Application of severe torsion straining process for grain refinement of steel

Severe torsion straining process (STSP) is a useful technique for grain refinement of metallic materials. With this process, a local heated zone is produced in a rod and one side of the rod is rotated with respect to the other so that torsion strain is introduced into the local heated zone. Severe straining is then achieved continuously throughout the rod by simultaneous rotation and longitudinal movement of the rod. Thus, the STSP is a continuous process and a die-less process for grain refinement. It is suggested that the STSP provide potential for commercialization. In this study, S45C steel rods with 12 mm in diameter were subjected to STSP. This process was conducted at a temperature of 923 K (650 degrees C) with various ratios of rotation to longitudinal movement of a rod. Local heating was made using an induction coil and both sides of the local heated zone were cooled by water spray. Microscopy observation revealed that the initial grain size of similar to 15 mu m was reduced to similar to 2 mu m using the STSP.