JP2003221654A - Free-cutting stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a free-cutting stainless steel with the machinability and the outgassing resistance considerably improved while maintaining the same level of the corrosion resistance, the hot-workability and the cold-workability as those of conventional stainless steel. <P>SOLUTION: The stainless steel contains Fe as its main component either without Ni content or with the Ni content of 2.0 mass% or less if Ni is contained, while containing Cr of 7-35 mass% and C of 0.01-0.4 mass%. If the mass content of Ti is expressed as WTi (mass%) and the mass content of Zr as WZr (mass%), at lest one of Ti and Zr is contained so as to satisfy the formula: 0.03 mass% ≤WTi+0.52 WZr≤3.5 mass%. Furthermore, at least one of S of 0.01-1 mass% and Se of 0.01-0.8 mass% is contained therein. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to stainless steel, and more particularly to a ferritic or martensitic free-cutting stainless steel having excellent machinability.

[0002]

2. Description of the Related Art In recent years, the use of free-cutting steel has been increasing in order to improve the productivity of members manufactured by cutting such as machine parts. In particular, stainless steel containing a considerable amount of alloying elements such as Cr for the purpose of improving corrosion resistance is expensive compared to ordinary steel, and therefore, from the viewpoint of reducing the manufacturing cost of the entire member, Improvement is especially important.

As the machinability improving element of the iron-based material, S,
Pb, Se, Bi, Te, Ca, etc. are known. Among these, Pb has been gradually shunned in recent years, when interest in environmental protection is increasing on a global scale, and the number of devices and parts that limit its use is increasing. Therefore, a material using S or Te as a main machinability improving element is considered as an alternative material. These mainly generate inclusions such as MnS and MnTe, and enhance the machinability and grindability due to the stress concentration effect on the inclusions during chip formation and the lubricating action between the tool and the chips. 2. Description of the Related Art In recent years, ferritic stainless steel, which is relatively inexpensive and has high corrosion resistance, has been widely used as a component material in order to make maintenance free of computers and their peripheral devices, and other weak electrical appliances. In particular, since the improvement of the machinability is emphasized for the parts which require the precise finishing for securing the dimensional accuracy and the parts of the complicated shape with a large machining allowance, the content of the free-machinability imparting element tends to be increased. In addition, these elements are used not only individually but also as a composite addition.

[0004]

However, when S is used as a free-machining property-imparting element, if S is added excessively,
It causes deterioration of the corrosion resistance, hot workability or cold workability of the alloy. Further, when exposed to the atmosphere, the S component contained in the alloy material is released as a sulfur-containing gas, which may easily cause sulfur contamination around the parts. Such sulfur contamination is particularly likely to be a problem in computer peripheral devices that are often used in a sealed state, for example, component parts such as a hard disk drive (HDD), and it is necessary to suppress the released sulfur-containing gas. (Hereinafter, referred to as "improving outgas resistance").

Therefore, the Mn content is limited to increase the Cr content in the sulfide, and when S is contained, Ti and S
It has been proposed to add spheroidizing compound to form spherical sulfides (for example, JP-A-10-46292 or JP-A-56-16653). However, since increasing the amount of Cr in the sulfide tends to significantly reduce machinability and hot workability, its use is often limited.

[0006] Further, the free-cutting property-imparting element such as S may be added not only for improving the machinability but also for the purpose of, for example, relaxing stress concentration in punching of a steel sheet or suppressing burrs generated during punching. However, since the hot workability or cold workability during steel plate production deteriorates,
Its use is very limited.

The object of the present invention is to improve not only corrosion resistance but also hot workability and cold workability comparable to those of conventional stainless steels, while the machinability is greatly improved and the outgas resistance is greatly improved. Another object of the present invention is to provide a free-cutting stainless steel having improved ferritic properties and characteristics close thereto.

