JPS63213641A - High-speed tool steel - Google Patents

Abstract

PURPOSE:To obtain a high-speed tool steel excellent in wear resistance, chipping resistance, machinability, etc., by specifying a composition consisting of C, Si, Mn, Cr, W, Mo, V, Al, and Fe and also by controlling respective contents of N, S, and O as impurities. CONSTITUTION:The high-speed tool steel has a composition which consists of, by weight, 0.5-1.5% C, 0.1-1% Si, 0.1-1% Mn, 3-7% Cr, 5-25% (W+2Mo) (where W is <=12% or unadded and Mo is 2-12%), 0.6-5% V, 0.02-0.2% Al, and the balance Fe with usual impurities and further contains, if necessary, 0.02-0.2% of one or more elements among La, Ce, Y, and Nb and/or 1-20% Co and in which N, S, and O are limited to <=0.01%, <=0.04%, and <=40ppm. In this steel, large amounts of high-hardness carbide are finely crystallized out and the fineness of the cast structure in the outside peripheral part is improved. In this way, machining property and wear resistance are improved and the occurrence of chipping in tips of cutting tools is inhibited.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-speed tool steel used as a material for cutting tools such as taps and end mills, as well as molds and other tools. The absolute amount of carbide increases, and at the same time, the size of individual carbides is fine and the distribution is uniform, especially because the structure on the outer periphery is fine.

This article relates to high-speed tool steel that is highly effective in applications such as taps that require strict characteristics on the outer periphery of the material.

[Conventional technology]

With the advancement of processing technology and the rationalization of processing man-hours, there is an increasing demand for tool materials to extend the life of tools used for cutting difficult-to-cut materials such as high hardness and achieving high finishing accuracy. . In response to this, the amount of V has been increased and hard carbides have been enriched to improve strength, wear resistance, heat resistance, and seizure resistance. High-speed tool steels have been developed and used as materials for tools used under severe operating conditions.

[Problem that the invention seeks to solve]

However, in these high-speed tool steels with a high V content, coarse MC-type carbides mainly composed of V that inevitably occur during casting and solidification do not disappear even during the subsequent manufacturing process1.For example, in cutting tools, Not only does this have negative effects such as poor finishing accuracy and poor grinding efficiency during finish grinding of the tool itself, but also chipping and cracking of the cutting tool's cutting edge occur from areas where these coarse carbides are segregated, shortening the tool life. , which caused variations in lifespan. In addition, attempts have been made to improve tool life by increasing the content of W and MO to increase the amount of MsC-type carbides instead of using high-quality materials, but similar to the above, segregation of carbides There were problems such as cracking and chipping.

The purpose of the present invention is to provide a high-speed tool steel with a fine and uniformly distributed carbide structure, which exhibits high performance as a tool and also has excellent machinability with less chance of chipping or chipping. This provides a tool material with a stable lifespan.

[Means for solving problems]

In order to solve these problems, the present invention conducted experiments on high-speed tool steels shown in Table 2, and found that a certain specific element Al. By adding T-a, Ce, Y, and Nb, carbides are finely crystallized, the amount of high-hardness carbide crystallized is increased, cutting performance and wear resistance are improved, and a-structure is finely crystallized. This is based on the discovery that it is possible to improve the properties of cutting tools, such as reducing the likelihood of chipping and chipping of the cutting edge of cutting tools, and that this effect works synergistically through the combination of additive elements. It is.

Specifically, C005 to 1.5% and Si 0.9% by weight.
1-1%, Mn0.1-1%, Cr3-7%, W+2
Mo 5-25% (but W 12% or less or no addition, Mo2-121, Vo, 6-5%, Al 0.0
Contains 2 to 0.2%, the balance consists of Fe and normal impurities, N≦0.01%, S≦0.04%, O≦40P
It is a high-speed tool steel characterized by an improved casting structure on the outer periphery that is regulated to PIll, and also contains La, Ce, Y
, Nb in an amount of 0.02 to 0.2% to obtain a synergistic effect with the addition of Al. Moreover, the present invention further includes those containing 1 to 20% of Co.

