JPH0411615B2 - - Google Patents

Description

[Detailed description of the invention]

High-speed tool steel used in cutting tools such as taps, broaches, and drills is of course required to have properties that directly control tool life, such as wear resistance, heat resistance, and toughness. On the other hand, softening of the cutting edge due to the heat of grinding during finish grinding, burring and sagging of the cutting edge, etc. often reduce tool life, and it can be said that grindability indirectly controls tool life. Furthermore, grindability is important for improving grinding efficiency and grinding finishing accuracy. especially
2.5% V series typified by SKH52 and 3% V series high speed steels typified by SKH53 have good wear resistance and are highly effective for cutting difficult-to-cut materials and general-purpose high-performance tools. The reality is that its use is limited to a very small number of people due to its extremely poor quality. It is well known that keeping the V content as low as 1.0 to 1.2% is effective in improving grindability, and several types of high-speed tool steels, including AISIM42, have been put into practical use. has been done. However, since the content of V is low, there is a problem that the wear resistance is insufficient. In addition, a method has been proposed to improve grindability by adding small amounts of Zr, Hf, and REM (Japanese Patent Application Laid-Open No. 52-118).
120216), but it has not been put to practical use because it is difficult to control the amount of added trace elements at a constant level. In view of the above, an object of the present invention is to provide a high-speed tool steel containing 1.8% or more of V, which has significantly better grindability than existing materials. Our objective is to provide a material with excellent grindability that has not been previously available, especially in 2.5% V-based and 3% V-based high-speed tool steels. In order to achieve the above objective, the influence of each alloying element on grindability was systematically studied. As a result, C 0.9~1.4%, Si 0.1~1.0%, Mn 0.1~
1.0%, Cr 3~7%, W 0.5~7%, Mo 6~
12% (18%≦W+2Mo≦25%), V 1.8~
3.6%, N≦0.03%, and the value of K obtained by K = 0.21Mo + 0.12W - 17.7N - 0.13C - 0.35V is C 0.9~1.15%, V
Satisfies K≧0.95 when 1.8 to 2.25%, K≧0.70 when C 1.0% to 1.25%, V over 2.25 and below 2.8%, K≧0.6 when C 1.15 to 1.40%, V above 2.8 and below 3.6%. However, it has been discovered that the object of the present invention can be achieved if each alloying element is contained such that the balance is Fe and impurities. The reason why each alloying element is limited to the above in the present invention will be described below with reference to Examples. Table 1 shows the Mo content (No. 1 to 4), W content (No. 5 to 7), and N content (No. 7) based on the existing AISIM7 (corresponding to No. 2 in Table 1). 8 to 12), C content (No. 13, 14), V content (No. 15, 16 and in Table 2)
No. 23 and No. 27 in Table 3) are the chemical compositions of the test materials whose effects on grindability were investigated. Each material is melted in the air or vacuum in a high-frequency melting furnace, and then
A small steel ingot weighing 1 kg was obtained and used after hot forging, annealing, and quenching and tempering.