[0008]

In order to solve the above problems, the free-cutting stainless steel of the present invention comprises:
Fe as a main component does not contain Ni, or even if it contains Ni, the content is 2.0 mass% or less, Cr is 7 to 35 mass%, C is 0.01 to 0.4 mass%. The content of Ti is WTi (mass%) and the mass content of Zr is WZr (mass%).
At least one of Ti and Zr is contained so that Ti + 0.52WZr is 0.03 to 3.5% by mass, and 0.01 to 1% by mass of S and 0.01 to 0.8% by mass.
At least one of Se, Ti and / or Zr as a main component of the metal element component, C as an essential component as a binding component with the metal element component, and at least one of S, Se and Te. A free-cutting property-containing compound (hereinafter, also referred to as (Ti, Zr) -based compound) contained therein is dispersed and formed in a structure, and further Ti, Zr, C, S and S are formed.
Each mol content of e is MTi, MZr, MC, MS and MSe
(Unit: mol%), α≡MC / (MTi + MZr); β≡ (MS + MSe) / (MTi + MZr), α ≦ 0.8; 0.27 ≦ β ≦ 0.8; and α-0. Each content rate of Ti, Zr, C, S, and Se is determined so that 45 ≦ β ≦ α + 0.65;

The above (T
The machinability of the stainless steel can be improved by the dispersed formation of the i, Zr) -based compound phase. Also,
Due to the formation of this compound, MnS or (Mn, Cr)
It is also possible to prevent or suppress the formation of compounds such as S, which are likely to cause deterioration in corrosion resistance and hot workability, and consequently maintain good corrosion resistance, hot workability, and cold workability of the alloy material. it can.

A feature of the present invention is (Ti, Zr).
Since the S-based compound is formed in the stainless steel, the added S is contained as one of the constituent elements of the (Ti, Zr) -based compound, and as a result, the substrate metal phase (Fe
The amount of S dispersedly present in the system matrix phase) is reduced, and the amount of S released from the stainless steel to the atmosphere is reduced. Therefore, by forming the (Ti, Zr) -based compound, the outgas resistance of stainless steel can be similarly improved. In this case, when the above outgas resistance test is performed, the sulfur component released from the test piece as a sulfur-containing gas is absorbed by the silver foil as a getter, and the sulfur content WSO in the silver foil is measured to measure the material. Quantify the outgassing resistance of. And it is desirable that the measured WSO be 0.035 mass% or less. As described above, the stainless steel of the present invention whose outgas resistance is regulated has a small amount of the S component released when exposed to the atmosphere, and is unlikely to cause sulfur contamination in the surroundings. Therefore, the outgas resistance is required. It can be preferably used as stainless steel used as a part of industrial equipment.

That is, according to the present invention, by selecting the composition as described above, the (Ti, Zr) -based compound phase is dispersed and formed in the substrate, and the hot workability and the cold workability are improved by the conventional stainless steel. Machinability can be greatly improved while making it comparable to steel. Further, the free-machining property-imparting compound is (Ti, Z
Since the r) -based compound is the main component, the outgas resistance is dramatically improved.

The free-cutting stainless steel of the present invention as described above is suitable for use as a constituent material of a member which is required to have both machinability or punchability and corrosion resistance and outgas resistance. Typically, it is applicable to the following members (but is not limited to them).・ Spindle motor parts used in HDDs: hubs, yokes, sleeves, shafts, etc.・ HDD parts: Spacer ring, arm pivot, actuator, top clamp, etc. -OA device parts such as printer shafts and ballpoint pen tips. -Connector parts used for optical fiber cables. -In addition, various mechanical parts such as various valves and shafts that require the above characteristics.

In order to enhance the machinability improving effect, the average particle diameter of the (Ti, Zr) -based free-machining-providing compound phase observed in the polished cross-section structure of the alloy material ( When the circumscribed parallel lines are drawn while changing the position, the average value of the maximum intervals of the circumscribed parallel lines is preferably, for example, about 0.1 to 30 μm. The area ratio is preferably about 1 to 20%. If the size and area ratio of the free-cutting property-imparting compound phase are out of these numerical ranges, it may not be possible to provide the necessary and sufficient free-cutting property to the stainless steel.

