JPH11229093A - Stainless steel with high corrosion resistance and high strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material with high corrosion resistance and high strength by providing a martensitic stainless steel with high N content. SOLUTION: The material has an alloy composition consisting of, by weight, <=0.30% C, <=1.0% Si, 6-18% Cr, <=2% Mo, 0.5-5% (in total in the case of >=2 elements) of one or >=2 elements among Mn, Cu, Ni, and Co, and the balance Fe with inevitable impurities. Further, the composition is regulated so that the Ni equivalent represented by (Ni equivalent) = Ni%+30C%+0.5 Mn%+0.4(Cu+Co)%+30 N% and the Cr equivalent represented by (Cr equovalent) = Cr%+Mo%+1.5 Si become 14 and 6 to 19, respectively, and the M value represented by (M value) = 502-810 C%-1230 N%-13 Mn%- 30 Ni%-12 Cr%-54(Cu+Co)%-46 Mo% becomes 1-30 to enlarge a solid-phase (γ) region, and N content is regulated to 0.07 to 0.2%. In addition to the above alloy components, 0.02 to 1.0% (in total in the case of both of either or both of V and Nb can further be incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a high-strength martensitic stainless steel requiring high corrosion resistance.
The stainless steel of the present invention includes machinery such as valves and compressors, mechanical parts such as springs, fastening members such as bolts and nuts, construction parts such as nails and drill screws, linear drive rails, rotating shafts, bearings and the like. Learning parts,
Furthermore, it is used for a wide range of uses, such as kitchen knives, household dishes such as Western tableware.

[0002]

2. Description of the Related Art Martensitic stainless steel is preferably used for applications requiring high corrosion resistance and high strength. It is generally known that when N component is added to steel, corrosion resistance and strength are improved.
Since the amount of N solid solution in the e-Cr system is low, and even in the 14.1% Cr steel, it is only 0.05%. Therefore, it is considered that the contribution of N to the improvement of the properties of the steel is small, and is not much studied. Was. S which is a typical Cr stainless steel
Taking US401 steel as an example, the solubility of N in the solidified structure is lower than the solubility of N in the molten metal, and a delta phase having a small amount of N solid solution crystallizes during solidification. And the amount of N in the solidified structure may be generated as blowholes in the steel, thereby forming defects.

[0003] The inventors of the present invention have studied with the intention of increasing the solid solution amount of N in martensitic stainless steel and thereby improving the properties thereof, and have studied Mn, Cu, Ni, Co.
By adding a small amount of such elements as above and properly balancing each alloy component, the crystallization of the gamma phase having a high N solid solution amount is promoted, and the N in the molten metal is solidified in the steel ingot at a high rate. It has been found that the corrosion resistance and strength of the martensitic stainless steel can be improved as a result.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to utilize the new knowledge obtained by the inventors to increase the N content,
An object of the present invention is to provide a novel martensitic stainless steel having improved corrosion resistance and strength.

[0005]

The high corrosion-resistant and high-strength stainless steel of the present invention that achieves the above object is, in weight%,
C: 0.30% or less, Si: 1.0% or less, Cr: 6 to
Mn, Cu, N in addition to 18% and Mo: 2% or less
One or more of i and Co (in the case of two or more, in total): containing 0.5 to 5%, the balance being an alloy composition consisting of Fe and unavoidable impurities, Ni equivalent = Ni % + 30C% + 0.5Mn% + 0.4
(Cu + Co)% + 30N% is 4 or more, Cr equivalent = Cr% + Mo% + 1.5Si% is 6 to 19, M value = 502-810C% -1230N% -13Mn%
-30Ni% -12Cr% -54 (Cu + Co)%-4
The solid phase γ region is expanded by adjusting the component composition so that 6Mo% is −30 or more, and N: 0.07 to 0.2%.

The high corrosion-resistant and high-strength stainless steel according to the present invention comprises, in addition to the above alloy components, one or two of V and Nb (in the case of two, a total of 0.02 to 1.0%).
May be contained. As a result, the carbide particles in the steel are refined, the cold workability is excellent, cracks are not generated at the time of working, and high-grade cold working such as cold header working and drawing is facilitated.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The high corrosion-resistant and high-strength stainless steel of the present invention can be produced by carrying out melting and refining in a nitrogen gas-rich atmosphere under atmospheric pressure using conventional equipment.

The reason why the alloy composition of the high corrosion resistant and high strength stainless steel of the present invention is determined as described above is as follows.

C: not more than 0.30% C is an element that promotes the formation of a gamma phase, which is important for increasing the solid solution amount of N. However, when added in excess of 0.30%, coarse carbides precipitate. As a result, the corrosion resistance and cold workability deteriorate, so the upper limit was set to 0.30%.

