WO2002077309A1

WO2002077309A1 - Cast steel and metal mold for casting

Info

Publication number: WO2002077309A1
Application number: PCT/JP2002/002729
Authority: WO
Inventors: Yasutaka Okada; Koji Watari
Original assignee: Sumitomo Metal Industries, Ltd.
Priority date: 2001-03-23
Filing date: 2002-03-20
Publication date: 2002-10-03
Also published as: TW539749B; US20040037731A1; JPWO2002077309A1; CN1498282A

Abstract

A cast steel with excellent internal quality and machinability after casting, wherein a steel composition is limited with respect to specific components and the contents of Ti, Zr, S, and N in the steel are adjusted to an appropriate range to form fine sulfides of Ti and Zr; a metal mold having such an internal quality in cast state that provides an excellent machinability equivalent to that of a forged steel product, wherein the metal mold is manufactured by casting the cast steel, whereby the cast steel can be used for cast materials for deep engraving having a working surface extending to the inside of a raw material and for finishing materials where the excellence of surface properties is requested strictly.

Description

Specification

錶 Steel and metal mold

The present invention relates to a steel having excellent internal quality and machinability after manufacturing, and a steel product obtained by manufacturing the above steel, especially a mold. The present invention relates to a steel which suppresses various defects, has an internal quality comparable to a forged steel product, and has excellent machinability, and a mold using the same. Background art

Molds are indispensable processing members (tools) for molding various materials including metals and plastics. Various steel materials are generally used for this.

For example, carbon steel containing 0.10 to 0.50% by mass of C or a steel material added with Cr, Mo, Cu, Ni, V, etc. is used for a plastic molding die. In addition, JIS SKD 6 Class 1 Cr, 1 to 9% by mass, 0.2 to 1.2% by mass, Mo: 0.2 to 2.0% by mass for hot forging dies Steel material is used as the main component. Further, a steel material containing, for example, about 1% C to 3.5% Cr by mass% is used for the cold forming die.

These dies are usually hot-worked from steel materials to form shaped materials, and cut as needed, and then cut into the desired shape by the user in many cases. However, the method of cutting after hot working requires many days to obtain a shaped material and finish it by cutting, and there is a limit in terms of shortening the delivery time. Furthermore, due to the hot working finish, it is difficult to machine the shape close to the required shape, so-called Nine Shade, so that most of the raw material is discharged as cutting swarf, resulting in loss and cutting. Long in It requires a lot of time and a lot of tool costs.

On the other hand, in the case of prefabricated materials, it is possible to produce a shape close to the final finished shape, including various cooling holes, but there are the following problems, and its application has been greatly restricted.

For example, Japanese Patent Application Laid-Open No. 11-279673 proposes to use a Zn alloy which has a low melting point and is easy to handle. That is, in terms of% by weight, Mg: 1.5 to 2.5%, 1: 3 to 5%, and ^: 2 to 4%, and the balance is substantially composed of Zn. The use of zinc alloy with 390 ° C or less, Vickers hardness of 150 or more, and suppressed generation of porosity.

Also, Japanese Patent Application Laid-Open No. H10-147840 proposes manufacturing a metal mold from steel. That is, in weight%, C: 0.5 to 1.0%, Si: 0.25 to: L. 5%, Mn: l. 0 to: L. 85%, Cr: 0.6 to 5. 0%, one or two types of Mo and W (Mo + W / 2) in the range of 0.06 to 0.80%, and S: 0.10 to 0.40%, with the balance substantially Fe This is a method of manufacturing a mold using free-cutting steel in which sulfide-based inclusions are dispersed in a matrix structure in a granular manner.

However, in the former, since the alloy is mainly composed of Zn, it has excellent machinability, but there is a limit to the hardness required to improve the life of the mold. Also, Zn alloys are significantly more expensive than steel materials.