[Effect]

The reason why each alloying element of the present invention is limited to the above will be described below.

C combines with carbide-forming elements such as Cr, W, Mo, and V to form carbides, imparts quenching-tempering hardness, and contributes to wear resistance, heat resistance, and seizure resistance.

If it is too large, the toughness will decrease and giant carbides will be formed, so the content is limited to 0.5 to 1.5% and balanced with the amounts of Cr, W, Mo, and V.

Si and Mn are mainly used for the purpose of deoxidation. Add 1%.

Cr improves hardenability, wear resistance, oxidation resistance, and high temperature strength and resistance to temper softening by setting an appropriate content. For the above purpose, the content should be 3% or more, but if it is too large, the high temperature strength and temper softening resistance will be reduced, and the toughness will also be reduced, so the content should be 7% or less.

W and Mo combine with C to form a special carbide, which contributes to improving wear resistance and seizure resistance. In addition, the secondary hardening effect due to tempering is large and contributes to high temperature strength. In order to obtain the above effects, W is added in a range of 12% or less and Mo in a range of 2 to 12%, so that the amount of W + 2 Mo satisfies 5 to 25%. If Moi is less than 2% and W+2Moi is less than 5%, the above effects cannot be obtained, and if it is too large, toughness and hot workability will be impaired.
25% or less.

V combines with C to form a hard carbide, contributing to wear resistance. However, this carbide is harder than the abrasive grain, so
Premature wear of the grinding wheel. In particular, if a large number of coarse carbides are produced and the distribution is not uniform, the grindability will be significantly reduced. For this reason, when conventionally placing importance on grindability, 1.2x
I kept it below.

However, the present inventor found that Al alone or in addition La, Ce
, Y, and Nb in combination, it was discovered that even if a large amount of V is contained, the generation of coarse MC-type carbides mainly composed of V can be prevented. In the present invention, depending on the application,
It is contained in an appropriate amount in the range of 0.6 to 5%. If it exceeds brocade, the effect of the present invention will be reduced, so it should be 5x or less, and if it is too small, it will not contribute to wear resistance, so it should be 0.6% or more.

A] is the most important element in the present invention, and the third
As shown in Fig. 4, it has the effect of developing dendrites during casting and making the structure fine and uniform on the outer peripheral side.
a, Ce, Y, and Nb also have similar effects. Also, Al
has the effect of increasing the absolute amount of MC type carbides, and also has the effect of making MC type carbides finer.Although the effect can be obtained even when added alone, when combined with La, Ce, Y, and Nb, these effects are increased. The effect is large.

If it is less than 0.02%, these effects will be small;
If it exceeds 2, it will have a negative effect on the carbide refinement effect, so it is set at 0.02 to 0.2%.

Like Al, La and Ce are effective in refining the casting structure at the outer periphery. Further, it is added for the purpose of finely crystallizing hard MC type carbides mainly consisting of (3) and increasing the absolute amount of these hard carbides.

The effect is even greater when combined with AI, so A
At the same time as 1, 0.02 to 0.2% of one or two of them is added. If it is less than 0.02%, these effects will be small, and if it exceeds 0.2%, it will combine with S and O to form inclusions.
In addition, 0.020 to 0.20% may cause casting defects.
limited to. Here, when adding La and Ce during actual manufacturing, it is common to add them as Mitshu metal, and in addition to La and Ce, Nd,
Pr is included, as shown in Table 1,
As a result of testing by adding each element individually, the effect of adding Nd and Pr was small.

For this reason, these elements are excluded from the scope of the claims of the present invention, but when added as Mitsushi metal, La and C
This does not impair the effect of e.

Y and Nb also have the same effects as La and Ce, and it is also effective to add these and Al in combination.

