JP5424120B2 - Alloy steel with excellent high temperature temper softening resistance - Google Patents

Description

  The present invention relates to an alloy steel having excellent high-temperature tempering softening resistance, and in particular, by providing excellent high-temperature tempering softening resistance even when the cutting edge is exposed to a temperature higher than the tempering temperature during high-speed cutting. The present invention relates to an alloy steel suitable for a tool material such as a hob, for example, which exhibits a superior wear resistance and toughness at a high temperature.

Alloy steels (JIS SKH, SKD, etc.), cemented carbide, cermet, cBN, diamond, etc. are known as materials for cutting tools. However, among the alloy steels for cutting tools, they have high wear resistance and toughness. High speed tool steel (JIS SKH) is frequently used because of its superiority.
High-speed tool steel is a tool steel to which a large amount of alloying elements such as C, Cr, W, Mo, V, Co, etc. are added to improve hardness and wear resistance especially at high temperatures. There are two types of high-speed tool steel manufactured by the method and powder high-speed tool steel (also referred to as powder high speed) manufactured by the powder metallurgy method.
In the case of the melting method, although it can be manufactured by a normal manufacturing method, the homogenization of the material due to segregation of coarse carbides tends to be a problem, while in the case of the powder metallurgy method, the manufacturing process is complicated and expensive. Although there are drawbacks, there is an advantage that even a material that is difficult to manufacture by a melting method can be manufactured and a uniform structure can be formed.

The high-speed tool steel by the melting method is described in, for example, Patent Documents 1 to 5. According to Patent Document 1, a trace amount of rare earth elements is contained as a component in the steel, and the shape control of the eutectic carbide is performed. It is known to improve impact resistance and cutting performance by performing.
Further, according to Patent Document 2, it is known to improve wear resistance by forming VC carbide in steel and to improve toughness by making the crystallization form of VC carbide fine and uniform. .
Further, according to Patent Document 3, it is known that hot workability, toughness, impact resistance, and fatigue strength are improved by adjusting alloy components and their contents in steel.
According to Patent Document 4, the contents of alloy components Si, Mo and W in steel are adjusted, and the relationship 0.4 ≦ 2Mo / (W + 2Mo) × Si ≦ 1.0 is satisfied, thereby tempering. It is known that it has high hardness and improves toughness and wear resistance.
Further, according to Patent Document 5, the wear resistance, heat resistance, and seizure resistance are improved by forming fine carbides with high hardness in the steel, and further, the tool cutting edge is obtained by refining the cast structure. It is known to improve chipping resistance.

The powder high-speed tool steel (powder high speed) by the powder metallurgy method is described in, for example, Patent Documents 6 and 7, and according to Patent Document 6, the amount of (W + 2Mo) in the steel and (C-Ceq) By regulating the value and regulating the value of Nb / V, it is said that powder high-speed tool steel having toughness and corrosion resistance and enhanced resistance to high-temperature temper softening can be obtained.
According to Patent Document 7, it is said that the wear resistance and toughness can be improved by adjusting the contents of the alloy components in the steel so as to satisfy a certain relationship.

JP-A-1-165748 JP-A-7-228946 Japanese Patent Application Laid-Open No. 8-100239 JP 2000-144333 A Japanese Patent No. 2573951 JP-A-5-171373 JP 2001-294986 A

  Recent progress in cutting technology is remarkable, and in addition, there are strong demands for labor saving, energy saving, cost reduction, and efficiency in cutting, and accordingly, high-speed cutting and high-efficiency cutting under dry conditions are also required. However, when dry high-speed cutting is performed using a hob or other gear cutting tool made from the above-mentioned conventional alloy steel, the cutting blade is exposed to high heat during the cutting process. However, there has been a problem that high temperature temper softening is caused and hardness is lowered. As a result, crater wear or the like is likely to occur, and the tool life is shortened.

  Therefore, the present inventors conducted intensive research to provide an alloy steel that does not cause high-temperature tempering softening and has a low hardness reduction even when dry high-speed cutting with high heat generation is performed. I got the following knowledge.

  Conventional alloy steels, particularly high-speed tool steels, usually contain C, Si, Mn, Cr, W, Mo, V, Co, etc. as their alloy components. Of these alloy components, Si Is added mainly in anticipation of the action as a deoxidizer, and also has the effect of improving hardness, but if the Si content is too high, the toughness of the high-speed tool steel will be deteriorated. Therefore, it was usually added in a range of 2% or less from the viewpoint of not adversely affecting toughness.

