Finite element simulation of butt welded 2·25Cr–1·6W steel pipe incorporating bainite phase transformation

Abstract

This article presents a newly developed global optimisation method for the finite element simulation of welding process considering bainite transformation. In this method, the pattern search algorithm was applied to determine kinetic parameters in Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation during a continuous cooling process. Meanwhile, the JMAK equation was modified into an explicit form as a function of welding temperature field to improve calculation efficiency in the optimisation process. This methodology improves the accuracy as calculating the temperature dependent volume fraction of bainite transformation in finite element simulation. The calculated welding residual stresses considering phase transformation effects exhibited better agreement with the measured results than those calculated without phase transformation. The influences of variable cooling rates on welding residual stresses were also investigated.

Effects of weld metal strength and transformation temperature on welding residual stress

“…Dilatometric specimens were heated to 1050uC at a rate of 100uC min 21 and held for 10 min to assure complete austenitising, 9 followed by continuous cooling to room temperature at a rate of 10uC s 21 , which is the cooling rate of butt welded plates in an actual welding process. 10,11…”

“…The stress versus strain curve was assumed to be expressed by linear kinematic hardening. 10 In this study, transformation induced plasticity was not taken into account. Ignoring this component, the strain increment can be then expressed by the following equation 10,15,16 1 Position of XRD measurement points 2?25Cr-1?6W 0?06 0?37 0?012 0?002 0?28 2?32 0?08 1?56 0?22 0?044 0?0035 ,0?015 0?0026 0?05 0?009 3?9 Chromet-23L 0?05 0?5 0?01 0?01 0?25 2?2 0?2 1?6 0?23 0?03 0?02 0?001 0?6 E8018-B2 0?04 0?8 0?015 0?012 0?3 1?25 0?55…”

“…Where De e , De p , De th and De DV represent the strain increment due to elastic, plastic, thermal loading and volumetric change respectively. The increment of volumetric strain at the ith increment during the austenite/bainite transformation process can be determined by the following equation 10…”

“…Therefore, the influence of austenitic transformation on stresses is relatively smaller than that of bainite transformation. A linear relation was assumed to estimate the increment of austenite volume fraction, as follows 10,12 Df…”

Part special issue on computer-aided welding engineering

“…The paper by Xu et al 1 presents a new developed global optimisation method for the finite element simulation of welding induced residual stress in multipass butt-welded 2?25Cr-1?6W steel pipes with considering bainite transformation. The pattern search algorithm was applied to determine the kinetics parameters in J-M-A-K equation which was further modified into an explicit form during a continuous cooling process to improve calculation efficiency.…”