JPS63118054A - High-speed tool steel having superior toughness - Google Patents

Abstract

PURPOSE:To obtain a high-speed tool steel having high toughness in conventional melting and gas atomization processes by specifying the amts. of Cr, Mo, W and V and the relation between the amts. of C and V and adding a specified amt. of Al in relation to the amt. of N. CONSTITUTION:The compsn. of a high-speed tool steel is composed of, by weight, 0.8-3.4% C, <=2% Si, <=1.0% Mn, 3-8% Cr, 0.1-10% Mo, 0.1-10% W (8<=W+2Mo<=30), 4-10% V (C>=0.2XV), 0.01-0.2% N, >0.6%Al (0.5<=Al-2N<=2) and the balance Fe with inevitable impurities. The high-speed tool steel ensures satisfactory toughness in the presence of N and has superior machinability and durability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-speed tool steel whose toughness is increased by A1.

[Conventional technology]

Since high-speed tool steel must have a high degree of wear resistance, MOLW and V are often contained. M
OlW, ■ combines with C to form a hard carbide,
These contribute to improving wear resistance, but
When the content of MOLW,
Manufacturing becomes difficult.

Therefore, manufacturing using powder metallurgy has progressed even in the field of high-speed tools, and Nt
Gas atomization method is the mainstream. The powdered metal is solidified to a true density state by a so-called HIP method or the like.

[Problem that the invention seeks to solve]

However, in the N2 gas atomization method, it is inevitable that a large amount of N (usually 0.05% or more) forms a solid solution in the metal matrix. It has been said that this N contributes to improving hardness and wear resistance, but according to the research conducted by the present inventors, in the M range where N is 0.03% or more, the effect on hardness and wear resistance is small ( However, it was found that this actually caused a decrease in toughness.

In other words, since N acts as solid solution strengthening in high-speed tool steel, a small amount of 0.02% or less will not lead to improvements in hardness and wear resistance, but for example, N2 gas atomization 0.05% contained in case of law
At higher content levels, the increase in hardness tends to be saturated, and the decrease in toughness becomes significant.

Needless to say, toughness is an important property in high-speed tool steel, along with strength and wear resistance, and increasing toughness is extremely important not only when using the Nt gas atomization method, but also when using the normal melting method. It is.

The present invention is applicable not only to ordinary dissolution methods but also to N2
The present invention provides a high-speed tool steel that has a high degree of toughness even when subjected to gas atomization.

[Means for solving problems]

As mentioned above, N is dissolved in the matrix, and depending on its content, it has little effect on hardness and wear resistance, and may cause a decrease in toughness. Considering this, removing N dissolved in the matrix can be one measure to improve toughness. Ti and Z are used to remove solid solution N.
It is possible to add nitride-forming elements such as r, A1, etc., but T
In addition to being expensive, Zr also forms carbides, so in high-C materials such as high-speed tool steel, coarse carbonitrides are formed, and its use is not allowed if toughness is important.

Therefore, the present inventors focused on the remaining A1, and A7! As a result of detailed investigation and research into the influence of
It has been found that in addition to combining with N to form A I N and improving toughness by reducing the amount of N dissolved in solid solution, it also dissolves in solid solution in the matrix and contributes to improving toughness. In other words, the addition of Af improves the toughness in terms of both ■ and ■.
It has become clear that a large effect on improving toughness can be obtained as a whole. The reason for (2) is considered to be that the Ms point increases due to the solid solution of Al, the retained austenite structure decreases, and the martensitic structure changes to a form that is advantageous for toughness.

The present invention was completed based on this knowledge by investigating and specifying the amount of Al that effectively exerts both the effects (1) and (2).The gist of this invention is that the weight ratio of C:0.
8 to 3.4% and C20,2■, Si: 2% or less, Mr
zl, 0% or less, Cr: 3-8%, Mo: 0.1-10
%, W: 091-10% and 8≦W + 2 M O≦
30, ■=4~1O%, N:0, O1~0.2%, Aj
! :Q, 0.5≦A7 for more than 5%! =2N≦2,
Furthermore, if necessary, it contains Co: 6% or less, and the balance is Fe and unavoidable impurities, making it a high-speed tool steel with low toughness.

In the high speed tool steel of the present invention, especially AN is 0.6%.
By containing 0.5≦, 1 to 2N≦2, the toughness is effectively improved from both of the above-mentioned (1) and (2).
A high degree of toughness is ensured as a whole. Furthermore, excellent performance in terms of hardness and wear resistance is ensured due to the inclusion of V and the like.

