Effect of rapid heat treatment on mechanical properties and precipitation behavior of medium carbon low alloy steel

Overcoming the trade-off relationship between strength and toughness has always been a challenge. In this paper, the control of double refinement of matrix microstructure and precipitation phase was used as a means to discuss the influence law on phase transformation, element diffusion, mechanical properties, carbide precipitation and kinetics of medium carbon low alloy steel under rapid heating conditions. The results showed that the prior austenite grain was significantly refined under rapid heating conditions; the matrix maintained a weak chemical heterogeneity under quenching conditions, and the elements silicon (Si) and carbon (C) had a similar distribution pattern. At 400 °C rapid tempering, the precipitation of cementite in some areas was arranged regularly, and the distribution of cementite particles was more dispersed. The rapid heating during high-temperature tempering effectively prevented the coarsening of carbide. Kinetic calculations demonstrated that rapid heating can effectively increase the nucleation rate. By employing a rapid heating rate and short holding time, the occurrence of tempering brittleness is effectively avoided. Rapid heat treatment provided optimal toughness matching for hardness levels less than 600 HV. The Hollomon-Jaffe parameters for conventional and rapid heat treatment correlated positively. Grain refinement, weak chemical heterogeneity, and rapid tempering effectively regulated the matrix microstructure. Through rapid heat treatment, the double refinement of grain and the precipitation of carbide were obtained, thereby leading to a superior match of strength and toughness.