The above (Ti, Zr) -based compound is a compound represented by the composition formula (Ti, Zr) ₄ (S, Se, Te) ₂ C ₂ (hereinafter, also referred to as carbon sulfide / selenide). Can be included at least. In this compound, either Ti or Zr may be contained, or both may be contained. Also, for S, Se, and Te, any one of
One kind may be contained, or two or more kinds may be contained. The formation of the compound represented by the above composition formula can improve the machinability of the alloy material, and is also effective in improving the corrosion resistance of the alloy material.

The identification of M ₄ Q ₂ C ₂ -based compounds in steel (hereinafter sometimes referred to as "TICS" as an abbreviation in this specification) is performed by X-ray diffraction (for example, diffractometer). Method) and electron probe microanalysis (EPM
A) method can be used. For example, M ₄ Q ₂ C ₂
Whether or not the system compound is present can be confirmed by whether or not the peak of the corresponding compound appears in the measurement profile by the X-ray diffractometer method. In addition, the formation region of the compound in the structure is obtained by performing surface analysis by EPMA on the cross-sectional structure of the steel material and comparing the two-dimensional mapping results of the characteristic X-ray intensity of Ti, Zr, S, Se or C. Can be specified.

The reasons for limiting the composition of the present invention will be described below. (1) Ni: 2% by mass or less Since Ni is effective in improving the corrosion resistance, particularly the corrosion resistance in a reducing acid environment, it can be added if necessary. However, excessive addition lowers the stability of the ferrite phase and causes an increase in cost, so the upper limit is 2% by mass. The amount of Ni added may be zero.

(2) Cr: 7 to 35 mass% Cr is an essential element for ensuring corrosion resistance, and is added in an amount of 7 mass% or more. On the other hand, excessive addition impairs the hot workability and lowers the toughness, so the upper limit is 35% by mass. In addition, when importance is attached to corrosion resistance, it is desirable to set it to 9 mass% or more.

(3) C: 0.01 to 0.4% by mass C is an important element which is indispensable for the free-cutting property imparting compound. If the content is less than 0.01% by mass, the formation of the free-machining property-imparting compound becomes insufficient and the sufficient machinability-imparting effect cannot be exhibited. On the other hand, if it exceeds 0.4%, a large amount of a simple carbonitride that is not effective for improving the machinability is generated, which is not preferable. The amount of C added depends on the amount of other constituent elements of the free-cutting property-imparting compound, for example, (Ti,
An appropriate amount should be added in consideration of the stoichiometric composition of Zr) ₄ (S, Se, Te) ₂ C ₂ . In particular,
When an excess amount of carbon that is much higher than the stoichiometric ratio of (Ti, Zr) ₄ (S, Se, Te) ₂ C ₂ is added, the carbon solid solution amount of the steel substrate increases, and the martensitic transformation occurs during cooling. Therefore, caution is required because it is easy to cause (that is, the structure mainly composed of ferrite cannot be obtained). Specifically, the free cutting property imparting compound phase is (Ti, Zr) ₄ (S, Se) ₂ C ₂
With the stoichiometric composition of Ti, Zr, C, S
And each mol content rate of Se is MTi, MZr, MC, MS and MSe (unit: mol% respectively), and 0.5 (MS +
Of the respective values of (MSe) and 0.25 (MTi + MZr), the surplus carbon amount expressed as a value obtained by converting MC-Q (unit mol%) to mass% is 0.0, where Q having a smaller numerical value is 0.0.
It is more preferable that the content be 1 mass% or less from the viewpoint of easily obtaining a structure mainly composed of ferrite.

(4) The content of Ti is WTi (mass%), Zr
Content of WZr (mass%), WTi + 0.52 WZr is 0.03 to 3.5 mass%: Ti and Zr play a central role in the machinability improving effect in the free-cutting alloy material of the present invention. It is an essential constituent element for forming a (Ti, Zr) -based compound. WTi + 0.52WZr is 0.03 mass%
If the amount is less than the above, the amount of the (Ti, Zr) -based compound formed is insufficient, and a sufficient machinability improving effect cannot be expected. On the other hand, W
When Ti + 0.52WZr becomes excessive, the machinability is also deteriorated. Therefore, WTi + 0.52WZr must be suppressed to 3.5 mass% or less. The above-mentioned effect when Ti and Zr are contained in the alloy is generally determined according to the total number of atoms (or the number of mols) contained regardless of the types of Ti and Zr. Since the atomic weight ratio of Zr and Ti is approximately 1: 0.52, titanium having a smaller atomic weight can exert a greater effect with a smaller mass. It can be said that WTi + 0.52WZr is a composition parameter that reflects the total number of atoms of Zr and Ti.