Since the latter uses the same steel composition as before, sufficient hardness can be obtained.However, if S is added aggressively to improve machinability and the amount of MnS is increased, it will be a steel. It promotes structural defects such as porosity and S segregation or cracks caused by these. In addition, in 鎵 steel, porosity is not subjected to hot working and is not pressed, resulting in surface defects after cutting.

Therefore, in the conventional technology, the processing surface of the 錶 It could not be used for deep sculpture or finishing, which requires strict surface properties. Disclosure of the invention

The present invention has been made to solve the above-described problems in the prior art, and its object is to provide a steel having excellent internal quality and machinability after forging, and a method for manufacturing the steel. The purpose of the present invention is to provide a die having an internal quality comparable to a forged steel product and excellent machinability, while suppressing various defects in a forged state obtained.

In order to solve the above-mentioned problems, the present inventors have promoted the development of steel and a mold that can simultaneously satisfy the following goals.

1) The die material is manufactured by die-casting, the amount of cutting for die finishing is greatly reduced, and the processing time and cost are greatly reduced.

2) Develop steel that can obtain a mold with sufficient hardness by forging.

3) 内部 To simultaneously solve the problems of machinability and forging defects, which are problematic in steel dies, to achieve the same internal quality as forged steel in as-forged form with a high S content component system.

The term “internal quality” as used herein refers not only to the internal quality of a product, but also to the quality of a surface portion that becomes a new surface by cutting. If the above problems can be solved, the steel described above can be applied to steel used for general mechanical parts.

As a result of the above development, the following findings were obtained.

a) When a large amount of S is contained in steel for the purpose of improving machinability and the necessary amount of Ti or Zr is added, a sulfide containing Ti or Zr is formed and MnS is completely eliminated. Or sulfides containing TiZr are finely dispersed in the steel.

b) As a result of the above a), not only the machinability is improved, but also Even when the S content is high, the segregation of S is greatly improved while the structure remains as it is, and the columnar crystals are reduced or disappear, and not only defects such as porosity and segregation, but also coarse Irregularities on the cutting surface due to columnar crystals are also improved, and epoch-making internal quality comparable to forged steel is obtained.

The gist of the present invention completed based on the above findings is as follows: o

① In mass%, C: 0.02 to 0.45%, S i: 0.1 to 2.5%, Mn: 0.1 to 2.5%, P: 0.10% or less, S: 0 02 to 0.60%, N: 0.002% or less, A1: 0.001 to 0.03%, Ti: 0.05 to 0.25%, and Zr: 0.05 ~ 0.50

% Of one or two kinds, and the balance consists of Fe and impurities, and the effective Ti equivalent (Ti *) given by the following equation (1) satisfies the relationship given by the following equation (2), A steel with excellent internal quality and machinability after fabrication, characterized in that the steel contains a sulfide containing at least one of Ti and Zr.

Ti * = T i + 0.53 X Z r

-3. 4xN (1)

T i * / S≥ 1.5 (2)

(2) In the steel No. described in (1) above, Cr: 0.2 to 9.0%, Ni: 0.2 to 2.0%, Mo: 0. 05 ~

2.0% and V: one or more selected from 0.01 to 1.5% may be contained.

(3) In the steel (2) described in (1) or (2) above, instead of part of Fe, the mass% is Cu: 0. 3.3.0% and 0 (oxygen): One or two of 0.005 to 0.002% may be contained.

(4) A mold made of (2) the steel described in any of (1) to (3) above. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a macrostructure photograph of a lump for a steel containing neither Ti nor Zr.

FIG. 2 is a view showing a macrostructure photograph of a mass of a steel containing Zr.

FIG. 3 is a view showing a microphotograph of inclusions at the center of a lump for a steel containing Ti.

FIG. 4 is a diagram showing a microphotograph of inclusions at the center of the ingot in the steel containing Zr. BEST MODE FOR CARRYING OUT THE INVENTION

The structure and chemical composition of the steel according to the present invention will be described in detail below. In the following description, “%” as the content of each element means “% by mass” unless otherwise specified.

