JP2001107181A - Tool steel excellent in machinability and heat treatability and die using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide tool steel excellent in antipodal characteristics of machinability and heat treatability. SOLUTION: This tool steel satisfies the relational formulae of, by mass, (Cr+5.9×C): 9.1 to 12.5, (Cr-4.2×C): <=5, and (Cr-6.3×C)>=2.2. Preferably, the tool steel has a composition, in addition to the above, containing 0.1 to 0.6% Si, 0.1 to 1.2% Mn, one or two kinds of Mo and W by (Mo+1/2W): 0.6 to 1.25% and <0.5% V, furthermore containing <=0.12% Si, <=100 ppm Ca, <=1% Ni and <=0.6% Al, and the balance Fe with inevitable impurities. In addition, in the tool steel, the matrix segregation width of Cr after quenching if <=1%, by mass, or, by tempering at >=500 deg.C, the maximum tempering hardness if >=57 HRC, or the heat treatment dimensional change generated by tempering at >=500 deg.C is <=0.1% expressed in terms of a linear expansion coefficient on a standard before the quenching, and also, the heat treatment dimensional change by tempering at 490 deg.C is <=0, and a die is produced by refining the tool steel to the hardness of >=55 HRC and executing machining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool steel used for a die for punching, bending, drawing or trimming a steel sheet used for automobiles, household appliances, agricultural equipment and the like.

[0002]

2. Description of the Related Art Automakers and the like have been reducing costs in various fields in order to overcome price competition and secure profits. The field extends to molds, and to reduce costs, shorten the manufacturing process of products formed by press dies, reduce the number of dies, and develop mold processing methods and tools. Various reduction measures have been implemented.

[0003] In such a mold, conventionally used mold materials, especially mold materials for cold working, contain a large amount of carbides for imparting wear resistance, and further have excellent hardenability and ensure toughness. Therefore, a material having a high Cr content is required, and for example, a high C-high Cr steel such as SKD11 which is an alloy tool steel according to JIS G4404 is used.

[0004]

However, in recent years, various movements for reducing the number of man-hours for cutting have become intense. Originally, among the molding technologies, the high cost cutting process became even more costly due to the advance of plastic working, and in opposition to it, CBN, the development of coating tools, the emergence of high-speed cutting machines, the NC algorithm Development of new technologies, such as progress, is progressing. In response to this trend, tool steels with improved machinability include S
There is a free cutting tool steel in which S is added to the KD11 approximate composition. However, there are various cutting modes, and mere addition of S does not correspond to various cutting modes and cutting conditions such as end mills, milling cutters, and drills.

[0005] Further, there have been reports that it is possible to perform processing in a quenched and tempered state of 60 HRC with the advent of high-speed cutting machines. However, cutting is still difficult due to rough machining and the like. The machinability of high hardness material is SKD1 as described above.
This is because the addition of S to 1 does not improve, and it is necessary to reduce the presence of carbides.

[0006] As in the case of cutting, size change during heat treatment is also a problem. If the heat treatment size is large, the margin must be increased, and as a result, the number of finishing steps is increased. SKS3 is a low alloy tool steel and SKD1
Although the machinability is much better than 1, the hardenability is poor and oil quenching is likely to cause warpage. The 8% Cr-based die steel developed in the 1980's has good hardenability, but tends to undergo heat treatment deformation and aging deformation, resulting in good heat treatment deformation of SKD11 which is difficult to cut. .

That is, at present, there is a demand for a tool steel having advantages and disadvantages, a heat treatment property comparable to that of SKD11 and a machinability similar to that of SKS3. In particular, in terms of heat treatment properties, it is strongly desired that the SKD 11 and the SKD 11 can be mixedly loaded in the same heat treatment furnace from the viewpoint of streamlining the heat treatment operation. Thus, the present invention provides a tool steel having excellent machinability and heat treatment characteristics without deteriorating mechanical properties such as toughness.

[0008]

Means for Solving the Problems In view of maintaining basic mechanical properties such as toughness and wear resistance, the present inventors
The basic conditions required for improvement in machinability and heat treatment were reviewed.