(5) 0.01 to 1% by mass of S, 0.01
At least one of Se and 0.8 mass% of Se:
S and Se are effective elements for improving machinability. By containing S and Se, a compound effective in improving machinability (for example, a composition formula (Ti, Zr))
₄ (S, Se) ₂ C ₂ (Ti, Zr) -based compound or the like is formed in the alloy structure. Therefore, the content of S and Se has a lower limit value of 0.01% by mass at which the effect becomes clear. Further, if excessively added, a problem that hot workability is deteriorated may occur in general, so that the upper limit value must be specified. Therefore, it is preferable to set S as 1 mass% and Se as 0.8 mass% as upper limit values. Further, it is desirable that S and Se are added in an amount necessary and sufficient for constituting the above-mentioned (Ti, Zr) -based compound which improves machinability.
From this viewpoint, the total content of S and Se (% by mass)
Is preferably set to twice or more the content (% by mass) of C. Further, excessive addition of S also leads to deterioration of outgas resistance.

(6) m of Ti, Zr, C, S and Se
Let ol content be MTi, MZr, MC, MS and MSe (unit: mol%), α≡MC / (MTi + MZr); β≡ (MS + MSe) / (MTi + MZr), α ≦ 0.8; 0.27 ≦ β ≦ 0.8; and α−0.45 ≦ β ≦ α + 0.65 (region of FIG. 1: (I)); when α (≡MC / (MTi + MZr)) exceeds 0.8, the material is cut. Carbide that does not contribute to the improvement of machinability is excessively generated, which leads to a decrease in machinability. Also, α is 0.0
When it is less than 5, it is effective in improving machinability (Ti, Z
The r) type compound is not sufficiently formed, and the machinability is similarly reduced.

On the other hand, β (≡ (MS + MSe) / (MTi + MZ
When r)) exceeds 0.8, excessive S and Se that do not contribute to the formation of the (Ti, Zr) -based compound are generated, which leads to deterioration in hot workability and corrosion resistance. Further, when S is used mainly (that is, MS / (MS + MSe) is 0.8 or more), there is a problem in outgas resistance. The factor that determines the outgas resistance of the material is mainly the material composition, but the S component that is solid-solved in the Fe-based matrix phase that constitutes the stainless steel tends to collect at the grain boundaries, In order to improve the outgassing property, it is desirable to fix the S component as a carbosulfide of Ti or Zr.
However, if S is dominant and β exceeds 0.8, F
Since the S component dissolved in the e-based matrix phase becomes excessive,
This leads to an increase in the amount of S compound-based gas that is released through the crystal grain boundaries and a reduction in outgas resistance. On the other hand, when β is less than 0.27, the (Ti, Zr) -based compound is not sufficiently formed, and the machinability deteriorates.

Further, when the value of β becomes smaller than the value of α-0.45, the C content becomes too large with respect to S + Se, and excessive formation of carbides that do not contribute to the improvement of machinability. As a result, machinability is reduced. On the other hand, when β is larger than α + 0.65, the C content is S
It becomes too small relative to + Se, which leads to deterioration in hot workability and corrosion resistance. Further, when S is used mainly (that is, MS / (MS + MSe) is 0.8 or more), there is a problem in outgas resistance.

In the composition region of (I) of FIG. 1, if it is desired to emphasize the improvement of the outgas resistance, an excessive S content is required.
In order not to occur, an area with a smaller value of β is selected. Specifically, 0.05 ≦ α ≦ 0.55; 0.27 ≦ β ≦ 0.55; and α−0.15 <β <(1/3) × α + 0.4; It is desirable to determine each content rate of Ti, Zr, C, S and Se. This is the area shown in (II) of FIG.

