JP3499275B2 - Precipitation hardening stainless steel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precipitation hardening stainless steel having excellent corrosion resistance and strength and improved toughness. [0002] As is well known, stainless steel containing a large amount of Cr has excellent corrosion resistance as compared with other steel materials, and is widely used in a corrosive environment. Generally, stainless steel has a tensile strength of 40 except for martensitic.
〜60 Kg / mm ² and relatively low strength. Although martensitic stainless steel has high strength, it is significantly inferior to other stainless steels in corrosion resistance. [0003] In view of the above, there is a demand for a material whose strength is improved by minimizing the sacrifice of corrosion resistance. Steel is being developed. An example of this is martensitic precipitation hardening stainless steel, which has excellent strength and corrosion resistance, and has a tensile strength of 14%.
A material having a corrosion resistance of at least 0 kg / mm ² and a corrosion resistance equivalent to that of 18-8 stainless steel has been developed. By utilizing the above characteristics, this stainless steel is particularly effectively used as a member requiring corrosion resistance and strength. [0004] As described above, according to the precipitation hardening type martensitic stainless steel, the strength is comparable to that of other high-strength steels and can be sufficiently satisfied. Characteristics have been obtained. However, in the toughness value represented by the Charpy impact value, compared to other high-strength steels,
Its value is rather low and inferior in toughness. For this reason,
It is difficult to adopt it for structural steel with severe use conditions or to use it in applications that receive a large shocking external force, and there is a problem that the field of use is limited. The present invention has as its basic object to solve the above problems, without impairing the corrosion resistance and strength inherent as precipitation hardening stainless steel,
It is an object of the present invention to provide a novel precipitation hardening stainless steel with improved toughness. [0005] In order to solve the above-mentioned problems, the precipitation hardening stainless steel of the present invention contains C: 0.05% or less and Cr: 12.5 to 13.5% by weight. N
i: 7.5 to 8.6% Mo: 2 to 2.5%, Al:
It contains 0.75 to 1.3% and Mg: 0.01% or less, with the balance being Fe and unavoidable impurities. The present invention is based on ASTM standard A693XM-13.
Is based on the composition of the precipitation hardening type stainless steel, and Mg is added thereto to improve the toughness. The reasons for limiting the range of components will be described below. C: 0.05% or less In the steel of the present invention, when the C content exceeds 0.05%, aging treatment causes excessive precipitation of carbides at the crystal grain boundaries,
Since the toughness and corrosion resistance deteriorate, the upper limit of the C content is limited to 0.05%. Cr: 12.5 to 13.5% Cr is a basic component in the steel of the present invention, and must be contained in an amount of 12.5% or more in order to obtain sufficient corrosion resistance. Further, in order to suppress crystallization of δ-ferrite and prevent embrittlement, it is necessary to suppress the Cr content to 13.5% or less. Ni: 7.5 to 8.6% Ni must be contained in an amount of 7.5% or more in order to maintain corrosion resistance and further improve toughness. Further, the upper limit of the Ni content is set to 8.6% in order to suppress the reduction of the martensite transformation point and the generation of retained austenite. Mo: 2 to 2.5% Mo must be contained in an amount of 2% or more to secure a desired strength. On the other hand, in order to prevent a decrease in toughness, the upper limit of the content is limited to 2.5%. Al: 0.75 to 1.3% Al has an effect of making austenite crystal grains finer, and also contributes to an increase in strength by forming an Al precipitate by aging treatment. If the Al content is less than 0.75%, both of these effects cannot be sufficiently exhibited. Further, when the content exceeds 1.3%, δ-ferrite is crystallized and the toughness is reduced, so the content is limited to the above range. Mg: 0.01% or less Mg has a function of improving toughness by containing a trace amount of Mg. However, if Mg is contained more than 0.01%, segregation is caused and the toughness is rather lowered. .01
%. Examples of the present invention will be described below in comparison with comparative examples. As shown in Table 1, the steel of the present invention containing Mg (sample Nos. 1 to 5) and the comparative steel not containing Mg (sample N
o. 6, 7) were melted in a vacuum melting furnace,
g of steel ingot was melted. The obtained steel ingot was subjected to heat treatment of quenching, deep cooling treatment and aging treatment after forging and drawing to obtain a test material. A tensile test and a Charpy impact test were performed on this test material, and the results shown in Table 2 were obtained. As is clear from Table 2, Mg
The steel of the present invention to which is added, the strength level is almost the same as that of the comparative steel without Mg, but the notch toughness (Charpy absorbed energy) is superior to that of the comparative steel. [Table 1] [Table 2] As described above, according to the precipitation hardening stainless steel of the present invention, the toughness can be improved without impairing the strength conventionally obtained as the precipitation hardening stainless steel. .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-125490 (JP, A) JP-A-60-155563 (JP, A) JP-A-4-268040 (JP, A) 11896 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (1)

(57) [Claims 1] C: 0.05% or less by weight%, Cr: 1
2.5 to 13.5%, Ni: 7.5 to 8.6%, Mo:
2 to 2.5%, Al: 0.75 to 1.3%, Mg: 0.2%
Precipitation-hardening stainless steel containing up to 01%, with the balance being Fe and unavoidable impurities