Heterogeneous quenching and partitioning from manganese-partitioned pearlite: retained austenite modification and formability improvement

Increasing quenching temperature in conventional quenching and partitioning (Q&P) process usually in-creases the fraction of retained austenite (RA) being dominant by blocky morphology, which ensures a good global formability but deteriorates the local formability. Instead of homogeneous austenite in con-ventional Q&P process, we propose a Q&P process purposely based on Mn-heterogeneous austenite inher-ited from Mn-partitioned pearlite. Therein, Mn-depleted austenite areas originated from ferrite lamellae are readily transformed into lath martensite during quenching; meanwhile, Mn-enriched austenite areas originated from cementite lamellae are readily retained as film RA at room temperature. Consequently, this heterogeneous Q&P process unusually achieves a large RA fraction being dominant by film morphol-ogy. The large RA fraction ensures a large total elongation and the dominant film morphology ensures a large post-uniform elongation, indicating good global and local formability, respectively. Additionally, the microstructure is refined through the above divided transformation of heterogeneous austenite, pre-dominantly contributing to the increased yield strength by 200 -300 MPa. Introducing heterogeneous austenite into Q&P process provides a feasible way to achieve a large RA fraction being dominant by film morphology, leading to the successful production of high-strength Q&P steels simultaneously with good global and local formability.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study proposes a new Q&P process that introduces heterogeneous austenite to achieve high-strength steel production with good global and local formability.