Parameters Optimization of Low Carbon Low Alloy Steel Annealing Process

A suitable match of annealing process parameters is critical for obtaining the fine microstructure of material. Low carbon low alloy steel (20CrMnTi) was heated for various durations near Ac temperature to obtain fine pearlite and ferrite grains. Annealing temperature and time were used as independent variables, and material property data were acquired by orthogonal experiment design under intercritical process followed by subcritical annealing process (IPSAP). The weights of plasticity (hardness, yield strength, section shrinkage and elongation) of annealed material were calculated by analytic hierarchy process, and then the process parameters were optimized by the grey theory system. The results observed by SEM images show that microstructure of optimization annealing material are consisted of smaller lamellar pearlites (ferrite-cementite) and refining ferrites which distribute uniformly. Morphologies on tension fracture surface of optimized annealing material indicate that the numbers of dimple fracture show more finer toughness obviously comparing with other annealing materials. Moreover, the yield strength value of optimization annealing material decreases apparently by tensile test. Thus, the new optimized strategy is accurate and feasible.