On the other hand, in the case where the improvement in machinability is to be emphasized more, especially in the case where the drilling property is emphasized, it is preferable to select a region having a larger β value. Specifically, Ti, Zr, C, S, and Se are set so that α ≦ 0.8; 0.55 ≦ β ≦ 0.8; and α−0.15 <β <α + 0.65; It is desirable that each content rate be set. This is (II
This is the area shown in I).

Hereinafter, examples of other components that can be contained in the free-cutting stainless steel of the present invention and their preferable contents will be described. (7) Si: 2% by mass or less Si can be contained as a deoxidizing agent. However, if the content is too large, the hardness after solution heat treatment becomes high, which is not only disadvantageous to the cold workability but also deteriorates the hot workability of steel, so the upper limit is made 2% by mass. When cold workability is particularly important, it is preferably 0.5% by mass or less.

(8) Mn: 2% by mass or less Mn is also useful as a deoxidizing element during refining,
It is often contained inevitably. Further, since a compound effective for machinability is generated by coexistence with S and Se, it is necessary to add it when machinability is important. On the other hand, especially MnS greatly deteriorates the corrosion resistance and hinders the cold workability, so the upper limit is 2.0% by mass. Particularly, when importance is attached to corrosion resistance, outgas resistance, and cold workability, it is desirable to limit the content to 0.4 mass% or less.

(9) P: 0.05% by mass or less P may segregate at the grain boundaries to increase the susceptibility to intergranular corrosion and may lead to a decrease in toughness. Therefore, it is preferable to keep the P content as low as possible. , 0.05 mass% or less is preferable. Further, it is more desirable to suppress the content to 0.03 mass% or less, but reducing the content more than necessary may cause an increase in manufacturing cost.

(10) Cu: 2% by mass or less Cu is effective in improving the corrosion resistance, especially in a reducing acid environment. However, if added excessively, the hot workability is deteriorated. Therefore, when it is contained, the content is adjusted within the range of 2% by mass or less. When the hot workability is particularly important, the content is 1% by mass or less.

(11) Co: 2% by mass or less Co is an element effective for improving the corrosion resistance, particularly the corrosion resistance in a reducing acid environment, and may be added if necessary. In order to obtain a more remarkable effect, it is preferable to contain 1% by mass or more. However, if added excessively, the hot workability is deteriorated and the raw material cost is increased. Therefore, it is preferable to set the content within the range of 2% by mass or less. When hot workability or cost is particularly emphasized, it is more desirable to suppress the content to 0.3 mass% or less.

(12) O: 0.03% by mass or less An oxide which is not effective for improving the machinability is formed by combining with Ti and Zr which are constituent elements of the compound effective for improving the machinability. Since it is formed, it should be suppressed as low as possible,
The upper limit is 0.03% by mass. Although considering the manufacturing cost, it is preferably 0.01% by mass or less.

(13) 0.05% by mass or less of N N is Ti or Zr which is an essential constituent element of the free-cutting property imparting compound.
Since it forms a nitride that is not effective in improving the machinability, it is desirable that it is not contained as much as possible. The reduction of its content is in balance with the manufacturing cost,
In the present invention, the upper limit is 0.05% by mass, preferably 0.03% by mass or less, and more preferably 0.01% by mass or less.

(14) 0.1 to 4% by mass of Mo and 0.
At least one of W of 1 to 3% by mass; Mo, W
Can further improve corrosion resistance and strength,
You may add as needed. The lower limits are Mo: 0.1% and W: 0.1%, respectively, which make these effects clear. On the other hand, excessive addition impairs the hot workability and, in martensite-containing stainless steel, excessively lowers the Ms point and causes an increase in cost.
o: 4% by mass and W: 3% by mass.

