The Contrast-study Of Crack Resistance Between Two Kinds Of Die Hardfacing Materials

Since dies usually work in extremely rigor working conditions, hardfacing can be used to repair or manufacture them in order to prolong their working-time. It is widely reported that the crack resistance (CR) of die hardfacing materials is vital to the working-time of dies, which will fail earlier with bad crack resistance.525 and 136 are two congener die surfacing materials used in the industry, the CR of which are different. In order to study the reason why CR of 136 is worse than that for 525, the comparison of crack sensitivity between 525 and 136 were taken out with rigid restraint crack resistance test, the morphology of crack fracture surface was observed. Also the cause of crack formation was analyzed and substantiated with the experiments of re-heating and quenching. The toughness and its effect on CR have also been studied for 525 and 136, with the efforts of testing toughness, tensile strength and hardness, analyzing metallurgical structure, the microstructure and components for inclusions and observing morphology for impact and tensile fracture surface. Finally, based on a comprehensive understanding of the reason for the difference of CRC between 525 and 136, several methods to improve CR for 136 were pointed out.The results show that the welding crack sensitivity of 136 is much higher than 525. This is probably due to the existence of low melting-point composite oxide impurities, formed during the process of welding among free-tree crystals, since the hardfacing material is highly oxidative when incorporated with slag system containing overdue acidic oxides. The grain size of 136 is larger than that of 525, which may debase the strength and CR of deposit metal. The asymmetrical distribution of some large-size and fragile inclusions in the deposit metal of 136 were observed, which may reduce the impact toughness and CR of 136. The crack sensitivity of 136 may be reduced and its CR may be improved by changing slag system prescription---increasing the composition ratio of alkaline oxides to acidic oxides and adding moderate grain refinement elements.