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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. 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. 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. The high temperature conditions that these steels operate under in fossil fuelled power stations induce type IV cracking. 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. 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. Unfortunately, the newer steels suffer from reduced cross-weld creep strength due to type IV cracking to a greater degree in the temperature range of operation expected of them, and thus many failures by this mechanism have occurred. The subject of type IV cracking has been an area of active research interest. This review aims to serve as an update, drawing selectively on some of the vast amount of literature that has been published over the last 30 years.
Abson et al. (Wed,) studied this question.