Abstract: A phenomenon is present in the industrial applications that the surface with lowerhardness shows a better wear-resistance than the surface with higher hardness. In order to clarify itsmechanism,the surface strengthening effect of a substrate with lower hardness in wear process wasinvestigated by using the fixed and free abrasives separately. Under the given test condition,boththe fixed and free abrasives can form an abrasive/iron composite mate rial layer on the surface ofspecimens,in consequence,their hardness and wear-resistance can be increased and their servicelife can be lengthened. The bigger the fixed a brasives,the casier the formation of this compositematerial layer. The effect of in creasing weight is m ore obvious for the free abrasives,and thethickness of the composite lay er is al so larger.The formation mechanism of composite layer ismainly due to the embedmen t and crack of abrasives and mixing with the iron substrate in thedeformation process induced by other big a brasives.The analvsis by EDX found that the ratios ofabrasives to iron in the composite layers are 2:1 regardless the abrasives are fixed or free,becausethe composite layer will peel off due to the damage of continuity of iron substrate when this ratiowas surpassed.Therefore,this surface strengthening measure by forming a composite material layercan be employed in practice very e conomically for lengthening the service life of machinecomponents in the condition of not too severe abrasive wear.