First, various cutting modes for cutting tool steel were examined, and it was found that chipping type damage and thermal damage could be classified. They have found that a method of forming both of them simultaneously on different parts of one tool can be realized by a square end mill under specific conditions. Specifically, they found that the cutting edge was mechanically damaged, and that thermal damage was generated at the boundary where the contact with the work material was completed. Various methods of free cutting to reduce the damage mechanism of both by this method were studied.

As a result, it has been found that the reduction of primary carbides present in the tool steel prevents mechanical damage and that the addition of S prevents thermal damage. Then, by considering both of these effects at the same time and considering a wide range of cutting styles and cutting conditions, the present inventors have found an optimum tool steel for achieving the effects.

That is, the present invention relates to the method of
When the value of (5.9 × C) is 9.1 or more and 12.5 or less, and (Cr−4.2 × C) is 5 or less, (Cr−6.3 × C)
C) is a tool steel satisfying the relational expression of 2.2 or more. Preferably, in addition to these, Si: 0.1 to 0.6
%, Mn: 0.1 to 1.2%, one or two kinds of Mo or W (Mo + 1 / 2W): 0.6 to 1.25%,
V: less than 0.5%, further S: 0.12% or less, Ca:
A tool steel containing 100 ppm or less, with the balance being Fe and unavoidable impurities. Alternatively, Ni: 1
%, Al: 0.6% or less.

A tool steel having a matrix segregation width of 1% or less by mass of Cr after quenching or a maximum temper hardness of 57HRC or more by tempering at 500 ° C. or more. In addition, the heat treatment dimensional change generated by tempering at 500 ° C. or higher is 0.1% in terms of the linear expansion coefficient based on the reference before quenching.
Tool steel having a heat treatment dimension of 0 or less after tempering at 490 ° C.
This is a mold produced by tempering to a hardness of RC or higher and cutting.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The feature of the present invention resides in that a tool steel having both heat treatment characteristics similar to SKD11 and machinability comparable to SKS3 has been achieved. Hereinafter, the details of finding the tool steel of the present invention will be described.

In the region where the amount of carbides is reduced, a component design capable of performing almost the same heat treatment as SKD11 which is a de facto standard tool steel was performed. In order to obtain the same heat treatment characteristics, the composition to be dissolved in the matrix during quenching is SKD11.
The basic policy was to get closer to. FIG. 1 is an entire component design diagram determined by thermocalc, and FIG. 2 is a component design diagram in which a region corresponding to the present invention is enlarged. The line (A) shows the line on the plane of the additive component that gives the same amount of solid solution C as SKD11 during quenching. Similarly, the line (B) indicates the same solid solution Cr amount line as that of SKD11. The reason why both are bent in the middle is that carbides remain from the line (C) or higher, so that alloying elements are taken into the carbides and the solid solution elements in the matrix cannot be maintained the same unless the amount of added components is increased. .

The two lines (A) and (B) are basically
Since it only intersects with the composition of SKD11, it is impossible to make the matrix composition the same as SKD11 at the same quenching temperature. However, the base composition approximates to SKD11 even after the line (C) because the lines (A) and (B) are close to each other. However, if the amounts of added C and Cr are increased in order to bring this line closer, the amount of residual carbide increases, and chipping type tool wear is accelerated and machinability deteriorates. In addition, since fatigue fracture is likely to occur also in terms of durability, use in a mold in which stress concentration is likely to occur is limited. This reciprocal relationship was clarified experimentally,
The region where the machinability is excellent and the heat treatment characteristic is close to that of SKD11 is the tool steel of the present invention shown in FIG.

In recent years, heat treatment dimensional change has been particularly emphasized among heat treatment characteristics. Regarding the quality of the mold, the shape accuracy has recently attracted particular attention in addition to the durability, and the SKD11 is also highly evaluated in this respect. The concept regarding the control of the heat treatment size change is described below.

