A multi-phase constitutive model has been established that accounts for phase dependent thermomechanical properties related to elasticity, thermal expansion, and metallurgical strains. Also transformation plasticity and phase dependent flow stresses during viscoplastic deformation, including strain hardening and strain rate sensitivity, are taken into account.

• Phase transformations are taken into account using both physical and phenomenological approaches based on CCT or TTT diagram information. Different CCT diagrams can be employed in the case of dissimilar base and weld metals.
• Thermal and mechanical properties are defined as weighted averages of properties of the present phases.
• For ferritic steels, a methodology for establishing the CCT diagram has been developed. It is based on dilatometry techniques and has been applied to the high strength pipeline steel X70.
• The Satoh test is used as a welding simulator to assess the effect of phase transformations on welding stresses and for model verification.
• A new method has been established by which the temperature and microstructural dependency of the flow stress in welding stress simulation tools such as WeldsimS can be relatively easily determined. The method is based on Satoh testing and on using an ideal plasticity law for the flow stress. It requires prior knowledge to the relevant CCT diagram.

Modelled final microstructure distribution in
the weld, assuming a martensitic weld metal.

Typical multi-cycle Satoh test result.

Modelled final austenite distribution and grain size in a cross section of a 3 pass welding of two duplex stainless steel plates using a physical model for phase transformations.