JP2001152298A - Free cutting martensitic stainless steel part free from emission of sulfurizing gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide pars such as electronic equipment parts where troubles due to sulfurizing gas should be avoided, which are practically free from emission of sulfurizing gas and provided with high hardness and corrosion resistance and further manufactured with high finishing precision. SOLUTION: A free cutting martensitic stainless steel, having an alloy composition consisting of, by weight, 0.05-0.65% C, 0.01-1.00% Si 0.1-2.5% Mn, 0.01-0.50% Cu, 0.01-0.50% Ni, 10.0-16.0% Cr, 0.01-0.15% N, 0.004-0.030% O, one or more kinds among <=0.50% Se, <=0.30% Pb, <=0.20% Bi and <=0.10% Te, <=0.010% S. <=0.04% P and the balance essentially Fe, is formed into product shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free-cutting martensitic stainless steel component which does not substantially emit "sulfurizing gas", ie, a corrosive gas mainly composed of H ₂ S.
The present invention is capable of precision cutting and finishing, and is applied to components of electronic devices required for hardness and corrosion resistance, such as a rotating shaft of a hard disk drive, and components arranged close to a printed circuit board. Especially meaningful.

[0002]

2. Description of the Related Art As is well known, Ag, Cu or Al is generally used as a material for contacts and circuits of electronic equipment. These metals are easily sulfided,
If the atmosphere contains H ₂ S or the like, troubles are caused by the formation of sulfides. Therefore, a material such as steel used for an electronic device component must not emit a sulfide gas such as H ₂ S even under the action of moisture in the atmosphere. For this purpose, the S content in the material should be reduced.

On the other hand, since electronic equipment is generally a precision machine, its parts are required to have extremely high finishing accuracy and high machinability. In addition, hardness and corrosion resistance are required.

Until now, martensitic stainless steel has been used for the production of such components. However, existing steels such as SUS410 and SUS420J are inferior in machinability, cannot provide sufficient finishing accuracy for products, and have low productivity. SUS416 or SUS4
Steel, such as 20F, to which S has been added to enhance machinability has a high finishing accuracy, but has a release of sulfide gas and is not usable.

[0005] A solution to this problem has been proposed to reduce the ratio of Mn / S in the steel and increase the resistance to sulfide elution, and to control the amount of S within an appropriate range. However, the reduced machinability is compensated for by the addition of Se. The disadvantage of this measure is that M
The reduction in n / S lowers the workability of the alloy and increases the material production cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a component manufactured using a free-cutting martensitic stainless steel as a material, and to avoid troubles caused by sulfide gas, such as components of electronic equipment. In parts
It is an object of the present invention to provide a part which has a high degree of avoidance of the emission of sulfur gas so as not to be substantially recognized, has high hardness and corrosion resistance, and is processed with high finishing accuracy.

[0007]

The parts of the present invention that do not emit sulfide gas are C: 0.05 to 0.65% by weight,
Si: 0.01 to 1.00%, Mn: 0.1 to 2.5
%, Cu: 0.01 to 0.50%, Ni: 0.01 to
0.50%, Cr: 10.0 to 16.0%, N: 0.0
In addition to 1 to 0.15% and O: 0.004 to 0.030%, Se: 0.50% or less, Pb: 0.30% or less, Bi: 0.20% or less, and Te: 0.10 % Or less, S: 0.010% or less, P: 0.04% or less, the balance being a free-cutting martensitic stainless steel having an alloy composition consisting essentially of Fe Is formed into a product shape.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The free-cutting martensitic stainless steel used as a material of a component that does not emit a sulfide gas according to the present invention has the following group I in addition to the basic alloy composition described above.
It can contain one to three optional elements belonging to the following groups III to III: I) One or two kinds of Mo: 2.0% or less and W: 2.0% or less II) B, Ca, Mg and REM Or more: 0.0005% or less III) One or more of Nb, V, Ti, Zr, Hf and Ta: 0.03 to 0.50%

The component of the present invention which does not emit a sulfide gas is obtained by processing a free-cutting martensitic stainless steel having any one of the above alloy compositions into a product shape by forging and / or machining, followed by quenching and tempering. Or a quenching-tempering treatment followed by machining into a part shape.

The reason why the alloy component of the free-cutting martensitic stainless steel used as the material of the component in the present invention is determined as described above will be described below.