Figure 1 is a macrostructure photograph of a lump of steel containing neither Ti nor Zr. This is a microstructure having a diameter of 144 mm produced from a steel having a steel number 16 in an example described later, and a macrostructure photograph thereof was taken. Although no cracks or extreme macrosegregation are observed at the center, the structure is coarse and columnar crystals cover a radius of about 30% from the surface in the radial direction.

FIG. 2 is a macrostructure photograph of a mass made of a steel containing Zr. In this example, a steel block with a diameter of 144 mm was manufactured from steel No. 2 of steel No. 2 and a macrostructure photograph thereof was taken. The microstructure is extremely fine, with no columnar crystals, comparable to the macrostructure after hot forging.

FIG. 3 is a microphotograph of the inclusions at the center of the ingot of the steel containing Ti (Steel No. 1 in the example), and FIG. This is a microphotograph of the inclusion at the center of the lump No. 2). From the sulfide composition analysis results obtained by point analysis of inclusions by EPMA, the inclusions in Fig. 3 are mostly inclusions containing sulfides of Ti, and the inclusions in Fig. 4 are mostly Was found to be an inclusion containing the sulfide of Zr.

This phenomenon is controlled by Ti, Zr, S and N among the elemental components in steel. That is, when the effective Ti equivalent given by the above formula (1) satisfies the above formula (2) by the content of these elements, a small amount of Ti or Zr first reacts with N at the time of solidification. It forms nitrides, and most of the remaining Ti and Zr form sulfides. This sulfide is the final solidified part that changes the solidification morphology, and promotes solidification at once without large enrichment of S, P, etc. Structural defects are improved.

The above equation (1) is the amount of Ti and Zr that can react as a sulfide. If the relationship given by the above equation (2) is satisfied, stoichiometrically, S is all of Ti and Zr. Becomes sulfide. In practice, a small amount of MnS may be observed after solidification, but this is not a problem. When the value on the left side of equation (2) is less than 1.5, a large amount of MnS is observed, and no improvement in the solidification structure or related defects can be observed.

If the Ti content or the Zr content is too large with respect to the S content, the amount of carbides of Ti or Zr increases and the toughness ゃ the machinability deteriorates. The value on the left side of 2) is preferably 10 or less.

Hereinafter, the reason why the range of the content of each element specified in the present invention is determined as described above will be described.

C:

C is an element that is effective to increase strength at low cost. Since machinability is important in plastic molds, it is necessary to keep the C content as low as possible and reduce the hardness of steel materials to reduce tool wear. But 0. If it is less than 02%, the hardness decreases remarkably, causing tearing during the cutting process, and rather deteriorating the machinability. On the other hand, if the content exceeds 0.60%, the hardness becomes too high, and the machinability and toughness deteriorate. Therefore, the range of the C content is set to 0.02 to 0.45%. A preferred range is from 0.08 to 0.45%.

S i:

Si is an element effective for deoxidation and improvement of machinability. If the content is less than 0.1%, this effect cannot be sufficiently obtained. In addition, the flow of molten metal during construction is impeded, and the filling of molten steel in the mold becomes insufficient. On the other hand, if the content exceeds 2.5% and is too high, the machinability improving effect and the toughness decrease. Therefore, the range of the Si content is set to 0.1 to 2.5%. A preferred range is 0.5 to 2.0%.

Mn:

Mn is an effective element as a deoxidizing agent, but when contained in large amounts, it deteriorates machinability. If the content is less than 0.1%, no deoxidizing effect can be obtained. On the other hand, if the content exceeds 2.5%, the machinability deteriorates. Therefore, the range of the Mn content is set to 0.1 to 2.5%. The preferred range is 0.1-1.5%.

P:

P promotes segregation during solidification and degrades toughness. On the other hand, P has the effect of improving machinability by being contained. P may be contained as an impurity or may be actively contained depending on the purpose of use of the steel. For example, when toughness is emphasized, the P content is preferably set to 0.02% or less, and when machinability is emphasized, it is preferable to contain 0.05% or more. However, if the content exceeds 0.10%, the toughness significantly deteriorates, so the P content was set to 0.10% or less.