(15) One or more of Te, Bi and Pb is Te: 0.005 to 0.1% by mass, B
i: 0.01 to 0.2 mass%, Pb: 0.01 to 0.3
Mass%; Te, Bi, and Pb can further improve the machinability, and thus may be added if necessary. Te: 0.005 mass% and Bi: where these effects become clear.
The lower limits are 0.01% by mass and Pb: 0.01% by mass.
On the other hand, excessive addition lowers the hot workability, so T
e: 0.1% by mass, Bi: 0.2% by mass, Pb: 0.3
The upper limit is mass%.

When the free-cutting alloy material of the present invention is made of stainless steel, Ca, Mg, B, and REM (where REM is one or two of the metal elements classified as Group 3A in the periodic table of elements). One or more selected from the above can be contained in a total amount of 0.0005 to 0.01% by mass. These elements are effective in improving the hot workability of steel. The effect of improving hot workability obtained by adding these is that the total content is 0.0
When it is 005 mass% or more, it is more remarkably exhibited.
On the other hand, if added excessively, the effect is saturated and conversely the hot workability is deteriorated. Therefore, the upper limit of the total content is set to 0.01% by mass. It should be noted that, as the REM, it is easy to handle by mainly using an element having low radioactivity,
In this respect, Sc, Y, La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
It is effective to use one kind or two or more kinds selected from m, Yb and Lu. In particular, from the standpoint of more prominent manifestation of the above effects and cost, light rare earths, particularly La or Ce.
Is preferred. However, a small amount of radioactive rare earth element (for example, Th or U) that is unavoidably left in the rare earth separation process may be contained. Further, from the viewpoint of cost reduction of raw materials, non-separated rare earths such as misch metal and didymium can also be used.

Further, 0.01 to 0.5 mass% of one or more selected from Nb, V, Ta and Hf may be contained. Nb, V, Ta, and Hf have the effect of forming carbonitrides and refining the crystal grains of the steel to enhance the toughness, so they can be added in a range of up to 0.5% by mass. In order to clarify the effect of enhancing the toughness, it is desirable to contain 0.01% by mass or more.

[0037]

EXAMPLES In order to confirm the effects of the present invention, the following experiments were conducted. First, 50 kg steel ingots each having the composition (mass%) shown in Table 1 were melted in a high frequency induction furnace, heated to 1050 to 1100 ° C., and hot-forged into a round bar having an outer diameter of 20 mm. Processed into. 80 more round bars
After heating at 0 ° C. for 1 hour, it was air-cooled (annealed) and subjected to each test.

[0038]

[Table 1]

The main inclusions of the steel of the present invention are (Ti, Zr) ₄
Although it was (S, Se) ₂ C ₂ , some inclusions such as (Ti, Zr) S and (Ti, Zr) S ₃ were also recognized. In addition, Nos. 2, 13 and 15 having a high Mn content include
A small amount of (Mn, Cr) S was recognized. In addition,
The method of identifying each inclusion is as follows.
That is, an appropriate amount of the test piece is taken out from each round bar, and a methanol solution containing tetramethylammonium chloride and 10% acetylacetone is used as an electrolyte to electrolyze the metal matrix portion. Then, the insoluble compound contained in the steel was extracted by filtering the electrolytic solution after dissolution and dried, and this was analyzed by the X-ray diffraction diffractometer method, and the appearance peak of the diffraction profile was obtained. The compound is identified from. The composition of the compound particles in the steel structure was separately analyzed by EPMA, and it was confirmed from its two-dimensional mapping that a compound having a composition corresponding to the compound observed by X-ray diffraction was formed. ing.

The following experiments were conducted for each of the above test products. 1. Hot workability test: The hot workability was evaluated by visually observing whether defects such as cracks occurred during hot forging. “○” indicates that virtually no defects were generated by the hot forging process, “x” indicates that a large crack was confirmed by the hot forging process, and “△” indicates a slight crack by the hot forging process. It shows that there are cracks.

