Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Patent
1985-10-03
1987-08-25
Andrews, Melvyn J.
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
420 53, 420 55, 420 57, 420 59, 420 66, 420 69, 148325, 148327, C22C 3844
Patent
active
046891986
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
This invention relates to austenitic stainless steel with high corrosion resistance in oxidative enviroments along with strength of high level, and a method for producing such a stainless steel.
STATE OF THE ART
The concerns over exhaustion of petroleum resources form the background of recent efforts for expansion and stabilization of energy resources, including efforts on the sea for the development of underwater oil fields and efforts on the ground in boring the so-called sour gases and sour oil which have thus far been neglected due to the contents of oxidative gases such as hydrogen sulfide and carbon dioxide. Naturally, the materials and equipments related to the production such energy sources are unavoidably brought into contact with chlorides and oxidative gases, and the steel materials to be useed in this field are required to have corrosion resistance first of all and to meet severer conditions in strength as the wells become deeper. In addition, they are required to have toughness at low temperature for use in cold regions.
As materials which can meet these requirements, there have been known various alloys such as Ni-base alloys, Ti-base alloys and Co-base alloys, which are however very costly as compared with ordinary low alloy steels. In contrast, austenitic stainless steels, for example, have been known as a relatively inexpensive material, but they are inferior in corrosion resistance-strength balance as well as in chloride corrosion resistance.
On the other hand, martensitic stainless steels which are almost satisfactory in strength have a drawback that they are extremely low in resistance to sulfide stress corrosion cracking.
The methods generally resorted to for the improvement of yield strength of austenitic stainless steels include, in addition to solid solution strengthening with C and N, precipitation hardening and work hardening. The precipitation hardening and work hardening impose adverse effects on corrosion resistance, while a larger C-content deteriorates the corrosion resistance of the steel by producing Cr carbides and a larger N-content gives rise to defects in the ingot-making stage.
DISCLOSURE OF THE INVENTION
Under these circumstances, the present invention has as its object the provision of an austenitic stainless steel with improved corrosion resistance and high strength, more particularly, an austenitic stainless steel which shows excellent corrosion resistance and high strength even in an enviroment containing chlorides and sulfides and which is improved also in machinability such as elongation and drawability.
It is another object of the present invention to provide a method for producing an austenitic steel which has improved corrosion resistance and strength as mentioned above.
In order to achieve the foregoing objectives, the present inventors conducted an intensive study and as a result found that both the yield strength and corrosion resistance of austenitic steel can be improved by delimiting the C and N contents of the steel to prevent degradations in corrosion resistance and defects of steel ingots in the casting stage, and suppressing production of Cr carbides by incorporating V in coexistence with Cr and Ni, while dispersing precipitation of carbides or nitrides of V for improvement of the yield strength. Further, the machinability such as elongation and drawability of the steel can be improved markedly by subjecting same to a heat treatment under predetermined conditions.
Namely, the austenitic stainless steel with high corrosion resistance and strength according to the invention contains by weight percentage:
According to the present invention, there is also provided a method for producing the above-mentioned austenitic stainless steel with high corrosion resistance and strength, the method comprising: subjecting an austenitic stainless steel of the above-defined composition to a solution treatment at a temperature of 1030.degree.-1100.degree. C., immediately followed by a tempering treatment at a temperature of 250.degree.-500.degr
REFERENCES:
patent: 3592634 (1971-07-01), Denhard et al.
patent: 4486231 (1984-12-01), Fujiwara et al.
Fujiwara Kazuo
Inoue Tsuyoshi
Kitahata Koujiro
Torii Yasushi
Yokoyama, deceased Tadamasa
Andrews Melvyn J.
Kabushiki Kaisha Kobe Seiko Sho
Yee Deborah
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