S: S is an element contained to improve machinability. If the content is less than 0.02%, the formation of sulfides of Ti and Zr is insufficient, and a sufficient effect cannot be obtained. On the other hand, if the content exceeds 0.60%, a large amount of FeS Mn S is generated, which promotes segregation, voiding or cracking during solidification. Therefore, the range of the S content is set to 0.02 to 0.60%. A preferred range is 0.05 to 0.40%, and a more preferred range is 0.05 to 0.20%.

T i and Z r:

Ti and Zr are elements having an effect of forming a sulfide, and in the present invention, one or two of these elements are contained. In any case, if the content is less than 0.05%, sufficient sulfide cannot be generated, so that a large amount of MnS is generated, and no improvement in the solidification structure and no improvement in defects related thereto are recognized. On the other hand, if Ti exceeds 1.0% and Zr exceeds 0.50%, the amount of carbides other than sulfides increases, thereby deteriorating machinability and toughness.

Therefore, the range of the Ti content is set to 0.05 to 0.25%. The preferred range is 0.10 to 0.25%.

The range of the Zr content was set to 0.05 to 0.50%. A preferred range is from 0.05 to 0.20%, and a more preferred range is from 0.10 to 0.20%.

These elements must be contained so that the effective Ti equivalent given by the above formula (1) satisfies the above formula (2).

N:

N is an element that suppresses the generation of sulfides of Ti and Zr because nitrides are generated before the sulfides of Ti and Zr are generated. In addition, the formed nitride is hard and damages the cutting edge of the tool, reducing tool life. Therefore, the upper limit was set to 0.020%. The lower the content, the better, less than 0.002% At full, the formation of nitrides, which can cause adverse effects of N, can be avoided and is preferred.

A1:

A1 is a powerful deoxidizing element and also has the effect of improving toughness. If the content is less than 0.001%, the effect cannot be obtained. On the other hand, if the content exceeds 0.03%, the deoxidizing effect is saturated and the machinability is reduced. Therefore, the range of the A1 content is set to 0.001 to 0.03%.

In the present invention, the A1 content refers to acid-soluble A1 content (sol. A1 content).

C r:

Cr is an element that has an effect on improving strength, toughness, and heat resistance. It may or may not be contained, but when improvement in strength, toughness and heat resistance is required, these effects can be obtained by containing 0.2% or more. In particular, it is preferable that the hot forging die contain Cr in an amount of 3.0% or more. On the other hand, if the content exceeds 9.0%, toughness deteriorates. Therefore, the range of the content when it is contained is set to 0.2 to 9.0%. A preferred range for the content is 0.5-5.0%.

Mo:

Mo is an element effective in improving strength, toughness and high-temperature strength. It may or may not be contained, but when improvement in strength, toughness and high-temperature strength is required, these effects can be obtained by containing 0.05% or more. On the other hand, if the content exceeds 2.0%, the effect of improving the high-temperature strength is saturated, and the toughness is deteriorated. Therefore, the range of the content when it is contained is set to 0.05 to 2.0%. A preferred range of the content is 0.05 to: L. 0%.

N i:

Ni is an element that has an effect on improving strength and toughness. Contains It is not necessary, but if improvement in toughness is required, the effect can be obtained by adding 0.2% or more. On the other hand, if the content exceeds 2.0%, the effect of improving toughness can be obtained, but the cost of Ni element is high, which impairs economic efficiency. Therefore, the range of the content when it is contained is set to 0.2 to 2.0%. The preferred range of the content is 0.2 to 1.

5%.

V:

V is an element that has the effect of improving the strength and has little toughness degradation due to its inclusion. It may or may not be contained, but if improvement in strength is required, the effect can be obtained by adding 0.01% or more. on the other hand,

If the content exceeds 1.5%, toughness will deteriorate. Therefore, the range of the content when it is contained is set to 0.01% to 1.5%. The preferred range of the content is 0.05-0.5%.