FIG. 3 shows a principle diagram of the heat-sizing behavior. In the as-quenched state, the crystal lattice is expanded by C that forms a solid solution in the main martensite structure,
Swell. As the tempering temperature is increased, cementite precipitates in the low and medium temperature regions (FIG. 3 (A) region), and the dimensional change tends to shrink. In the high temperature range, the dimensional change is maximized at substantially the same temperature as the secondary curing. This maximum occurs when
The low temperature side (FIG. 3 (B) region) and the high temperature side (FIG.
(C) region) mainly due to two mechanisms. On the low temperature side, the decomposition of the retained austenite increases as the temperature increases, and the tendency to expand occurs. M ₇ on the higher temperature side than the maximum value
Since the amount of solid solution C in martensite decreases due to precipitation and agglomeration of C ₃ and M ₂₃ C ₆ based carbides, a tendency to shrink occurs.

Using the mechanisms (A), (B), and (C), the SKD 11 has a composition that suppresses the size change that occurs between (B) and (C) while maintaining the hardness. Here is the source of the idea of the present invention in which is approximated to SKD11. Therefore, C, the main alloying element of SKD11,
As shown in FIG. 3, not only Cr but also Si, M ₇ C ₃ , and M ₂₃ C ₆ based carbides for controlling the precipitation of cementite are optimized.

In the component system of the present invention, primary carbides are hardly crystallized in the equilibrium diagram, so rapid solidification or diffusion annealing at about 1100 to 1400 ° C. is performed to eliminate or reduce the primary carbides. The treatment leads to a further improvement in machinability.

In addition, the effect of heat treatment sizing due to the addition of S was examined. As a result, it has been found that when the S content exceeds 0.12%, the heat treatment size change increases. Conventionally, there has been no such report, but it is considered that the cause is that heat treatment sizing is hardly regarded as a problem in a free-cutting steel system that frequently uses S addition. On the other hand, it is presumed that the tool steel system has a large amount of residual carbide, so that the effect of restraining the size change worked and the effect on the size change of S could not be detected. As a result, it has been found that it is necessary to adjust the composition to 0.12% or less, which is small in size.

Next, the heat treatment and surface treatment properties of the present invention will be described. The present invention sufficiently secures the surface treatment properties in order to cope with the case where the wear resistance is insufficient due to the suppression of the C content. Carburizing, nitriding,
There are PVD and CVD processes. Among them, the CVD process is difficult depending on the properties of the base material. This treatment chemically deposits the vaporized film-forming element at about 1000 ° C. on the material surface. As a result, problems such as insufficient quenching and large heat treatment dimensional changes are raised as in the case of heat treatment of the material.

That is, the quenchability, which is a representative index of the heat treatment property, is given to enable application to any surface treatment apparatus. Therefore, they are fully satisfactory. In addition, the dimensional change of heat treatment during quenching and tempering is S
In order to improve the industrial convenience by making the properties equivalent to KD11, the C and Cr compositions of the matrix are changed to SKD11.
It is important to adopt the region shown in FIG. SKD11 is also used as a gauge steel as a steel with little heat treatment dimensional change.

The reason why the SKD 11 has the low heat treatment sizing characteristic is that the hardness in the high temperature tempering region is maintained by adopting a method of suppressing the precipitation of cementite almost exclusively with solid solution Cr. That is, Mo, W, and V such as high-speed tool steel capable of high-temperature tempering are actively added.
In the secondary hardened steel, fresh martensite generated by the decomposition of residual austenite generated during secondary hardening does not readily undergo tempering shrinkage, so that high heat treatment deformation occurs.

However, when the same effect is aimed at with Cr,
C such as M ₇ C ₃ quickly in fresh martensite
Since r-based carbides are precipitated and tempered martensite occurs promptly, the amount of solid solution C in martensite can be reduced and extreme expansion can be suppressed, which is the cause of the low heat treatment dimensional change of SKD11. Since heat treatment size changes the amount of margin for finishing before heat treatment, it is an important factor that affects machining efficiency as well as machinability.

In any case, the amounts of solid solution C and Cr are adjusted to SKD1.
By approximation to 1, there is a characteristic that can be regarded as practically the same as SKD11 in terms of surface treatment dimensional change, quenching property, hardness and aging change in which heat treatment dimensional change such as CVD becomes a problem.
As a result, mixed loading in the same furnace as the SKD 11 becomes possible, so that the cost of surface treatment work can be greatly reduced.

