JPH06200355A - Stainless steel excellent in corrosion resistance and machinability - Google Patents

Abstract

PURPOSE:To obtain a stainless steel where rusting is prevented even at the time of washing with water and use in a high temp. and high humidity environment and which has corrosion resistance. CONSTITUTION:This steel is a stainless steel which has a composition consisting of, by weight ratio, <=0.50% C, <=1.00% Si, <=0.50% Mn, <=0.060% S, 0.1-4.0% Ni, 10-18% Cr, 0.1-2.0% Mo, 0.03-0.30% Bi or 0.03-0.30% of Bi and Pb, further 0.01-0.30% Ti and/or 0.01-0.30% Zr, and the balance Fe with impurity elements and also has superior corrosion resistance and machinability. This stainless steel is free from rusting even if cleaning is converted to washing with water in order to eliminate the use of fluorocarbon in a cleaning stage in the course of the production of parts related to electronics and has superior corrosion resistance and further has excellent machinability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for electronics-related parts, precision machine parts, etc., which does not cause rust even if it is washed with water at the time of manufacturing parts or used in a high temperature and high humidity environment. Relates to stainless steel with excellent properties.

[0002]

2. Description of the Related Art Conventionally, electronics-related parts and precision machine parts are not used in a special corrosive environment such as acid, but SUS410, SUS420J2, etc. are required for parts requiring a certain degree of corrosion resistance. It is used. In addition, the parts that are required to have the above-mentioned corrosion resistance and that are manufactured into the final shape by cutting include Cr containing S such as SUS416 and SUS420F.
Based stainless steel is used.

[0003]

In the above-described cleaning process during the manufacture of parts, a cleaning agent containing chlorofluorocarbon has hitherto been used. However, recently, the ozone layer depletion due to CFC gas has become a global problem, and the movement to tighten CFC regulations has become active, and the implementation of CFC reduction measures in various industrial fields has been strongly demanded.

An inexpensive cleaning method using abundant water is conceivable as an effective cleaning method in place of the cleaning agent using chlorofluorocarbon. As a result of carrying out a production test by replacing the cleaning agent with water, the following problems occur. I knew it was.

That is, it was found that when the cleaning method was replaced with water cleaning and the above-mentioned parts were manufactured, red rust was generated in the parts in the process of manufacture and the conventional chromium-based stainless steels could not be used at the corrosion resistance level. Further, since chrome-based stainless steel sometimes causes red rust when used under high temperature and high humidity, the requirement for improving the corrosion resistance of chrome-based stainless steel has become stronger with the Freon gas regulations.

Further, the above-mentioned electronics-related parts and precision machine parts are often finished into the final part shape by cutting, and it is required to have excellent characteristics in terms of corrosion resistance and machinability.

In response to the above requirements for corrosion resistance, SUS410 and SUS420 which are conventional steels, SUS416 containing SUS420J2 and S, SUS42
Chromium-based stainless steels such as 0F do not have corrosion resistance that can withstand water washing and use under high temperature and high humidity environment, as is clear from the above-mentioned manufacturing test results. Further, although the requirement of machinability can be satisfied by using S-containing chromium-based stainless steel, it has been hindered from being applied due to poor corrosion resistance as described above. Therefore, there has been a strong demand for the development of a chromium-based stainless steel having excellent corrosion resistance and machinability that can solve this problem.

The present invention has been made in consideration of the above-mentioned problems of the conventional chromium-based stainless steel, and does not cause red rust even if it is washed with water or used in a high temperature and high humidity environment, and The purpose is to provide stainless steel having excellent machinability.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have completed the present invention by obtaining the following knowledge.

That is, it was found that the starting point of the generation of red rust is a sulfide-based inclusion such as MnS, and the cause of the starting point is that the sulfide-based inclusion such as MnS is water-soluble. In other words, conventional steel SUS410, SUS420
Since J2 contains about 0.01% and SUS416 and SUS420F contain about 0.2% S, it is a water-soluble sulfide inclusion in the steel.
It was discovered that MnS exists and that it is the starting point and deteriorates the corrosion resistance to water.

As a result of further study, when Ni and Mo are added in appropriate amounts to improve the corrosion resistance, especially when a small amount of Ti or Zr is added to Bi or Bi and Pb, these elements become S.
Binds with and prevents the formation of water-soluble sulfide MnS,
Moreover, it was found that corrosion resistance that can withstand water washing and use in high temperature and high humidity environments can be secured because it forms water-insoluble TiS, ZrS sulfides, and a certain amount of S can be added to improve machinability. Can be improved.