The inventors focused on the content and action of the Si component, and investigated the influence on the high-temperature temper softening characteristics when the Si amount was variously changed. As a result, the C content contained in the steel was specified. Surprisingly, it has been found that the high-temperature temper softening property is greatly improved when a large amount of Si is added and contained under the conditions regulated within the range.
In addition, in this case, a large amount of Si is much more than the amount added as a deoxidizer in ordinary alloy steel. For example, in the high-speed tool steels of Patent Documents 1 to 6 mentioned above. The Si content is 2% by mass at the maximum, and in Patent Document 7 that can contain 3% by mass of Si at maximum, the preferable upper limit of the Si content is 1% (see paragraph 0022). The present inventors have found that the addition of Si in an amount exceeding 3% by mass greatly improves the high temperature temper softening properties of the alloy steel, and the gear cutting formed by this alloy steel. The tool was found to have excellent cutting performance.

This invention has been made based on the above findings,
“(1) in mass%, C: 2.0 to 3.0%, Si: 3.5 to 6.0%, Mn: 1.0% or less, Cr: 3.5 to 4.0%, W And one or two of Mo: 10.0 to 12.0%, V: 3.0 to 3.5%, Co: 4.0 to 5.0%, the balance being Fe and inevitable impurities An alloy steel having excellent high-temperature tempering softening resistance, characterized by comprising:
(2) A hob characterized in that the base of the hob is made of the alloy steel having high-temperature temper softening resistance described in (1) above. "
It has the characteristics.

The present invention will be described in detail below.
First, the reasons for limiting the numerical values of the alloy component composition range of the alloy steel of the present invention are as follows.

C: 2.0-3.0 mass% (in the following, mass% is simply indicated by%)
Part of C is hardened and solidifies in the matrix to strengthen the matrix, and part of it combines with W, Mo, Cr, and V to form carbides, and the hardness and wear resistance of the alloy steel. Improve sexiness.
If the C content is less than 2.0%, not only the hardness and wear resistance can be expected to be improved, but also the high temperature temper softening property cannot be improved by the interaction with Si described later. Further, if the C content exceeds 3.0%, it becomes too hard and deterioration of toughness occurs, and the uniformity of the material cannot be ensured due to the formation of a non-uniform microstructure. Was determined to be 2.0 to 3.0%.

Si: 3.5-6.0%
As in the case of ordinary alloy steel, Si has a function as a deoxidizer, but in addition to this, it is the most important alloy component in the present invention in order to improve the high temperature temper softening property.
The present inventors conducted a detailed investigation on the relationship between the contents of C and Si, which are alloy components of alloy steel, the tempering temperature, and the high temperature hardness.
An example is shown in FIG.
From FIG. 1, the high-temperature hardness change (softening ratio (HRC hardness) of the invention steel 1 of C2.0% and Si4.0%, the steel of the invention 2 of C2.5% and Si4.0% according to the tempering temperature (° C.). In the as-quenched state, the hardness of the steel 1 of the present invention was inferior to that of the conventional alloy steel (Comparative Example Steel 11 and Comparative Example Steel 12). About this invention steel 2, tempering is carried out in the temperature range of 600-700 degreeC which shows the high-temperature hardness substantially equivalent to the as-quenched state of the conventional alloy steel (Comparative example steel 11, Comparative example steel 12). When it performed, both this invention steel 1 and this invention steel 2 showed much higher tempering hardness compared with the tempering hardness of the conventional alloy steel (Comparative example steel 11 and Comparative example steel 12).
From this, the present invention in which the C content is set to 2.0 to 3.0% and the Si content is set to 3.5 to 6.0%, preferably 3.5 to 4.0%. hot temper softening resistance of the steel alloy, the conventional alloy steel (comparative example steels 11, Comparative example steel 12) it can be seen that excellent far than that of.
The reason why the high-temperature tempering softening resistance is improved in the present invention is not yet clear, but probably in the temperature range of 600 to 700 ° C., Si contained in a large amount in the steel suppresses the formation of cementite. It is speculated that the hardness will improve and, as a result, the temper softening resistance will improve.

Mn: 1.0% or less In the present invention, since M contains a large amount of Si and acts as a deoxidizing agent, it is not always necessary to add Mn that acts as a deoxidizing agent as in Si, but Mn is quenched. Since there is also a property improving effect, it can be added within a range of 1.0% or less.

Cr: 3.5-4.0%
Cr needs to be added in an amount of 3.5% or more in order to secure the hardenability of the steel, increase the oxidation resistance during heat treatment, and improve the wear resistance, but it exceeds 4.0%. Even if added, the effect of improving the cutting performance as a tool is small, so the Cr addition amount was determined to be 3.5 to 4.0%.

Total of one or two of W and Mo: 10.0 to 12.0%
W forms MC-type and M ₆ C-type carbides, and some of them dissolve in the matrix, improving wear resistance and high-temperature tempering softening resistance. However, if the W content is excessive, , Leading to coarsening of carbides and toughness.
Mo, like W, forms MC-type and M ₆ C-type carbides to improve wear resistance and high-temperature temper softening resistance and improve toughness, but when the Mo content becomes excessive The crystal grains become coarse and brittle, and decarburization is likely to occur during heat treatment.
Therefore, in order to improve wear resistance and high temperature temper softening resistance, the total of one or two of W and Mo needs to be 10.0% or more, but the total amount is 12.0%. If it exceeds 1, the carbides become coarse, the toughness is lowered due to the coarsening of crystal grains, etc., so the content of one or two of W and Mo is 10.0 to 12.0% It was determined.