In addition, Aj! A high-speed tool steel with a composite addition of N and N is known from JP-A-53-14691. However, this steel aims to refine the VC carbide by the combined addition of A1 and N, and the purpose of the addition is completely different from that of the steel of the present invention. In addition, the Aβ content itself is 0.6% at maximum in this known steel, and with such a small amount of A1, the toughness improvement effect from both (1) and (2) which is the aim of the present invention cannot be obtained.

The reason for limiting the composition of the steel of the present invention will be described below.

C: Useful as a carbide-forming element and as a matrix-strengthening element. The amount required for VC carbide precipitation is:
It is 0.2% per 1% of V, and from the viewpoint of carbide precipitation, an amount equivalent to at least 0.2 x V is required. On the other hand, considering the balance between hardness and toughness of the matrix, the optimum range of the solid solution amount of C in the matrix is 0.44 to 0.5%. From these facts, the Cl required to make ■ work effectively as a carbide and to dissolve an optimum amount of C in the matrix is 0.8% for the lower limit of 4% for ■.
%, 2.0% against the upper limit of 10%, but MO
Since lW also generates carbides, when the W equivalent is 30, which is the maximum, the required amount of C is 3.4%, which is the upper limit of C.

Therefore, C should be 0.8 to 3.4%, and at the same time C≧0
．． 2×V was defined. If it is less than 0.8%, matrix hardness decreases and wear resistance deteriorates, and if it exceeds 3.4%, toughness deteriorates.

Si: Used as a deoxidizing agent, Si has the effect of increasing temper hardening resistance at around 0.8%. However, when the W equivalent is high, this effect is small, and on the other hand, Si produces oxide inclusions, etc., which causes a decrease in toughness.
The upper limit was %. The lower limit is not particularly specified because a small amount of Si has little effect on hardness and toughness, but it goes without saying that the amount necessary for deoxidation is contained.

Mn: Like Si, it is used as a deoxidizer, but
If it exceeds 1.0%, the austite structure will be stabilized and expanded and the amount of retained austenite will increase, causing a decrease in hardness and toughness, so it is specified to be 1.0% or less. In addition,
Regarding the lower limit, since a small amount of Mn has a small effect on hardness and toughness, it is not particularly specified, but it goes without saying that the amount necessary for deoxidation is contained.

Cr: It is an element that mainly improves hardenability, but if it is less than 3%, this effect is small (on the contrary, if it is added in excess of 8%, it will coarsen the carbide and make it more likely to become brittle.
The range was set to 8%.

MOlW: Combines with C to form MbC type and MtC type carbides, improving wear resistance. Further, secondary hardening due to tempering is increased. Furthermore, it also imparts heat resistance. In order to fully exhibit these hardening effects, it is necessary to contain Mo and W in an amount of 0.1% or more, and the W equivalent (W'+ 2 Mo
) must be 8 or more. However, if MOLW exceeds 10%, the toughness improvement effect will be canceled by AIL, so the upper limit for each should be 10%, and hot workability should be ensured for W equivalent. For the sake of meaning, the upper limit was set at 30.

Note that if the W equivalent is less than 20, there is no problem with the ingot material, but if it is more than 20, the precipitated carbides will become coarse and the toughness will decrease significantly, so the W equivalent! If it is 20 or more, powder material is preferable.

■: Combines with C in copper steel to form hard VC carbide,
It greatly contributes to improving wear resistance. However, if it is less than 4%, the amount of precipitated carbides is small and the effect on wear resistance is small, so 4% is set as the lower limit. The upper limit is set at 10% because even if it is added in excess of 10%, the precipitated carbides will become coarse and the effect on wear resistance will be saturated, and hot workability will also decrease.

N: Basically, it is effective for improving the hardness and wear resistance of the matrix, so it is contained in an amount of 0.01% or more.

However, as the amount of solid solute N increases, the effect on hardness and wear resistance becomes smaller, and rather starts to have an adverse effect on toughness. One of the characteristic effects of the high-speed tool steel of the present invention is to suppress the increase in the amount of solid solute N, but this effect becomes insufficient when N exceeds 0.2%, and Machinability also deteriorates. Therefore, N rat is 0
．． The range is 0.01 to 0.2%. In addition, when employing the N2 gas atomization method, about 0.05 to 0.2% of N will be contained whether desired or not.

Co: By adding Co as necessary, heat resistance and temper hardening resistance can be increased. However, even if added in excess of 6%, these effects will be saturated and the hardenability and hot forgeability will deteriorate, so the upper limit is set at 6%. The lower limit is not particularly stipulated since a corresponding effect can be expected even with a small amount of Co.

