Some European Developments in Welding Consumables

This paper represents a selected survey of incisive research on novel welding consumables which contribute to the structural integrity of advanced engineering structures. It is evident that there are tremendous advances to be made by applying the most sophisticated instrumentation available to Materials Science, together with theory and insight based on metallurgical experience. We congratulate the Japan Welding Society for organising this special issue of their journal. 1 High Strength Steel Weld Metals The increasing use of steels with a strength in excess of 700 MPa has led to a demand for stronger welding consumables. In contrast to production of wrought steel, the strength and toughness of weld metals must generally be achieved by means of alloying. Whereas there are many ways of increasing the strength, doing so while maintaining good toughness has proven to be more challenging. And the properties achieved must also be robust in the sense that they should not be sensitive to practical variations in the welding parameters. Other risks become more prominent at high strengths, for example, fatigue resistance and hydrogen embrittlement. The traditional argument is that the concentration of solutes added to ferritic weld metals must be kept to a minimum in order to avoid martensite and avoid the risk of brittle fracture. Weld metal yield strengths therefore usually lie in the range 350–550 MPa, with occasional higher values achieved at the expense of toughness. The microstructure of such weld metals consists of mixtures of allotriomorphic ferrite (α), Widmanstätten ferrite (αw), acicular ferrite (αa) and the so–called microphases (small quantities of retained austenite and martensite) [1, 2]. Allotriomorphic ferrite is weak, and Widmanstätten ferrite suffers from poor toughness. This leaves acicular ferrite as a good strengthener with its ability to deflect cracks. However, welds containing mostly acicular ferrite still do not meet the requirements of the strongest of structural steels, as illustrated in Fig. 1 [3].