JP2001200345A - Ferritic free-cutting stainless steel with excellent cold workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To be used for parts for automobiles such as oxygen sensors manufactured by cold working and cutting using ferritic stainless steel, and precision machine parts such as hubs and sleeves for hard disks. Provide ferritic free-cutting stainless steel with excellent cold workability. SOLUTION: In weight%, C: 0.05% or less, Si:
1.0% or less, Mn: 3.0% or less, Cr: 10.0 to
30.0%, S: 0.10% or less, Se: 0.
03 to 0.30%, Te: 0.01 to 0.10%, P
b: 0.03 to 0.30%, Bi: 0.03 to 0.30
% Of the crystal grains having a circle-equivalent diameter of 200 μm or less occupying 60% or more, and having a Charpy transition temperature of 5% or more.
Ferritic stainless steel with excellent toughness of 0 ° C or less, cold workability, and surface texture after processing. Alternatively, a steel having the above-described composition, which has been subjected to processing such as drawing and drawing with a reduction in area of 10% or more during the manufacturing process, and has a circle-equivalent diameter of 200 μm.
A free-cutting ferritic stainless steel having an area ratio of crystal grains of m or less of 60% or more, a Charpy transition temperature of 50 ° C. or less, excellent toughness, cold workability, and excellent surface texture after processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for automotive parts such as oxygen sensors manufactured by cold working and cutting using ferritic stainless steel, and for precision machine parts such as hard disk hubs and sleeves. It relates to a free-cutting ferritic stainless steel excellent in cold workability.

[0002]

2. Description of the Related Art Conventionally, automobile parts such as oxygen sensors,
Cutting is mainly applied to the processing of ferrite stainless steel bars and wires used for precision machine parts such as hard disk hubs and sleeves. Sex was not as important. However, in recent years, for the purpose of high precision, improvement of production efficiency, and cost reduction, not only cutting but also application of a working method using cold working has been increasing, and it has excellent cold workability. Bars and wires made of ferritic free-cutting stainless steel are required. Further, with the downsizing and high precision of automotive parts, precision machine parts, and the like, in addition to excellent cold workability, good surface texture after processing is often required. On the other hand, Japanese Patent Laid-Open No.
No. 0449 proposes a ferritic stainless steel excellent in cold workability, toughness, and machinability and a method for producing the same.

[0003]

However, the above-mentioned patent publication is characterized by the essential addition of Nb and the rolling with a reduction in area of 80% or more at a temperature of 1000 ° C. or less, control of the grain size, and control of the Charpy transition temperature. Ferrite having excellent cold workability and excellent surface texture after processing is different from the present invention characterized by improving cold workability and surface texture after processing by control. It is not enough to obtain a series stainless steel.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively developed and as a result, in addition to making the Charpy transition temperature 50 ° C. or lower,
The area ratio of crystal grains having a circle equivalent diameter of 200 μm or less is 6
It has been found that it is important to make it 0% or more. The gist of the invention is as follows: (1) By weight%, C: 0.05% or less, Si: 1.0%
Hereinafter, Mn: 3.0% or less, Cr: 10.0 to 30.0
%, S: 0.10% or less, Se: 0.03 to
0.30%, Te: 0.01 to 0.10%, Pb: 0.
At least one of 0.3 to 0.30% and Bi: 0.03 to 0.30%, the balance being Fe and impurities, and the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less is 60% or more; A free-cutting ferritic stainless steel with excellent toughness with a Charpy transition temperature of 50 ° C or less, cold workability, and excellent surface texture after processing.

(2) By weight%, C: 0.05% or less, S
i: 1.0% or less, Mn: 3.0% or less, Cr: 10.
0 to 30.0%, further S: 0.10% or less, Se:
0.03 to 0.30%, Te: 0.01 to 0.10%,
Pb: 0.03 to 0.30%, Bi: 0.03 to 0.3
0%, at least one kind is included, and the balance consists of Fe and impurities, and has been subjected to processing such as drawing and drawing with a reduction in area of 10% or more during the manufacturing process.
A ferritic free-cutting stainless steel having an area ratio of crystal grains of m or less, 60% or more, and excellent in toughness, cold workability, and surface skin properties after working at a Charpy transition temperature of 50 ° C. or less.

(3) By weight%, S: 0.010% or less,
P: 0.050% or less, O: 0.0050% or less, N:
A free-cutting ferritic stainless steel excellent in cold workability according to the above (1) or (2), wherein at least one of 0.030% or less is regulated. (4) By weight%, Al: 0.0001-0.05%, N
b: 0.05 to 1.0%, V: 0.05 to 1.0%, T
i: 0.05 to 1.0%, Zr: 0.05 to 1.0%,
A ferritic free-cutting stainless steel excellent in cold workability according to the above (1) to (3), wherein one or more kinds are included.

