Investigation of Causes for Abnormal Microstructure of N80-1 Casing and Relevant Corrective Measures

Described here are the morphological abnormal characteristics as observed at the end of the N80-1 casing.Also analyzed are the mechanical properties,the abnormal structural morphology and micro-hardness of the casing.Furthermore,the root cause for the said abnormal microstructure is investigated,and accordingly countermeasures are put forward.The analysis result reveals that it is the banded bainite structure that acts as the root cause for the morphological abnormality as observed at the end of N80-1 casing.Therefore under the present manufacturing process conditions,owing to reducing the C and Mn contents in the steel the abnormal bainite structure of the casing can be eliminated,and meanwhile the yield strength of the material can be controlled to the ideal level,and its impact toughness can be dramatically improved.