Coiled springs made of 3Kh13 steel

Abstract

1. It has been experimentally ascertained that the hardening of 3Kh13 steel when tempered between 300 and 500°C is due to the decomposition of the alpha (martensite) and the precipitation of dispersed particles of iron carbide (Fe, Cr)3C in the form of fine plates less than 10−5 mm thick. The precipitation of chromium carbide (Cr, Fe)7C3 during tempering (from 470°C and higher) only supplements the process of dispersion-hardening and work-hardening of the steel. 2. The temper brittleness of 3Kh13 steel at 474–550°C is evidently due to precipitation of dispersed chromium carbides (Cr, Fe)7C3. 3. It has been established that the tempering temperature producing maximum relaxation resistance of this steel is a function of the relaxation test temperature. As the test temperature is raised from 300 to 350°C, the optimum tempering rises from 450 to 500°C. 4. The maximum relaxation resistance of 3K13 chromium steel for relative thermal stability of the solid solution and cementite (Fe, Cr)3C is a function of their structural state and is evidently determined by the large area of the interface between the alpha-phase and dispersed carbide particles which play the part of barriers and prevent the movement of dislocations. 5. The optimum heat treatment for cylindrical coiled compression springs made of 3Kh13 steel can be recommended: oil quenching from 1000–1050°C, tempering at 450°C for one hour, cooling in air, HRC 44–50. 6. 3Kh13 steel is recommended for cylindrical coiled compression springs working at temperatures up to 300°C.