The amount of C that forms a solid solution in the austenite structure at a surface treatment temperature such as CVD is important for producing an MX type compound (TiC, VC, etc.) having a sufficient film thickness. In other words, solid solution C is required to be supplied from the steel material in order to generate an MX-type compound particularly in the CVD surface treatment,
The optimum amount depends on the amount of C which forms a solid solution in the martensite structure before the surface treatment temperature is maintained. Since the tool steel of the present invention achieves a solid solution C content of 0.4% or more, a sufficient film formation is possible. Based on these, the elements constituting the tool steel of the present invention and the reasons for limiting the contents thereof will be described.

C and Cr adopt the regions shown in FIGS. 1 and 2 from the viewpoint of similarity to SKD11 and the amount of residual carbide immediately after quenching is 5 (mass%) or less. Specifically, in the structure immediately after quenching at 1000 ° C. to 1050 ° C., it is preferable that the amount of undissolved carbides calculated by, for example, thermocalc is 5 (mass%) or less for improving machinability. Is what you do.

The heat treatment characteristics of SKD11 are such that in the region where the tempering temperature is 490 ° C. or less, the heat treatment dimension in the rolling direction becomes negative, and at higher tempering temperatures, it turns positive. In addition, the maximum heat treatment deformation at a tempering temperature higher than 490 ° C. is characterized in that it has a positive value when the tempering temperature is 0.1% or less. Also, there is a feature that there is a heat treatment condition that can secure the temperature.

The component regions satisfying all the characteristics are the component regions shown in FIGS. 490 ° C
The characteristic that always undergoes negative scaling in the following, and turns positive at higher temperatures, the condition that when the tempering temperature is increased little by little, the heat treatment scaling always becomes zero in some conditions Therefore, it is possible to find a process for reducing the size to zero under heat treatment conditions. This is also the background that SKD11 has been supported by highly skilled heat treatment companies and has been de facto standardized, and the balance between C and Cr shown here is particularly important.

Basically, Si is also SKD11 (Si = 0.
25 (mass%)). However,
Si is originally contained for the purpose of improving the deoxidizing agent and the castability, but when this is reduced, toughness is improved. However, since the machinability also deteriorates, 0.1% or more is necessary. On the other hand, the excessive content suppresses the precipitation of cementite, and consequently causes the heat treatment in the tempering region of 500 to 550 ° C. to become large. Therefore, the content of Si is 0.1 to
0.6%.

Mn is also basically SKD11 (Mn = 0.
4 (mass%)). Mn
Is contained for improving the hardenability, but if it is less than 0.1%, it is insufficient to stably obtain the hardenability. on the other hand,
If it is too large, it will cause deterioration of weldability, and like Si, segregation of the matrix components will be intensified.
1 to 1.2%. However, Mn is expensive Cr or Mo
Although it is an economical element that can be replaced with, for example, Cr, Mo, and the like are sufficiently exerted, and Mn may be omitted when S is not added.

Mo and W are also SKD11 (Mo = 0.8
5 (mass%)). M
o and W improve hardenability. Further, even if tempering is performed on the high temperature side, softening does not occur suddenly. Therefore, adjustment of hardness becomes easy. Since the atomic weight of W is about twice that of Mo, the content of Mo 1% has the same effect as the content of W 2%, and the effect can be expressed by the (Mo + ／ W) content. In the present invention, one or two types of Mo and W can be contained, that is, the entire content of Mo may be replaced with twice the content of W, and a part of Mo may be replaced with the corresponding W. It may be used in place of the amount. (Mo + 1
/ W) which component should be preferentially used in the amount may be determined in consideration of economy. However, since W replacement basically deteriorates the frame hardware, it is preferable to add Mo.

If the amount of (Mo + 1 / 2W) is less than 0.6%, the hardness during high-temperature tempering decreases sharply, making it difficult to control the hardness. On the other hand, if the amount is too large,
Delays precipitation and aggregation of carbides in martensite
Unstable austenite remains even if it is thought that tempering at 0 to 550 ° C. results in a large heat treatment dimensional change, or a delay in austenite decomposition due to a delay in martensite tempering. Since aging occurs during use after production, the content is set to 0.6 to 1.25%. Preferably it is 0.6-1.10%.