(5) The method according to the above (1) to (4), wherein one or two of Ca: 0.010% or less and B: 0.010% or less are contained by weight. Ferritic free-cutting stainless steel with excellent cold workability. (6) Mo: 0.05-5.0% by weight, Ni:
The cold workability according to the above (1) to (5), wherein one or two or more of 0.05 to 1.0% and Cu: 0.05 to 1.0% are contained. Excellent in ferritic free-cutting stainless steel.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of the components according to the present invention will be described below. C: C: 0.05% or less C is a typical solid-solution strengthening element, but a large amount causes deterioration of corrosion resistance and toughness, so the upper limit is made 0.05%. Si: 1.0% or less Si is necessary for deoxidizing steel, but a large amount of Si causes deterioration of cold workability, so the upper limit is made 1.0%.

Mn: 3.0% or less Mn is necessary for deoxidizing steel, but the upper limit is 3.0% because a large amount of Mn is inferior in cold workability. Cr: 10.0 to 30.0% Cr is necessary for securing the ferrite phase stability and corrosion resistance. However, if the content is less than 10.0%, the effect is not obtained. The upper limit is 30.0
%.

S: 0.10% or less S is effective for improving the machinability, but the upper limit is set to 0.10% because a large amount of S deteriorates the workability. When it is necessary to suppress the generation of corrosive gas such as hydrogen sulfide gas, the amount is reduced to 0.010% or less. Se: 0.03 to 0.30%, Te: 0.01 to 0.1
0%, Pb: 0.03 to 0.30%, Bi: 0.03 to
At least one of 0.30% Se, Te, Pb, and Bi are effective for improving the machinability, but a large amount degrades the machinability, and therefore, each of S
e: 0.03 to 0.30%, Te: 0.01 to 0.10
%, Pb: 0.03 to 0.30%, Bi: 0.03 to
0.30%.

P: 0.050% or less If P is contained in a large amount, corrosion resistance and workability deteriorate, so the upper limit is made 0.050%. O: 0.0050% or less O content in a large amount promotes an increase in the amount of oxides and coarsening of sulfides, and causes deterioration of toughness and workability.
050%. N: 0.030% or less N contains a large amount, which causes deterioration of toughness and workability, so the upper limit is made 0.030%.

Al: 0.0001-0.05% Al is effective in deoxidizing steel, but if it is less than 0.0001%, the effect cannot be obtained, and addition of a large amount deteriorates workability. , The upper limit of which is 0.05%. Nb, V, Ti, Zr: 0.05 to 1.0% Nb, V, Ti, Zr improves corrosion resistance and workability. Addition causes the deterioration of workability, so the range is made 0.05 to 1.0%.

Ca: not more than 0.010% Ca improves toughness and workability by controlling the form of sulfides and oxides, but when added in a large amount, the workability is deteriorated. And B: 0.010% or less B raises the grain boundary strength, but the addition of a large amount deteriorates the workability, so the upper limit is made 0.010%.

Mo: 0.05-5.0% Mo is effective in improving corrosion resistance, but if it is less than 0.05%, the effect is not sufficient, and addition of a large amount deteriorates workability. Is 5.0%. Ni: 0.05 to 1.0% Ni is effective in improving the corrosion resistance, but if the content is less than 0.05%, the effect is not sufficient, and a large amount of addition deteriorates the workability. 0%. Cu: 0.05 to 1.0% Cu is effective for improving corrosion resistance, but if it is less than 0.05%, the effect is not sufficient, and a large amount of addition deteriorates workability. 0%.

In the present invention, the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less is 60% or more and the Charpy transition temperature is 50 ° C. or less. In general, importance is given to hardness, deformation resistance, elongation in a tensile test, drawing, and the like as indices of the cold workability of a steel material. However, as a result of repeated studies, in the cold working of ferritic free-cutting stainless steel with a strain rate of about 10 / s or more, even if the above properties are excellent, the Charpy transition temperature exceeds 50 ° C. In order to obtain excellent cold workability, the Charpy transition temperature must be 50 ° C.
We have found that it is very important to:

In recent years, along with the miniaturization and high precision of automobile-related parts, precision machine parts, etc., in addition to excellent cold workability, good surface texture after processing is often required. In addition to the Charpy transition temperature of 50 ° C. or less, it has been found that it is important to further increase the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less to 60% or more. If the rolling temperature is high and the crystal grains are likely to become coarse, processing such as cold drawing with a reduction of 10% or more is applied during the manufacturing process. It is important that the area ratio of crystal grains having an equivalent diameter of 200 μm or less be 60% or more and the Charpy transition temperature be 50 ° C. or less.

