Annealing of HC340LA tailor rolled blanks—Control of mechanical properties and formability

Abstract

Abstract Tailor rolled blanks (TRB) have been extensively used in the automotive industry because of lightweight. Through the flexible rolling process and appropriate annealing treatment, the target geometry, required mechanical properties, and good formability of TRB can be achieved. In this study, two types of annealing processes were attempted, i.e. batch annealing and continuous annealing. The effects of annealing parameters on the microstructure, mechanical properties and formability of HC340LA TRB were investigated. First, a series of batch annealing and continuous annealing were conducted on cold rolled TRB. Next, the microstructure distribution of TRB was evaluated. The mechanical properties and formability of annealed specimens were tested through the uniaxial tensile test and Erichsen cupping test, respectively. The results showed that the mechanical properties and formability were controlled by reduction, annealing type and annealing parameters. During the batch annealing, mechanical properties along the rolling direction were influenced by the degree of recrystallization and the average grain size, the formability increased with the increase of annealing temperature. TRB annealed at 700 °C for 60 min showed relatively homogeneous mechanical properties and good formability in the reduction range of 36–54 %. During continuous annealing, the mechanical properties and formability were determined by the degree of austenitization and the average grain size. TRB annealed at 930–950 °C for 3 min showed homogeneous mechanical properties and good formability for the entire range of reduction.