Despite the occurrence of type IV cracking experienced in lower alloy predecessors, successor alloys have been introduced and widely used with insufficient consideration given to the consequences of welding them. This type of cracking occurs in the intercritical or fine grain region of the heated affected zone via a creep mechanism, and results in fractures with relatively little total cross-weld strain. The high temperature conditions that these steels operate under in fossil fuelled power stations induce type IV cracking. They are also finding use in high temperature process plant within the oil and gas sector, and are being considered for use in generation IV nuclear designs. Good progress has been made in developing such steels, which are being used particularly in the wrought form as tubes and pipes for fossil fuelled power stations. The improvement of thermal efficiency of power plants has provided the incentive for the development of the martensitic–ferritic 9–12%Cr creep-resistant steels. Review of Type IV Cracking of Weldments in 9-12%Cr Creep Strength Enhanced Ferritic Steels
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