RWL34 粉末冶金不锈钢热处理过程中的碳化物演变及性能变化

The carbide evolution and properties changes of RWL34 powder metallurgy martensitic stainless steel during austenitizing at 900-1200 ℃ were systematically investigated. Further,the mechanical properties of the steel after tempering at 150-600 ℃ were also investigated. The results show that with the increase of quenching temperature,M₂₃ C₆ carbides gradually dissolve and coarsen following the Ostwald ripening mechanism;the dissolution rate accelerates after quenching at 1080 ℃,and a large number of carbides dissolve at 1200 ℃, with the undissolved carbides coarsening to 2. 03 μm and the number of carbides per unit area decreasing significantly. With the increase of quenching temperature,the strength and hardness generally increase first and then decrease. After quenching at 950 ℃,the Orowan strengthening of fine dispersed carbides dominates,and the tensile strength reaches a peak value of 1750. 02 MPa. After quenching at 1080 ℃,solid-solution strengthening and Orowan strengthening work together,and the microhardness reaches a peak of 816. 14 HV. When the quenching temperature exceeds 1100 ℃,a large number of carbides dissolve,and the matrix microstructure after cooling transforms from martensite-dominated to austenite-dominated,resulting in decreased tensile strength,while the elongation increases significantly due to the good ductility of austenite,reaching 5. 73% at after quenching 1200 ℃ . After tempering,the hardness reaches a peak of 740. 50 HV after tempering at 180 ℃,the tensile strength reaches a maximum of 1901. 74 MPa after tempering at 300 ℃,and the secondary hardening and secondary strengthening appear when tempering at 400 ℃ and 550 ℃,respectively. The elongation is 2. 53% when tempering at 300 ℃ and increases to 3. 25% when tempering at 600 ℃ . Considering the comprehensive balance of hardness and strength,the optimal heat treatment process is quenching at 1080 ℃ + double tempering at 300 ℃,achieving excellent comprehensive properties with hardness of 639. 57 HV and tensile strength of 1901. 74 MPa,which meets the service requirements of tool steels.