Microstructural evolution and strain hardening behavior of a novel two-stage warm rolled ultra-high strength medium Mn steel with heterogeneous structures

A strong and ductile medium Mn steel manufactured via ultrafast heating process

Improving strength–ductility synergy in medium Mn steel by combining heterogeneous structure and TRIP effect

Advanced high-strength steels have been widely used to improve the crashworthiness and lightweight of vehicles. Different from the popular cold stamping, hot forming of boron-alloyed manganese steels, such as 22MnB5, could produce ultra-high-strength steel parts without springback and with accurate control of dimensions. Moreover, hot-formed medium-Mn steels could have many advantages, including better mechanical properties and lower production cost, over hot-formed 22MnB5. This paper reviews the hot forming process in the automotive industry, hot-formed steel grades, and medium-Mn steel grades and their application in hot forming in depth. In particular, the adaptabilities of medium-Mn steels and the presently popular 22MnB5 into hot forming were compared thoroughly. Future research should focus on the technological issues encountered in hot forming of medium-Mn steels to promote their commercialization.

Medium-Mn steels for hot forming application in the automotive industry

A novel medium-Mn steel with superior mechanical properties and marginal oxidization after press hardening

Flash processing (FP) has attracted considerable attention due to its high efficiency, economic advantages, and the extraordinary opportunity if offers to improve the mechanical properties of steel. In this study, we investigated the influences of FP on the recrystallization (REX) behavior and mechanical performance of cold-rolled IF steel. Using a thermomechanical simulator, we performed both single-stage FPs, at heating rates of 200°C/s and 500°C/s, and two-stage FP, with an initial preheating to 400°C at a rate of 5°C/s and then to peak temperatures at a rate of 200°C/s. In comparison to continuous annealing (CA), single-stage FP can effectively refine the recrystallized grain sizes and produce a similar or even sharper γ (ND (normal direction)//{111}) texture component. In particular, the heating rate of 500°C/s led to an increase in the yield strength of about 23.2% and a similar ductility. In contrast, the two-stage FP resulted in a higher REX temperature as well as a certain grain refinement due to the stored strain energy, i.e., the driving force of REX, which was largely consumed during preheating. Furthermore, both stronger {110} and weaker γ texture components appeared in the two-stage FP and were believed to be responsible for the early necking and deterioration in ductility.

Effect of flash processing on recrystallization behavior and mechanical performance of cold-rolled IF steel

In the past decades, several 9–12 wt% Cr-containing martensitic steels have been researched for the application in ultra-supercritical power plants at 650 °C, which is still a worldwide challenge. Among them, G115 martensitic steel, which was developed in China, is one of promising candidates. It has the basic composition of 9% Cr-3% W-3% Co and contains 1% Cu (all in wt%) and the optimized contents of B and N, leading to much better creep strength and creep ductility than P92 steel. Both M23C6 carbides and e-Cu particles were found during the tempering of G115 steel, and the former have finer size than those in P92 steel, which results in Laves phase to form with the refined size too during the latter creep stage. All these formed precipitates shall contribute to improved creep rupture strength of G115 steel.

Pengyu Wen

Papers

A novel medium-Mn steel with superior mechanical properties and marginal oxidization after press hardening

A strong and ductile medium Mn steel manufactured via ultrafast heating process

Effect of flash processing on recrystallization behavior and mechanical performance of cold-rolled IF steel

The Evolution of Precipitates in a Novel Heat-Resistant Martensitic Steel During Creep