Microstructure and hardness investigation of 17-4PH stainless steel by laser quenching

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2012-02, Vol.534, p.536-541
• Main Authors: Chen, Zhaoyun, Zhou, Guijuan, Chen, Zhonghua
• Format: Article
• Language: English
• Subjects: 17-4PH stainless steel; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hardening. Tempering; Hardness; Heat treatment; Laser quenching; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase transformation; Physics; Production techniques; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.12.004

► Surface hardening of 17-4PH is highly achieved by laser transformation hardening. ► A hardened layer with a thickness of 1.75mm is formed. ► The phase similar to ɛ-Cu precipitates re-segregation after dissolved. ► The strengthening phase is composed of classic lath martensite, coarse NbC and a lot of finer fcc copper-rich phases. Surface hardening of 17-4PH was achieved by laser transformation hardening using 5kW continuous wave CO2 laser system. The microstructure of the laser-quenched sample was investigated by optical microscopy, transmission electron microscope and 57Fe Mössbauer spectrometer. The hardness profile was determined by a Vickers hardness tester. The hardened layer with a thickness of 1.75mm was formed, and it was composed of classic lath martensite, coarse NbC and a lot of finer fcc copper-rich phases which were similar to ɛ-Cu precipitates. The maximal hardness value of hardened zone is 446HV which is 50HV higher than that of the substrate (386–397HV). The higher hardness in laser transformation layer of the 17-4PH steel could be attributed to the following aspects: the matrix with a high dislocation density; the fine microstructure; the finer fcc copper-rich phases that were similar to the ɛ-Cu precipitates as well as the transforming of retained austenite into lath martensite.