C: 0.05 to 0.65% C is necessary to secure hardness, but is not preferable for corrosion resistance. It is advisable to add N in the range and then add the amount of C necessary to obtain the desired hardness. From such a viewpoint, the lower limit of 0.05% is necessary for securing hardness. The upper limit of 0.65% is that when the amount of addition increases, the increase in hardness saturates, and when the amount exceeds this limit, unnecessarily large primary carbides are formed, resulting in machinability such as machinability during annealing. It was set because of the decrease.

Si: 0.01 to 1.00% Si is useful as a deoxidizing agent, but promotes the precipitation of intermetallic compounds, and also increases the strength of the matrix to reduce machinability. Therefore, it is better not to add a large amount.
It is preferable to keep it at 5% or less.

Mn: 0.5 to 2.5% Mn is a deoxidizing agent and should be added at least 0.5%. If the amount is less than this, the production cost increases. On the other hand, since the presence of a large amount lowers the corrosion resistance,
The amount is 2.5% or less.

S: 0.010% or less Since S causes generation of sulfide gas, its content is reduced as much as possible. However, since the production of ultra-low sulfur steel causes an increase in cost, an upper limit of 0.010% was set in order to balance sulfide gas and cost. If the S content is below this limit, as shown in the execution data described below,
It is possible to obtain an alloy which does not substantially emit a sulfurizing gas. An S content of 0.005% or less is more preferable. Since there is no particular difficulty in producing a steel having an S content of about 0.004 to 0.005% by refining steel by a conventional AOD method, the cost of producing the material of the component of the present invention is usually No higher than the material. S
Of course, steel whose content does not reach 0.010% has poor machinability. To compensate for this, free-cutting elements such as Se are added.

Cu: 0.01 to 0.50% Ni: 0.01 to 0.50% Cu and Ni enhance the corrosion resistance, particularly in the environment of a reducing acid. In order to obtain this effect, 0.01% or more is added, respectively. However, if the amount is too large, phase stability is impaired and hardness during annealing is increased.

Cr: 10.0 to 16.0% Cr is an element serving as a core responsible for corrosion resistance.
Was determined from this viewpoint. Excessive addition lowers phase stability and worsens hot workability, so the upper limit is 16.0.
% Addition only. The preferred range of the amount of Cr is 1
1.5 to 13.0%.

N: 0.01 to 0.15% As described for C, N is useful for securing the hardness in an alloy composition in which the amount of C is kept low.
Add at least 01%. In addition, it also has the function of improving corrosion resistance. However, the addition of a large amount of N unnecessarily increases the production cost and may impair the soundness of the steel ingot at the time of production, so the upper limit of 0.15% was set.

O: 0.004 to 0.030% O is added at a lower limit of 0.004% or more for the purpose of enhancing machinability. Excessive oxides will be generated more than necessary if present in excess, and the machinability will be rather reduced.
Select the amount of addition in the range up to%.

Se: 0.50% or less, Pb: 0.30%
Below, Bi: 0.20% or less, and Te: 0.10%
One or more of the following As described above, in the present invention, S is eliminated as much as possible, so that free-cutting elements of this group are indispensable to secure necessary machinability. Although the machinability is improved by the addition, the hot workability is reduced, so the above upper limits are respectively set. The preferred ranges in which the effect of improving machinability is clearly obtained and there is no significant decrease in hot workability are Se: 0.2 to 0.4, respectively.
%, Pb: 0.12-0.25%, Bi: 0.07-
0.20%, Te: 0.02 to 0.05%.

P: not more than 0.04% P is an undesired impurity that segregates at the grain boundaries and degrades various properties of the steel. Therefore, the lower the content, the better. 0.0
4% is an acceptable limit. Since the production cost is increased to realize an extremely low phosphorus steel, the content is determined in consideration of the characteristics required for the part and the cost.

The action of each element that can be arbitrarily added and the reason for limiting the composition range are as follows.

Group I Mo: 2.0% or less and W: 2.0% or less One or two types of Mo and W both increase the corrosion resistance. The addition of a large amount not only lowers the hot workability but also raises the cost. Therefore, the addition amount is selected from the range of up to 2.0%.

Group II B, Ca, Mg and REM
One or more of the following: 0.0005 to 0.0100% These elements improve hot workability and machinability. This effect is observed with a small addition of about 0.0005%. However, a large amount impairs the cleanliness of steel.
The amount added should be within 100%.

