Adiabatic Shear Banding and Cracking Phenomena Occurring During Cold-Forging Simulation Tests of Plain Carbon Steel Wire Rods by Using a Split Hopkinson's Pressure Bar

摘要

Adiabatic shear banding and cracking phenomena occurring during cold forging of plain carbon steel wire rods, whose carbon content was varied from 0.2 to 0.8 wt%, were analyzed by forging simulation test using a split Hopkinson's pressure bar. The test results indicated that the 0.2C and 0.3C steels were dynamically compressed without surface defects after the fifth hit, whereas a deep crack was formed along the 45A degrees direction in the 0.8C steel. In all the steels, adiabatic shear bands were formed diagonally inside forging-simulated specimens, and grains were extremely elongated within shear bands. The higher the volume fraction of pearlite was, the easier was the adiabatic shear banding. Particularly in the 0.8C steel, the shear band was white-colored and narrow, along which a long crack was formed. After the spheroidization treatment of the 0.8C steel, adiabatic shear bands or cracks were not found during the forging simulation test as the steel was relatively homogeneously deformed, which indicated that the spheroidization effectively prevented the adiabatic shear banding or cracking. The present forging simulation test plausibly evaluated the cold-forging performance by controlling the number and amount of hit, and provided an important idea on whether the spheroidization was needed or not.