Cu:

Cll is an element effective in improving machinability, strength and toughness. It may or may not be contained, but when improvement in machinability, strength and toughness is required, the effect can be obtained by containing 0.1% or more. On the other hand, if the content exceeds 3.0%, toughness deteriorates. Therefore, the range of the content when it is contained is set to 0.1 to 3.0%. The preferred range of the content is 0.2 to 1.0%.

0:

O (oxygen) has an effect of improving the machinability by forming an oxide having a low melting point in steel by appropriately containing 0 (oxygen). It may or may not be contained, but when improvement in machinability by formation of an oxide is required, the effect can be obtained by adding 0.005% or more. On the other hand, 0.0

If the content exceeds 20%, giant inclusions are formed in the steel, and the finishing accuracy of the mold surface is reduced, and the toughness is also deteriorated. Therefore, when including The range of the weight was 0.005 to 0.0020%. A preferable range of the content is 0.010 to 0.020%.

Here, 0 (oxygen) refers to the total oxygen in the steel.

Heat treatment:

The micromass obtained by the present invention can be further improved in microstructure, hardness and toughness by a subsequent heat treatment. It can also be softened to the required hardness to improve machinability. In this heat treatment, after heating to 850 to 1050 ° C, normalizing or quenching is performed, and then softening by tempering at 700 ° C or lower, or strain relief annealing, or tempering and distortion This can be achieved by performing annealing.

(Example)

A test steel having the chemical composition shown in Table 1 on the next page was melted to produce a cylindrical lumps having a diameter of 143 mm.

After the macro test was performed as it was, the following tests were further performed.

[Hardness] Using the test plate used for the macro test, the hardness was measured at the center of the lump, 1/2 of the radius and near the surface according to the Brinell hardness test method specified in JISZ 2243. Then, evaluation was made based on these average values.

[Toughness] In accordance with the Charpy impact test method specified in JISZ 2242, (1) A U-notch test piece (with a width of 10 mm specified in JISZ 2202) A full-size test piece was sampled, and the impact value was measured at room temperature.

[Milling workability] After collecting each test piece for hardness test and impact test, 錡 after cutting the lump in the cylindrical axis direction including the diameter, milling was performed, and the milling workability was determined by the wear amount of the tool. evaluated. steel

Chemical forceps (暂暂, balance Fe and impurities)