[0034] The tool steel of the present invention may contain V in the above component composition in accordance with the other effects required. V was basically set to be equivalent to SKD11 (V = 0.25 (mass%)). V is an element that increases the softening resistance required for the tool steel, and the preferred content is 0.05
% Or more, but V-based carbides are formed and cause the machinability to be reduced.

S is an element which is detestable in the fields of welding and high hardness steel as a representative embrittlement element. However, since it has a free cutting effect, it can be added because the amount of carbide is reduced and the toughness is improved. . Therefore, in consideration of the increase in heat treatment size change, up to 0.12% is allowable. The content is preferably 0.005% or more, more preferably 0.02% or more, for obtaining the above effects.

[0036] Ca is an ideal free-cutting element without a decrease in mechanical properties or a change in structure. The free-cutting mechanism is
This is because oxides, which are slightly dispersed in the steel, have a low melting point, and this is melted by the cutting heat to form a protective film on the cutting edge. However, since the vapor pressure is high, it is easy to escape from the molten steel, and up to about 100 ppm is the current technical level due to the addition technology. In order to obtain the above effect, it is preferable that 10
ppm or more.

In addition, rare earth elements can be contained in an amount of 0.2% or less for the purpose of improving machinability in the tool steel of the present invention. Further, the total amount of unavoidable impurities is preferably 0.5% or less. However, if toughness and weldability are required, Ni should be 1%
Or less, preferably 0.01 to 1%, and when further addition of wear resistance is required, Al is 0.6% or less, preferably 0.1 to 0.1%.
It is also possible to increase the nitriding hardness by adding from 01 to 0.6%. In addition, according to other required effects, P
b, Se, Te, Bi, In, Be, Ce, Zr, Ti
Even if one or more of them are contained in an amount of 0.2% or less, the basic characteristics are not changed.

In the present invention, in order to further improve the present effect, it is effective to adjust the condition after quenching. That is, the contents of C and Cr dissolved in the martensite structure after quenching are made to approximate SKD11, and the weight of residual carbide immediately after quenching is set to 5 (mass%) or less. The amount of residual carbide immediately after quenching can be reduced by the steel material manufacturing process. The powder method, heat treatment of the steel ingot immediately after melting at 1100 ° C. or higher for about 1 to 10 hours, that is, the soaking method, miniaturization of the steel ingot, and the rapid solidification method also reduce the amount of residual carbide immediately after quenching (Mass%) or less. In addition, it is also preferable to reduce the matrix segregation width of Cr after quenching to 1% or less by mass% in order to improve machinability.

With the tool steel of the present invention described above, in addition to imparting excellent weldability, quenching from 1000 to 1050 ° C., which is a heat treatment condition equivalent to that of the conventional SKD11,
A hardness of 57 HRC or more can be ensured even by tempering at 500 ° C. or more. In addition to achieving excellent machinability with a hardness of 57 HRC or more, it is also excellent in surface treatment properties such as a salt bath method and a CVD treatment.

When the tool steel of the present invention is used for a mold or the like, a frame hardware or the like may be implemented only in a necessary portion according to the required function, and the number of manufacturing steps or required characteristics should be taken into consideration. What is necessary is just to select the heat treatment method for obtaining hardness. For example, a so-called pre-hardened mold is prepared by cutting the tool steel of the present invention to a hardness of 55 HRC or more and performing cutting.

[0041]

EXAMPLES Next, examples of the present invention will be described in detail, but the present invention is not limited to these examples. (Example 1) First, a material was melted using a 100 kg high frequency furnace, and an ingot having a chemical composition shown in Table 1 was produced. The comparative material 1 is a material equivalent to SKD11. Next, hot rolling was performed so that the forging ratio was about 5, and after cooling, annealing was performed at 850 ° C. for 4 hours.

