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A systematic experimental study has been conducted on the simulated intercritical coarse‐grained heat affected zone of 690 MPa grade heavy‐plate medium Mn steel by tailoring heat input of the first welding pass to obtain the influence of initial microstructure on the austenite reversion mechanism, recrystallization, and resultant impact toughness. Results reveal that prior austenite grain size significantly increases from 30 ± 11, 41 ± 14 to 54 ± 15 μm with the increasing heat input from 15, 30 to 50 kJ cm−1, which affect the nucleation site of reversed austenite, recrystallization mechanism, and final microstructure. Accordingly, impact toughness is better at the heat input of 30 kJ cm−1 (75.2 ± 0.8 J) in comparison with that of 15 kJ cm−1 (63.3 ± 13.3 J) and 50 kJ cm−1 (26.7 ± 6.5 J) at −40 °C, which is mainly ascribed to the formation of lamellar heterogeneous structures, multiplication of slip system and morphology of high‐angle grain boundaries. [ABSTRACT FROM AUTHOR]

Effect of initial martensite and tempered carbide characteristics on mechanical properties of 3Cr2MnNiMo mold steel were investigated. The results indicated that the initial martensite microstructure can be effectively adjusted by changing the quenching temperature. With the increase of quenching temperature from 760 °C to 1010 °C, the initial microstructure gradually changed from acicular ferrite + plate martensite + M 7 C 3 carbides to lath martensite, and the grain size increased monotonically. The coarsening of the initial martensite led to the increase of tempered carbide size, and the morphology of tempered carbide gradually changed from spherical to long strip-shaped. The large-size and long strip-shaped carbides promoted the formation of micro-voids during the tensile deformation and significantly decreased the elongation. In addition, with the coarsening of the martensite microstructure, both the decrease of high-angle grain boundaries (HAGB) density and the appearance of long strip-shaped tempered carbides significantly reduced the impact absorbed energy. The fracture mechanism transformed from ductile fracture caused by micro-voids coalescence to intergranular cleavage fracture. Moreover, when the initial microstructure completely transformed into lath martensite, the yield and tensile strength remained approximately unchanged. The precipitation strengthening compensated the adverse effect of martensite coarsening. [ABSTRACT FROM AUTHOR]

The evolution of eutectic carbide and granular pearlite, including secondary carbide and matrix ferrite, in 1.12C–8.1Cr–2.3Mo–1.08Si–0.32V alloy steel under spheroidization annealing is investigated. This procedure can be divided into two stages: austenitization in the range of 780–900 °C for 0.5–5 h and second annealing in the range of 740–780 °C for 3–7 h. The area fraction, size, number per unit area, and sphericity of carbides are analyzed under different annealing processes. The result indicates that the mean diameter of secondary carbides increases and the number of carbides per area decreases with the increase in temperature in two ranges of 780–900 and 740–780 °C. At >860 °C, the secondary carbide sufficiently spheroidizes, the eutectic carbide dissolves at the tip with a larger radius of curvature, and ferrite grains of the matrix are basically equiaxed. It can be found that the austenitizing stage plays a crucial role in nucleation and coarsening of secondary carbides, dissolution and segmentation of eutectic carbides, and recrystallization of matrix ferrite grains. The microhardness of the sample presents a decreasing tendency from fast to slow with the increase of the average diameter of secondary carbides. [ABSTRACT FROM AUTHOR]

Mechanical properties of 11Cr–3Co–2.3W steel are affected by various parameters, and normalizing temperature is an important parameter. OM, FESEM, EBSD, and TEM are carried out to study the microstructure evolution of 11Cr–3Co–2.3W steel normalized at different temperature ranging from 900 °C to 1150 °C and tempered at 780 °C. The tensile and impact properties are evaluated from the tempered specimens. The results show that an obvious grain coarsening occurs and the tempered strength of 11Cr–3Co–2.3W steel increases with increasing normalizing temperature. The specific strengthening mechanisms are discussed. The fracture morphology shows mainly dimples and cleavage facets, implying mixed‐mode of fracture mechanism when the normalizing temperature is up to 1050 °C. Normalizing at 1150 °C, the mixed‐mode of fracture mechanism is transformed to brittle fracture. [ABSTRACT FROM AUTHOR]