Si: 1.0% or less Si is necessary for deoxidation, but is an element forming a delta phase having a low solid solution amount of N. If added in a large amount, cold workability is reduced. Therefore, a limit of 1.0% was set.

Cr: 6 to 18% Cr is the most important additive component for stainless steel, and if added less than 6%, the corrosion resistance is insufficient. On the other hand, if it exceeds 18%, a sufficient quenching / tempering effect cannot be obtained. For these reasons, 6-18
% Range was determined.

Mo: 2% or less Mo is an important element for improving the corrosion resistance of stainless steel, but is a delta phase forming element. Therefore, the addition is limited to 2% in consideration of the balance.

One or more of Mn, Cu, Ni and Co (total of two or more): 0.5 to 5% Mn is added for deoxidation and also for forming a gamma phase. Useful. However, if added in excess of 5%, not only does corrosion resistance deteriorate, but also the amount of retained austenite is increased and the quenching hardness is reduced. Cu, Ni and Co promote the formation of a gamma phase, but when added in a large amount, the gamma phase becomes rather unstable and the quenching and tempering effects characteristic of chromium stainless steel cannot be exhibited. For these reasons, Mn, Cu, Ni and Co are one or two types.
0.5% or more of the seeds (in the case of two or more kinds, in total) is added, and the maximum addition amount is 5%.

Ni equivalent = Ni% + 30C% + 0.5Mn
% + 0.4 (Cu + Co)% + 30N% is 4 or more Unless this value is 4 or more, a sufficient solid solution of N cannot be realized,
The N content cannot be increased to 0.07% or more.

The condition that Cr equivalent = Cr% + Mo% + 1.5Si% is a condition to be satisfied in order to be a 6-19 chromium stainless steel.

M value = 502-810C% -1230N%
-13Mn% -30Ni% -12Cr% -54 (Cu +
Co)%-46Mo% is a condition to be satisfied in order to be a martensitic stainless steel of -30 or more. When the M value is lower than -30, the structure becomes austenite, and a sufficient quenching / tempering effect is obtained. Absent.

N: 0.07 to 0.2% This high N content is a feature of the martensitic stainless steel of the present invention, and is useful for improving corrosion resistance and further increasing strength. 0.07% is the minimum content that makes this effect clear, and 0.2% is the upper limit of the N content that can be contained.

[0018]

EXAMPLES A martensitic stainless steel having an alloy composition shown in Table 1 was produced by using an AOD furnace and operating at atmospheric pressure by melting and refining while blowing nitrogen gas from a lance into molten steel.

Table 1 No. C Si Cr Mo Mn Cu Ni Co V Nb N Example 1 0.02 0.4 6.3 0.1 0.7 0.1 4.2---0.07 2 0.25 0.8 8.0 0.1 0.2 0.1 2.8-0.05 0.08 3 0.12 1.3 9.6 0.1 0.4 3.0 0.3---0.09 4 0.25 0.6 9.6 0.1 0.2 1.2 0.1---0.11 5 0.02 0.8 8.0 0.1 0.2 2.1 2.5---0.08 6 0.30 0.8 8.0 0.1 0.3 0.1 2.8---0.08 7 0.02 0.5 15.6 0.1 0.8 0.1 2.0-0.09-0.20 8 0.18 0.8 13.7 0.1 0.2 0.1 0.2---0.16 9 0.12 0.6 15.6 0.1 0.5 0.1 0.4--0.05 0.17 10 0.30 1.1 5.8 0.1 1.3 0.1 0.5---0.08 11 0.02 0.7 17.6 0.1 0.2 0.1 0.2 1.9--0.15 12 0.18 0.8 9.6 0.1 0.6 2.1 0.3---0.11 13 0.30 0.6 8.6 0.1 0.2 0.6 0.3-0.09 0.03 0.11 14 0.02 0.2 11.6 0.1 2.9 0.1 0.3--0.09 0.15 15 0.12 0.8 17.6 0.1 0.2 0.1 0.3 0.3--0.15 16 0.12 0.7 11.6 0.1 2.7 0.1 0.2 0.02--0.15 17 0.18 1.6 6.7 1.3 0.8 1.4 0.7---0.11 18 0.12 1.3 16.4 0.1 0.3 0.3 0.5-0.06-0.15 19 0.15 1.7 8.6 0.5 1.8 0.3 1.4---0.11 20 0.25 0.6 8.0 0.1 0.2 0.1 2.8 0.3--0.08 Comparative example 1 0.05 0.3 12.0-0.8 0.1 0.2---0.01 2 0.05 0.5 17.0-0.8 0.1 0.2---0.02 3 0.30 0.8 13.0-0.8 0.1 0.2---0.01 4 0.05 0.8 16.0- 0.8 0.1 1.8---0.03 5 0.10 0.8 13.0 0.3 1.0 0.1 0.2 --- 0.01 The total amounts and characteristic values of Mn to Co in each of the examples and comparative examples are as shown in Table 2.

