INFLUENCE OF HEAT TREATMENT ON THE IMPACT STRENGTH OF MATERIALS PRODUCED VIA METAL INJECTION MOLDING

Abstract

It is established that hardening on the sorbitol structure of tempered sintered steel AISI8740 with cooling in nitrate and tempering at 550 ° C allows to combine significant hardness with relatively high as for porous steel, impact strength (KCV 7.75 J/cm²). For “Catamold8740”, chemical inhomogeneity was found after sintering and heat treatment due to the uneven distribution of alloying powders in the initial mixture. Areas with high nickel content stabilize austenite during steel cooling, thereby leading to phase inhomogeneity. The austenite phase is relatively plastic, but has lower tensile strength, which can adversely affect the mechanical properties of the sintered material. The highest impact strengths of the material (KCV 17 J/cm²) were obtained for the samples after complete annealing, due to the approach of the structure to the equilibrium perlite-ferrite state. Subsequent hardening with tempering can significantly increase the tensile strength, but leads to a significant reduction in the toughness of the material. It was also found that double heat treatment of Catamold8740 material in the temperature range 850 ÷ 600 °С increases the impact strength of the material from 11.7 to 12.7 J/cm², but a further increase in the number of cycles does not significantly affect this parameter.