Al--An element that characterizes the high-speed tool steel of the present invention.

This A7! A part of the ions combine with N to form AIN nitride. However, instead of all N combining with A1,
A portion becomes solid solution N. As a result, a certain amount of solid solution N is generated, which is effective in improving hardness and wear resistance. The remaining Al that did not bond with N is dissolved in the matrix, and Mi
Improves toughness from the woven surface. That is, solid solution of Al raises the Ms point, reduces retained austenite, and produces a martensitic structure that is advantageous for developing toughness. According to the research conducted by the present inventors, in order to significantly exhibit these two toughness-improving effects, Al must exceed 0°6% and (Al-2N), which is considered to be hard 78Afl, must be 0.5 or more. It is necessary that there be. However, it has been found that when (81-2N) exceeds 2, a ferrite structure is formed and the toughness is conversely reduced. Therefore, for All, more than 0°6% and 0.5≦A7! −2N≦2.

〔Example〕

○ Sample fi11ml~4 with a W equivalent of about 8 as shown in Table 1
, test steels 1lk15 with a W equivalent of about 10 to test steels 11 to 16 with a 1O1W equivalent of about 18 were manufactured by a melting method, respectively. Then, each test steel was quenched at 1230°C, and
After tempering three times at 75°C, the hardness and transverse rupture strength as toughness of each sample steel were measured. The bending test is 5n thickness x 10f1
A test piece of width x 55 length was used and the distance between gauges was 40. The results are shown in Table 2. Moreover, FIG. 1 illustrates the same results by equivalent weight. As is clear from FIG. 1, the high-speed tool steel of the present invention has excellent toughness and high hardness, and is clearly different from comparative steels.

Table 2 O After quenching the test steels numbered 1 to 16 shown in Table 1 at 1230°C, the tempering hardness was adjusted to HRC65.0 ± 0°5 in order to eliminate the influence of hardness on transverse rupture strength. The same bending test as above was performed. The results are shown in Table 3. Moreover, FIG. 2 shows the same results in relation to Al-2N. As is clear from Figure 2, the toughness is 0.5≦/1
It is significantly improved within the range of ~2N≦2.

Table 3 ○ Test steels 17 to 21 with a W equivalent of approximately 18 shown in Table 4
, and test tunings 22 to 26 having a W equivalent of about 25 were manufactured by powder metallurgy. N2 gas atomization method is used for powdering, and HIP method is used for solidification (1150℃ x 1hr at 2000℃).
kg/cm") was used. Table 5 shows the results of the hardness test and bending test conducted on each of the produced test steels in the same manner as above.
It is shown in Table 6.

Table 6 shows the results when the hardness was adjusted to I (RC65,0±0.5).As is clear from these results, the high speed tool steel of the present invention was manufactured by the 15) advanced metallurgy method. It retains high hardness and toughness even in extreme cases.

Table 5 Table 6 [Effects of the Invention] As is clear from the above explanation, the high-speed tool steel of the present invention is in a state where N is co-produced to improve toughness and hardness and wear resistance. Since there is no sacrifice, sufficient toughness, machinability and durability are ensured, not only for steel types that can be manufactured using the melting method, but also for high-hardness steel types that can only be manufactured using the N2 gas atomization method. This is a high-quality high-speed tool steel that is extremely superior in both aspects.

[Brief explanation of the drawing]

Fig. 1 is a chart showing the relationship between the hardness and transverse rupture strength of the test steel by W equivalent, and Fig. 2 is a chart □ showing the transverse rupture strength of the test steel in relation to Aff-2N. 7s 2 (71 Al-2(N) #L bamboo force (kq/m♂) yL bamboo force (kl/1m')

Claims (2)

[Claims] (1) C: 0.8-3.4% by weight and C≧0.2V
, Si: 2% or less, Mn: 1.0% or less, Cr: 3 to 8
%, Mo: 0.1-10%, W: 0.1-10% and 8
≦W+2Mo≦30, V: 4-10%, N: 0.01-
0.2%, Al: more than 0.6%, 0.5≦Al-2N≦2
A high-speed tool steel with low toughness, the balance being Fe and unavoidable impurities. (2) C: 0.8-3.4% by weight and C≧0.2V
, Si: 2% or less, Mn: 1.0% or less, Cr: 3 to 8
%, Mo: 0.1-10%, W: 0.1-10% and 8
≦W+2Mo≦30, V: 4-10%, N: 0.01-
0.2%, Co: 6% or less, Al: 0.5 over 0.6%
A high-speed tool steel with low toughness, containing ≦Al-2N≦2, with the balance being Fe and inevitable impurities.