TWI Industrial Member Report Summary 937/2009
L S Smith and J Nicholas
The performance of steel weldments often depends upon the characteristics of the heat affected zone (HAZ) and, in particular, the grain-coarsened HAZ (GCHAZ). This zone of the weldment poses significant challenges for modelling, since thermal cycle and grain growth must be successfully predicted before phase transformation modelling during cooling can be attempted.
A collaborative ECSC programme, partnered with Corus, CEIT, Arcelor and CSM, covered five main themes aimed at modelling GCHAZ microstructure and performance in plain and microalloyed C-Mn steel power beam and single and multipass arc weldments:
- Prediction of thermal profiles, led by CSM.
- GCHAZ single pass microstructure prediction, led by Corus.
- Prediction of martensite-austenite (MA) constituent in multipass welds, led by Arcelor.
- Effect of postweld heat treatment (PWHT), led by TWI.
- Prediction of toughness, hardness and strength, led by CEIT.
- Drawing together of the disparate models into one single integrated piece of computer software (HAZMET), led by TWI.
The present report covers the modelling of precipitates and grain growth. The prediction of hardness in the as-welded condition and after PWHT and the generation of electron beam (EB) welded coupons have been reported previously[i], as has the compilation of the HAZMET software. [ii]
Any models must be used with care, with the knowledge of the assumptions made in the model and the limitations of validation kept in mind.
- Predict precipitate development and prior austenite grain size during a weld thermal cycle.
- Predict precipitate nucleation and growth during PWHT.