Abstract
We conducted a brief review of current production and application of duplex and super duplex steels for manufacture of equipment exposed to the hazard of sulphide stress-corrosion cracking, sea water and other corrosive environment. The super duplex steel with enhanced corrosion-mechanical characteristics in comparison with the known steels of austenitic-ferritic class was developed. Based on the concepts of formation of a special structure of two-phase austenitic-ferritic steels in the process of crystallization, the possibilities of compositional, technological, thermal and special impact techniques are considered and advanced ways of controlling physical, chemical, structural homogeneity and properties of super duplex steels are developed. Electroslag remelting with the application of low-frequency alternating current provides effective control over the length of the two-phase area, the size of the primary dendrites of the austenitic and ferritic phases, the average distance between their axes, the parameters of the crystallizing cell, the development of liquation phenomena and the size of the growing non-metallic phases. Within framework of the proposed approach, the thermodynamic and kinetic conditions for the formation and growth of hardening phases are assessed, a new composition and a complex technology for the manufacture of corrosion-resistant super duplex steels for gas and oil production equipment has been developed. Thermodynamically stable, having sizes of 30-300 nm, niobium nitrides and carbonitrides are located inside the grains of the ferritic phase. At the same time, the sigma phase and chromium carbide precipitates at the intergrain boundaries are not observed. The results of the determination of mechanical and corrosion properties in accordance with the NACE TM 0177 standard (method A), tests of corrosion witness-samples in field conditions demonstrate the advantages and prospects of using new super duplex steel for the manufacture of oil and gas production equipment operating in an environment with high H2S content and CO2 under significant mechanical loads, without the risk of brittle fracture.
Highlights
We conducted a brief review of current production and application of duplex and super duplex steels for manufacture of equipment exposed to the hazard of sulphide stress-corrosion cracking, sea water and other corrosive environment
The history of stainless nickel-chromium and nickelchromium-molybdenum steels of austenitic class goes back more than 100 years, to the moment, when steels V2A and V4A were patented by Krupp
Upgrade of super duplex stainless steel (SDSS) composition is aimed at elimination of the effect of weakening of grain boundaries with large chromium carbides formed due to high chromium content, replacing them with small niobium nitrides and carbonitrides, dispersion strengthening ferritic grains
Summary
The history of stainless nickel-chromium and nickelchromium-molybdenum steels of austenitic class goes back more than 100 years, to the moment, when steels V2A and V4A were patented by Krupp. High strength and increased resistance to chloride and sulphide stress corrosion cracking compared to traditional austenitic steels ensured the growing popularity of duplex steels. Forta LDX 2101 EN 1.4162,UNS S32101 1.4507(URANUS52N+) EN10088-2,2005 A182 Grade F55 These developments are aimed at enhancement of strength characteristics and corrosion resistance of steel. Along with the said upgrades of the duplex steel composition, there is a particular interest to steels not having a high PREN value, alloyed with less expensive elements, for example S32101. The developers of such modifications of duplex steel make a choice in favor of improved produce-ability of products. The reserves for increasing the physical, chemical, structural homogeneity of the SDSS are not exhausted and research in this area is still relevant
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