JP2507765B2 - High speed tool steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Use] The present invention is a high-speed tool steel used as a material for a cutting tool typified by a tap and an end mill, and a tool such as a mold. The absolute amount of carbides increases, and at the same time the size of individual carbides is fine and the distribution is uniform. Especially, the microstructure on the outer peripheral side is very fine. Regarding speed tool steel.

[Conventional technology]

With the advancement of processing technology and the rationalization of processing man-hours, there is an increasing demand for tool materials to improve the life of the tools used for cutting hard-to-cut materials such as high hardness and high finishing accuracy. . Correspondingly, the amount of V is increased and the hard carbide is enriched to improve the strength, wear resistance, heat resistance, and seizure resistance of 2.5% V type and 3% V type typified by SKH52 and SKH53. Speed tool steel has been developed and used as a material for tools used in harsh service conditions.

[Problems to be solved by the invention]

However, these high-speed tool steels with a high V content are:
Coarse MC-type carbides mainly composed of V, which are inevitably generated during casting and solidification, cannot be eliminated even in the subsequent manufacturing process. For example, in the case of a cutting tool, the finishing accuracy of the tool itself is poor and the grinding efficiency is poor. In addition to such adverse effects, chipping and cracking of the cutting edge of the cutting tool occur from the segregated portion of this coarse carbide, which shortens the tool life and causes variations in the life. Attempts have also been made to improve the tool life by increasing the W and Mo contents instead of the high V material to increase the amount of M ₆ C type carbides. There was a problem that cracking, chipping, etc. occurred from the segregated portion.

An object of the present invention is to provide a high-speed tool steel having a fine and uniformly distributed carbide structure, which shows high performance as a tool, and is also excellent in machinability in which chipping and chipping are unlikely to occur. A tool material having a stable life is provided.

[Means for solving problems]

In order to solve such a problem, the present inventor previously conducted an experiment on a high-speed tool steel having a high V content, and as a result, by adding a specific element Al, La, Ce, Y, , Minutely crystallize carbides, increase the amount of high-grade carbides crystallized, improve cutting performance and wear resistance, miniaturize the casting structure, make chipping of the cutting edge of the cutting tool less likely to occur, etc. It has been found that the characteristics of the compound can be improved, and that the effect thereof acts synergistically by the combination of additional elements (Japanese Patent Application No. 62-44473).

According to the present invention, as a result of further experiments on the high speed tool steels shown in Table 1, the effect of refining carbides by addition of La, Ce and Y is influenced by the contents of coexisting elements Ti and N. It is based on the new finding of.

Specifically, by weight ratio, C 0.5 to 1.5%, Si 0.1 to 1%,
Mn 0.1-1%, Cr 3-7%, W + 2Mo 5-25% (however, W
12% or less or no additive, Mo 2-12%), V 0.6-5%,
Al 0.02-0.2%, balance Fe and normal impurities, Ti ≦ 0.02%, N ≦ 0.006%, S ≦ 0.004%, O ≦
It is a high speed tool steel characterized by refining the casting structure of the outer peripheral portion regulated to 40 ppm, and also contains 0.02 to 0.2% of one or more of La, Ce, Y, and with addition of Al. It is a synergistic effect. Further, the present invention further provides Co
Including those containing 1 to 20%. Further, the limit amount of Ti is more than 0.01% and 0.02% or less in practical use.

[Action]

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

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

If it is too large, the toughness is lowered and a huge carbide is generated. Therefore, it is contained in balance with the amounts of Cr, W, Mo and V, and is limited to 0.5 to 1.5%.

 Si and Mn are added in an amount of 0.1 to 1% mainly for the purpose of deoxidation.

Cr improves hardenability, wear resistance, oxidation resistance, and improves high temperature strength and temper softening resistance by setting an appropriate content. For the above-mentioned purpose, it is 3% or more, but if it is too large, it rather lowers the high temperature strength, the temper softening resistance and the toughness, so it is made 7% or less.

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

V combines with C to form a hard carbide and contributes to wear resistance. However, since this carbide is harder than the abrasive grains, it causes the grinding wheel to wear early. In particular, a large number of coarse grains cause carbides, and if the distribution is not uniform, the grindability is significantly reduced. For this reason, when the conventional grindability is important, 1.2
% Was kept below.

