Study of cooling methods on the properties of structural alloy steel during laser hardening

The article presents the results of a study of the effect of air and water cooling methods on the structural and mechanical characteristics of the surface layer of 40X structural alloy steel after laser quenching. The experiments were carried out on the FL-Clad-R-4 robotic installation using an ytterbium fiber laser at a constant power of 2000 W and a scanning speed of 10 mm/s. Metallographic analysis and micro hardness measurements have shown that water cooling promotes the formation of fine-needle martensite, providing maximum surface hardness (up to 489 HV) at a lower depth of the hardened layer (up to 882 microns). At the same time, air cooling, which leads to the formation of a mixed ferrite-pearlite structure, demonstrates lower hardness (about 401 HV), but a greater depth of hardening (up to 1249 microns). The relationship between the cooling mode, phase composition, and operational properties of the hardened layer has been established. Recommendations on the choice of the cooling method are determined depending on the operating conditions of the parts: water cooling — to increase wear resistance, air cooling — to increase the depth of hardening under cyclic loads.