An investigation on thermomechanical properties of heat affected zones of nickel free high nitrogen austenitic stainless steel

Abstract

Nickel-free High Nitrogen Austenitic Stainless Steel (NFHNSS) is a newlinenitrogen alloyed stainless steel used in defence, chemical, energy, oil and gas newlineand pressure vessel applications, due to its low cost along with high strength, newlineductility, toughness and corrosion resistance. Fusion welding is widely used for newlinewelding NFHNSS components. However, problems such as nitrogen desorption, newlinenitrogen-induced porosity, solidification cracking and liquation cracking are newlineencountered in welding of NFHNSS steel. To reduce the likelihood of such newlineissues, proper selection of welding parameters is necessary. It is important to use newlinesuitable filler wire to produce the required amount of delta ferrite in the weld newlinemetal, to reduce solidification cracking and porosity. Deterioration in newlinemechanical properties and the possibility of liquation cracking in Heat Affected newlineZone are other problems in welding of this steel. newlineIn this study, Heat-Affected Zone (HAZ) in NFHNSS plates was newlineinvestigated experimentally by welding with Shielded Metal Arc Welding newline(SMAW) process. The HAZ was divided into three zones based on grain size newlineand hardness values. Subsequently, the microstructural evolution and mechanical newlineproperties associated with each of the HAZs were studied by physically simulating newlinethe HAZ using a thermo-mechanical simulator (Gleeble 3500). Results showed a newlinesignificant decrease in mechanical properties due to grain coarsening as well as newlineprecipitation of Cr2N in the HAZ near the fusion boundary. Phase diagram and newlineprecipitation kinetics of Cr2N were simulated based on CALPHAD approach. newlineSecond phase of the investigation involved simulating different HAZ newlinespecimens by varying the peak temperatures and cooling rates. An increase in newlinepeak temperature led to recrystallization at lower peak temperatures, while grain newlinecoarsening was observed at higher peak temperatures. Cooling rate had similar newlineimpact on the HAZ properties during the weld thermal cycle. newline