If Y is less than 0.020%, these effects will be small, and if Y exceeds 0.20%, it will combine with S and 0 to form inclusions, degrading the quality of the product, so it should be kept at 0.20% or less.

Nb has a small bonding force with S and 0, but in the present invention it is added for the purpose of controlling carbides mainly consisting of 0.2
The upper limit is %.

Go is dissolved in the matrix to improve the strength and heat resistance of the steel of the present invention, and is not directly involved in controlling the carbide morphology and improving the cast structure according to the present invention, but it is added in an amount of 1 to 20% as necessary.

N is an impurity in the steel of the present invention. If the amount of N exceeds 0.01%, it is disadvantageous in terms of controlling the form of V shown in Table 2 among the effects of joint addition of Al, La, Ce, etc.
．． 01% or less.

S and O are also impurities in the steel of the present invention, and these are the additive elements that characterize the steel of the present invention, especially L.
a, has a strong bonding force with Ce, and the effect of these additions is
As shown in FIG. 3, S is limited to S≦0°04% and 0≦40ρpo+ in order to not only damage it, but also combine with La and Ce and remain as inclusions in the steel, lowering the quality of the product.

Example Examples of the present invention will be described below.

Alloys having the chemical composition shown in Table 1 were melted in a vacuum induction furnace, and steel ingots were produced under the same casting conditions such as medium temperature and mold cooling capacity.

Each steel ingot was annealed, a sample was taken from the same position on the upper side of each steel ingot, and the shapes of the carbides crystallized during casting were classified into the three types shown in Figure 1. Of which A
As shown by the arrow, the MC type carbide mainly consists of irregularly shaped lumps and is coarse.This type of MC remains as it is even when it is made into a product, and is difficult to use in tools. This is known to significantly reduce grindability.

In type B, MC-type carbide crystallizes as a eutectic in the form of ribs, but coarse MC is seen in one peripheral area as indicated by the arrow.

In the C type, each MC is very finely crystallized as a eutectic MC type carbide.

The carbide morphology of the samples shown in Table 1 was classified as shown in Table 2.

Comparative steel 9 is classified as A type, and comparative steel 17 with increased W content is classified as B type.
The generation of type carbides is suppressed by adding Ai, La, Ce, Y, and Nb (10.12.
13,]-5,18°19.24.28) is Nb,
Even when Pr, Hf, Zr, and Mg were added, the morphological change of MC was still small.

Coarse MC crystallization is observed (11..14.16.2
0.21).

Table 2 also shows items whose N content exceeds 0.01% by weight (2
In case 9), even if Al, La, and Ce were added in combination, the morphological change of MC was small, and coarse MC was present. Furthermore, the effect of the MC form change extends to the invention steel 36.38, which has a significantly increased content.

The effect of MC form change is greater as the content of did. In addition, the morphological changes of MC are W, Mo
In terms of the amount ratio, the more Mo there is, the greater the ratio is.

Next, in order to investigate the absolute amount of MC in the sample whose carbide shape was observed earlier,
Find the ratio of line strength to ferrite iron, and calculate this as La-
Figure 2 shows the results organized by Ce content. L
It can be seen that as the content of a and Ce increases, the absolute amount of MC also increases. In other words, the effects of these on MC are
This shows that it not only makes the morphology finer, but also increases its quantity.

Next, samples were taken continuously from the surface of the steel ingot to the center.
Table 3 shows the results of organizing the area occupied by dendrites according to the distance from the steel ingot surface, where the steel ingot diameter is D.
As shown in the figure.

Table 3 Al. By adding La, Ce, Y, and Nb, the area occupied by dendrites expands, but when Al, La, and C
The effect is particularly large when e, Y, and Nb are added in combination. Also, those with a large amount of S and 0 (30, 31) are
Even if La and Ce are added in combination, the area occupied by dendrites is significantly narrowed.

Figure 4 shows the results of measuring the cell size of the D/8 section where the diameter of the steel ingot is D. In Figure 3, the larger the area occupied by the dendrites, the smaller the cell size. It can be seen that there is a correlation.

