JP2001152297A - Free cutting martensitic stainless steel parts where emission of sulfurizing gas is suppressed, and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide parts such as electronic equipment parts where troubles due to sulfurizing gas should be avoided, in which emission of sulfurizing gas is effectively suppressed and high hardness and corrosion resistance are provided and which are 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, 0.5-2.5% Mn, >0.010-0.25% S, 0.01-0.50% Cu, 0.01-0.05% Ni, 10.0-16.0% Cr, 0.01-0.15% N, 0.004-0.030% O, <=0.04% P and the balance essentially Fe and satisfying Mn/S>=8.5, is used. This steel is worked into product shape by forging and/or machining and subjected to quench-and-temper treatment or is previously subjected to quench-and-temper treatment and them worked into product shape by machining. The resultant worked part is immersed in an oxidizing acid solution, by which sulfides existing at the surface are eluted and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a free-cutting martensitic stainless steel part which suppresses the emission of "sulfurizing gas", that is, corrosive gas mainly composed of H ₂ S, to a practically acceptable level. And its manufacturing method. The component of the present invention can be precisely cut and finished, and is useful as a component of an electronic device requiring hardness and corrosion resistance, for example, a rotating shaft of a hard disk drive, or a component disposed close to a printed circuit board. is there.

[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 electronic equipment components must not emit a sulfide gas such as H ₂ S 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 have poor machinability, cannot provide sufficient accuracy for products, and have low productivity. SUS416 and SUS420F
In the case of steel with added machinability by adding S as described above, the finishing accuracy is high, but the sulfide gas is released, and the steel cannot be used.

[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 production cost of the material.

[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 component which has a high level of hardness and corrosion resistance and has a high finishing accuracy, in which the release of sulfide gas is suppressed to a practically acceptable limit. It is also an object of the present invention to provide a method for manufacturing such a part.

[0007]

The parts of the present invention in which the release of the sulfide gas is suppressed are: C: 0.05 to 0.65 by weight%.
%, Si: 0.01-1.00%, Mn: 0.5-2.
5%, S: more than 0.010% to 0.25% or less, Cu:
0.01 to 0.50%, Ni: 0.01 to 0.50%,
Cr: 10.0 to 16.0%, N: 0.01 to 0.15
% And O: 0.004 to 0.030%, and P:
0.04% or less, and the balance substantially consists of Fe;
However, a free-cutting martensitic stainless steel having an alloy composition of Mn / S: 8.5 or more is formed into a product shape, and sulfide on the surface is eluted and removed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The free-cutting martensitic stainless steel of the present invention, which is used as a material for a component in which emission of sulfide gas is suppressed, belongs to the following groups I to IV in addition to the basic alloy composition described above. It may contain one to four optional elements: I) Se: 0.50% or less, Pb: 0.30% or less, B
i: one or two or more of 0.20% or less and Te: 0.10% or less II) one or two kinds of Mo: 2.0% or less and W: 2.0% or less III) B, Ca , Mg and / or REM: 0.0005% or less IV) One or more of Nb, V, Ti, Zr, Hf and Ta: 0.03 to 0.50% The method of manufacturing parts with suppressed gas emission is:
Free-cutting martensitic stainless steel having any one of the above alloy compositions is processed into a product shape by forging and / or machining, and is subjected to quenching and tempering, or quenching and tempering and then machining to produce a product. It is formed into a shape, and the obtained processed product is immersed in a solution of an oxidizing acid to elute and remove sulfide present on the surface.

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 for securing 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 in an amount of 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: more than 0.010% to 0.25% or less S is added in an amount exceeding 0.010% to ensure machinability. Although a large amount of S causes the generation of sulfide gas, in the present invention, sulfide on the surface of the component is dissolved and removed, so that a high S amount can be adopted to the extent that high machinability is obtained. Nevertheless, if the content of S exceeds 0.25%, it is difficult to suppress the release of sulfide gas, and there is also a problem that corrosion resistance is reduced.

Cu: 0.01 to 0.50% Ni: 0.01 to 0.50% Cu and Ni enhance the corrosion resistance, particularly in a reducing acid environment. 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 in relation to C, N is useful for securing 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% For the purpose of enhancing machinability, O having a lower limit of 0.004% or more is added. 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%.

P: not more than 0.04% Since P is an undesired impurity that segregates at grain boundaries and deteriorates various properties of steel, the lower the content, the better. 0.04
% 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.

