the life of tools and dies compared to conventional methods. It can be greatly increased or used as a material for tools and molds that perform processing under more severe conditions.

Next, sample steel Nos. 1 to 10 are selected from the steels shown in Table 2, and die forging is performed by manufacturing a forging die for the stamped parts shown in Table 4 using these as raw materials. The durability of each mold was investigated. These results are also shown in Table 4. In Table 4, the durability of the molds is set as 1 for the molds made of the comparative steels, and the durability of the molds made of the steels of the present invention is expressed based on this.

Table 4 As shown in Table 4, it was clear that all the molds made of the steel of the present invention had better durability than the molds made of the comparative steel.

As explained above, the hot work tool steel according to the present invention has, in weight percent, C: 0.15% or more and 0.80% or less, Si: less than 0.10%, Mn: 3.0% or less, and Ni: 4.0% or less, Cr: 10.0% or less, C
u: one or more of 3.0% or less, Mo: 5.0% or less, and W: 5.0% or less.

V: 3.0% or less; Ti: 1.0% or less, Nb: 1.0
% or less, Zr: 1.0% or less, Co: 5.0% or less, and Ca: 0.0O05%
0.010% or more, Mg: 0.001% or more and 0.5
Less than 0%.

Sentence A: O, 0015 or more and 0.10% or less.

B: O,005% or more and o,oio% or less.

REM (one or more rare earth elements) = 0.0
0.005% or more and 0.40% or less, and if necessary, S: 0.03% or more and 0.20% or less, Se: 0.03% or more and 0.20% or less, Te: 0.
0.01% or more and 0.15% or less.

Bt: 0.02% or more and 0.15% or less, Pb: 0.03
% or more and 0.20% or less, the balance being Fe and impurities, so compared to conventional hot work tool steel, it has better toughness, especially impact resistance and heat check resistance. It has extremely excellent mechanical properties, and can significantly improve resistance to the occurrence and propagation of heat checks caused by thermal shock, and can overcome the contradictory properties of wear resistance, cracking resistance, and chipping resistance. At the same time, it is possible to improve materials such as tools and dies used in these processes, and it is possible to sufficiently cope with the increased degree of processing in press working, forging, etc. that has been increasingly required in recent years. It is suitable as a tool and mold, and it is possible to extend the tool and mold life and reduce tool and mold costs based on this. By adding machinability-improving elements to the basic ingredients, tools and molds can be This has very excellent effects in that it is possible to improve dimensional accuracy and reduce tool and tool costs based on this.

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing an example of the results of investigating the effects of Si on heat check resistance and impact resistance, respectively, in hot work tool steel. Mg, AM, B. It is a graph which shows an example of the result of investigating the effect on impact resistance when adding one or more elements of REM. Patent applicant: Daido Steel Co., Ltd. Representative patent attorney: Yutaka Oshio

Claims (2)

[Claims] (1) In weight%, C: 0.15% or more and 0.80% or less, Si: less than 0.10%, M n: 3, 0% or less, and Ni: 4.0% or less, Cr: 10. 0% or less, C
u: one or more of 3.0% or less, Mo: 5.0% or less, and W: 5.0% or less. V: 3.0% or less, Tj: 1.0% or less, Nb: 1.0
% or less, Zr: 1.0% or less, CO: 5.0% or less, one or more types, rough Ca: '0.0005
% or more and 0.010% or less, Mg: 0.001% or more and 0.01% or more.
Less than 50%. Sentence A: O, 001% or more 0', 10% or less, B: 0.0
005% or more and 0.010% or less, REM: 0.0005
% or more and 0.40% or less, the balance being Fe and impurities. (2) In weight%, C: 0.15% or more and 0.80% or less, Si: less than 0.10%, Mn: 3.0% or less, and Ni: 4.0% or less, Cr: 10.0 %below,
Cu: one or more of 3.0% or less, Mo: 5.0% or less, and W: 5.0% or less. Vco 3.0% or less, Ti: 1.0% or less, Nb: 1.0
% or less, Zr: 1.0% or less, Co: 5.0% or less, and Ca: O, 0O05%
0.010% or more, Mg: 0.001% or more 0.5
Less than 0%. Sentence A: O, 001% or more and 0.10% or less, B: 0.00
05% or more and 0.010% or less, REM: 0.0005%
One or more of the above 0.40% or more, and S: 0.03% or more and 0.20% or less. Se: 0.03% or more and 0.20% or less, Te: 0.01
% or more and 0.15% or less, BE: 0-02% or more 0.15
% or less, Pb: one or more of 0.03% or more and 0.20% or less, the balance being Fe and impurities.