The Coarse Microstructure of Medium‐Carbon Microalloyed Steel Crankshafts: Formation Mechanism and Finish Forging Control

Abstract

The effect of hot deformation parameters on microstructure coarsening of the medium‐carbon microalloyed steel is studied by means of hot compression experiments. The effective strain of finish forging in a crankshaft is simulated by means of finite element numerical simulations. The microstructure and properties of the crankshaft are also analyzed. The hot compression experiments result shows that with the deformation increasing from 2% to 18%, the austenite grain size first increases and then decreases, and it reaches the maximum when the deformation is 6%. The microstructure coarsening is mainly caused by critical deformation. With the increase in deformation temperature and the decrease in strain rate, the austenite grains can also be coarsened. When the effective strain of finish forging exceeds 0.2 in the main journal section of the crankshaft, the microstructure is refined significantly, and mechanical properties are improved. To avoid coarse microstructure, the reduction of finish forging should reach 15–20 mm.