The Kinetic Behaviour Of Grain Growth In Weld Heat-Affected Zone

In this paper, the kinetic behaviour of grain growth in weld heat affected zone(HAZ) and the response of carbc-rdtride particles to weld thermal cycle have beenstudied.Theoretical kinetic models for grain growth, particles dissolution and particlescoarsening in weld HAZ are proposed. Based on these models and some data from simulated welds of four microalloyed steels, the diagram for austenite grain growth in weld HAZ for each steel is presented. Other data from the simulated welds were in good a-greee with the value the diagrams predicted. The work showed that the grain growth on heating is not sensitive to the change of heating rate.The behaviour of (Ti_xV_1-x) (C_yN_1-y)particle in steel when subjected to weld thermal cycles has been studied. Three types of response of this particle were observed:(a)dissolution lag, (b)very slow rate of coarsening and (c)dissolution followed by 1² type of reprecipitation on cooling.Observation by analytical electron microscopy showed that the (Ti_xV_1-x)(C_yN_1-y) particles may be act as a role to slow the growth of grain boundary nucleated ferrite side plate (FSP) or not depending on the growth direction of the FSP.The((TixVl-x)(C_yN_1-y) particles wraped by MnS promoted the intragranuclar ferrite plate (IFP) nucleation on cooling. A benefical effect of the IFP was that it can avoid the recovery of original austenite on reheating whether it was tempered or not.