Mn / S ratio: 8.5 or more As described above, when the Mn / S ratio is small, the workability is low. Therefore, in order to secure good workability, the Mn / S ratio is set to 8.5 or more. As a result, the sulfide is easily eluted, and the sulfide gas is easily generated as it is. In the present invention, the sulfide is eluted and removed by an acid treatment prior to the production, so that the Mn / S ratio is set to a large value of 8.5 or more. Preferably, it is 10 or more.

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

Group I Se: 0.50% or less, P
b: 0.30% or less, Bi: 0.20% or less and T
e: One or two or more of 0.10% or less When a higher machinability is required, a free-cutting element of this group is added. 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 the hot workability is not significantly reduced are, respectively, Se: 0.2 to
0.4%, Pb: 0.12 to 0.25%, Bi: 0.0
7 to 0.20%, Te: 0.02 to 0.05%.

Group II One or two types of Mo: 2.0% or less and W: 2.0% or less Both Mo and W enhance 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 III B, Ca, Mg and RE
One or more of M: 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 IV Nb, V, Ti, Zr, Hf
And one or more of Ta: 0.03 to 0.50
% These elements increase the toughness of the steel through refinement of the 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.

The process of immersing a part formed into a product shape in a solution of an oxidizing acid may be performed by a passivation process, which is performed as one type of metal surface treatment. The passivation treatment is, for example, using a nitric acid solution containing potassium dichromate and immersing the object to be treated in the solution at a slightly elevated temperature.
It can be carried out according to a conventional method. As a result, the sulfide existing on the surface of the component is eluted and removed. As a result, even if moisture acts in the environment in which the component is used, the sulfide no longer reacts and reacts with H ₂ S.
Since there is no sulfide that generates sulfide, release of the sulfide gas is suppressed.

[0026]

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 Mn PS Cu Ni Cr Cr NO Other Mn / S 1 0.12 0.21 2.21 0.024 0.21 0.02 0.15 12.8 0.03 0.0053-10.5 2 0.24 0.18 1.95 0.018 0.17 0.05 0.21 12.4 0.02 0.0095- 11.5 3 0.47 0.05 2.14 0.020 0.16 0.09 0.12 12.7 0.04 0.0077-13.4 4 0.14 0.52 1.77 0.031 0.09 0.19 0.32 12.4 0.07 0.0058 Se 0.26 19.7 Pb 0.18 5 0.09 0.18 1.56 0.019 0.09 0.14 0.21 13.1 0.06 0.0102 Pb 0.24 17.3 Te 0.02 6 0.14 0.26 1.08 0.027 0.05 0.06 0.31 12.6 0.02 0.0088 M0 0.48 21.6 Se 0.25 7 0.08 0.08 1.93 0.033 0.14 0.02 0.03 11.2 0.07 0.0059 W 1.5 13.8 Se 0.28 Pb 0.16 8 0.15 0.30 0.95 0.015 0.07 0.08 0.27 13.2 0.03 0.0074 Pb 0.17 13.6 Se 0.19 B 0.0022 9 0.16 0.25 1.31 0.022 0.02 0.11 0.25 12.7 0.05 0.0162 Pb 0.25 65.5 Te 0.04 La + Ce 0.0023 10 0.24 0.22 1.21 0.029 0.13 0.03 0.29 12.2 0.04 0.0055 Se 0.15 9.3 Nb 0.21 Ca 0.0019 11 0.35 0.16 0.99 0.030 0.06 0.08 0.38 13.3 0.13 0.0108 Pb 0.19 16.5 Mg 0.0015 12 0.15 0.31 1.05 0.012 0.09 0. 15 0.18 12.7 0.06 0.0067 Pb 0.18 11.7 V 0.16 Zr 0.13 13 0.18 0.19 0.69 0.008 0.03 0.22 0.22 14.1 0.02 0.0088 Mo 0.40 23.0 Bi 0.15 Hf 0.18 14 0.33 0.20 1.25 0.026 0.07 0.08 0.17 11.9 0.03 0.0054 Se 0.32 17.9 Ti 0.24 Ta 0.17

Table 2 (Comparative Example) No. C Si MnPS Cu Cu NiCrNO Other Mn / S 15 0.13 0.56 0.63 0.027 0.02 0.06 0.17 12.2 0.02 0.0051-31.5 16 0.12 0.44 1.12 0.032 0.21 0.03 0.11 12.5 0.02 0.0069 Mo 0.3 5.3 17 0.14 0.28 1.24 0.021 0.16 0.08 0.24 12.6 0.05 0.0111-7.8 18 0.21 0.44 0.96 0.021 0.15 0.02 0.33 13.1 0.03 0.0049 Pb 0.19 6.4 19 0.45 0.23 0.88 0.033 0.24 0.12 0.08 11.2 0.04 0.0093 Mo 1.2 3.7 Se 0.12 20 0.31 0.52 0.89 0.024 0.005 0.09 0.22 13.5 0.06 0.0121-178.0 21 0.16 0.33 0.63 0.018 0.005 0.15 0.35 6.2 0.01 0.0071-126.0 No. No. 15 is SUS410; Reference numeral 16 denotes SUS416.