2. Machinability evaluation: The machinability is evaluated by the cutting resistance at the time of machining, the roughness of the finished surface, and the chip shape. Cermet is used as the cutting tool, and the peripheral speed is 200m /
Turning was carried out for 40 minutes in a dry manner with a min of 0.05 mm per revolution and a feed of 0.015 mm per revolution. The evaluation was carried out based on the tool wear amount. The tool wear amount was the average tool wear amount of the lateral flanks. A drilling test was also conducted on some of the test products. Tool is TiAlN coated outer diameter 6mm
Using a HSS made drill, a hole depth of 15 mm, feed 0.0
While performing lubrication with a water-soluble oil under the condition of 7 mm / rev, the tool life until holes are no longer punched in the cutting speed range of 8 to 90 m / min is calculated, and from the curve, 1000 is obtained.
The speed when the tool life was mm was calculated as VL1000 and evaluated.

3. Corrosion resistance evaluation: J
It was carried out by the salt spray test specified in IS: Z2371. As a test piece, the dimension diameter 10mm, height 50mm
The surface is ground to # 400 using emery paper, washed, and then exposed in a 5 mass% sodium chloride aqueous solution spray environment at 35 ° C. for 96 hours. The evaluation was performed by visually observing that the unripened rust was A, the spotted rust was B, the red rust rust having an area ratio of 5% by mass or less was C, the same 20% by mass or less was D, and the same 20% by mass or more was E.
In addition, when it is difficult to discriminate between ranks, − (minus) is added to indicate that the rank is followed.

3. Outgas resistance evaluation: Outgas resistance was evaluated by defining the amount of S generated.
Specifically, the dimensions are 15 mm in length, 25 mm in width, and 3 mm in thickness, and the entire surface is # 400.
The test piece polished by the emery paper is used. Then, in a closed container having a volume of 250 cc, the test piece and the silver foil (dimensions: length 10 mm, width 5 mm, thickness 0.1) were used.
mm, purity: 99.9% or more) and 0.5 cc of pure water were added, and the temperature in the container was maintained at 85 ° C. for 120 hours. Also, the lightness N of the appearance of the silver foil after the test
Was measured by collating with a color sample specified in JIS: Z8721, and determined as follows. A: N ≧ 9.0 B: 9.0> N ≧ 8.0 C: 8.0> N ≧ 6.8 D: 6.8> N ≧ 5.0 E: 5.0> N As described above The silver foil acts as a getter when a gas containing S is generated, and when the amount of the adsorbed S component increases, the silver foil surface turns black due to the formation of silver sulfide and the brightness decreases.
When the present inventors separately measured the sulfur component content WSO (mass%) in the silver foil by the combustion infrared absorption method, the brightness was 8
It has been confirmed that the value of S content WSO in the silver foil is about 0.035 mass% or less when the above is satisfied.
Therefore, it can be said that the one which obtained the above judgment result of A or B is excellent in the outgas resistance.

[0044]

[Table 2]

That is, it is understood that all of the invention steels of the examples of the present invention have good results in all of hot workability, machinability, corrosion resistance and outgas resistance. Further, the steel belonging to the composition range (II) in FIG. 1 is more excellent in outgas resistance than the steel belonging to (III), while the steel belonging to (III) is more drill machinable than the steel belonging to (II). It can be seen that is superior to.

The embodiments of the present invention have been described above, but these are merely examples, and the present invention can be carried out in a mode in which various improvements or modifications are made based on the knowledge of the parties without departing from the spirit of the invention. It goes without saying that it is possible.

[Brief description of drawings]

FIG. 1 is an explanatory view of a composition range of free-cutting stainless steel of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shunji Noda             2-30, Daido-cho, Minami-ku, Nagoya-shi, Aichi             Daido Steel Co., Ltd. Technology Development Laboratory

Claims (12)

