Application of Quenching and Partitioning Processing to Medium Mn Steel

Abstract

The present work analyzes the application of quenching and partitioning processing to medium Mn steel to obtain a new type of ultra-high-strength multiphase medium Mn steel. The selection of the quench temperature makes it possible to vary the ultimate tensile strength within a range of 500 MPa. The processing leads to lowcarbon lath martensite matrix with a controlled volume fraction of retained austenite. Increasing requirements related to passenger safety and weight reduction in the automotive industry have led to the development of a first generation of advanced high strength steels (AHSS) such as dual phase and transformation-induced plasticity (TRIP) steels. Second generation austenitic high-Mn twinning-induced plasticity (TWIP) steel with a Mn content in the range of 15 to 25 wt pct exhibits an excellent combination of tensile strength (~1 GPa) and ductility (~60 pct) due to a dynamic Hall-Petch effect resulting from the gradual increase of the density of mechanical twins during deformation.[1,2] The higher alloying costs and the lower productivity associated with high-Mn TWIP steel are currently the main drivers behind the development of the intermediate and medium Mn steel. Adequate combinations of mechanical properties have been reported for intercritically annealed intermediate and medium Mn steels. Their high work-hardening rate is achieved by the TRIP effect or a combination of two plasticity-enhancing mechanisms, the TWIP effect and the TRIP effect. [3][4][5] The Mn content in these materials is typically one third of the Mn content of the high-Mn TWIP steels, but despite their lower Mn content, these steels achieve excellent mechanical properties with a strength-ductility balance in the range of 35,000 to 45,000 MPa pct.Quenching and partitioning (Q&P) processing was proposed by Speer et al.[6] as a new approach to produce steel microstructures consisting of a low-C martensitic matrix containing a considerable volume fraction of retained austenite. Earlier studies have shown that the Q&P processing of various AHSS enables the use of the TRIP effect to achieve a pronounced improvement of mechanical strength and ductility. [7][8][9] The Q&P processing consists of three stages: an initial quenching stage, a partitioning stage, and a final quenching stage. The austenitized steel is initially quenched to a temperature, T Q , in the M s À M f temperature range, and partially transformed to primary martensite. It is then partition treated at the partitioning temperature, T P . During the partitioning stage, C diffuses from the supersaturated primary martensite into the untransformed austenite. As a result, the M s temperature of the C-enriched austenite is lowered. This leads to the stabilization of the untransformed austenite upon cooling to room temperature. If C does not partition enough to austenite, some of the austenite will transform to secondary martensite in the final quenching stage. The final microstructure consists of C-enriched austenite islands in a low-C lath martensite matrix. The martens...

Combination of ductility and toughness by the design of fine ferrite/tempered martensite–austenite microstructure in a low carbon medium manganese alloyed steel plate

“…Recently, medium Mn transformation induced plasticity (TRIP) steels containing 5-8 mass% Mn have been attracting more attentions due to the outstanding combination of strength and ductility [1][2][3][4][5][6][7][8]. Moreover, Since Miller proposed 0.11C-5.7Mn steel [9], the reverse transformation behavior, stabilization mechanisms of retained austenite, strain hardening behavior and tensile properties had been further understood [1][2][3][4][9][10][11][12][13][14].…”

Near-Ac3 austenitized ultra-fine-grained quenching and partitioning (Q&P) steel

“…The microstructure can in general also contain ferrite, bainite, or isothermal martensite depending on the alloy system and the cooling rate. In the present alloy system, no bainite or isothermal martensite is formed during the partitioning stage, but carbides are formed in the primary martensite.Most reports on the Q&P processing make use of a process which involves a full austenitizing stage as the first stage prior to quenching and partitioning [7,[9][10][11][12][13][14][15]. In a few case, an IA stage is used instead of a full austenitizing [14,16].…”

“…In a few case, an IA stage is used instead of a full austenitizing [14,16]. To the best of the authors' knowledge, no information is available about the influence of the full austenitization temperature (T A ) or IA temperature (T IA ) on the mechanical properties of Q&P processed steels, although much attention has been given to the study of the influence of T Q [7,12,14,15], partitioning temperature [9][10][11]14], and partitioning time [9][10][11][13][14][15][16]. It is well known that the selection of T Q is primarily important for the mechanical properties of Q&P steels because it influences the final phase fractions.…”

“…Seo et al [7,8] previously showed that Q&P processing can successfully be applied to medium Mn steel and that it is an ideal alloy system for Q&P processing due to the suppression of the bainite transformation. They reported that the Q&P processed medium Mn steel typically achieved a yield strength (YS) of 1.2 GPa, a UTS of 1.4 GPa and a TE of 18%.…”

Prediction of Ac₃ and Martensite Start Temperatures by a Data-driven Model Selection Approach

“…However, from an engineering point of view, the explicit correlation is usually more important, so the previous empirical regression models are still widely used. 10,11) Recently, another data-driven approach called as data driven model selection has been increasingly introduced to solve the physical problems. The data-driven model selection is a method where the model most suitable for a given dataset is selected based on the information criteria.…”