No. C Si P S Ti Zr N A1 0 Other

1 0.10 1.01 0.12 0.010 0.052 0.49 one 0.0009 0.018 one one

2 0.10 1.06 0.23 0.020 0.055 one 0.43 0.0038 0.010 one-

3 0.08 0.48 0.21 0.012 0.340 0.68 one 0.0043 one Cr: 0.56, Mo: 0.23

4 0.07 0.23 0.75 0.063 0.580 0.86 0.48 0.0051 1 1 1

5 0.09 0.47 0.21 0.014 0.180 0.08 0.44 0.0035 0.015 One Cu: 1.18

6 0.25 0.67 0.22 0.038 0.040 0.26 one 0.0068 0.002 0.0098 Cu: 2.45

7 0.23 0.48 0.67 0.025 0.080 0.18-0.0098 0.012 0.0087 Cu: 0.16, Cr: 1.53

8 0.24 0.16 1.20 0.013 0.058 0.12 ― 0.0089 0.001 0.0150 Cr: 0.12

g 0.20 0.12 1.77 0.022 0.076 0.23 0.05 0.0055 0.028 0.0057 Ni: 1.02

10 0.08 1.51 0.78 0.026 0.093 0.24-0.0120 0.006 i Ni: 1.68

11 0.22 1.67 0.28 0.086 0.150-0.49 0.0069 0.009 V: 0.19

12 0.38 1.22 0.45 0.059 0.059 0.15-0.0079 0.009 0.0058 V: 0.14

13 0.26 1.02 0.80 0.009 0.021 0.05 0.06 0.0059 0.005 Cr: 1.48, V: 0.10

0.56 0.23 0.89 0.035 0.034 0.12 0.0114 0.003

15 0.35 0.76 0.58 0.007 0.026 0.18 0.0036 0.002 Cr: 6.8, V: 0.82, Mo: 1.57

16 0.08 0.23 0.23 0.022 0.060 0.04 * 0.03 * 0.0057 0.002 0.0052

17 0.07 0.58 2.64 * 0.022 0.160 0.05 0.0029 0.043 *

18 0.10 0.27 0.34 0.120 * 0.050 0.27 0.15 0.0236 * 0.001 0.0068 Cr: 1.05

19 0.29 0.75 1.18 0.027 0.025 1.09 *-* 0.0068 0.017

20 0.24 0.25 0.82 0.035 0.016 *-*-* 0.0086 0.020 Cr: 1.69, V: 0.13

21 0.64 * 0.25 0.96 0.029 0.014 *-* Single 0.0096 0.001

22 0.42 0.22 0.92 0.025 0.540-*-* 0.0080 0.024 Cr: 1.2

(Note) *: Indicates a value outside the range specified in the present invention.

Table 2

(Note) * Indicates a value outside the range specified in the present invention.

(*!) X indicates the macrostructure of Fig. 1 (Steel No. 16), and the macrostructure of Fig. 2 (Steel No. 2) and those which are equivalent to or better than X and X show improvement. And XX for those with cracks or cracks in the center of the steel ingot.

(* 2) Tool Material: TiCN coating Carbide, Cutting speed: 428m / min, Feed:. 0.22瞧/ blade Depth of cut: 5 anonymous X25 thigh, ³ 000 Momokiayaka !! at unlubricated condition After the maximum wear Vbmax (listening), the tool wear is reduced. Table 2 on the previous page shows the calculated values of each test steel according to the above formulas (1) and (2), the above test results, and the results of the macrostructure investigation.

Among the test steels shown in Table 1, steels with steel numbers 1 to 15 are the steels of the present invention, and all of the steel components satisfy the range of the chemical composition specified in the present invention. Also, as shown in Table 2, the value of equation (1) calculated based on the chemical composition of the steel satisfies the relationship given by equation (2).

The macrostructure of the test steel was evaluated as follows.

The macrostructure of steel No. 16 (comparative steel) shown in Fig. 1 (comparative steel) is represented by a cross mark as a coarse and undesirable structure, and the macrostructure of steel No. 2 (steel of the present invention) shown in Fig. 2 is Fine and good structures are indicated by triangles, and equivalent or better structures are also indicated by triangles. The organization between X and X is indicated by △.

The macrostructure of the steel of the present invention is generally evaluated as 〇. Some of the test steels (Steel Nos. 7, 8, 14 and 15) had a rating of △, but this was because Ti and Zr had relatively low S content and contributed to the improvement of solidification structure. This is because the amount of sulfide produced was small.

The steels of Nos. 14 and 15 have too high hardness as-forged, so that after tempering, they are tempered and softened to facilitate post-forging cutting. In particular, steel No. 15 is used for hot forging dies, so after cutting, it is subjected to another heat treatment of quenching and tempering. Despite the high S content, the impact values are good for all of the steels of the present invention, except for steel No. 15 steel.

Further, all of the steels of the present invention have a small amount of tool wear during milling and have good machinability.

Steel No. 7 contains Cr and Cu, and steel No. 13 contains Cr and V. Although the hardness is increased, the toughness is improved.

Steel Nos. 9 and 10 contain Ni and have an effect of improving toughness. You. Steel No. 3 contains Cr and Mo and has an effect of improving strength and toughness.

Steels Nos. 11 and 12 contain V and have greatly improved strength and toughness. Steel No. 5 contains Cu and has increased strength, but also has improved machinability.