V: 3.0-3.5%
V is a strong carbide-forming element, and when combined with C, forms fine MC-type carbides, and is effective in improving wear resistance. Further, V has a crystal grain refining action, prevents a decrease in toughness due to crystal grain coarsening, and increases high-temperature temper softening resistance. In order to exert such an effect, it is necessary to contain 3.0% or more, but if it is contained excessively, grindability is impaired, so the upper limit was set to 3.5%.

Co: 4.0-5.0%
Co itself does not form carbides, but increases heat resistance, wear resistance, and high temperature temper softening resistance by dissolving in a matrix. In order to obtain these effects, the content of 4.0% or more is necessary. However, if excessively contained, the segregation of carbides is promoted or the decarburization is promoted, so the upper limit is 5.0. %.

  As described above, the alloy steel of the present invention is, in mass%, C: 2.0 to 3.0%, Si: 3.5 to 6.0%, Cr: 3.5 to 4.0% W and Mo. Total of one or two of them: 10.0 to 12.0%, V: 3.0 to 3.5%, Co: 4.0 to 5.0%, the balance is Fe, As described above, it is allowed to contain Mn of 1.0% or less, and as an inevitable impurity, P, S, N, in a range that does not affect the high temperature temper softening resistance of the alloy steel of the present invention. Inclusion of Ni, Nb, Cu, As, Sb, etc. is allowed.

Moreover, when the high temperature temper softening resistance of the alloy steel of the present invention was quantified by experiment, the softening ratio (%) at 600 to 700 ° C.
Softening ratio (%) = (H _T −H ₆₀₀ ) × 100 / H ₆₀₀
In the alloy steel of the present invention, it was confirmed that the softening ratio (%) was in the range of 0 to -20%.
Here, the softening percentage, as a reference hardness at tempering temperature of 600 ° C. The _{(H 600),} tempering temperature T (° C.) (where, 600 ≦ T ≦ 700) The hardness at was _{H T} This is an index indicating the degree of hardness reduction due to tempering temperature.

  In the alloy steel of the present invention, in particular, the C content as the alloy component is set to 2.0 to 3.0%, the Si addition amount is increased, and the Si content is 3.5 to 6.0%, preferably, When it is set to 3.5 to 4.0%, even when tempering is performed in a temperature range of 600 to 700 ° C., excellent high temperature temper softening resistance is exhibited. When made of alloy steel, the cutting edge does not soften (decrease in hardness) even under high-speed cutting conditions exposed to high temperatures, so it exhibits excellent cutting performance over a long period of use. can do.

It is a graph which shows the relationship between tempering temperature (degreeC) and a softening ratio (%) at the time of performing tempering. It is a schematic perspective view of a solid hob.

  The invention is illustrated below by means of examples.

A powder having a predetermined component composition produced by a nitrogen gas atomization method is filled into a capsule and degassed, and then subjected to HIP treatment (hot isostatic pressing) at a temperature of 1150 ° C. and a pressure of 100 MPa to obtain the component composition shown in Table 1. The powder alloy steels 1 to 10 of the present invention (hereinafter referred to as the present invention steels 1 to 10) were produced.
Similarly, powder alloy steels 11 to 15 of comparative examples (hereinafter referred to as comparative example steels 11 to 15) having component compositions deviating from the present invention were produced.
Similarly, Table 1 shows component compositions of Comparative Example Steels 11 to 15.

About the said invention steel 1-10, it heat-processes on the conditions shown in Table 2, this invention steel 1-A to 1-D, this invention steel 2-A to 2-D, this invention steel 3-A, 3- B, Invention Steel 4-A, 4-B, Invention Steel 5-A, 5-B, Invention Steel 6-A, 6-B, Invention Steel 7-A, 7-B, Invention Steel 8 -A, 8-B, Invention steels 9-A, 9-B, Invention steels 10-A, 10-B were produced.
Similarly, it heat-processed on the conditions shown in Table 3 also about the comparative example steels 11-15, comparative example steel 11-A-11-D, comparative example steel 12-A-12-D, comparative example steel 13-A. 13-B, Comparative Example Steels 14-A and 14-B, and Comparative Example Steels 15-A and 15-B were produced.
That is, after performing austenitizing treatment under conditions of 850 to 950 ° C. × 60 to 90 minutes, quenching is performed by holding at 1130 to 1180 ° C. for 30 minutes, then holding at 600 to 700 ° C. for 1 hour, and the number of times of return is 3 times Tempering was performed.

