Laser Surface Hardening of AISI 431 Martensitic Stainless Steel by Using Different Laser Sources

Laser surface hardening process is an advanced technology used to enhance metal surface properties through phase transformation. In recent decades, it has gained significant attention for its efficiency and precision. The glassmaking industry has shown interest in this technology as an alternative to laser cladding process, which causes environmental risks and machining challenges. This study aims to enhance AISI 431 stainless steel mold hardness without molten powder deposition. Surface hardening of AISI 431 stainless steel was carried out using continuous wave diode (940-1020 nm) and fiber (1070 nm) 4 kW laser sources. The influence of process parameters such as laser power (500-3040 W), scanning speed (4.5-8.5 mm/s) and number of laser head passes (1-4) were investigated on the hardened zone’s geometry, microhardness, and microstructure. Microstructural analysis was conducted using optical microscopy and scanning electron microscopy (SEM). The current findings revealed a significant increase in microhardness due to martensite formation, which decreased with depth as martensite content reduced. Results showed that beyond a certain limit, the hardness reaches a maximum value that, regardless of the parameters, can no longer increase. This mainly depends on several factors, such as material properties, processing parameters, and cooling conditions. Achieving a target hardness is possible by adjusting the number of passes, while the desired depth will primarily depend on the power and scanning speed.