On the other hand, among the conventional steels, SUS416, SUS420F
S contained in is added to improve the machinability, and even if a certain amount of S can be contained, other machinability-improving elements are added to supplement the decrease in S and not deteriorate the corrosion resistance. There is a need. However, among the elements added for suppressing the above MnS formation, the present inventors
The present invention has been completed by confirming by experiments that it has an effect of improving the machinability and can sufficiently compensate for the deterioration of the machinability due to the reduction of S.

That is, according to claim 1 of the present invention, C: 0.50% or less, Si: 1.00% or less, Mn: 0.50% or less, S: 0.06 by weight.
0% or less, Ni: 0.1 to 4.0%, Cr: 10 to 18%, Mo: 0.1 to 2.0%,
Bi: 0.03 to 0.30%, Ti: 0.01 to 0.30%, Zr: 0.01 to 0.
Stainless steel with excellent corrosion resistance and machinability, characterized in that it contains one or two of 30% and the balance is Fe and impurity elements. Claim 2 further comprises Pb: 0.03.
.About.0.30% is included to further improve the corrosion resistance of claim 1.

Next, the reasons for limiting the component composition of the stainless steel of the present invention having excellent corrosion resistance and machinability will be described below. C: 0.50% or less If the C content is high, the corrosion resistance and the machinability, which are important properties of the present invention, are impaired, so the upper limit was made 0.50%.

Si: 1.00% or less Si is an element effective in deoxidizing, but if added in a large amount, it becomes brittle and deteriorates hot workability, so the upper limit was made 1.00%.

Mn: 0.50% or less Mn is an element effective in deoxidizing, but if it is added in a large amount, the corrosion resistance decreases and it becomes brittle, so the upper limit is 0.50%.
And

S: 0.060% or less S exists as an impurity even if it is not positively added, and a part of it is contained in the steel as MnS. Since this inclusion is water-soluble, it becomes the starting point of the generation of red rust by washing with water during the manufacture of parts and use in a high temperature and high humidity environment, so it is desirable to limit the upper limit to 0.060%.

Ni: 0.1 to 4.0% Ni is an essential element for the steel of the present invention, which can prevent the occurrence of red rust in water washing and high temperature and high humidity environment and ensure the corrosion resistance. In order to obtain the above effect, at least 0.1% is required to be contained. However, if contained in a large amount, the above effect is saturated, the machinability is reduced, and the cost is increased, so the upper limit was made 4.0%.

Cr: 10-18% Cr is an essential element for maintaining the basic corrosion resistance of stainless steel, and it is necessary to contain 10% or more.
However, if a large amount is contained, the above effect is saturated and the cost increases, so the upper limit was made 18%.

Mo: 0.1 to 2.0% Mo is an essential element for the steel of the present invention, which can prevent the occurrence of red rust in water washing and high temperature and high humidity environment and ensure the corrosion resistance. In order to obtain the above effect, at least 0.1% is required to be contained. However, if contained in a large amount, the above effect is saturated, the machinability is reduced, and the cost is increased, so the upper limit was made 2.0%.

Bi: 0.03 to 0.30% Bi is an important element in the present invention, which is effective in preventing the generation of red rust by suppressing the formation of MnS which is a water-soluble inclusion and also in improving the machinability. . In order to obtain the above effects sufficiently, the content of 0.03% or more is necessary. However, if contained in a large amount, the machinability is improved, but the hot workability is deteriorated and the production by hot rolling is hindered.
The upper limit was 0.30%.

Pb: 0.10 to 0.30% Pb is an element which prevents the generation of red rust by suppressing the formation of MnS, which is a water-soluble inclusion, and is also effective in improving machinability. In order to obtain the above effect, the content of 0.30% or more is required. However, if contained in a large amount, the machinability is improved, but the hot workability is deteriorated and the production by hot rolling is hindered, so the upper limit was made 0.30%.

Ti: 0.01 to 0.30%, Zr: 0.01 to 0.30% Ti and Zr combine with S to form water-insoluble TiS, ZrS sulfides, and suppress the formation of MnS to prevent corrosion. Is the most important element in the present invention, which is effective in improving Therefore, in order to obtain this effect, it is necessary to contain at least one of Ti and Zr in an amount of 0.01% or more. However, even if it is contained in a large amount, the above effect is saturated and the cost becomes high, so the upper limits were made 0.30% respectively.

