Hot-rolled and continuously cooled bainitic steel with good strength–elongation combination

Abstract

The current work demonstrates the microstructural evolution and mechanical property evaluation of a newly designed steel composition after hot rolling in laboratory-scale rolling mill, followed by continuous cooling. The steel thus developed has typically about 80% carbide-free bainite; about 20% retained austenite and can deliver ∼1400 MPa ultimate tensile strength along with more than 20% total elongation. The presence of ultra-fine bainite plates (∼100–130 nm thick) with high dislocation density was thought to be responsible for ultra-high strength. Excellent ductility at such strength level could be due to the presence of sufficient amount of retained austenite (∼20%) thermally stable at room temperature but starts transforming to martensite during deformation exhibiting transformation-induced plasticity effect.

Studies of Bainitic Steel for Rail Applications Based on Carbide-Free, Low-Alloy Steel

“…These unique properties result from the submicron or nanometric grain size of bainitic ferrite and the appropriate content of retained austenite (blocky as well as filmy). The carbide-free bainitic steel developed by Das et al [15] has about 80 pct of bainitic ferrite and 20 pct of retained austenite. This microstructure provided the ultimate tensile strength ~1400 MPa and total elongation above 20 pct.…”

Ductile ultra high strength hot stamped steel obtained by Q&P treatments

“…Although precipitation hardened steels could offer a good combination of strength and ductility [3,4], it is difficult to achieve strength beyond 1200 MPa with such a philosophy. Speer and co-workers [5,6] as well as some other research groups [7][8][9] have successfully developed steel following the quenching and partitioning philosophy (Q & P) whereas Das and co-workers have developed continuously cooled bainitic (CCB) steel [10,11]. Both of these steels (Q & P and CCB) can provide a similar strength level ( ∼ 1500 MPa UTS) that can be offered by hot stamped steels but with much improved elongation.…”

Recent Progress of Low and Medium-Carbon Advanced Martensitic Steels

“…one-step and two-step quenched and partitioned (Q&P) steels [7][8][9]25,[34][35][36][37][38][39][40][41], carbidefree bainitic (CFB) steel [42][43][44][45][46][47][48][49], and duplex type medium manganese (D-MMn) steel [9,25,[50][51][52][53][54][55][56][57].…”

“…Metals 2021, 11, x FOR PEER REVIEW 2 (III). Third-generation AHSS (Type A): TRIP-aided bainitic ferrite (TBF) steel [9,10,29one-step and two-step quenched and partitioned (Q&P) steels [7][8][9]25,[34][35][36][37][38][39][40][41], bide-free bainitic (CFB) steel [42][43][44][45][46][47][48][49], and duplex type medium manganese (D-MM steel [9,25,[50][51][52][53][54][55][56][57]. (IV).…”