Group III Nb, V, Ti, Zr, H
One or more of f and Ta: 0.03 to 0.5
0% These elements increase the toughness of the steel through refinement of crystal grains and solid solution strengthening, while forming carbonitrides when added excessively, lowering the cleanliness of the steel. The range of 0.03 to 0.50% is provided from this viewpoint.

[0025]

EXAMPLES Alloys having the compositions shown in Tables 1 and 2 were melted in an air induction furnace and cast into 50 kg ingots. Each ingot was hot forged, forged into a steel bar having a diameter of 60 mm or 20 mm, and then subjected to an annealing treatment of heating to 750 ° C. and air cooling.

Table 1 (Examples) No. C Si MnPS Cu NiCrCrNO ^* Others 1 0.14 0.33 1.05 0.027 0.004 0.07 0.33 12.9 0.03 73 0.28Se 0.21Pb 2 0.11 0.23 1.56 0.036 0.002 0.02 0.09 13.0 0.06 57 0.22 Se 0.15Bi 3 0.35 0.35 0.45 0.010 0.005 0.07 0.25 13.3 0.05 108 0.20Pb 0.04Te 4 0.51 0.24 0.82 0.015 0.001 0.32 0.14 11.9 0.05 66 0.19Se 0.23Pb 0.81Mo 5 0.33 0.52 0.63 0.032 0.001 0.06 0.36 13.2 0.07 71 0.26Pb 0.52W 6 0.12 0.22 0.99 0.021 0.008 0.05 0.25 12.8 0.05 62 0.18Se 0.19Pb 0.46Mo 0.0031B 7 0.21 0.19 0.55 0.018 0.002 0.08 0.22 13.5 0.05 111 0.24Pb 0.03Bi 0.0029Ca 8 0.34 0.32 1.77 0.025 0.007 0.03 0.31 12.1 0.05 51 0.31Se 0.03 Te 0.41Mo 0.0018Mg 9 0.14 0.28 1.12 0.022 0.004 0.06 0.31 13.2 0.02 84 0.25Se 0.18Pb 0.28Mo 0.0014 (La + Ce) 10 0.15 0.31 0.98 0.025 0.005 0.08 0.29 12.8 0.03 91 0.19Se 0.10Bi 0.18W 0.21Nb 11 0.19 0.22 0.66 0.030 0.004 0.06 0.30 13.0 0.04 71 0.20 Pb 0.08Bi 0.24V 12 0.19 0.21 0.65 0.031 0.005 0.05 0.31 12.9 0.05 67 0. 23Pb 0.11Bi 0.31Mo 0.11Ti 13 0.31 0.35 1.09 0.021 0.005 0.05 0.29 13.1 0.04 77 0.18Se 0.15Pb 0.02Te 0.45Mo 0.15Zr 14 0.32 0.32 1.12 0.022 0.004 0.04 0.30 12.9 0.03 81 0.24Se 0.23Pb 0.13Hf 0.17Ta * ppm

Table 2 (Comparative Example) No. C Si MnPS Cu Cu NiCrNO ^* Others 15 0.13 0.56 0.63 0.027 0.017 0.06 0.17 12.2 0.02 51-16 0.12 0.44 1.12 0.032 0.21 0.03 0.11 12.5 0.02 69 0.3Mo 17 0.21 0.44 0.96 0.021 0.15 0.02 0.33 13.1 0.03 49 0.19 Pb 18 0.45 0.23 0.88 0.033 0.24 0.12 0.08 11.2 0.04 93 0.12Se 1.2Mo 19 0.16 0.33 0.63 0.018 0.005 0.15 0.35 6.2 0.01 71- * Ppm No. No. 15 is SUS410, No. Reference numeral 16 denotes SUS416.

The following tests were performed on each sample in an annealed state. [Drilling test] Tool: Cermet Cutting speed: 120 m / min. Feed: 0.05mm Cutting depth: 0.1mm Cutting oil: Water solubility Evaluation: Flank wear after cutting for 60 minutes (μm) [Drill test] Tool: SKH9 φ5mm Feed: 0.07mm Hole depth: 15mm Dry evaluation: Tool Cutting speed (m / min.) At which the life (unperforable) becomes 5000 mm

Next, a sample having a diameter of 20 mm was
Quenching and tempering under the conditions of heating to 30 ° C for 30 minutes → oil cooling, and heating to 180 ° C for 1 hour → air cooling, and checking the hardness.
The average of 5 points was taken.