For each, by measuring the hardness as quenched, hardness at 600 ° C. (H ₆₀₀ ), and hardness at a predetermined tempering temperature T (H _T ) with a Rockwell hardness meter (both average values of 5-point measurement) The hardness is obtained, and the softening ratio (%) from the hardness value (= (H _T -H ₆₀₀ ) × 100 / H ₆₀₀ )
Was calculated.
These values are shown in Tables 2 and 3.
In addition, about this invention steel 1, this invention steel 2, the comparative example steel 11, and the comparative example steel 12, the relationship between tempering temperature and hardness was shown in FIG.

As is apparent from Tables 2 and 3 and FIG. 1, even when high temperature tempering of 600 to 700 ° C. is performed, the steels 1 to 10 of the present invention have excellent tempering hardness (HRC is 50 or more). The high-temperature tempering softening resistance superior to those of Comparative Steels 11 to 15 was exhibited. For example, the softening ratio (%) at a tempering temperature of 700 ° C. was −20% at maximum (invention steel 6-B). .
In contrast, the comparative steels 11 to 15 have not only low tempering hardness but also poor high-temperature tempering softening resistance. For example, the softening ratio (%) at a tempering temperature of 700 ° C. is −26% (comparative steel). 11-D), -26% (Comparative Steel 12-D), -27% (Comparative Steel 13-B), -34% (Comparative Steel 14-B), -26% (Comparative Steel 15-) B), which is clearly inferior in high temperature temper softening resistance.

Next, the steels 1 to 5 according to the present invention have a general dimension of outer diameter: 108 mm × length: 160 mm by machining, and a schematic perspective view in FIG. 2 having the shape of three right-hand twists × 12 grooves. Solid hobs 1 to 5 (referred to as hobs 1 to 5 of the present invention) shown in FIG.
Similarly, Comparative Hobbes 11 to 15 were produced for Comparative Steels 11 to 15.

Next, for each of the present invention hobs 1 to 5 and comparative example hobbs 11 to 15, a thin layer A made of (Al _0.45 , Cr _0.40 , Si _0.15 ) N and having a layer thickness of 100 nm and A hard coating layer having a layered structure (50 layers) with a thin layer B having a single layer thickness of 80 nm made of (Al _0.75 , Ti _0.15 , Si _0.10 ) N is deposited by arc ion plating. Formed. (The subscripts of the constituent elements Al, Cr, Si or Al, Ti, Si constituting the thin layer A and the thin layer B indicate the atomic ratio of each element.)
In addition, after arc ion plating, the rake face was polished and the hard coating layer on the rake face was removed.

  Subsequently, using the present invention hobs 1 to 5 and comparative example hobs 11 to 15 on which the hard coating layer was formed by vapor deposition, a cutting test was performed under the following conditions to evaluate the cutting performance.

Work material: JIS / SCr420H
Gear specifications: Module 2.0,
Pressure angle 20 degrees,
Number of teeth: 28
Twist angle: 25 degree left twist,
Tooth width: 50 mm,
Cutting speed (rotational speed): 200 m / min,
Feed: 2.0mm / rev,
(Climb, no shift, dry (air blow))
Under these conditions, high-speed dry gear cutting was performed, and the number of gears processed until the flank wear width reached 0.2 mm was measured.
Table 4 shows the measurement results.

From the results shown in Table 4, even when the hobbs 1 to 5 of the present invention are exposed to high temperatures during cutting, the high-temperature tempering softening resistance of the cutting edge is high, so that the occurrence of crater wear due to softening (hardness reduction) In addition, it does not cause abnormal damage such as defects, takes a normal wear form, has a large number of gear cutting processes, and has a long life.
On the other hand, Comparative Hobbes 11 to 15 had a short life due to abnormal wear such as crater wear due to a decrease in hardness due to lower softening resistance than the hobbs of the present invention.

  As described above, the alloy steel of the present invention has excellent high temperature temper softening resistance, and the hob made of the alloy steel of the present invention has excellent cutting performance and a long life. In addition, the alloy steel of the present invention can be used not only as a hob but also as a cutting tool material such as a pinion cutter and a shaving cutter, and also has excellent wear resistance and toughness. By this, it is possible to achieve longer life of the cutting tool.

Claims (2)

  % By mass, C: 2.0 to 3.0%, Si: 3.5 to 6.0%, Mn: 1.0% or less, Cr: 3.5 to 4.0%, W and Mo The total of one or two of: 10.0 to 12.0%, V: 3.0 to 3.5%, Co: 4.0 to 5.0%, the balance consisting of Fe and inevitable impurities Alloy steel with excellent high temperature temper softening resistance.   2. A hob characterized in that a base of the hob is made of an alloy steel having high-temperature temper softening resistance according to claim 1.

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