【table】

【table】

[Table] *: Comparative steel

[Table] *: Comparative steel In order to quantitatively understand the grindability of each material,
After a certain amount of grinding was performed under certain conditions using a tap groove screw grinder, the amount of wear on the grindstone was measured. The conditions are shown below. Machine used: Matrix No. 33 screw grinder Grinding wheel used: WA320MI0V Grinding wheel speed: 1570m/min Depth of cut: 0.02mm/Pass Pitch: 1.0mm Total depth of cut: 0.9mm Figure 1 shows the effect of Mo content on grindability This is a graphical representation of the results summarizing the effects of here
G ₂ is the _ratio of the grinding wheel wear amount _△ T It is an index that indicates, and is a value obtained from G ₂ = △T ₂ / △T _x . Therefore, the specific grindability index
The larger G ₂ is, the better the grindability is. 1st
From the results shown in the figure, as the Mo content increases, G ₂ increases almost linearly, and the slope of the straight line is approximately 0.21.
It is. That is, for 1% Mo content, G ₂ is
It is clear from Figure 1 that the amount increases by 0.21.
Figure 2 shows the results of determining the correlation between the W content and the grindability index _G2 , which is similar to Figure 1 and the children's song.As the W content increases, _G2 increases, and its slope is about 0.12. Figure 3 is a diagram showing the correlation between C content and _G2 .
In the case of C, the grindability index G ₂ decreases as the C content increases, contrary to Mo and W. Its slope is −0.13
It is. Similarly, in Figure 4, -
0.35, and in Figure 5, a straight line with a slope of -17.70 was obtained with respect to the N content. In other words, the influence of each alloy element on grindability is such that the higher the content of W and Mo, the lower the content of C, V, and N, the better the grindability. It became clear that the contribution rates (the slopes of the straight lines in each figure) were different. Therefore, at K = 0.21Mo + 0.12W - 17.7N - 0.13C - 0.35V, the content of all alloying elements and the grindability index G ₂
When determining the relationship between the two, it was discovered that the grindability was correlated with the K value as shown in FIGS. 6, 7, and 8. FIG. 6 is a diagram showing the correlation between the grindability index G ₂ and the K value in 2% V series high speed tool steels such as AISIM7 and SKH9. From Figure 6, when we examine the chemical composition that can improve grindability, we find that the existing material
Increase the grindability of AISIM7 (No. 2) by 20% or more (G ₂ ≧
1.2) To improve, C, so that K≧0.95,
It is necessary to contain W, Mo, V, and N.
Specifically, the chemical compositions No. 4, No. 7, No. 11, and No. 12 in Table 1 correspond to this. All of these high-speed tool steels have a new alloy composition that is completely different from the chemical composition of existing high-speed tool steels.
(No.15 satisfies K≧0.95, but the V content is 1.21
%, which does not meet the purpose of the present invention. )In addition,
More preferably, C, W,
By adjusting the blend of Mo, V, and N, the existing material AISIM7
The grindability is improved by more than 50% (G ₂ ≧1.5) compared to the above. Next, experiments on the grindability similar to those described above were conducted for the chemical compositions of many of the 2.5% V-based high-speed tool steels shown in Table 2. In this case, SKH52 (No. in Table 2).
Based on the amount of wear on the grinding wheel (equivalent to 19). G ₁₉ = △T ₁₉ / △T _x T ₁₉ is the amount of wear on the grindstone ridge after grinding No. 19, and △T _x is the amount of wear on the grindstone ridge after grinding Nos. 20 to 26, which is used as the grindability index. As shown in FIG. 7, the grindability index G ₁₉ can also be correlated with the K value in the 2.5% series high speed tool steels No. 19 to 26. From Figure 7, in order to improve the grindability by 20% or more compared to the existing material SKH52, it is necessary to control the C, W, Mo, V, and N contents so that K≧0.7, and furthermore, K≧ If the ingredients are blended so that it becomes 0.95, the grindability can be improved by more than 50% compared to SKH52. Specifically, No. 22, 24, 25, 26 in Table 2
The object of the present invention can be achieved by the chemical composition of . Similarly, the relationship between the grindability index and the K value was determined for the 3% V-based high-speed tool steel shown in Table 3.
At this time, the grindability index is SKH53 (No. 27 in Table 3)
G ₂₇ was used, which is based on the amount of wear on the grinding wheel when grinding (equivalent to). Figure 8 shows the relationship between the grindability index G ₂₇ and the K value for 3% V series high-speed tool steel, which shows that the grindability is improved by more than 20% (G ₂₇ ≧1.2) compared to the existing material SKH53. It can be seen that it is good to control the contents of C, W, Mo, V, and N so that K≧0.6. Furthermore, if the contents of C, W, Mo, V, and N are controlled so that K≧0.92, the grindability improves by more than 50% compared to SKH53. That is, the object of the present invention is achieved by the chemical compositions Nos. 30 to 35 in Table 3. As shown in the examples above, the grindability of high-speed tool steel is correlated with the value K = 0.21Mo + 0.12W - 17.7N - 0.13C - 0.35V, and the grindability of 2% V-based high-speed tool steel ( C