When examining discarded tools such as taps, there are many examples of short-life tools whose cutting edges are chipped and the tool life ends, especially when the workpiece material is highly hard. In many cases, chipping occurs in areas where carbides are segregated and dense, and developing dendrites and making the casting structure on the outer periphery finer will reduce the density of carbides, which will shorten the life of the tool. It is believed that this will have a significant effect on improving

Next, in order to quantitatively understand the grindability of each material, we used a tap groove screw grinder to grind the sample under the constant grinding conditions shown in Table 4, and then measured the amount of wear on the grinding wheel. It was measured. The results are shown in Table 5. Each sample was produced by forging a steel ingot, finishing it to 20φ, annealing it, and then subjecting it to quenching and tempering. Comparison #! Compared to No. 117, the grindability of the steel of the present invention is clearly improved.

Table 4 Table 5 [Effects of the Invention] As described above, the steel of the present invention has improved wear resistance by enriching hard carbides, and at the same time, by dispersing them finely and uniformly. Grindability, heat resistance, and seizure resistance have been improved, and chipping resistance has been improved by making the cast structure particularly fine on the outer periphery, extending and stabilizing tool life and improving the finish of the tool itself. This brings about both higher precision and improved efficiency in grinding, and the effects are very large.

Although Table 1 does not cover all combinations of the additive elements of the present invention, it can be easily understood from the above description that these also include the additive elements of the present invention.

[Brief explanation of the drawing]

The crystallized product of Nuki is MC type carbide. Figures 2 to 4 show the absolute amount of MO carbide and the area occupied by Puntorai 1 to 3, respectively, relative to the total amount of La and Ce. This is a plot of the coagulation cell size of part D/8.
The figure also shows the relationship between the amounts of Y and Nb and high S and high O. In addition, in Fig. 3.4, the broken line indicates the case where only La and Ce are added, and the solid line indicates the case where only La and Ce are added.

Claims (1)

[Claims] 1. C0.5 to 1.5%, Si 0.1 to 1% by weight,
Mn0.1-1%, Cr3-7%, W+2Mo5-25
% (However, W12% or less or no additives, Mo2~12
%), V0.6~5%, Al0.02~0.2%, the balance consists of Fe and normal impurities, N≦0.0
1%, S≦0.04%, and O≦40ppm. A high-speed tool steel characterized by an improved casting structure in the outer peripheral part. 2 C0.5-1.5%, Si0.1-1% by weight ratio,
Mn0.1-1%, Cr3-7%, W+2Mo5-25
% (However, W12% or less or no additives, Mo2~12
%), V0.6-5%, Al0.02-0.2%, and further contains 0.02-0.2% of one or more of La, Ce, Y, and Nb, the balance being Fe and normal N≦0.01%, S≦0.04%, O≦4
A high-speed tool steel characterized by an improved casting structure in the outer peripheral part, which is regulated to 0 ppm. 3 C0.5-1.5%, Si0.1-1% by weight ratio,
Mn0.1-1%, Cr3-7%, W+2Mo5-25
% (However, W12% or less or no additives, Mo2~12
%), V0.6-5%, Al0.02-0.2%, Co
1 to 20%, the balance consists of Fe and normal impurities, N≦0.01%, S≦0.04%, O≦40pp
A high-speed tool steel characterized by an improved casting structure at the outer periphery, which is regulated to m. 4 C0.5-1.5%, Si0.1-1% by weight ratio,
Mn0.1-1%, Cr3-7%, W+2Mo5-25
% (However, W12% or less or no additives, Mo2~12
%), V0.6-5%, Al0.02-0.2%, Co
Contains 1 to 20%, further contains 0.02 to 0.2% of one or more of La, Ce, Y, and Nb, and the balance consists of Fe and normal impurities, N≦0.01%, S≦ 0
．． 04%, a high-speed tool steel characterized by an improved casting structure at the outer periphery, regulated to O≦40ppm.