C+n austenitic stainless steel having high strength and excellent corrosion resistance, and fabrication method thereof

Abstract

A C+N austenitic stainless steel with high mechanical strength and excellent corrosion resistance and a fabrication method thereof are provided. The C+N austenitic stainless steel consists of: 8 to 12 wt. % manganese; 15 to 20 wt. % chromium; 2 wt. % or less nickel; 4 wt. % or less tungsten; 2 wt. % or less molybdenum; 0.6 to 1.0 wt. % of total C+N content; a balance of iron; and unavoidable impurities. The austenitic stainless steel fabricated provides mechanical properties of a tensile strength of 850 MPa or higher and an uniform elongation of 45% or higher, obtained through controlling the contents of the interstitial elements and those of the substitutional elements. The alloy also provides corrosion resistance and a biocompatibility due to the minimized content of nickel which causes allergic reaction to the human body. Therefore, the C+N austenitic stainless steel is applicable in the fabrication of a variety of functional components and structural fields.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a C+N austenitic stainless steel having high mechanical strength and excellent corrosion resistance, and a fabrication method thereof.[0003]2. Description of the Related Art[0004]Generally, unlike carbon steels whose mechanical properties such as strength and ductility can be improved through thermo-mechanical treatments or phase transformation by various heat treatments, it is difficult to improve the mechanical properties of austenitic stainless steels using the heat treatment methods. Thus, the austenitic stainless steels mainly depend on the addition of alloying elements for the improvement of most properties.[0005]Therefore, the most important technical subject in the development of new alloy is to ensure optimum properties including strength, ductility or corrosion resistance, with low fabrication costs by minimizing a content of a high priced alloying element or by replacing it wi...

AI Technical Summary

Benefits of technology

[0015]An aspect of the present invention is to resolve the problems mentioned above, and accordingly, it is an object of the present invention to provide a C+N austenitic stainless steel which has increased strength and excellent corrosion resistance through controlling the contents of the interstitial elements (C+N, C / N) and those of the substitutional elements (Mn+Cr, Mn / Cr, or 0.5W+Mo).

[0017]In one embodiment, a C+N austenitic stainless steel is provided, to which carbon (C) and nitrogen (N) as interstitial elements are added simultaneously, so that the content of nickel (Ni) is minimized, which is high-priced alloying element, and harmful to an environment and a human health. As a result, the developed austenitic stainless steel provides improved economic efficiency.

[0018]With the fabrication method according to one embodiment of the present invention, it is possible to fabricate an alloy with economic manufacturing cost, and hence the price competitiveness of the alloy can be increased. Furthermore, the austenitic stainless steel according to one embodiment provides favorable mechanical properties of a tensile strength higher than 850 MPa and an uniform elongation more than 45%, which are obtained through controlling the contents of the interstitial elements (C+N, C / N) and those of the substitutional elements (Mn+Cr, Mn / Cr, or 0.5W+Mo). In addition, the invented alloy also provides an excellent corrosion resistance and a biocompatibility due to the highly alloyed nitrogen (N) and minimized content of nickel (Ni) which causes allergic reaction to the human body. Therefore, the austenitic stainless steel according to the present invention is efficiently applicable in the fabrication of a variety of functional components including medical biosubstances, watches and accessories, as well as the fields of the conventional structural austenitic stainless steel and offshore structures, desalination plants, materials for oil and gas installing / mining, and materials for transportation facilities, which require high level of strength and corrosion resistance.

Problems solved by technology

Generally, unlike carbon steels whose mechanical properties such as strength and ductility can be improved through thermo-mechanical treatments or phase transformation by various heat treatments, it is difficult to improve the mechanical properties of austenitic stainless steels using the heat treatment methods.

In addition to the economical point of view, nickel (Ni) also gives adverse effects to human health and environment since nickel (Ni) can cause allergic reaction to human skin and give off toxic gas during recycling.

So far, the high-nitrogen stainless steel has not been commercialized due to the difficulty in the fabrication process to ensure high nitrogen (N) content in the steel.

However, the major obstacle to the commercialization of the high-nitrogen stainless steel is the requirement for a special fabrication processing facilities such as pressurized induction melting furnace or PESR, which requires expensive equipments and complicated processing steps.

Thus, a modification of conventional melting equipment or an incorporation of new equipments for the pressurizing process are inevitable to fabricate the high-nitrogen stainless steels employing the pressurized melting facility, therefore, the high-nitrogen stainless steel has not been commercialized yet.

However, the invention disclosed by H. Berns et al. contains a relatively high manganese (Mn) content, which subsequently degrades corrosion resistance.

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