Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

Abstract

The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.

Development of hybrid model for modeling of diffusion phase transformation

“…One of the main aspects considered in the work was the modeling of interface migration between two phases – austenite and martensite. Figure 3 in Wang et al (2018) shows the carbon redistribution during partitioning at 425°C for 500 s after quenching to 300°C. The basic assumptions for modeling and the results included in the cited work can be referred to the modeling results, which can be obtained using the LBM and CA methods.…”

Full Field Model Describing Phase Front Propagation, Transformation Strains, Chemical Partitioning, and Diffusion in Solid–Solid Phase Transformations

“…The diffusion coefficients D C 𝛾 = 2 × 10 −5 × exp(−140 kJ∕RT) and D C 𝛼 = 2 × 10 −6 exp(−10115∕T) × exp(0.5898[1 + (2∕𝜋)arctan (1.4985 − 15309∕T)]), [35] where R is the ideal gas constant (kJ is kilojoules), were used for the austenite and ferritic phases.…”

“…The diffusion coefficients $$D_\gamma ^\text{C}=2\times 10^{-5} \times \mathrm{exp}(-140\nobreakspace \mathrm{kJ} / RT)$$ and $$D_\alpha ^\text{C}=2\times 10^{-6}\mathrm{exp}(-10115 / T)\times \mathrm{exp}(0.5898 [1+(2/\pi ) \mathrm{arctan} (1.4985-15309 / T)])$$, [ 35 ] where R is the ideal gas constant (kJ is kilojoules), were used for the austenite and ferritic phases.…”

Quasi-Situ Characterization of Retained Austenite Orientation in Quenching and Partitioning Steel via Uniaxial Tensile Tests

“…In order to achieve lightweight vehicles, development of the advanced high strength steel (AHSS) is required. Up till now, researches for the high-strength steel mainly focus on generating high-strength matrix structure and ensuring enough retained austenite content [ 1 , 2 ]. As a third generation of advanced high-strength steel proposed in 2003 [ 3 ], quenching and partitioning (Q&P) steel can meet the requirements of high strength and high plasticity at the same time.…”