Effect of quenching temperature on microstructures and mechanical properties of S590 powder metallurgy high speed steels

S590 powder metallurgy high speed steels (S590 HSS) were prepared by plasma rotating electrode atomization and hot isostatic pressing. The S590 HSS samples were quenched at 1050, 1100, 1150, and 1180 ℃, respectively, followed by the tempering at 550 ℃ for 1 h (once), −196 ℃ cryogenic treatment for 4 h (once), and tempering at 550 ℃ for 1 h (twice). The effect of quenching temperature on the microstructure and mechanical properties of S590 HSS was studied. The results show that, the microstructure of S590 HSS after the heat treatments mainly consists of martensite, M₆C carbides, and MC carbides. With the increase of quenching temperature, the carbides gradually dissolve into the matrix, the carbide content decreases, and the matrix grain size increases. The hardness and compressive strength of S590 HSS increase with the increase of quenching temperature. After quenching at 1180 ℃ and the subsequent heat treatments, the hardness of S590 HSS is up to HRC 67.8, and the compressive strength is 3827 MPa. With the increase of quenching temperature, the bending strength first increases and then decreases, and the impact toughness decreases. The bending strength of the samples quenched at 1100 ℃ reaches the highest as 5473 MPa. The impact toughness of the samples quenched at 1050 ℃ reaches the highest as 76.9 J·cm⁻². Considering the microstructure and mechanical properties, the optimum quenching temperature of S590 HSS is 1100 ℃.