0.9~1.15%, V 1.8~2.25%), K≧
0.95, 2.5% V series high speed tool steel (C 1.0~1.25%,
V > 2.25 and 2.8% or less), K≧0.70,
and 3% V series high speed tool steel (C 1.15~1.40
%, V > 2.8 and 3.6% or less), K≧
If C, W, Mo, V, and N are contained so that the ratio becomes 0.60, a material with excellent grindability can be provided. Next, the reason for limiting the component range of each additive element will be described. C is contained in a range of 0.9 to 1.4% so as to satisfy the above K value. From the viewpoint of grindability, it is best to use as little C as possible, but if the content is small, the quenching-tempering hardness decreases, and the wear resistance and heat resistance decrease, which is not consistent with the purpose of the present invention. Therefore, C is contained in a balance with the Cr, W, Mo, and V contents so that the desired quenching-tempering hardness of 0.9% or more can be obtained. Further, since toughness significantly decreases when the content exceeds 1.4%, the content of C is limited to 0.9 to 1.4%. Si and Mn are 0.1 to 1.0 mainly for the purpose of deoxidation.
%Added. Furthermore, when Si is contained in a range of 0.5 to 1.0%, toughness is also improved. Si
and Mn was limited to 0.1-1.0%. Cr improves hardenability, wear resistance, and oxidation resistance, but if it is less than 3%, it has little effect, and if it exceeds 7%, the toughness and tempering hardness will decrease, so it should be 3 to 7%. limited to. W and Mo combine with C to form a hard M ₆ C type carbide, improving wear resistance. In addition, the secondary hardening effect due to tempering is large, and it also provides heat resistance. Furthermore, as shown in FIGS. 1 and 2, it is a useful alloying element that improves grindability. Therefore, it must be contained in a range of W 0.5 to 7% and Mo 6 to 12% so as to satisfy the above K value. If W is less than 0.5 and Mo is less than 6%, wear resistance and heat resistance are insufficient, and W is more than 7% and Mo is 12%.
If it exceeds W, toughness and hot workability will decrease.
It was limited to 0.5-7% and Mo6-12%. Also W, Mo
If W + 2Mo content is not 18% or more, the above K value cannot be satisfied with a reasonable chemical composition, and conversely, if it exceeds 25%, toughness and hot workability will be impaired, so 18%≦W
+2Mo≦25%. V is an element that combines with C to form a hard VC carbide and imparts wear resistance. On the other hand, since VC carbide is harder than abrasive grains and wears out the grinding wheel early, it is generally undesirable to contain a large amount of V from the viewpoint of grindability, and if grindability is important, 1.2 % or less. However, if the alloy is blended to satisfy the above K value, 1.8
It has been discovered that the grindability can be improved even if V is contained in an amount of 1.8 to 3.6% in the present invention, depending on the application. 3.6
Even if the grindability is improved by about 50% if the V content exceeds 50%, it is still difficult to grind efficiently on an industrial scale, so the upper limit of the V content was limited to 3.6%. Co improves heat resistance and improves tool performance. This effect becomes noticeable at 4.5% or higher. However, if it is added in excess of 8.5%, the toughness will decrease. Therefore, in the present invention, Co is set at 4.5 to 8.5%. As shown in FIG. 5, the content of N should be reduced as much as possible in order to improve the grindability. Therefore, it is necessary to strictly control so as to satisfy the above-mentioned K value. If N exceeds 0.03%, the K value cannot be satisfied with a reasonable chemical composition, so it was limited to N≦0.03. In addition to the above, B,
It may contain trace amounts of Ti and Zr. It is also effective to add 0.5 to 2.0% Ni for the purpose of improving toughness. Next, high-speed tool steels having the chemical composition obtained according to the present invention were industrially manufactured and compared in terms of improvement in grindability and the number of grindable tools per grindstone dressing during tap groove grinding. As a result, while the conventional material AISIM7 could only grind 12 grooves per dressing, the steel to which the present invention was applied and whose chemical composition corresponds to No. 12 in Table 1 could grind 17 grooves per dressing. I was able to grind the grooves on a book. Also contains 3% V
With SKH53, it was virtually impossible to machine tap grooves, but with steel whose chemical composition corresponds to No. 33 in Table 3, it was possible to grind 13 grooves per dressing.
It was confirmed that the grindability was not significantly different from that of 2% V AISIM7.

