Papers by Author: Lei Yang

Abstract: The hardening behavior of the welding heat affected zone (HAZ) with different heat input for 500MPa grade screw thread steel is investigated in this paper. The single welding thermal cycle was applied to the test steel by a Gleeble-3500 thermal simulator. With the definition of hardness ratio, relative hardness factor and partial hardness zone, the HAZ Max hardness, hardness distribution and hardness mechanism of steel were analyzed. The results show that the HAZ hardness is always higher than the base steel hardness. The hardness ratio is increasing with the heat input decreased. The distribution of relative hardness factor of HAZ can be expressed by the Avrami equation which can describe the distribution of HAZ hardness. The width of partial hardness zone increases rapidly with the heat input increased. But at a certain degree of heat input, the width of partial hardness decreases slightly. The microstructure generated by heat input is the intrinsic factor of the HAZ hardness variation. The HAZ hardness enhances as the martensite content increases. On the contrary the HAZ hardness reduces as the ferrite content enhance on condition the heat input increase or the observed area is far away from the HAZ.

Abstract: This paper proposes an integrated model for the prediction of the pass-by-pass evolution of the austenite grain size of the ribbed steel bar hot rolling. The integrated model consists of a strain model, a temperature model, a microstructure evolution model of austenite grain size and a flow stress model. Hot rod rolling experiments are conducted to examine the proposed analytical models. The integrated model is employed to examine the effects of modifications of the refined austenite grain size of the 500MPa ribbed steel bar. Refinement of ferrite could be realized by refining the austenite grain size at the final pass.

Abstract: This paper proposes a semi-analytical method for the prediction of rolling force for rod rolling. The grooves of the passes are oval-round and round-oval. The mathematical model of rolling force is based on Shinkura and Takai’s model, but incorporates the effects of recrystallization and the alloy elements. Hot rod rolling experiments are conducted to examine the proposed semi-analytical method. The predicting values are compared with the mill log data, and they agree excellently over the whole rolling course. The predictions indicate that recrystallization affects the resistance of the material during hot rod rolling.