[0017]

EXAMPLES Table 1 shows the chemical composition of the test material, and Table 2 shows the area ratio and the Charpy transition temperature of crystal grains having a circle equivalent diameter of 200 μm or less. Regarding the equivalent circle diameter, in each test material, image analysis was performed by a computer for 10 visual fields of 1 mm x 1 mm, and the particle size distribution (assuming equivalent circle diameter) when each crystal grain was assumed to be a circle was determined. Diameter 200
The area ratio occupied by crystal grains of μm or less was determined. The Charpy transition temperature was a temperature corresponding to a half of the absorbed energy at a ductile fracture rate of 100%. Using the test materials shown in Table 1, cold working corresponding to a strain rate of about 30 / s and an upsetting rate of about 80%, and a drill piercing test were performed. The drill piercing test was performed using a drill material: SKH51, a drill diameter: φ5, and a rotation speed of 1190 rpm.
m, thrust 414 N, and drilling depth 10 mm. Table 2 shows test results on cold forgeability, surface texture after processing, and drill piercing property. Regarding the cold forgeability, ○ indicates that there was no crack after working, and X indicates that there was cracking.
Regarding the surface skin characteristics, the case where the difference between the heights of the peaks and the valleys of the surface irregularities after processing was 0.1 mm or less was evaluated as ○, and the case where it exceeded 0.1 mm was evaluated as ×. Regarding the drill piercing property, 場合 was given when the piercing time was less than 15 seconds, and × was given when it exceeded 15 seconds.

[0018]

[Table 1]

[0019]

[Table 2]

In Table 1, Nos. 1 to 24 are steels of the present invention, and Nos. 25 to 36 are comparative steels. Table 2 shows the results. According to Table 2, the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less in the present invention of Nos. 1 to 24 is 60% or more, and the Charpy transition temperature is 50 ° C. or less, and furthermore, it is cold forgeable. No cracking occurred, the surface texture after processing was excellent, and the drilling performance was less than 15 seconds in all cases.
No. 25, 28 to 30, 32, 33, and 36, the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less was less than 60%, and the Charpy transition temperature was:
In the case of Nos. 26 and 30 to 33, a value exceeding 50 ° C. was exhibited, and cracking occurred after processing which was cold forging, or irregularities were observed in the surface skin characteristics after processing, and the drill piercing property was observed. For Nos. 34 and 35, the perforation time exceeded 15 seconds.

[0021]

As described above, according to the present invention, a ferritic stainless steel bar having excellent toughness, cold workability, and good surface skin properties after working, and excellent cutting properties.
Being able to obtain a wire is extremely useful industrially.

Claims (6)

[Claims] 1. In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 3.0% or less, Cr: 10.0 to 30.0%, and S: 0. 10% or less, Se: 0.03 to 0.30%, Te: 0.01 to 0.10%, Pb: 0.03 to 0.30%, Bi: 0.03 to 0.30% Contains at least one kind, the balance being Fe and impurities, and a circle equivalent diameter of 200
A ferritic free-cutting stainless steel having an area ratio of crystal grains of μm or less of 60% or more, excellent in toughness with a Charpy transition temperature of 50 ° C. or less, cold workability, and excellent surface texture after processing. 2. In% by weight, C: 0.05% or less; Si: 1.0% or less; Mn: 3.0% or less; Cr: 10.0 to 30.0%; 10% or less, Se: 0.03 to 0.30%, Te: 0.01 to 0.10%, Pb: 0.03 to 0.30%, Bi: 0.03 to 0.30% Contains at least one element, the balance consisting of Fe and impurities, which has been subjected to processing such as drawing and drawing with a reduction in area of 10% or more in the course of the manufacturing process, and the area ratio of crystal grains having a circle equivalent diameter of 200 μm or less. Is a ferritic free-cutting stainless steel having a toughness of not less than 60%, a Charpy transition temperature of 50 ° C. or less, excellent cold workability, and excellent surface texture after processing. 3. At least one of the following: S: 0.010% or less, P: 0.050% or less, O: 0.0050% or less, N: 0.030% or less by weight%. The free-cutting ferritic stainless steel having excellent cold workability according to claim 1 or 2, characterized in that: 4. Al: 0.0001-0.05%, Nb: 0.05-1.0%, V: 0.05-1.0%, Ti: 0.05-1. The ferritic free-cutting stainless steel excellent in cold workability according to any one of claims 1 to 3, wherein one or two or more of 0% and Zr: 0.05 to 1.0% are contained. 5. The cold workability according to claim 1, wherein one or two of Ca: 0.010% or less and B: 0.010% or less are contained in% by weight. Excellent free-cutting ferritic stainless steel. 6. One or two of Mo: 0.05-5.0%, Ni: 0.05-1.0%, Cu: 0.05-1.0% by weight. The free-cutting ferritic stainless steel having excellent cold workability according to claim 1, wherein the stainless steel contains: