Study of precipitation hardening of welded joint heat affected zones in the 15Kh2MFA and 15Kh2NMFA steels

The time behavior of hardening of simulated heat affected zones was studied for the 15Kh2MFA and 15Kh2NMFA steels at 500, 580, 650 and 720 degC. The time corresponding to the hardness maximum in the HV 10 = f(t) dependences at 650 degC annealing temperature was found shorter than the time in which incoherent particles of the carbide MC appeared in the steel structure. This fact is consistent with the precipitation hardening concept. The kinetics of the MC carbide precipitation is dependent on the chemical composition of the steel. Carbides of the M3C, M7C3 and MC types appear in the simulated heat affected zone during the annealing at 650 degC, and their chemical composition depends on the dwell time at the annealing temperature. At temperatures higher than 580 degC, precipitation hardening takes place in the two steels in very short dwell times (shorter than 1 hour). (P.A.). 4 figs., 2 tabs., 9 refs