Effect Of Heat Treatment On Microstructure And Properties Of H13 Die Steel Formed By Selective Laser Melting

Selective Laser Melting?SLM?is an advanced manufacturing technology,which uses laser as heat source to melt metal powder and manufactures parts through layer by layer.It is one of the most promising additive manufacturing technologies and has many advantages such as simple equipment structure and near net forming parts with excellent mechanical properties.In this research,the SLM forming parameters of H13 die steel powders are optimized.The effects of temper treatment and hot isostatic pressing on microstructure and properties have been systematically studied.The result provides an important reference for the use of SLM formed H13 die steel in the field of mold.The results of orthogonal SLM experiment on H13 steel powders indicate that laser power,scanning speed and scanning spacing in the SLM forming process have a significant impact on the forming quality.Scanning speed affects mainly on surface quality,while the laser power and scanning speed have a greater influences on the relative density.The optimal technological parameters of SLM formed H13 die steel is confirmed by using orthogonal method as 255 W,1120 mm/s,100?m for laser power,scanning speed,scanning spacing.After formed at the condition of optimum technological parameters,the H13 steel exhibited good comprehensive properties,including relative density of 98.6%,surface roughness Ra of6.9?m,ultimate tensile strength of 1479.1 MPa,elongation of 4.5%,microhardness of 579.8HV_0.5,and impact energy of 4.89 J.The microstructure was mainly composed of lath martensite and a minor amount of retained austenite.Due to the mechanical properties of H13 steel formed by SLM were characterized with high hardness,high strength and low plastic toughness,so temper treatment at different temperatures was carried out changing microstructure and mechanical properties.The temper treatment was carried in the range of 450?700°C for 2 h.With the increasing of tempering temperature,the ultimate tensile strength and microhardness increased at first and then decreased.The change of elongation and impact energy were small in the range of 450?600°C,however,the elongation and impact energy were significantly increased in the range of 650?700°C.The microhardness reached a maximum of 714 HV_0.5 at 550°C,and the highest ultimate tensile strength was 1958 MPa at 600°C.The highest elongation and impact energy after tempering treatment at 700°C was 11.2%and 20.76 J,respectively.With the increasing of tempering temperature,the volume content of retained austenite in H13 steel decreases gradually and carbide precipitates grows gradually in the surface morphology.The network feature of H13 die steel formed by SLM disappears and becomes tempered sorbite in the range of from 650 to 700°C.The wear profile of H13 steel with Si₃N₄ceramic ball first decreased and then increased.After tempering treatment at 550°C,the minimum amount of wear was 1.23 mg,and the maximum amount of wear at 700°C was 5.79 mg.The relative density of H13 steel formed by SLM was increased from 98.6%to 99.86%,the microhardness was decreased from 579.8 HV_0.5 to 504.2 HV_0.5,the ultimate tensile strength was increased from 1479.1 MPa to 1180.5 MPa,the elongation was increased from4.5%to 15.9%,and the fracture mode was changed from quasi-cleavage to mixed ductile with brittle fracture after HIP at 1170°C.The microstructure transformed from lath martensite to alloy carbide which was distributed in acicular ferrite matrix as submicron particles.Additionally,HIP can effectively reduce the difference of the average linear expansion coefficient of H13 steel formed along the 0°and 90°inclinations of SLM and eliminate the anisotropy.