Laser and induction hardening of refractory steels

BACKGROUND: Steam turbine blade erosion during operation is a serious problem in the energy industry. Today, there are methods to prevent it; however, they have significant limitations. The laser and induction hardening technology proposed in the paper allows to mitigate erosion and significantly increase the service life of turbine blades by combining state-of-the-art process tools. AIM: To study the capabilities of laser and induction heat sources, i.e. to create a variable deep-hardened layer in blade steel test pieces by surface hardening, and its properties (structure and hardness, test piece deformations). MATERIALS AND METHODS: This paper presents the experimental studies of laser and induction hardening of flat test pieces made of refractory steels 15H11MF, AISI 420, and EI961. The study was conducted during the development of a hardening technology to treat the surface of steam turbine blades made of martensitic steels to protect their leading edges from erosion. RESULTS: We obtained a single hardening zone on the leading edge and the adjacent section on the back of the test pieces with no defects, i.e. microcracking, discontinuities, and surface glazing. Hardness within the boundaries of the hardened layer on the leading edge side is at least 400 HV0.5. In this case, the hardened layer depth in the area of the leading edge is at least 5 mm and at least 2 mm in the adjacent section of the blade back. The maximum test piece deformation after strengthening is 1.2 mm. CONCLUSION: Experiments on laser and induction hardening of flat test pieces made of refractory steels 15H11MF, AISI 420, EI961 show that this treatment is a promising method to replace conventional surface hardening of products made from these materials to protect them from erosion.