[Claims] 1. Fe is a main component and does not contain Ni, or even if it contains Ni, its content is 2.0 mass% or less, Cr is 7 to 35 mass%, and C is 0.01 to 0. 0.4% by mass
The content of Ti is WTi (mass%), the mass content of Zr is WZr (mass%), and WTi + 0.52WZr
Is at least 0.03 to 3.5% by mass, and at least one of Ti and Zr is contained, and 0.01 to 1% by mass S and 0.01 to 0.8% by mass Se are included. Of Ti and / or Zr as a main component of the metal element component, C as an essential component of the bond with the metal element component, and S, S
The free-cutting property-imparting compound phase containing at least one of e and Te is dispersed and formed in the structure, and the molar content of Ti, Zr, C, S and Se is MTi,
MZr, MC, MS and MSe (unit: mol%), α≡MC / (MTi + MZr); β≡ (MS + MSe) / (MTi + MZr), 0.05 ≦ α ≦ 0.8; 0.27 ≦ β Free-cutting stainless steel characterized in that the respective contents of Ti, Zr, C, S and Se are determined so that ≦ 0.8; and α−0.45 ≦ β ≦ α + 0.65; steel. 2. 0.05 ≦ α ≦ 0.55; 0.27 ≦ β ≦ 0.55; and α−0.15 ≦ β ≦ (1/3) × α + 0.4; The free-cutting stainless steel according to claim 1, wherein the respective contents of Ti, Zr, C, S and Se are set. 3. Ti, Zr, C, S, and Se such that α ≦ 0.8; 0.55 ≦ β ≦ 0.8; and α−0.15 ≦ β ≦ α + 0.65; The free-cutting stainless steel according to claim 1, wherein each content rate is determined. 4. Si: 2 mass% or less, Mn: 2 mass% or less, P: 0.05 mass% or less, Cu: 2 mass% or less,
Co: 2 mass% or less, O: 0.03 mass% or less, N:
Free cutting stainless steel according to any one of claims 1 to 3, wherein the content is 0.05% by mass or less. 5. Mo in an amount of 0.1 to 4% by mass and 0.1 to 3
% Of W and at least one of them is contained.
The free-cutting stainless steel according to any one of 1 to 4. 6. Te of 0.005 to 0.1% by mass,
The pleasant sensation according to any one of claims 1 to 5, containing one or more selected from 0.01 to 0.2% by mass of Bi and 0.01 to 0.3% by mass of Pb. Ground stainless steel. 7. Ca, Mg, B, REM (however, REM
Is 0.005 to 0.01% by mass in total of one or more selected from the group consisting of one or more metal elements classified as Group 3A in the Periodic Table of Elements. Free-cutting stainless steel according to item 1. 8. The free-cutting stainless steel according to claim 1, which contains 0.01 to 0.5 mass% of one or more selected from Nb, V, Ta, and Hf. 9. An alloy material test piece having a rectangular parallelepiped shape having a length of 15 mm, a width of 25 mm, and a thickness of 3 mm, and the entire surface of which is polished using an emery paper having a count of # 400, is prepared as a sulfur component getter. , 10 mm in length, 5 mm in width, and 0.1 mm in thickness, and having a purity of 99.9% or more, and 0.5 cc. Of pure water are sealed together with the test piece in a container having an internal volume of 250 cc. Temperature is 85 ℃
9. When the sulfur component content WSO (mass%) in the silver foil is analyzed after the temperature is raised to 20 ° C. and held for 20 hours, the value of WSO is 0.035 mass% or less. Free-cutting stainless steel according to any one of 1. 10. The free-cutting property imparting compound phase is (Ti, Z
r)_Four(S, Se) _TwoC_TwoHaving a stoichiometric composition of
And the respective mol contents of Ti, Zr, C, S and Se are
MTi, MZr, MC, MS and MSe (unit: mol
%) And 0.5 (MS + MSe) and 0.25 (MTi + MZ)
r-) of each value, the one with the smallest numerical value is Q, and MC-
Expressed as Q (unit mol%) converted to mass%
The surplus carbon content is claimed to be 0.1 mass% or less
Item 10. Free-cutting stainless steel according to any one of items 1 to 9.
steel. 11. The area ratio of the free-cutting property imparting compound phase observed on the polished surface of the material is 0.1 to 20%.
11. A free-cutting tool steel according to any one of 1 to 10. 12. The free-cutting tool steel according to claim 1, wherein the average particle size of the free-cutting property-imparting compound phase observed on the polished surface of the material is 0.1 to 30 μm. .