The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in weldments. Welding distortion and residual stress in welded structures can result in problems such as dimensional inaccuracies during assembly and raise concerns regarding safety during service. Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment. In the present paper a new method of analysis is proposed to predict welding residual stress by considering solid phase transformations during the welding process. This method is applied to two cases, involving medium carbon steel and low carbon steel respectively. The analysis of medium carbon steel revealed the presence of compressive residual stress due to martensite formation when phase transformation was considered. However, in low carbon steel the residual stress obtained considering the effect of phase transformation did not differ significantly from that obtained when phase transformation was ignored.
Using hot torsion tests, the in¯uence of Mn on the recrystallisation behaviour of a Nb microalloyed steel was studied. Continuous and interrupted torsion tests were performed in the temperature range 950 ± 1050°C at strain rates of 0 . 05 ± 5 s 1 . The kinetics of static and metadynamic recrystallisation (MRX) were characterised and appropriate expressions were formulated for the effect of Mn and of the other deformation parameters on the kinetics. The rate of MRX increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallisation (SRX). The strain rate dependence of MRX is about twice that of SRX, whereas the activation energy Q MRX is about Q SRX /2. Thus, results obtained under laboratory conditions must be corrected before application to industrial strain rates. When extrapolated to the much higher mill strain rates (4100 s 1 ), the present results indicate that SRX is much slower than MRX and is also unlikely to produce much softening in the 1 s interpass times available in such mills.MST/5033
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