Creep resistant steels encompass the chromium steels (containing 1-13%Cr, 0.5-1%Mo, plus other alloying elements) and, if the service temperature is high enough, austenitic stainless steels and Ni based alloys.
Chromium steels are susceptible to the cracking mechanisms listed -
- Hydrogen cracking not only in the heat affected zone HAZ but also (with increasing weld metal strength) in the weld metal.
- Reheat cracking (in either the HAZ or weld metal) during subsequent postweld heat treatment.
- Liquation cracking.
- Temper embrittlement during subsequent postweld heat treatment (of some Cr-Mo steels).
With knowledge of the factors that control these cracking mechanisms, it is possible for weld procedures to be developed for these steels to avoid crack formation during fabrication. Please see Fabrication cracking mechanisms in ferritic steels(a TWI best practice guide) for more information.
For austenitic stainless steels and Ni based alloys, fabrication cracking concerns largely centre on solidification cracking and liquation cracking, and can be minimised as described in "What is hot cracking?".
Sorry, but the next two items are only available to TWI Industrial Member companies: Welding and fabrication of high temperature components for advanced power plant; Part 1and Part 2.