JP2002038241A - Free cutting stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a free cutting stainless steel, greatly improved in machinability by clarifying an effect of Se and Te in the S free cutting stainless steel with Mn of low content. SOLUTION: This free cutting stainless steel is composed of, by mass %, below 0.50% C, 0.05-2.0% Si, 0.05-1.00% Mn, 0.05-0.50% S, 0.02-0.20% Se, 0.01-0.10% Te, 10.00-30.00% Cr and the balance Fe with unavoidable impurities, satisfying the component ratio of Mn/S of below 2, Se/S of above 0.2 and Te/S of above 0.04.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to free-cutting stainless steel.

[0002]

2. Description of the Related Art Conventionally, OA equipment, precision machine parts, etc.
Not only free-cutting stainless steels to which S is added, such as SUS430F and SUS303, but also free-cutting steels in which so-called free-cutting elements such as Pb and Te are added in combination to improve machinability have been used. However, the need for free-cutting stainless steel with even better machinability is extremely strong. In recent years, the required level of machinability has become severe in order to respond to miniaturization and high precision of equipment. In particular, hard disk drives (H
Free-cutting stainless steel, which is frequently used as a component for precision equipment parts such as DD), has excellent corrosion resistance inherent in stainless steel, and has machinability that satisfies the beauty and dimensional accuracy of the machined surface. In addition, it is required that the amount of hydrogen sulfide gas (out gas) generated by the reaction of sulfide in free-cutting steel with moisture in the air is small.

As a countermeasure against outgassing, Japanese Patent Laid-Open
As disclosed in JP-A-46292, etc., low Mn
Free-cutting stainless steel has been invented. However, the free-cutting steel with reduced Mn has a problem that the machinability is significantly inferior to that of a conventional free-cutting steel having a high Mn content of about 1%. This is because sulfide is changed from MnS to (Cr,
This is because, as a result of the composition change to Mn) S, the sulfide hardness increases and the hot stretchability is enhanced, and the effect of improving machinability is reduced.

[0004]

As a method for improving the machinability of a conventional high-Mn S free-cutting steel, it is known to add Se or Te for the purpose of controlling the form of sulfide (MnS). . However, there is no conventional finding that clarifies the effect of Se or Te when sulfide (Cr, Mn) S is generated by reducing Mn. Japanese Unexamined Patent Application Publication No. 10-4, which has been used for components that require excellent corrosion resistance and hydrogen sulfide outgassing properties and high machinability, such as computer HDD components.
In Japanese Patent No. 6292, it is becoming difficult to satisfy the processing dimensional accuracy of a part which becomes strict with the recent miniaturization and high performance of precision equipment, and further higher machinability is required.
In the present invention, Se and Te in a low Mn S free-cutting steel are used.
It is an object of the present invention to clarify the effects of the present invention and to provide a free-cutting stainless steel in which a work steel is greatly improved by utilizing the effects.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively developed and found that S, S
It has been found that as a result of controlling the composition of the inclusions by simultaneously adding e and Te in an optimum balance in combination, the shape and hardness of the inclusions can be made suitable for controlling the tool wear during cutting. The gist of the invention is as follows: (1) In mass%, C: 0.50% or less, Si: 0.05
2.00%, Mn: 0.05-1.00%, S: 0.
05 to 0.50%, Se: 0.02 to 0.20%, T
e: 0.01 to 0.10%, Cr: 10.00 to 30.
00%, Mn / S ratio: 2 or less, Se / S ratio: 0.
2 or more, satisfying a component ratio of Te / S ratio: 0.04 or more;
Free-cutting stainless steel with the balance being Fe and unavoidable impurities.

(2) In mass%, O: 0.005 to 0.0
The free-cutting stainless steel according to the above (1), which contains 40%. (3) Al: 0.0001 to 0.020% by mass%;
Ca: 0.0005 to 0.010%, Mg: 0.000
The free-cutting stainless steel according to the above (1) or (2), comprising one or more of 5 to 0.010%. (4) The free-cutting stainless steel according to any one of (1) to (3), wherein Mo: 3.00% or less is contained by mass%.

(5) The above (1) to (4), wherein one or two of Ni: 20.00% or less and Cu: 4.00% or less are contained by mass%. Free-cutting stainless steel as described. (6) In mass%, Pb: 0.03 to 0.30%, Bi:
The free-cutting stainless steel according to (1) to (5), containing one or two of 0.03 to 0.30%.

