TWI Industrial Member Report Sumamry 756/2002
L S Smith
The mechanical performance of C-Mn and low alloy steel weldments is often controlled by the microstructure developed in the heat-affected zone (HAZ) of the parent metal. In particular, it is commonly the grain-coarsened region of the HAZ (GCHAZ) that exhibits the greatest hardness and lowest toughness.
It is desirable to design steels that produce favourable GCHAZ microstructures and develop welding procedures that maintain a balance between, say, productivity and toughness. A great deal of empirical knowledge is applied to the design of C-Mn and low alloy steels, but much effort is still expended on developing welding procedures by trial and error to achieve toughness levels that are within specification for a given application. Modelling of weld and CGHAZ microstructure marks a first important step to achieving the ultimate goal of predicting mechanical performance from a fundamental approach.
Computer modelling is finding increasing application in the prediction of microstructure, utilising established kinetic and thermodynamic theory. Previous work has demonstrated the applicability of such an approach for the prediction of weld metal microstructure in C-Mn steels. A similar approach applied to the prediction of heat affected zone (HAZ), and particularly grain coarsened HAZ (GCHAZ), microstructure is required to complement the work performed on weld metals and provide a more complete tool to steel producers and fabricators.
To develop and establish the validity of a computer model capable of simulating the thermal cycle, precipitate coarsening and dissolution, grain growth and phase transformations in the GCHAZ of C-Mn and microalloyed C-Mn steels.