Machinability, Weldability of Duplex Stainless Steels

Authors

  • Ch. Lakshmi Poornima, Dr. Ch. Srinivasa Rao

Abstract

One of the most essential and fast growing materials in engineering world is stainless steel. The stainless steels family belongs to duplex alloys. Over the last 70 years, many researchers have examined the duplex stainless steel covering ferrites /austenitic fe- Cr-Ni alloy with 30% to 70% ferrite austenitic-ferrite stainless steels generally called as Duplex Stainless Steels (DSS). The DSS contains two primary phases that are austenite A and ferrite F and these are presented in equal amounts (but each phase should not less than 30%). In ferrite phase, the DSS will be completely solidified to standard cooling rates and standard grades. These two steps have their corrosion resistance to higher chromium (Cr) contents. In chloride-containing environments high level of Ni, Cr, and Mo steels will exhibits higher pitting and stress corrosion cracking resistance. Generally modern duplex stainless steels have a good understanding of weld ability and DSS is considered as poor machinable material due to its alloy composition, nitrogen content and high austenite. Several investigators have proved the DSS machining capabilities by non-conventional and conventional processes. This present research is intended for duplex stainless steel tool wear mechanism and machining behavior. In addition findings of few researches are presented with respect to the balanced composition in which nitrogen plays a vital role, austenite formation is done in HAZ (Heat- Affected Zone) and welding metal will be rapid. Acceptable amount of austenite is build under general welding conditions for maintaining good resistance to localize the corrosion. Further, the effect of cooling rate on the formation of ferrites is discussed. Too fast cooling will result additional amount of ferrite and toughness will be reduced. Different types of welding techniques are electron beam welding, laser welding and resistance welding. Electron beam welding causes highly fast cooling and utilized with extreme location or avoided. Too slow cooling will lead to inter-metallic phases formation, toughness and detrimental to corrosion resistance.

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Published

2022-03-19