Study On Austenite Nucleation And Growth Behavior Of 18Cr2Ni4WA Steel

Taking 18Cr2Ni4 WA large gear steel as the research object,this paper studies the formation and growth behavior of austenite nucleus during post forging heat treatment.When the heating temperature is in the range of AC1 ～AC3 and at a lower temperature,acicular austenite nucleates preferentially between lath martensite strips and at the beam boundary.With the extension of holding time,the acicular austenite nucleus becomes longer along the direction of lath bundle and wider perpendicular to the direction of lath bundle,At the same time,globular austenite nucleates at the grain boundary;When the heating temperature rises to the medium temperature range of AC1 ～ AC3,the spherical austenite at the grain boundary merges and grows into the crystal,showing a long island shape and uneven grain size.At the same time,the nucleation and growth of the material are consistent with α Phase recrystallization;When the heating temperature is 860 ℃,the growth tends to be equiaxed and the austenite is homogenized.Because the forged structure of 18Cr2Ni4 WA material is usually nonequilibrium bainite structure,it is found that there are structural genetic characteristics by studying the formation and growth behavior of austenite nucleus during reheating of forged structure;It was found that 18Cr2Ni4 WA material with non-equilibrium structure was reheated before austenitizing,α The degree of phase recrystallization directly affects the nucleation and growth behavior of austenite.In order to cut off tissue inheritance,eliminate mixed crystal structure and make α The phase is fully recrystallized.Firstly,the quenched sample is reheated to different temperatures(550 ℃,600 ℃,650 ℃)for high-temperature tempering,and then the tempered sample is heated to AC3 + 60 ℃ for 15 min for quenching.The results show that the martensite orientation elimination effect is obvious when it is tempered at 650 ℃.Under this heating process,the grain can be refined and homogenized,and the mixed crystal structure can be effectively eliminated.