Steel No. 6 contains Cu and O (oxygen) and has improved machinability. Steels 7 and 8 contain 0 (oxygen) and have improved machinability.

On the other hand, the steels of steel numbers 16 to 22 are comparative steels, and at least one of the steel composition or the relation given by the formula (2) is out of the range defined by the present invention.

Among these, the steels of steel numbers 16, 17, 20, 20, 21 and 22 do not satisfy the relationship given by the equation (2), and the macrostructure evaluation is X or XX. The steels of Nos. 18 and 19 satisfy the relationship given by equation (2). However, since the contents of P and Ti are excessive, respectively, Intense prying with a crack in the center of the ingot was observed.

Steel No. 16 had a macrostructure in which columnar crystals grew remarkably. As a result, a remarkable segregation structure such as P and S was observed in the center of the ingot. In addition, porosity and cracks were also observed at the location where the segregated structure was present. The same applies to steel No. 20.

Steel No. 22 had poorer toughness as shown by the lower impact value.

Steel No. 17 was inferior in milling workability because the Mn and A1 contents were too high, and steel No. 18 was too high in N content. Steel No. 19 has a large TiC content due to too high Ti content and high hardness, and steel No. 21 has a high C content. Was too high, and the S content was insufficient, resulting in poor milling workability.

As is clear from the above results, by adjusting the contents of Ti, Zr, S and N in the steel to an appropriate range, fine sulfides of Ti and Zr can be formed, and It is possible to manufacture a steel having excellent internal quality and machinability afterwards, and a mold having excellent machinability such that internal quality in a forged state is comparable to a forged steel product. Industrial applicability

According to the steel and the metal mold of the present invention, the steel composition is restricted for specific components, and the Ti, Zr, S, and N contents in the steel are adjusted to an appropriate range, whereby the T By forming fine sulfides of i and Zr, it is possible to ensure excellent internal quality and machinability after forging. By manufacturing this steel, the internal quality in the forged state is improved. A mold having excellent machinability comparable to products can be manufactured. As a result, it can be widely applied to deep engraving, in which the processed surface extends inside the shaped material, or to finishing, which requires strict surface properties, which could not be applied in the past. Can be.

Claims

The scope of the claims

1. By mass%, C: 0.02 to 0.45%, S i: 0.1 to 2.5%, Mn: 0.1 to 2.5%, P: 0.10% or less, S: 0.02 to 0.60%, N: 0.002% or less, A1: 0.001 to 0.03%, Ti: 0.05 to 0.25%, and Zr: 0. 05-0. 50

% Of one or two kinds, the balance being Fe and impurities, and the effective Ti equivalent (T i *) given by the following equation (1) satisfies the relationship given by the following equation (2); A steel excellent in internal quality and machinability after fabrication, characterized in that the steel contains a sulfide containing at least one of Ti and Zr.

Ti * = Ti + 0.53 X Z r

— 3.4 N (1)

T i * / S≥ 1.5 (2)

2. Instead of part of Fe, in mass%, Cr: 0.2 to 9. ◦%, Ni:

0.2 to 2.0%, Mo: 0.05 to 2.0% and V: 0.01 to: L. 5%, one or more selected from the group 2. The steel according to claim 1, which is excellent in internal quality and machinability after fabrication.

3. Instead of part of Fe, contains one or two of mass%, Cu: 0.1 to 3.0% and 0 (oxygen): 0.005 to 0.020%. The steel according to claim 1, which is excellent in internal quality and machinability after fabrication.

4. Instead of part of Fe, in mass%, Cr: 0.2-9.0%, Ni: 0.2-2.0%, Mo: 0.05-2.0% and V: 0.01-: Contains 1 or 2 or more selected from 1.5%, and further contains Cu:

2. The internal quality after production according to claim 1, characterized in that it contains one or two of 0.1 to 3.0% and 0 (oxygen): 0.005 to 0.020%. And steel with excellent machinability.

5. A mold made of the stainless steel according to any one of claims 1 to 4.