Each sample was subjected to the following test in an annealed state. [Drilling test] Tool: Cermet Cutting speed: 120 m / min. Feed: 0.05mm Depth of cut: 0.1mm Cutting oil: water solubility Evaluation: 60min. Flank wear amount after cutting (μm) [Drill test] Tool: SKH9 φ5 mm Feed: 0.07 mm Hole depth: 15 mm Dry evaluation: Cutting speed (m / min.) At which the tool 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 was put in a container together with 0.05 cc of pure water, sealed, and kept at 85 ° C for 20 hours.
The change in the color of the g foil (the degree of generation of Ag ₂ S) was examined and evaluated according to the following five grades. No discoloration A>B>C>D> E Discoloration is remarkable (large amount of sulfide gas generated) [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 1 330 70 36 BB 2340 67.5 46 BB 3350 65 59 BB 4 290 77.5 41 AB 5305 305 37 37 AB 6 330 67.5 37 AA 7 275 82.5 36 BB 8285 80 39 B A 9 320 70 42 A A 10 340 65 47 CB 11 335 70 57 A A 12 320 70 42 BB 13 330 67.5 41 A A 14 315 70 54 AB

Table 4 (Comparative Example) No. Turning Test Drill Test Hardness Sulfurized Gas Wet μm m / min. HRC test Test 15> 500 <40 37 AB 16335 67.536 EC 17350 72.5 39 DB 18 290 80 44 DB 19 335 67.5 58 EB 20> 500 <40 55 AA 21 > 500 <40 34 AE

[0034]

According to the present invention, by using a free-cutting martensitic stainless steel having an alloy composition in which an Mn / S ratio is selected to be high and an appropriate amount of S is present as a material, high forgeability and machinability are obtained. As a result, a product having a part shape can be manufactured with high finishing accuracy. Finally, the component is subjected to an acid treatment to elute and remove sulfides present on the component surface, whereby a component in which emission of sulfide gas is effectively suppressed can be manufactured.

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 characteristics brought by each of the additional elements can be used. Can be enjoyed.

In the method of manufacturing a component according to the present invention, there is no element that causes a rise in cost, and it is possible to provide an inexpensive component. The component of the present invention is particularly suitable as a component of electronic equipment in which a trouble caused by sulfide gas is avoided.

Claims (6)

[Claims] (1) C: 0.05 to 0.65% by weight,
Si: 0.01 to 1.00%, Mn: 0.5 to 2.5
%, S: more than 0.010% to 0.25% or less, Cu:
0.01 to 0.50%, Ni: 0.01 to 0.50%,
Cr: 10.0 to 16.0%, N: 0.01 to 0.15
% And O: 0.004 to 0.030%, and P:
0.04% or less, and the balance substantially consists of Fe;
However, Mn / S: A component that suppresses the release of sulfide gas by forming a free-cutting martensitic stainless steel having an alloy composition of 8.5 or more into a product shape and eluting and removing sulfide on the surface. 2. A free-cutting martensitic stainless steel,
Se: 0.50 in addition to the alloy components defined in claim 1.
% Or less, Pb: 0.30% or less, Bi: 0.20% or less and Te: 0.10% or less. 3. A free-cutting martensitic stainless steel,
Mo: In addition to the alloy components defined in claim 1 or 2, Mo:
A component containing one or two of 2.0% or less and W: 2.0% or less, in which the release of sulfide gas is suppressed. 4. A free-cutting martensitic stainless steel,
In addition to the alloy components specified in any one of claims 1 to 3, one or more of B, Ca, Mg and REM: 0.0005% or less, which suppresses the release of sulfide gas. parts. 5. 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 4, containing 0.03 to 0.50%. , Parts with suppressed sulfide gas release. 6. A free-cutting martensitic stainless steel having an alloy component as defined in any one of claims 1 to 5, which is processed into a product shape by forging and / or machining, and then quenched and tempered. Alternatively, after quenching and tempering, the product is processed into a product shape by machining, and the obtained processed product is immersed in a solution of an oxidizing acid to elute and remove sulfide present on the surface. Of manufacturing parts with reduced noise.