[Brief explanation of drawings]

Figures 1 to 5 show the effect of Mo on grindability.
It is a figure which calculated|required the influence of W, C, V, and N content.
The numbers in circles in the figure indicate the sample material numbers listed in Table 1.
FIG. 6 is a diagram showing the relationship between the grindability index and K value of the 2% V series high speed tool steel listed in Table 1.
FIG. 7 is a diagram showing the relationship between the grindability index and K value of the 2.5% V series high-speed tool steel listed in Table 2. The numbers in circles in the figure are the sample material numbers listed in Table 2. FIG. 8 is a diagram showing the relationship between the grindability index and K value of the 3% V series high speed tool steel listed in Table 3.

Claims (1)

[Claims] 1% by weight: C 0.9-1.4%, Si 0.1-1.0%, Mn 0.1-1.0%, Cr 3-7%, W 0.5-7%, Mo 6-12% (however, 18%) ≦W + 2Mo ≦ 25%), V 1.8 to 3.6%, N ≦ 0.03%, and the value of K obtained by K = 0.21Mo + 0.12W - 17.7N - 0.13C - 0.35V is C 0.9 to 1.15%, V
Satisfies K≧0.95 when 1.8-2.25%, K≧0.70 when C 1.0-1.25%, V over 2.25 and 2.8% or less, K≧0.6 when C 1.15-1.40%, V 2.8 and 3.6% or less. A high-speed tool steel with excellent grindability, consisting of Fe and impurities. 2 When C is 0.9 to 1.15% and V is 1.8 to 2.25% by weight, K
A high-speed tool steel with excellent grindability according to claim 1, which satisfies ≧1.01. 3. The high-speed tool steel with excellent grindability according to claim 1, which satisfies K≧0.95 when C is 1.0 to 1.25% and V is more than 2.25 and 2.8% or less. 4 Weight%: C 1.15-1.40%, V over 2.8
A high-speed tool steel with excellent grindability according to claim 1, which satisfies K≧0.92 when 3.6% or less. 5% by weight: C 0.9-1.4%, Si 0.1-1.0%, Mn 0.1-1.0%, Cr 3-7%, W 0.5-7%, Mo 6-12% (18%≦W+2Mo≦25%) , V 1.8 to 3.6%, Co 4.5 to 8.5%, N≦0.03%, and the value of K obtained by K = 0.21Mo + 0.12W - 17.7N - 0.13C - 0.35V is C 0.9 to 1.15%, V
K≧0.95 when 1.8-2.25%, K≧0.70 when C 1.0-1.25%, V over 2.25 and 2.8% or less, K≧0.6 when C 1.15-1.40%, V over 2.8 and 3.6% or less. A high-speed tool steel with excellent grindability, consisting of Fe and impurities. 6 In weight%, when C is 0.9 to 1.15% and V is 1.8 to 2.25%, K≧
A high-speed tool steel with excellent grindability as claimed in claim 5, which satisfies the condition 1.01. 7. The high-speed tool steel with excellent grindability according to claim 5, which satisfies K≧0.95 when C is 1.0 to 1.25% and V is more than 2.25 and 2.8% or less. The high-speed tool steel with excellent grindability according to claim 5, which satisfies K≧0.92 when C is 1.15 to 1.40% and V is more than 2.8 and 3.6% or less at 8% by weight.