Analysis of α→γ and γ→α Phase Transformation of Si, Mn Added Steel Sheet Using Diffusion Simulation

Abstract

  The transformation phenomena of α→γ during intercritical annealing and of γ→α during subsequent cooling are important to achieve precise control over the mechanical properties of low-carbon cold-rolled Dual Phase steels. Taking advantage of multi-component diffusion simulation, this paper aims to investigate the partition of Si and Mn at the early stages of α→γ and γ→α transformation.
   The steel with the chemical composition of 0.13 mass% C-1.4 mass% Si-2.0 mass% Mn was intercritically annealed at 800°C for 0∼1000s, then air-cooled to 600∼800°C, followed by water-quenching. Its microstructural observation and elemental analysis were conducted using a field emission electron probe microanalyser. At the early stages of the α→γ transformation during annealing at 800°C, substitutional alloying elements such as Mn and Si are hardly partitioned. Even if the volume fraction of γ is the same before cooling, the γ→α transformation kinetics differs depending on the Mn concentration in γ. The diffusion simulation shows similar tendency with the experimental data.