Subsequently, the quenched-tempered diameter 20
The sample of mm was subjected to a passivation treatment in which the sample was immersed in a 30% nitric acid solution containing 2% of potassium dichromate at 50 ° C. for 1 hour, and the following test was performed in that state. [Sulfidation gas test] From the sample of 20 mm in diameter subjected to the passivation treatment, two test pieces of 25 mm in length x 15 mm in width x 3 mm in thickness were cut out for each sample, and the entire surface was polished with # 400 emery. This test piece and 10m
An mx 5 mm Ag foil and 0.05 cc of pure water were placed in a sealed container and kept at 85 ° C for 168 hours.
The change in the color of the Ag foil (the degree of Ag ₂ S generation) was examined and evaluated according to the following five grades. No discoloration A>B>C>D> E Significant discoloration (large outgassing amount) [Wet test] A 20 mm diameter rod was machined into a 10 mm diameter rod.
Three test pieces of mm × 50 mm in length were prepared for each sample. This surface is polished with # 320 emery,
The film was exposed to an atmosphere of 90% RH at 40 ° C. for 120 hours, and the amount of rust was examined and evaluated according to the following five grades. A (No rust) B (Some spots) C (Many spots) D
(A small amount of red rust: area ratio 10% or less) E (a large amount of red rust: area ratio 10% or more) The test results described above are shown in Tables 3 and 4.

Table 3 (Example) No. Turning test Drill test Hardness Sulfurized gas Wet μm m / min. HRC Test Test 1 280 80 37 AB 2310 72.5 37 AB 3325 70 54 AB 4285 80 58 A A5 315 72.5 55 A A 6 305 75 36 36 A A7 310 72.5 45 A B8 320 70 53 A A9 285 77.5 36 A A10 290 77.5 38 A B 11 305 75 43 43 AB 12 275 82.5 44 A A 13 270 85 52 A A 14 280 80 52 A B

Table 4 (Comparative Example) No. Turning Test Drill Test Hardness Sulfurized Gas Wet μm m / min. HRC test Test 15> 500 <4037BB1633567.536EC172908036CB1833567.539CB19 > 500 < 4034AE The examples of the present invention are usually 20 No discoloration of the Ag foil was observed even in a severe test in which the sulfide gas test conducted for a long time was extended to 168 hours.

[0033]

The component of the present invention is obtained by selecting a free-cutting martensitic stainless steel having a composition in which the amount of S present in the steel is reduced to a certain limit or less.
With regard to sulfide gas, its emission is virtually not observed,
Advanced characteristics are realized. On the other hand, a specific amount of Se, Pb, B
An alloy composition to which one or more of i and Te is added ensures excellent machinability,
A part-shaped product can be manufactured with high finishing accuracy.

If a free-cutting martensitic stainless steel having a composition in which one or several optional elements are added to the basic alloy composition as required is used as a material, the properties brought by each of the additional elements are obtained. Can be enjoyed.

The component of the present invention is suitable as a component of a delicate electronic device for which a trouble caused by a sulfide gas is to be eliminated as much as possible and a component of an electronic device for which a long-term high reliability is required.

Claims (4)

[Claims] (1) C: 0.05 to 0.65% by weight,
Si: 0.01 to 1.00%, Mn: 0.1 to 2.5
%, Cu: 0.01 to 0.50%, Ni: 0.01 to
0.50%, Cr: 10.0 to 16.0%, N: 0.0
In addition to 1 to 0.15% and O: 0.004 to 0.030%, Se: 0.50% or less, Pb: 0.30% or less, Bi: 0.20% or less, and Te: 0.10 % Or less, S: 0.010% or less, P: 0.04% or less, the balance being a free-cutting martensitic stainless steel having an alloy composition consisting essentially of Fe Parts that do not emit sulfide gas. 2. A free-cutting martensitic stainless steel,
Mo: 2.0% in addition to the alloy components specified in claim 1
And W: a component containing one or two types of not more than 2.0% and having no emission of a sulfide gas. 3. A free-cutting martensitic stainless steel,
B, C in addition to the alloy components specified in claim 1 or 2
a, one or more of Mg and REM: 0.00
Parts containing no more than 05% and which do not emit sulfide gas. 4. A free-cutting martensitic stainless steel,
One or more of Nb, V, Ti, Zr, Hf and Ta, in addition to the alloy components specified in any one of claims 1 to 3, containing 0.03 to 0.50%. Parts that do not emit sulfide gas.