Effect of Austenite Grain Size on Transformation Behavior, Microstructure and Mechanical Properties of 0.1C–5Mn Martensitic Steel

Abstract

The effect of austenite grain size on martensitic transformation, particularly with regard to martensite structure, Ms/Mf temperatures, and mechanical properties was investigated in 0.1C-5Mn martensitic steel. Utilizing a newly developed experimental technique that makes it possible to examine phase transformation behavior and conduct tensile testing with the same specimen, we examined these relationships and obtained the following results. Ms temperature decreases as much as 40 K with a decrease in austenite grain size from 254 to 30 μm. Regarding martensite structure, the packet size and the block length decrease, while the lath width does not change, with the refinement of austenite grain size by about one tenth. Grain boundary density, especially high-angle grain boundary density, increases with decreasing austenite grain size. Tensile strength slightly increases though austenite grain size decreases about one tenth. However, reduction in area significantly improves particularly at refined grain sizes of 30 μm. True stress -true strain curves obtained up to fracture elucidates that the austenite refinement substantially improves true fracture strength and greatly increases true fracture strain of martensite, potentially invalidating the conventional concept of a trade-off between strength and ductility. Low C-5Mn martensitic steel produced from fine austenite shows a great possibility having an excellent total balance of strength, ductility and toughness.

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

“…Dislocation Density Figure 7(a) shows measurements of the crystalline domain size (D) and dislocation density (q XRD ) after the application of the modified Williamson-Hall method to XRD diffractogram. According to literature, [4] martensite lath dimensions are not expected to vary extensively with PAGS. Therefore, the contribution of lath boundary to q XRD is considered similar in all specimens.…”

“…[3][4][5][6][7] Packet and block sizes are commonly observed to be reduced with a reduction of PAGS. [3] This implies an increase of high-angle boundaries in as-quenched martensite microstructure, which are effective barriers to dislocation movement during deformation of lath martensite and strongly affect the strengthening of the material.…”

“…An interesting method for PAGS reduction and thus microstructure reduction even to submicron scale [3,4,6,[14][15][16] is the employment of a successive martensite-austenite reversion processes through rapid heating and quenching . However, there is a lack of investigations that methodically study the effect of PAGS reduction by thermal cycling on the microstructure of lath martensite.…”

Austenitic Grain Size Prediction in Hot Forging of a 20MnCr5 Steel by Numerical Simulation Using the JMAK Model for Industrial Applications

“…Several studies report the phenomena of hardening, dynamic recovery, dynamic recrystallization and austenitic grain growth, and how these phenomena affect the steel mechanical properties. The control of such mechanisms by thermomechanical processing is most commonly implemented in rolling processes [1][2][3][4][5][6] . However, they are often more challenging to be implemented for forging processes.…”

Emissão magnética espontânea (SME) na transformação martensítica.

“…GOMES, 1979) importante, muitas pesquisas foram feitas a respeito (NISHIYAMA, 1978;UMEMOTO;OWEN, 1974;HANAMURA et al, 2013;RONG, 2005;MENG et al, 2002;YANG;BHADESHIA, 2009;RIOS, 2010), seu crescimento é um processo que depende do tempo e da temperatura de austenitização, entre outros fatores. O resultado do incremento de Ms (Mb) com o incremento do tamanho do grão é grande para amostras de grão fino (com uma morfologia de placa fina), incremento baixo para amostras com tamanho de grão médio (com uma morfologia acicular), e incremento zero para amostras de grão grande, como é apresentado na figura 3, demostrando uma mudança na morfologia da martensita devido à mudança do tamanho de grão austenítico (com o carbono ocorre comportamento similar para alterar a morfologia conhecida da martensita).…”