[0024]

EXAMPLES The features of the present invention will be described below in comparison with comparative steels and conventional steels with reference to examples. Table 1 shows the chemical composition of the test materials used in the examples.

[0025]

[Table 1]

In Table 1, 1 to 6 steels are steels of the present invention and 7 to 6 steels.
The 11th steel is a comparative steel, and the 12th to 14th steels are conventional stainless steels SUS410, SUS416, and SUS420F.

Using the materials having the composition shown in Table 1,
A round bar having a diameter of 20 mm was manufactured by hot rolling and annealed to obtain a test material. Table 1 also shows the test results of corrosion resistance and machinability evaluated by the test method described later.

The corrosion resistance of the test material is 15 mm in diameter by machining.
mm test pieces were prepared, washed with water, left for 7 days in a high temperature and high humidity environment at a temperature of 60 ° C. and a humidity of 90% or more, and evaluated for the occurrence of red rust. It should be noted that in Table 1, ⊚ indicates that no red rust was generated at all, ∘ indicates that 10 or less points of red rust were observed, and ∘ indicates 10 or more points and red rust of less than 10% in area ratio The sample was shown as Δ, and the sample showing red rust of 10% or more in area ratio was shown as x.

The machinability was evaluated by a drilling test.
In the test, the drill was a straight shank drill with a diameter of 5 mm, the material of the drill was SKH51, and the drill rotation speed was 759 r.p.
m., no cutting oil, load 72 kg. The measurement results show the perforation time per fixed length of conventional steel SUS410.
It is set to 100, and each drilling time is arranged by an integer ratio, and Table 1
It was shown to.

As is clear from Table 1, when comparing the comparative steels and the conventional steels 7 to 14 with the steels of the present invention, since the 7 steel has a high C content, both corrosion resistance and machinability are inferior. ,
8 steel has a high Mn content and thus a little inferior corrosion resistance, 9 steel has a low Ni and Mo content and thus a poor corrosion resistance, and 10 steel has a high S content and therefore a considerably poor corrosion resistance. Since the 11th steel has a low Bi content, it has excellent corrosion resistance due to the effect of Ti content, but its machinability is slightly inferior to the steels of the present invention. Further, the conventional steels 12 to 14 are poor in corrosion resistance because they contain S and do not contain Bi, Ti, and Zr that suppress the formation of MnS. Has excellent machinability, but has extremely poor corrosion resistance.

On the other hand, the steels 1 to 6 of the present invention are S
The upper limit of the content rate is regulated to 0.060%, and Bi, Pb, Ti,
By adding a small amount of Zr, it is possible to prevent the formation of water-soluble sulfide (MnS) that causes the generation of red rust, and to add S to the water-insoluble
It was confirmed that the corrosion resistance superior to that of SUS410 and the machinability close to that of SUS416 and SUS420F can be obtained by not using TiS and ZrS and by adding an appropriate amount of Bi and Pb.

[0032]

INDUSTRIAL APPLICABILITY The stainless steel which is excellent in corrosion resistance and machinability according to the present invention has excellent corrosion resistance that does not cause rust even if it is washed with water at the time of manufacturing a part or used in a high temperature and high humidity environment. It is a thing. Moreover, by adding an appropriate amount of Bi and Pb, the machinability could be improved without deteriorating the corrosion resistance. Therefore, the steel of the present invention contributes to the realization of the reduction of CFC, which is a global problem, and also enables the expansion of the range of application of chromium-based stainless steels, which greatly contributes to the industry.

Claims (2)

[Claims] 1. A weight ratio of C: 0.50% or less, Si: 1.00% or less, Mn: 0.50% or less, S: 0.060% or less, Ni: 0.1 to 4.0%, C
r: 10 to 18%, Mo: 0.1 to 2.0%, Bi: 0.03 to 0.30%, Ti:
0.01 to 0.30%, Zr: 0.01 to 0.30%, 1 or 2
Stainless steel with excellent corrosion resistance and machinability, which contains seeds and the balance is Fe and impurity elements. 2. A weight ratio of C: 0.50% or less, Si: 1.00% or less, Mn: 0.50% or less, S: 0.060% or less, Ni: 0.1 to 4.0%, C
r: 10 to 18%, Mo: 0.1 to 2.0%, Bi: 0.03 to 0.30%, Pb: 0.
03-0.30%, Ti: 0.01-0.30%, Zr: 0.01-0.30%
A stainless steel having excellent corrosion resistance and machinability, characterized by containing one or two of the above, and the balance being Fe and impurity elements.