However, the present inventor has found that Al alone or further La, Ce, Y
When combined with V, even if it contains a large amount of V,
It was discovered that it is possible to prevent the generation of MC type carbides mainly composed of. In the present invention, V is 0.6 to 5 depending on the application.
An appropriate amount is included in the range of%. If it exceeds 5%, the effect of the present invention becomes small, so it is set to 5% or less, and if it is too small, it does not contribute to wear resistance, so it is set to 0.6% or more.

Al is the most important element in the present invention, the effect of increasing the absolute amount of MC type carbide, further has the effect of finely crystallizing MC type carbide, the effect can be obtained by adding alone, La When these are added in combination with Ce, Y, or Ce, these effects are great.

Further, Al has the effect of developing dendrite crystals during casting and making the structure on the outer peripheral side fine and uniform, and La, Ce, and Y also have the same effect.

If it is less than 0.02%, these effects are small, and if it exceeds 0.2%, it has an adverse effect on the effect of refining carbides.
It was set to 02 to 0.2%.

Similar to Al, La and Ce are added for the purpose of finely crystallizing hard MC type carbide mainly containing V and further increasing the absolute amount of these hard carbides. Since the effect is further increased by the combined addition with Al, 0.02 to 0.2% of one or two kinds of La and Ce are added simultaneously with Al. If it is less than 0.02%, these effects are small, and if it exceeds 0.2%, it will combine with S and O to form inclusions and cause casting defects.
Limited to 0.02-0.2%. Here, during actual manufacturing, La, C
When adding e, it is common to add it as a misch metal.
Although d and Pr are contained, the effect of addition of Nd and Pr was small as a result of confirming by adding each of these elements alone.
Therefore, these elements are excluded from the scope of the claims of the present invention, but the effects of La and Ce when added as misch metal are not impaired.

Y has the same effect as La and Ce, and it is also effective to add these and Al in combination. If it is less than 0.02%, these effects are small, and if Y exceeds 0.2%, it is combined with S and O to form inclusions and the quality of the product is lowered, so the content is made 0.2% or less.

Co dissolves in the matrix to improve the strength and heat resistance of the steel of the present invention and does not directly contribute to the control of the carbide morphology and the improvement of the cast structure according to the present invention, but is added in an amount of 1 to 20% as required.

Ti is an impurity in the present invention, and combines with N and C at high temperature during solidification to form TiN and TiC. Since these have a property of easily forming crystallization nuclei of VC carbides, they have an action of crystallizing VC carbides at a high temperature. These are Al, La, Ce and Y mentioned above.
The effect of the addition of is impaired. On the other hand, Ti is introduced into molten steel from raw materials and refractories during ingot making, and its content is 0.01
It is industrially difficult to limit it to less than%. But above A
When the limit amount that does not impair the effect of addition of l, La, Ce, and Y was limited, it was 0.02% or less. Therefore, Ti is set to 0.02% or less.

N, like Ti, is an element whose content must be strictly limited. When N content exceeds 0.006%, Al, La, C
In order to impair the effect of joint addition of e, Y, etc., the amount was made 0.006% or less.

S and O are also impurities of the steel of the present invention, and these have a strong bonding force with the additional elements, particularly La and Ce, which are features of the steel of the present invention. In order to combine with each other and remain as inclusions in the steel and reduce the quality of the product, S ≦ 0.004% and O ≦ 40 ppm were limited.

〔Example〕

 Examples of the present invention will be described below.

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

The present invention, when Al, La, Ce, Y and other elements described in the previously filed invention (Japanese Patent Application No. 62-44473) are added,
Since the limitation range of the Ti and N contents when the effect on the MC carbide is effectively exerted is described, the MC content and the composition of V content 3 to 3.5% in which the absolute amount is remarkably changed. The example will be described below.

Each steel ingot was annealed, samples were taken at the same position on the upper side of each steel ingot, and the shape of the carbide that crystallized during casting was observed. Depending on the Ti and N contents, the three types shown in Fig. 1 were obtained. It was classified into the form. Fig. 2 shows the morphology of carbides for each melting.
This is a summary of the Ti and N contents. Al, L
a, Ce, and Y are added to finely crystallize MC carbide, and the form of MC carbide sufficiently satisfying the purpose is as follows.
As shown in Fig. 1, type A, from Fig. 2 Ti 0.02
% And N 0.006% (60 ppm) or less.

FIG. 3 shows the grain size distribution of MC carbide at a position of 1 mm from the surface of the cross section of the bar, which was obtained by hot rolling the above steel ingot. Inventive Steels 1 and 3 have almost no coarse MC carbides (> 8 μm) as compared with Comparative Steel 9,
There are many fine MCs (≦ 4 μm), and the overall area ratio is also large.

