Browsing by Author "Squires, IF"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    HAZ cold cracking - a restrained view
    (Welding Technology Institute of Australia, 1994) Squires, IF; Feng, B; Mercer, D; Payten, WM; Dunne, D; Alam, N
    Heat affected zone (HAZ) hydrogen cracking occurs after the weld has cooled to ambient temperature when the HAZ has transformed and hydrogen has had time to diffuse into it from the weld metal. It is therefore referred to as “cold cracking”. For cracking to occur, a stress needs to be present This will arise inevitably from the local heating and cooling when making the weld, however, the magnitude of the stress will depend on the restraint applied to the weld, the welding conditions used and the geometry of the weld. Recommendations to assist with the avoidance of HAZ cold cracking are available in publications such as WTIA Technical Note 1 “Weldability of Steels” but these cover essentially only the control of the thermal cycle and hydrogen level. The more complex issue of restraint is not included. Consequently the recommendations tend to be either over conservative, hence not fully cost effective, or present unquantied risks. Research work by various authors in this area has been summarised by Suzuki(l) and a basic model produced. The work covered a variety of methodologies and these could not be considered consistent. The present study provides a consistent approach, based on the use of the rigid restraint cracking (RRC) test which allows direct measurement of weld stress. To enable the effect of local stresses to be understood and general models of restraint effects to be developed a finite element analysis (FEA) computer model is being developed in parallel with work on the RRC test Further inputs to the modelling process are being or will be generated from localised studies of mechanical properties in the weld and heat affected zone and from dilatometric studies of the weld. The former will allow more accurate assessment of the behaviour of local stress concentrators in the weld and HAZ. The latter will assist in quantifying the weld metal and HAZ contribution to stress generation.