[0042]

[Table 1]

Next, 21 test pieces each having a diameter of 10 mm and a length of 80 mm were prepared so that the rolling direction coincided with the longitudinal direction, and their lengths were measured. Next, ten of them were heated and maintained at 1025 ° C. using a vacuum heating furnace, and then gas-cooled and quenched with an inert gas. Further, tempering was performed twice at 530 ° C. for one hour. When the hardness of the obtained test piece was measured, Comparative Examples 2 and 3 did not show 57 HRC or more. Next, measure the length in the length direction of the material having 57HRC or more, calculate the dimensional change rate based on the length before quenching measured in advance, and calculate the number of pieces exceeding 0.1%. I checked whether it occurred. Table 2 shows the results.

[0044]

[Table 2]

From Table 2, it can be seen that all of the present invention has a size change of 0.1%.
It was below. In the comparative example, 0.1 was added to 4, 5, and 6
%.

Next, in addition to those whose deformation at 530 ° C. was 0.1% or less, 10 pieces each of Comparative Examples 4 and 5 were subjected to 1025 ° C. in a vacuum heating furnace using the remaining annealed ones. After heating and maintaining the temperature, gas cooling quenching was performed with an inert gas.
Further, tempering was performed twice at 490 ° C. for one hour. Thereafter, the length of the test piece in the length direction was measured, and the dimensional change rate was calculated based on the length before quenching measured in advance. It was examined how many of those dimensional changes expanded to the plus side. Table 3 shows the results.

[0047]

[Table 3]

Thus, Comparative Example 5 expands to the plus side, making it difficult to adjust the size.
4 and Comparative Example 1, in addition to the results shown in Table 2 above, show that the swelling is easy to adjust because it does not expand to the plus side, and that the same heat treatment as SKD11 is possible.

Example 2 Next, the machinability was evaluated. First, among the materials shown in Table 1, those obtained by adding Comparative Example 4 to the materials (Examples 1 to 14 and Comparative Example 1 of the present invention) whose sizing behavior in Example 1 can be regarded as equivalent to SKD11 have a hardness of 24H.
The sample was placed in an annealing state of RC or less, and the machinability of the square end mill was evaluated. The cutting test was performed under the conditions shown in Table 4. From the results shown in Table 5, Examples 1 to 1 of the present invention
No. 4 shows high machinability with a tool life (edge wear of 0.3 mm) of 10 m or more. However, Comparative Examples 1 and 4 have poor machinability due to the chromium carbide.

[0050]

[Table 4]

[0051]

[Table 5]

Next, a material obtained by adding Comparative Example 4 to a material (inventive examples 1 to 14 and Comparative Example 1) which can be regarded as having a size change behavior equivalent to that of SKD11 was subjected to quenching at 1030 ° C. and tempering at 500 ° C. or more. A test material tempered to a hardness of 57 to 60 HRC was prepared, and the machinability of the test piece was evaluated with a square end mill. The cutting conditions are shown in Table 6. From the test results shown in Table 7, the invention examples 1 to 14 show the tool life (edge wear 0.1 m)
m) is good and the machinability is high, but it can be seen that Comparative Examples 1 and 4 have poor machinability.

[0053]

[Table 6]

[0054]

[Table 7]

(Example 3) Among the materials shown in Table 1, Comparative Examples 1 and 2 which were excellent in heat treatment characteristics and Comparative Examples 1 and 2 which were comparatively inferior in machinability of the inventive materials. Is subjected to soaking at 1160 ° C. for 10 hours in the ingot state, and after annealing, quenching at 1030 ° C.
A machinability test was performed on the steel sheet adjusted to 57 HRC by tempering at 00 ° C. or higher. The conditions were the conditions shown in Table 8 and the cutting distance at which the edge wear was 0.1 mm was defined as the life. Also,
In order to evaluate the segregation state of the matrix, a characteristic X-ray of 1 mm linear Cr was detected by EPMA using the as-quenched material, and a statistical analysis was also performed with a Cr change width of a non-carbide portion as 2σ. Table 9 shows the results of both.