In order to examine the corrosion resistance of each steel, JIS
A 24-hour salt spray test was performed according to the method specified in -Z2371. Separately, a 15 mm square test piece having a length of 20 mm was prepared, subjected to quenching after heating at 1050 ° C. for 30 minutes, oil cooling, and holding at 150 ° C. for 1 hour, followed by tempering by air cooling, and the hardness HRC was measured. . The results are shown in Table 2.

Table 2 No. Mn + Cu + Ni + Co Cr equivalent Ni equivalent M value Salt spray Hardness HRC Example 1 5.0 7.0 7.2 190 3 31.2 2 3.1 9.1 9.2 12.8 11 3 52.6 3 3.7 11.7 7.9 14 46.7 41.5 10.5 11.5-26 4 54.6 5 4.8 9.2 6.4 96 3 34.2 6 3.2 9.2 14.3-30 353.07 2.9 16.8 9.0-265 37.2 80.5 14.9 10.5-224 51.191.016. 8 9.4 -18 5 46.7 10 1.9 7.0 12.6 51 3 50.0 11 2.4 18.8 6.2 -29 5 36.2 12 3.0 10.8 9. 9-24 3 51.1 13 1.1 9.5 12.9 -28 3 54.0 14 3.3 12.8 6.8 113 4 36.2 15 0.9 18. 8.6-27 5 46.7 16 3.02 12.8 9.8 32 4 46.9 17 2.9 10.4 10.4 -264 47.118 18 1.1 18.5 9.0 -29 5 46.7 19 3.5 11.7 10.6 -17 4 47.6 20 3.4 9.2 12.8 11 3 52.6 Comparative Example 1 13.1 12.4 2.0 300 1 29.4 2 18.1 17.8 2.0 240 240 3 29.6 3 14.1 14.1 9.5 85 1 53.6 4 18.7 17.1 3.6 204 4 29.4 5 14.3 14.4 2.2 272 2 40.9 The evaluation of the corrosion resistance is as follows: 5 No rust is generated 4 Rust occurs on about 25% or less of the surface 3 About 25% or more of the surface is exceeded Rust is generated in less than 50% 2 Rust is generated in more than about 50% of the surface and less than 75% 1 About 7 in the surface % Excess ~ entire surface rust occurs.

In the comparative examples, those having excellent corrosion resistance have low hardness (No. 4), or those having sufficient hardness have low corrosion resistance (No. 3), and both have poor hardness (No. 4).
On the other hand, in the embodiment of the present invention, in the embodiment of the present invention, even if the corrosion resistance is poor, it is stage 3, and the hardness is at the level of 34 to 55.

[0023]

The martensitic stainless steel according to the present invention is selected from Cu, Ni and Co in addition to Mn.
By adding a specific amount of a kind or two or more kinds, and by appropriately adjusting the balance between the respective alloying components, the N component, which has not been considered so far, is positively used to provide high corrosion resistance and high strength. Succeeded in achieving both. By using this stainless steel, it is possible to provide parts superior to the conventional ones for the various uses described above.

Claims (2)

[Claims] C .: 0.30% or less by weight, Si:
1.0% or less, Cr: 6 to 18% and Mo: 2% or less, in addition to one or two of Mn, Cu, Ni and Co.
Species or more (in the case of two or more kinds, in total): contains 0.5 to 5%, the balance has an alloy composition composed of Fe and unavoidable impurities, and Ni equivalent = Ni% + 30C% + 0.5Mn% + 0 .4
(Cu + Co)% + 30N% is 4 or more, Cr equivalent = Cr% + Mo% + 1.5Si% is 6 to 19, M value = 502-810C% -1230N% -13Mn%
-30Ni% -12Cr% -54 (Cu + Co)%-4
A high corrosion-resistant and high-strength stainless steel characterized in that the solid phase γ region is expanded by adjusting the component composition so that 6Mo% is -30 or more, and N: 0.07 to 0.2% or less. 2. In addition to the alloy component according to claim 1, V
And one or two of Nb (in the case of two, in total):
2. The high corrosion resistant and high strength stainless steel according to claim 1, having an alloy composition containing 0.02 to 1.0%.