Surface enhancement of cold work tool steels by friction stir processing with a pinless tool

• Published in: Applied surface science Vol. 296; pp. 214 - 220
• Main Authors: Costa, M.I., Verdera, D., Vieira, M.T., Rodrigues, D.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.03.2014; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Friction stir processing; Mechanical properties; Microstructure; Physics; Surface engineering; Tool steel; Mechanical properties; Surface engineering; Friction stir processing; Microstructure; Tool steel; Tool steels; Friction; Surface treatments; Cold working
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2014.01.094

•AISI D2 surface processing/enhancement with a pinless tool.•Surface properties vary with increasing tool rotation speeds.•Tool slippage takes place at very high tool rotation rates.•Carbides distribution is enhanced/homogenized during processing.•Surfaces hardness is deeply increased by processing. The microstructure and mechanical properties of enhanced tool steel (AISI D2) surfaces produced using a friction stir welding (FSW) related procedure, called friction stir processing (FSP), are analysed in this work. The surface of the tool steel samples was processed using a WC–Co pinless tool and varying processing conditions. Microstructural analysis revealed that meanwhile the original substrate structure consisted of a heterogeneous distribution of coarse carbides in a ferritic matrix, the transformed surfaces consisted of very small carbides, homogenously distributed in a ferrite- bainite- martensite matrix. The morphology of the surfaces, as well as its mechanical properties, evaluated by hardness and tensile testing, were found to vary with increasing tool rotation speed. Surface hardness was drastically increased, relative to the initial hardness of bulk steel. This was attributed to ferrite and carbide refinement, as well as to martensite formation during solid state processing. At the highest rotation rates, tool sliding during processing deeply compromised the characteristics of the processed surfaces.