(7) In mass%, Ti: 0.02 to 1.0
0%, Nb: 0.02 to 1.00%, V: 0.02
1.00%, W: 0.02 to 1.00%, wherein (1) to (2) or more are contained.
Free-cutting stainless steel according to (6). (8) By mass%, N: 0.005 to 0.10%, B:
The free-cutting stainless steel according to any one of (1) to (7), containing one or two of 0.001 to 0.010%.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of the present invention will be described below. C: 0.50% or less C is an element necessary for increasing the strength. However, 0.
If it exceeds 50%, the corrosion resistance and toughness deteriorate, so the upper limit was made 0.50%. Si: 0.05 to 2.00% Si is a useful element as a deoxidizing element.
If the amount is too high, the annealing hardness will increase.
5 to 2.00%.

Mn: 0.05 to 1.00% Mn is a deoxidizing element like Si, and is useful for controlling the composition of sulfide inclusions. However, if the content is less than 0.05%, the effect cannot be achieved, and if the content is too large, the effect reaches saturation, and the range is set to 0.05 to 1.00%. S: 0.05 to 0.50% S is a free-cutting element. However, if the content is less than 0.05%, the effect cannot be obtained, and if the content is large, the hot workability is deteriorated. Therefore, the range is set to 0.05 to 0.50%.

Se: 0.02 to 0.20% Se, like S, is a free-cutting element. However, 0.02
%, The effect cannot be obtained, and if it is too large, the hot workability deteriorates. Therefore, the range is set to 0.02 to 0.20%. Te: 0.01 to 0.10% Te is a free-cutting element like S. However, 0.01
%, The effect cannot be obtained, and if it is too large, the hot workability is deteriorated. Therefore, the range is set to 0.01 to 0.10%.

Cr: 10.00-30.00% Cr is a basic element for improving corrosion resistance. But,
If it is less than 10.00%, the effect is small, and if it is too large, machinability deteriorates and embrittlement easily occurs.
It was set to 00 to 30.00%. O: 0.005 to 0.040% O reduces the hot deformability of the sulfide-based inclusions and improves the machinability. However, a large amount increases unnecessary oxides,
The range was 0.005 to 0.040%.

Al: 0.0001 to 0.020% Al is a powerful deoxidizing element and is effective for controlling the oxide composition. However, if the content is less than 0.0001%, the effect is small, and if it is too large, the hard oxide deteriorates machinability. Therefore, the range is set to 0.0001 to 0.020%. Ca: 0.0005 to 0.010% Ca is a powerful deoxidizing element and is effective in controlling the oxide composition. However, if the content is less than 0.0005%, the effect is small, and it is difficult to add more than 0.010%. Therefore, the range is set to 0.0005 to 0.010%.

Mg: 0.0005-0.010% Mg is a powerful deoxidizing element and is effective in controlling the oxide composition. However, if it is less than 0.0005%, the effect is small, and if it is too large, the hard non-ductile oxide deteriorates machinability.
Therefore, the range is set to 0.0005 to 0.010%. Mo: 3.00% or less Mo is an element for improving corrosion resistance. However, when the content is too large, the material is easily embrittled and expensive, so the upper limit is set to 3.00%.

Ni: 20.00% or less Ni is an element for improving the corrosion resistance and stabilizes the austenite phase. However, if it is too large, the ductility increases and the machinability deteriorates. Therefore, the upper limit is 20.00%
And Cu: 4.00% or less Cu is an element that improves cold workability and also stabilizes the austenite phase. However, when the content is too large, the hot workability deteriorates. Therefore, the upper limit is set to 4.00%.

Pb: 0.03 to 0.30% Pb is a free-cutting element. However, if the content is less than 0.03%, the effect cannot be obtained. If the content is too large, the free cutting property is saturated and the hot workability is deteriorated.
It was set to 3 to 0.30%. Bi: 0.03 to 0.30% Bi is a free-cutting element like Pb. However, 0.
If the content is less than 03%, the effect cannot be obtained. If the content is too large, the free-cutting property is saturated and the hot workability deteriorates. Therefore, the range is set to 0.03 to 0.30%.

Ti: 0.02 to 1.00% Ti improves corrosion resistance by forming carbonitrides. However, the effect is saturated when the amount is large, so the range is set to 0.02 to 1.00%. Nb: 0.02 to 1.00% Nb improves corrosion resistance by forming carbonitrides, like Ti. However, the effect is saturated when the amount is large, so the range is set to 0.02 to 1.00%.

V: 0.02 to 1.00% V, like Ti, improves the corrosion resistance by forming carbonitrides. However, since the effect is saturated when there are many,
The range was set to 0.02 to 1.00%. W: 0.02 to 1.00% W, like Ti, improves the corrosion resistance by forming carbonitrides. However, since the effect is saturated when there are many,
The range was set to 0.02 to 1.00%.

N: 0.005 to 0.10% N is an element useful for increasing the strength. However, if the content is too large, the toughness is deteriorated.
%. B: 0.001 to 0.010% B is an element that improves hot workability. However, if the content is too large, the hot workability deteriorates conversely, so the range was made 0.001 to 0.010%.

