Nitriding behavior and corrosion properties of AISI 304L and 316L austenitic stainless steel with deformation-induced martensite

• Published in: Surface & coatings technology 2017-09, Vol.324, p.121-128
• Main Authors: Biehler, J., Hoche, H., Oechsner, M.
• Format: Article
• Language: English
• Subjects: Annealing; Austenitic stainless steel; Austenitic stainless steels; Chromium nitride; Chromium steels; Cold rolling; Cold working; Corrosion properties; Corrosion resistance; Corrosion resistant steels; Corrosion tests; Critical temperature; Deformation effects; Deformation resistance; Deformation-induced martensite; Hardening; Ion nitriding; Martensite; Martensitic stainless steel; Martensitic stainless steels; Mechanical properties; Microstructure; Plasma nitriding; Plasmas (physics); Reaction kinetics; Shot peening; Wear resistance
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2017.05.059

AISI 304L and AISI 316L are metastable austenitic stainless steels, which exhibit a good corrosion resistance due to their chromium contents but suffer from poor mechanical properties and therefore exhibit poor wear resistance. A slight hardening effect is gained by the formation of deformation-induced martensite either by cold-rolling or shot-peening. A considerable surface hardness could be achieved by plasma nitriding processes due to the formation of the so-called S-phase, the nitrogen diffusion zone. In industrial manufacturing processes cold-deformation could not be avoided and no final annealing is carried out to eliminate the deformation-induced martensite. Therefore, the knowledge about the behavior of the microstructure regarding the nitriding process and the resulting properties is fundamental. The S-phase is also assumed to improve the corrosion resistance if the plasma nitriding is performed below a critical temperature. Above this temperature chromium nitrides precipitate in the matrix and decrease the corrosion resistance. In this study, AISI 304L and AISI 316L were solution annealed and afterwards work hardened with a cold rolling degree of 38%. The surfaces were polished and shot-peened, respectively. The amount of deformation induced martensite depends on the material and this, in turn influences the nitriding behavior. It will be shown, that a highly deformed microstructure promotes the growth of the S-phase. Furthermore, the resulting surface hardness and corrosion resistances in saline solution were examined. The corrosion properties are highly dependent on the surface topography. Shot-peening increases the roughness and also induces crack like artifacts which accelerate corrosion kinetics. The results were evaluated statistically to derive correlations between the microstructure, the plasma nitriding behavior and the resulting properties. •Phase transformation from austenite to martensite induced by cold-rolling was only observed in AISI 304L.•Thickness of nitrogen diffusion zone is dependent of the microstructure formed during cold-rolling.•Surface hardness is increased by plasma nitriding independent of material or surface condition.•Statistical evaluations show significant parameters that deteriorate the corrosion resistance.