TWI Industrial Member Report Summary 690/1999
Solidification cracking in modified 9Cr1Mo weld metals has resulted in delays to fabrication projects and the need for repair. The cracking has principally occurred in low dilution submerged arc weld metal, although cracking in manual metal arc and tungsten inert gas welds has also been observed.
There are clear economic penalties associated with this cracking, and there is also the potential for buried solidification cracks to act subsequently as sites for hydrogen cracking as the joint cools to ambient temperature. It is important that further understanding be gained of the influential factors, to allow consumables and weld procedures to be formulated to minimise the cracking risk.
A programme of transvarestraint testing was carried out to assess the effect of variations in composition and welding parameters on the solidification cracking susceptibility of Ni-free modified 9Cr1Mo weld metals. Variations in Nb and Mn were studied; niobium was selected as it has received much attention due to its powerful but opposing effects on toughness and creep strength, and because earlier work at TWI had revealed a light-etching phase associated with the cracking and indicated that this may be Nb-rich. Manganese is one element generally considered to have a beneficial effect on the cracking susceptibility of both ferritic and austenitic steels; thus, its effect on the modified 9Cr1Mo system was investigated in the present study.
- To assess the effect of Mn and Nb and changes in welding parameters on the solidification cracking susceptibility of modified 9Cr1Mo weld metal.