Next, the effect of the combined addition of Se and Te at a specific ratio, which is a feature of the present invention, will be described. Generally, sulfide-based inclusions (any of S, Se, Te, or inclusions containing several types) work as a stress concentration source during cutting to improve the machinability by embrittlement. In particular, it is said that the larger the size and the more spherical inclusions, the greater the contribution to machinability. As a result of a detailed investigation of inclusions of steel grades in which the amounts of Se and Te added were changed, Te suppressed the elongation of inclusions as conventionally known, kept spherical or spindle-shaped, and added Se. When added, the inclusions were slightly increased in size and tended to suppress inclusion stretching.

Further, Se also tended to increase the hardness of inclusions. The inclusions increased in hardness by the addition of Se showed that the inclusions themselves were broken under the shear stress applied during cutting, which promoted slip and facilitated the generation and propagation of cracks. It is inferred that the increase in the height may be effective in improving machinability. Thus, Se and T
It is considered that the various properties of the sulfide-based inclusions changed by the addition of e improve the machinability.

The influence of the amounts of Se and Te added on the structure, hardness and size of the sulfide-based inclusions has the following tendency. In the case of Se, the inclusion structure is Se
As the / S ratio increases, the Se concentration also increases uniformly. Inclusion hardness increases with an increase in the Se / S ratio, and thereafter becomes constant. Inclusion size tends to increase uniformly as the Se / S ratio increases. In addition, the extensibility of the inclusions (aspect ratio: evaluated by the major axis length / minor axis length of the inclusions) is Se / S
Decreases slowly with increasing ratio. In the case of Te, Te /
As the S ratio increases, the Te concentration in inclusions increases,
The / S ratio saturates at around 0.1, and the effect of suppressing the elongation of inclusions by Te also increases with the increase of this ratio until the Te / S ratio reaches around 0.1. Inclusion hardness tends to increase slightly, but changes are small and almost constant.

The effective addition amounts of Se and Te are determined by the ratio with S, and the Se / S ratio is 0.2 or more (to obtain a suitable inclusion hardness and to suppress stretching), and Te / S The ratio is required to be 0.04 or more (for suppressing inclusion stretching). Thus, only when the effects of Se and Te are combined, a suitable inclusion is generated, and the effect of remarkably improving the machinability is exhibited. In addition, the hydrogen sulfide outgas of free-cutting steel has conventionally been based on a high Cr content of sulfide-based inclusions due to a decrease in the Mn / S ratio.
It has been known that the outgassing characteristics are also suppressed by the Mn / S ratio in S-Se-Te free-cutting steel in which Se or Te is dissolved in sulfide-based inclusions. I found out. The same applies to the corrosion resistance.

Mn / S ratio: 2 or less Sulfide can be converted to (Cr, Mn) (S,
(Se, Te) composition, but also in this case, the corrosion resistance and outgas characteristics (the amount of generated hydrogen sulfide) of the material are determined by the Mn / S ratio. These characteristics are improved as the Mn / S ratio is lower. However, if the Mn / S ratio is 2 or less, it can often be practically used industrially. Se / S ratio: 0.2 or more The Se concentration in the sulfide-based inclusion increases as the Se / S ratio increases. The Se-containing sulfide-based inclusions break during cutting to facilitate the generation and propagation of cracks and to facilitate shear deformation. It is effective when the Se / S ratio is 0.2 or more.

Te / S ratio: 0.04 or more The Te concentration in the sulfide-based inclusions increases with an increase in the Te / S ratio. And the effect is remarkable when the Te / S ratio is 0.04 or more. However, since the machinability improving effect continues until the Te concentration is saturated at a Te / S ratio of 0.1, it is preferable that the machinability be improved to 0.1.
1 or more.

[0026]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples. A 100 kg steel ingot was melted in a vacuum induction furnace, and a steel having the chemical composition shown in Table 1 was forged into a bar having a predetermined size, and then heat-treated. That is, No. 1 shown in Table 1 was used.
Nos. 1 to 18 are ferritic stainless steels that have been annealed. Nos. 19 to 23 are of martensite type, and the shapes of inclusions and machinability were annealed, the outgas test and the corrosion resistance test were quenched and tempered. 24-2
Reference numeral 9 denotes an austenite system, which was subjected to a solution heat treatment.
Table 2 shows the results.

