Effects of plastic strain on grain growth in the heat affected zone in austenitic stainless steel

Abstract

This paper describes application of an FEM thermal elastic-plastic analysis to investigate effects of plastic strain in the heat affected zone (HAZ) of austenitic stainless steel. The relationship between the amount of grain growth and the development of plastic strain is also examined. The results obtained may be summarised as follows: 1. The amount of plastic strain introduced into the HAZ grains is mostly applied up to around 0.9 mm ahead of the solidification onset point during the heating process, with little plastic strain being added beyond around 0.9 mm ahead of the solidification onset point. This feature corresponds well with the temperature gradient near the weldpool. The amount of plastic strain to which the HAZ grains are susceptible during the welding heating process increases with increasing specimen width. At a specimen width of more than 84 mm, however, the amount of plastic strain is virtually constant. This is due to the fact that the thermal expansion strain near the weldpool is replaced by plastic strain near the weldpool without causing any elastic deformation of the specimen. 2. When the amount of grain growth in the welding HAZ varies depending on the magnitude of restraint, the amount of this grain growth is affected by the amount of integrated equivalent plastic strain to which the grains are susceptible below the recrystallisation temperature during the heating process. That is to say, the relationship between the amount of integrated equivalent plastic strain and grain growth in the HAZ below the recrystallisation temperature is such as to add plastic strain at normal temperature and is equal to the relationship between the amount of plastic strain and the amount of grain growth when the simulated thermal cycle is applied. This is due to the fact that the welding HAZ grains preserve their dislocation structure below the softening temperature to give essentially the same recrystallisation effect in the welding HAZ in the case of the strain being either dynamically or statically applied during welding.