TWI Industrial Member Report Summary 590/1997
Heat input limits are imposed for the welding of large steel structures since use of high arc energies results in slower cooling rates, which may adversely affect both weld metal and heat affected zone (HAZ) properties. In the HAZ, the deterioration in mechanical properties, in particular toughness, arises partly from increased grain coarsening.
A review of previous work carried out on the effect of Ti-containing particles on the HAZ microstructure and toughness properties of steels has been carried out. In addition, a series of bead-in-groove test welds using arc energies in the range 1-9 kJ/mm, have been carried out on steels supplied by several steelmakers as being suitable for high heat input welding in order to investigate the effect of heat input on the HAZ grain size and microstructure. Transmission electron microscopy was used to characterise the second phase particles in the parent steels and in the HAZs in order to identify their role with respect to HAZ grain coarsening and microstructure. HAZ toughness testing was carried out using 9 kJ/mm heat input multipass butt welds made from the steels showing the most promising HAZ characteristics, in terms of both grain coarsening behaviour and microstructural development.
- To identify which particles are effective in restricting grain growth and nucleating ferrite, and to identify which characteristics of the particles control their effectiveness.