[0056]

[Table 8]

[0057]

[Table 9]

According to Table 9, the as-quenched Cr segregation width was 1%.
The following materials of the present invention have a further improved life than the previous Example 2, but the comparative materials 1 and 4 have a Cr segregation width exceeding 1%, so that the life of the tool can be greatly improved. There was no result.

[0059]

As described above, according to the present invention, it is possible to provide a steel material having excellent machinability in an annealed state and high toughness and weldability in quenching and tempering as compared with SKD11. Furthermore, since the heat treatment changes, the hardenability, and the change in hardness with respect to the tempering temperature have characteristics similar to those of SKD11, they can be mixed and loaded in the same furnace as SKD11, eliminating the need for productivity and setting conditions. In addition, the machinability after quenching and tempering is remarkably higher than that of SKD11, and there is no deterioration in film characteristics even in surface treatment such as CVD which is affected by the amount of solid solution C in steel, so that gold having excellent wear resistance is used. The industrial value according to the present invention is great because the mold substrate has high manufacturing easiness.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an effect of the present invention.

FIG. 2 is a detailed view of FIG. 1 for explaining the effect of the present invention.

FIG. 3 is a view for explaining the behavior of heat treatment dimension change.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshihiro Kada 2107-2 Yasugi-cho, Yasugi-shi, Shimane Pref.

Claims (10)

[Claims] (1) In mass%, the value of (Cr + 5.9 × C) becomes 9.1 or more and 12.5 or less, and (Cr-4.2 × C)
C) A tool steel excellent in machinability and heat treatment characteristics, which satisfies a relational expression of not more than 5 and (Cr-6.3 × C) being not less than 2.2. 2. In mass%, the value of (Cr + 5.9 × C) becomes 9.1 or more and 12.5 or less, and (Cr-4.2 × C)
C) satisfies the relational expression of not more than 5 and (Cr-6.3 × C) being not less than 2.2, Si: 0.1 to 0.6%, Mn:
0.1 to 1.2%, one or two types of Mo or W (Mo + 1 / 2W): 0.6 to 1.25%, V: 0.5
%, With the balance being Fe and inevitable impurities, the tool steel having excellent machinability and heat treatment properties. 3. The value of (Cr + 5.9 × C) in mass% becomes 9.1 or more and 12.5 or less, and (Cr−4.2 × C).
C) satisfies the relational expression of not more than 5 and (Cr-6.3 × C) being not less than 2.2, Si: 0.1 to 0.6%, Mn:
0.1 to 1.2%, one or two types of Mo or W (Mo + 1 / 2W): 0.6 to 1.25%, V: 0.5
%, S: 0.12% or less, the balance being Fe and unavoidable impurities, characterized by having excellent machinability and heat treatment properties. 4. The value of (Cr + 5.9 × C) in mass% is 9.1 or more and 12.5 or less, and (Cr−4.2 × C).
C) satisfies the relational expression of not more than 5 and (Cr-6.3 × C) being not less than 2.2, Si: 0.1 to 0.6%, Mn:
0.1 to 1.2%, one or two types of Mo or W (Mo + 1 / 2W): 0.6 to 1.25%, V: 0.5
%, S: 0.12% or less, Ca: 100 ppm or less, the balance being Fe and unavoidable impurities, the tool steel having excellent machinability and heat treatment properties. 5. The tool steel having excellent machinability and heat treatment properties according to claim 2, wherein the steel contains Ni: 1% or less by mass%. 6. A tool steel having excellent machinability and heat treatment properties according to claim 2, wherein the steel contains 0.6% or less of Al by mass%. 7. The tool steel according to claim 1, wherein a matrix segregation width of Cr after quenching is 1% or less by mass%. 8. The tool steel according to claim 1, wherein the maximum temper hardness by tempering at 500 ° C. or more is 57 HRC or more. 9. The heat treatment dimensional change caused by tempering at 500 ° C. or more is 0.1% or less in terms of linear expansion coefficient before quenching and the heat treatment dimensional change at tempering at 490 ° C. is 0 or less. The tool steel according to any one of claims 1 to 8, having excellent machinability and heat treatment properties. 10. A mold prepared by tempering the tool steel according to claim 1 to a hardness of 55 HRC or more and performing a cutting process.