300 Ksi Maraging Steel Microstructure And Properties Research

Maraging steel has excellent mechanical properties, and it is widely used in the aerospace, marine development, atomic energy related products and other high-tech fields as well as general industrial structural materials and functional parts. This article selects a kind of maraging steel in the ultra-high strength maraging steel as a research object which strength level reach for300ksi. Through the comprehensive mechanics performance test, discussed the effect on mechanical properties of under different aging temperature and aging time, and come to the optimum heat treatment process. Studied the low cycle fatigue fracture characteristics of experimental steel by using of Hydraulic servo fatigue test machine of MTS810.23M, and observed the fracture morphology of fatigue sample by SEM while analysis the chemical composition of crack source. The growth law of austenite grain growth in experimental steel has been studied by Leica Metal Work. The hot deformation behavior of experimental steel under high temperature has been studied by using of Gleeble-3800simulator. The main conclusions obtained are as follows:The tensile strength and yield strength gradually increases while the aging temperature rises when experimental steel has been aging between200℃～600℃for5h, the strength reached a peak when the aging temperature improve to500℃, while the strength gradually reduced as aging temperature increase; The tensile strength and yield strength of experimental steel gradually increases while the aging time extend, and it get to a peak value at500℃which is the peak temperature while the aging time is8h, we got the optimum hot treatment process of experimental steel:Aging for3～5h between480～500℃, then air-cooling. On the condition of different aging time the low cycle strain fatigue performance of the experimental steel is not obvious, but the whole low cycle fatigue life is higher than the others when the aging time is3h, the stress amplitude raises while the ageing time increasing; Observed the fracture morphology of sample by SEM, We can find that the fatigue cracks is mainly originated from the inclusions which is in surface of the sample, and the inclusions distributed on the edge of fracture, the type of inclusions are Ti (C, N) and oxide.The average austenite grain size of experimental steel increases with increasing heating temperature and holding time in the isothermal heating process, the growth of austenite grain follows the Beck’s relationship. With increasing of temperature the grain growth index decreases, we obtained the austenite grain growth index and the average activation energy Q of austenite grain growth (Q=108.5kJ/mol) in experimental steel at850℃～1150℃, and the equation of austenite grain growth in isothermal heating process has been established.Under the temperature850～1150℃while the true stain is0.92and the strain rate of0.01s-1～10s-1, The high temperature deformation flow stress of experimental steel decreases with the increase of temperature, while it increases with the increase of deformation rate; In the condition of this experiment, experimental steel has high dynamic recrystallization temperature, it is higher than1050℃; the activation energy of the experimental is391.2kJ/mol and the hot deformation equation is built.