Indian Journal of Science and Technology

Abstract

Objective: In this study, the micro structural and hardness properties of friction stir welded (FSW) of steel-TiO2 composite was studied. Methods/Statistical Analysis: A homogeneous mixture of HSLA steel particles and TiO2 particles with a mean size of 300 µm was inserted into the weld groove of HSLA X70 steel and; consequently FSW was applied. To investigate the microstructure and hardness properties of composited weld metal, optical microscopy and Vickers micro hardness measurements were employed. Findings: The microstructure of nugget zone in FSW X70 steel with no additive TiO2 is consist of large grains of Polygonal Ferrites (PF) as well as Ferrite Side Plate (FS) phases. By inserting TiO2 particles into the weld groove, different kinds of particles dispersion, consequently changed the microstructure, were achieved. The microstructure was influenced by the type of dispersion as well as the particle size which both are strongly dependent on the stirring action. In this regard, the sufficient stirring action resulted in a fine homogeneous dispersion of particles with acicular ferrite (AF) dominant microstructure with a hardness of 300HV while, lower stirring action caused to the coarser dispersion of particles in the structure resulting in Polygonal Ferrite (PF) structure with a hardness of 185 HV. Coarse incorporated particles also results in very fine grains of PF with a hardness of 260 HV. Application/Improvements: Achieving a very fine-grained microstructure in case of FSW of HSLA steels with enhanced properties is available through FSW process.

Keywords: Composite, Friction Stir Welding (FSW), Hardness Microstructure