Dt300 Ultra-high Strength Steel In The Organization And Performance Of Research And Exploration The Dt300 Steel Heat Treatment Process

DT300 steel is a new model ultra-high strength low-alloy steel, belong to middle and low carbon content steel with Si, Mn, Cr, Ni, Mo and V elements. It can gain enough high strength (Rm=1800MPa, R_p0.2=1450MPa), high toughness (A_ku2=75J/cm²,K_IC=110MPam^1/2 ). Thus DT300 steel can be widely used in the fields for ultra-high loadcapacity, such as high precision driving part and component crust.The effects of heat treatment at microscopic structures and mechanics capability were studied by metallurgical microscope, SEM, TEM, X-ray diffraction and mechanical testing. The types, amounts and precipitating orders of precipitate phases in different heat treatments were studied either.It was founded that:(1) Excellent machining properties are obtained under the condition of annealing at 660°C 20h followed furnace cool until 300°C.(2) The optimum comprehensive properties could be obtained for the sample reheating to some temperature between 860°C and 920 ℃ for 1 hour then oil quenching and tempering at some temperature between 260 °C and 340 °C for 2 hours, which can get a mass of lath martensites, carbide grains and retained austenitic film with volume fraction between 9.6% and 7.6%.(3) DT300 steel precipitated very little phases at quenching, among which M₆C phases were the majority. After quenching and tempering treatment, amount of precipitate phases increased markedly, Fe, Cr and C elements mainly precipitated in M₃C phases, a few Mn elements precipitated in M₆C phases, Ni and Mo elements mainly precipitated both in M₆C and M₃C phases, among which M₃C phase was the majority after tempering.