Indian Journal of Science and Technology

Abstract

Objectives: Friction Stir Processing (FSP) is being attempted in this study to process the surface layer of mild steel and to explore the possibility of incorporating B4 C particle into surface layer of mild steel to form surface composite by means of FSP technique. Methods: FSP with B4 C particle was carried out on 5.0 mm mild steel and specimens 250 mm x 100 mm were processed in a single pass. The tool material used was tungsten carbide. Trial runs were carried out at different process parameters and the final parametric windows have been developed for getting the defect free surface. With optimized process parameters sound and defect free surface was made. Mechanical Properties were investigated through microstructure and hardness test. The micrographs and hardness graph have been presented and discussed in this paper. Findings: The Micrographs were taken using optical microscope at different location of the processed zone. There was distinct alteration in size and shape of the grains at different location of the processed area. Temperature in the stir zone is sufficient to convert the base material ferrite into austenite region of phase diagram. Since the recovery is slow in austenite, dynamic recrystallization occurs. The amount of deformation in friction stir processing is very large, therefore the critical condition for discontinuous dynamic recrystallization are met. This leads to very fine austenite grain formation. These fine recrystallized grains of austenite transform back into ferrite when the temperature falls down. Macro hardness test was also done using the Vickers hardness test. It was found that the average hardness has increased to more than three to four times in the processed zone as compared to the parent metal. Applications: Technology developed in this study can be effectively used in several areas like mining, mineral processing, aerospace and railway industry, where surface modification is a need to reduce various losses like wear and corrosion.

Keywords: Boron Carbide (B4 C), Friction Stir Processing (FSP), Metal Matrix Composites, Nano Particles