The prediction of HAZ microstructures and properties in structural steel

The overall aim of this project has been to derive quantitative thermodynamic and kinetic algorithms and use them to develop personal computer based programs that can predict microstructural development as a series of contours around welds. The work has covered both single- and multi-pass conventional arc and high energy density welding processes. The work on single-pass welds has been based on the prediction of the metallurgical structure of the HAZ from the chemical composition and relevant welding process. This validated program, called HAZMET, provides for both the expert and non-expert user by altering the number of variables the user can employ and decisions that have to be made. It can provide a property prediction, explore the effects of different welding processes and weld geometries and the influence of PWHT on the final results. The results of the microstructural predictions have been extensively validated against a wide range of real welds and an improved microstructure characterisation procedure has been developed within the project to permit this. The model for multi-pass welds has been developed from an existing model which is based on the prediction of the location of Martensite-Austensite zones within the HAZ. The software has been re-developed and it can now be used for parametric studies or joint simulations. It represents a first step in the prediction of the properties and mechanical behaviour of multi-pass welds. The software (MULTIPASSE3) has been validated by comparison with a real welded joint and the hardness values and amount of MA obtained on an E450 TMCP steel were satisfactory. The software links the local brittle zone locations and associated high hardness values to low toughness. The code can be readily improved as understanding increases.