Papers by Keyword: Low Ni

Abstract: A new low Ni maraging steel, based on 18Ni (300) type has been developed. The optimized chemical composition (complex alloyed with Al-Si-Ti or Si-Zr-Nb) in accordance with optimum heat treatment was found (solution: 970 °C/1h/air and ageing: 550 °C/3h/air), in order to obtain maximum service temperature of over 600 0C and ensured the good combination of strength and toughness properties. The precipitates, such as Ni3(Mo, Ti), were well controlled in lath martensite (R_m=2090N/mm2 and Rp_0,2=1930N/mm²)and the presence of Si, Zr and Nb enhance structure stability at high temperature (for example the ultimate tensile strength at 5500C is about 1440N/mm²). Therefore, this new type of maraging steel was the subject of a national patent: “Maraging steel for high temperature service and heat treatment technology” – PATENT No.120356/30.08.2010.

Abstract: The continuous improvement of the applications of duplex stainless steels (DSS) is justified mainly by their excellent corrosion resistance in very aggressive environments and by their mechanical strength, often twice than that of conventional austenitic grades. Therefore more extensive applications have been suggested, like constructions, structural components, automotive applications, etc. However for such not advanced but quantitatively important applications the base cost of the alloy is one of the more constraining features. A way to obtain leaner alloys is to reduce the Ni content and to compensate with manganese and nitrogen additions. In the present paper the structural and mechanical properties of two low Ni duplex grades are analyzed in order to investigate the structural stability of the austenite against its possible transformation to martensite and the secondary phase’s precipitation. The detailed characterization has been performed with SEM-EDS on as received and heat treated (600-850 °C) alloys. A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades. The martensite formation has been revealed only in the 2101 grade. With regard to the impact toughness the behaviour of 2101 grade is quite similar to that of the common DSS, while in the 2304 the drastic drop of toughness is avoided. The corrosion behaviour of both grades in aggressive chloride environments is quite similar to that of austenitic AISI 304 grade.