Microstructural modification due to reheating in multipass manual metal arc welds of 9Cr–1Mo steel

The present paper describes the modification of the primary solidification structure of the weld region of a 9Cr–1Mo steel weldment, due to reheating during multipass welding. The ‘primary’ microstructure is represented by that region of the weld, solidified from the liquid state. In a multipass weld, this microstructure is considerably modified as further layers are deposited on the top and on either side of a pass. The secondary or reheated structure as it is called is sensitive to the welding process parameters and to the physical metallurgical behaviour of the steel. The microstructural evolution depends on the thermal cycle experienced by the weld section due to the two types of deposits, namely one layer over another and passes laid side by side. The observed microstructural variations were correlated to hardness and X-ray FWHM measurements. Thus, the paper presents a study of all the microstructural changes that take place in weld region during multipass welding.