Microstructure and Hardness of Surface Melting Hardened Zone of Mold Steel, SM45C using Yb:YAG Disk Laser

Abstract

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and 800 ㎛ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

Experimental Investigation of Al-CuMgMn Alloy Developed by Laser Beam Surface Modification for Wear Resistance

“…Similarly, when the laser scan speed was increased by 300 to 500 mm, both alloy depth alloy widths were decreased [35]. The effect of the beam diameter was also observed in [36,37], where there is an optimum beam diameter for the best performance. During laser alloying, the phenomena occurring are slightly more complicated due to the input of additional elements or compounds to the substrate material with other laser parameters.…”

Effect of Laser Heat-Treatment and Laser Nitriding on the Microstructural Evolutions and Wear Behaviors of AISI P21 Mold Steel

“…Appropriate surface treatments can prevent damages to the mold, resulting in an extended mold lifespan. Several studies have investigated the application of surface treatments to mold steels and tool steels in the form of surface heat-treatment [2][3][4][5], nitriding [3,[6][7][8], surface coating and alloying [9][10][11][12], and peening [5,13,14]. Lee et al [2] investigated the laser melting-induced microstructural evolution and surface hardening of SM45C mold steel.…”

“…Several studies have investigated the application of surface treatments to mold steels and tool steels in the form of surface heat-treatment [2][3][4][5], nitriding [3,[6][7][8], surface coating and alloying [9][10][11][12], and peening [5,13,14]. Lee et al [2] investigated the laser melting-induced microstructural evolution and surface hardening of SM45C mold steel. Telasang et al [4] reported that laser surface hardening/melting improved the wear and corrosion resistances of AISI H13 tool steel.…”

Microstructural Characterization of Surface Softening Behavior for Cu-Bearing Martensitic Steels after Laser Surface Heat Treatment

“…Among the numerous available manufacturing processes, laser-beam-assisted processes are particularly versatile because of their diverse application range and superior manufacturing efficiency, including welding [6][7][8], cladding [9], surface alloying [10,11], selective melting [12][13][14], shock peening [15,16], and riveting [17]. Selective control of surface material properties is also possible through laser processing.…”