Abstract: Analyzed in the paper are the causes for the raised surface scar of the semi-trailer axel as heat treated,and accordingly improvement measures are prepared.It is identified via the analysis that the said raised scar has clear boundary;the microstructure in the scar area is dense,and contains abnormal foreign elements like Cr,P,and Ca,etc.,of which all sources can be traced in the graphite lubricant that therefore is regarded as the main cause for the raised scar defect of the said semi-trailer axel.Following the mechanism as above revealed,it is suggested to use the graphite lubricant that contains rather low contents of phosphate and silicate,and to keep cleanness of the lubricant.