In Table 2, (1) The shape of the sulfide-based inclusions was measured by using an image analyzer to measure the shape of the sulfide-based inclusions on a plane parallel to the forging direction of a φ20 mm steel bar. The analysis items were inclusion size distribution and inclusion aspect ratio (long / short diameter). (2) Regarding the machinability, turning was performed using a carbide tool in the longitudinal direction of a φ60 mm bar (peripheral speed 200 m / min, depth of cut 1.0 mm, feed 0.2 mm / rev, no cutting oil),
The tool wear on the flank and rake face after 10 minutes turning was measured. Furthermore, as a finish cutability evaluation, φ24 mm
The end face of the bar is cut using a cermet tool (peripheral speed 15
0m / min, depth of cut 0.04mm, feed 0.03mm
/ Rev, using a cutting oil), the surface roughness of the finished surface of the work material after cutting 200 mm, and the presence or absence of wrinkles to evaluate the quality of the finish machinability.

(3) Hydrogen sulfide outgas characteristics include:
A rod-shaped test piece of φ12 mm × L21 mm was sealed together with an Ag plate under saturated steam at 80 ° C. for 20 hours, and the amount of hydrogen sulfide generated was evaluated based on the degree of discoloration of the Ag plate. That is, the Ag plate changes from white to brown as the hydrogen sulfide outgas increases. (4) Regarding the corrosion resistance, a rod-shaped test piece of φ12 mm × L21 mm was (20 ← → 70) ° C. × 90% RH.
The substrate was left standing for 20 cycles, and the rust state on the surface was examined.

[0029]

[Table 1]

[0030]

[Table 2]

As shown in Table 2, as shown in FIG. 1-14 and N
o. Nos. 15 to 18 are ferritic stainless steels. 1
9 to 23 are martensitic stainless steels; 24
29 are examples of austenitic stainless steel. N
o. Nos. 1 to 9; 15-16 (ferrite type), N
o. Nos. 19 to 21 (martensite type); 24-2
7 (austenitic) is an example of the present invention, and is an unprecedented excellent material having machinability, hydrogen sulfide outgassing properties, and corrosion resistance.

No. 3 is a comparative example. 10 is SUS430
And the machinability is particularly poor because it is not free-cutting steel. No. 1
No. 1 is SUS430F, which has good machinability but has poor outgassing properties and corrosion resistance. No. 12 is high Mn and Mn / S
Outgassing properties and corrosion resistance are poor due to large ratio. No.
No. 13 has a small amount of Se, the inclusions are slightly smaller than the inventive steel, and the machinability is inferior. No. No. 14 has a small amount of Te, a large aspect ratio, and slightly inferior machinability. No. 17 and 18 do not contain any Se and Te, respectively, and have poor machinability. No. Reference numeral 22 denotes a case where neither Se nor Te is contained, and since the inclusion form control is not performed, the machinability is poor. No. No. 23 has poor outgassing properties and corrosion resistance due to a high Mn / S ratio. No. 28 is SUS3 of conventional steel
03; As with No. 11, the machinability is good, but the outgassing properties and corrosion resistance are poor. No. Reference numeral 29 denotes a case of low Te, in which the inclusion form control is insufficient and the machinability is poor.

[0033]

As described above, according to the present invention, S, S
The composition of inclusions can be controlled by simultaneously adding e and Te in an appropriate balance, thereby making the shape and hardness of the inclusions suitable. It has become possible to provide a material with much better machinability.

Claims (8)

[Claims] 1. Mass%, C: 0.50% or less, Si: 0.05 to 2.00%, Mn: 0.05 to 1.00%, S: 0.05 to 0.50%, Se: 0.02 to 0.20%, Te: 0.01 to 0.10%, Cr: 10.00 to 30.00%, and Mn / S ratio: 2 or less, Se / S ratio: 0. 2 or more,
Te / S ratio: Satisfies the component ratio of 0.04 or more, and the balance is F
Free-cutting stainless steel consisting of e and unavoidable impurities. 2. O: 0.005 to 0.040 by mass%
The free-cutting stainless steel according to claim 1, wherein the stainless steel contains 0.1% by weight. 3. One or more of Al: 0.0001 to 0.020%, Ca: 0.0005 to 0.010%, and Mg: 0.0005 to 0.010% by mass%. The free-cutting stainless steel according to claim 1 or 2, further comprising: 4. The free-cutting stainless steel according to claim 1, which contains, by mass%, Mo: 3.00% or less. 5. The free-cutting machine according to claim 1, wherein one or two of Ni: 20.00% or less and Cu: 4.00% or less are contained by mass%. Stainless steel. 6. The composition according to claim 1, wherein one or two of Pb: 0.03 to 0.30% and Bi: 0.03 to 0.30% are contained by mass%. 6. The free-cutting stainless steel according to 5. 7. In mass%, Ti: 0.02-1.00%, Nb: 0.02-1.00%, V: 0.02-1.00%, W: 0.02-1. The free-cutting stainless steel according to any one of claims 1 to 6, wherein the steel contains one or two or more of the following components. 8. The method according to claim 1, wherein one or two of N: 0.005 to 0.10% and B: 0.001 to 0.010% are contained by mass%. 7. The free-cutting stainless steel according to 7.