Next, in order to quantitatively grasp the grindability of each material, using a tap groove screw grinder, under the constant grinding conditions shown in Table 2, after grinding the sample, the wear amount of the grindstone was measured. It was measured. The results are shown in Table 3. In addition, each sample was manufactured by finishing the above-mentioned 7φ and then annealing-tempering it. The grindability of the steel of the present invention is clearly improved.

Further, a tap was prepared from the rod shape, and a cutting test was conducted under the constant cutting conditions shown in Table 4. When evaluating the cutting performance by the number of holes tapped until the life of the tap,
As shown in Table 5, MC carbide mfp (mean free path)
The cutting performance of the steel of the present invention in which mfp is small, that is, the amount of MC carbide is large and fine and uniformly dispersed, is good.

[Effects of the Invention] As described above, the steel of the present invention is improved in wear resistance by enriching hard carbides, and at the same time, finely and uniformly disperses them, thereby improving grindability and heat resistance. And the seizure resistance are improved, the tool life is extended and stabilized, the precision of the finishing grinding of the tool itself is improved, and the efficiency is improved. The effect is 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 have the additive effect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a metallographic photograph of the shape of as-cast carbide observed with a high-power microscope at 400 times. In the figure, white crystals are MC-type carbides. FIG. 2 shows the morphology of MC carbides with respect to the contents of Ti and N according to the classification of FIG.
The numbers in parentheses show the sample numbers listed in Table 1, and Fig. 3 shows the number of particles of MC carbide and the area ratio at the sample position 0.01 mm ² measurement area described in the text. Is.

Claims (8)

(57) [Claims] 1. A weight ratio of C 0.5 to 1.5%, Si 0.1 to 1%, Mn
0.1-1%, Cr 3-7%, W + 2Mo 5-25% (however, W 1
2% or less or no additive, Mo 2-12%), V 0.6-5%, Al
0.02 to 0.2%, balance Fe and ordinary impurities, Ti ≦ 0.02%, N ≦ 0.006%, S ≦ 0.004%, O ≦ 40
A high-speed tool steel characterized in that the casting structure of the outer peripheral part regulated to ppm is refined. 2. The high speed tool steel according to claim 1, characterized in that Ti> 0.01 wt%. 3. A weight ratio of C 0.5 to 1.5%, Si 0.1 to 1%, Mn
0.1-1%, Cr 3-7%, W + 2Mo 5-25% (however, W 1
2% or less or no additive, Mo 2-12%), V 0.6-5%, Al
0.02 to 0.2%, 0.02 to 0.2% of one or more of La, Ce and Y, and the balance of Fe and ordinary impurities, Ti ≦ 0.02%, N ≦ 0.006%, S ≦ 0.004%, O ≦ 40
A high-speed tool steel characterized in that the casting structure of the outer peripheral part regulated to ppm is refined. 4. The high speed tool steel according to claim 3, wherein Ti> 0.01 wt%. 5. A weight ratio of C 0.5 to 1.5%, Si 0.1 to 1%, Mn
0.1-1%, Cr 3-7%, W + 2Mo 5-25% (however, W 1
2% or less or no additive, Mo 2-12%), V 0.6-5%, Al
0.02 to 0.2%, Co 1 to 20%, balance Fe and ordinary impurities, Ti ≦ 0.02%, N ≦ 0.06%, S ≦ 0.00
A high-speed tool steel characterized by refining the casting structure of the outer peripheral part regulated to 4% and O ≦ 40 ppm. 6. The high speed tool steel according to claim 5, wherein Ti> 0.01 wt%. 7. A weight ratio of C 0.5 to 1.5%, Si 0.1 to 1%, Mn
0.1-1%, Cr 3-7%, W + 2Mo 5-25% (however, W 1
2% or less or no additive, Mo 2-12%), V 0.6-5%, Al
0.02 to 0.2%, Co 1 to 20%, further containing 0.02 to 0.2% of one or more of La, Ce and Y, the balance Fe and ordinary impurities, Ti ≤ 0.02%, N ≤ 0.006%, S ≤0.0
High-speed tool steel characterized by refining the casting structure of the outer peripheral part regulated to 04%, O ≦ 40 ppm. 8. The high speed tool steel according to claim 7, wherein Ti> 0.01 wt%.