Effect of Reheating Temperature and Cooling Treatment on the Microstructure, Texture, and Impact Transition Behavior of Heat-Treated Naval Grade HSLA Steel
“…Ten (10) micrographs (each covering 30 μm × 30 μm area) were taken from four (4) different locations on each sample so that a statistically significant area as large as 1.2 mm × 1.2 mm can be studied from each sample. The average grain size (or martensitic island size) was determined by the measurement of at least 500 grains from each sample based on the 'equivalent circle diameter' (ECD) method [24]. Thickness of ferrite and martensite films was also measured by image analysis.…”
Section: Methodsmentioning
confidence: 99%
“…The average grain size (or martensitic island size) was determined by the measurement of at least 500 grains from each sample based on the ‘equivalent circle diameter’ (ECD) method [24]. Thickness of ferrite and martensite films was also measured by image analysis.…”
In order to find an alternative choice for structural load-bearing components, an effort was made to improve the impact toughness of medium Mn steel through inter-critical annealing treatment without significant reduction in strength. Besides, the relative effect of C and Mn contents on microstructure and mechanical properties of medium Mn steels was also studied. Fibrous microstructures with fine, alternate films of ferrite and martensite with retained austenite were obtained. The low-C, high-Mn steel showed a superior combination of yield strength, ductility and impact toughness due to finer microstructure and higher retained austenite fraction, as compared to high-C, low-Mn steel. Thus, the beneficial effect of Mn enrichment in stabilising retained austenite and improving mechanical properties by transformation induced plasticity effect becomes evident.
“…Ten (10) micrographs (each covering 30 μm × 30 μm area) were taken from four (4) different locations on each sample so that a statistically significant area as large as 1.2 mm × 1.2 mm can be studied from each sample. The average grain size (or martensitic island size) was determined by the measurement of at least 500 grains from each sample based on the 'equivalent circle diameter' (ECD) method [24]. Thickness of ferrite and martensite films was also measured by image analysis.…”
Section: Methodsmentioning
confidence: 99%
“…The average grain size (or martensitic island size) was determined by the measurement of at least 500 grains from each sample based on the ‘equivalent circle diameter’ (ECD) method [24]. Thickness of ferrite and martensite films was also measured by image analysis.…”
In order to find an alternative choice for structural load-bearing components, an effort was made to improve the impact toughness of medium Mn steel through inter-critical annealing treatment without significant reduction in strength. Besides, the relative effect of C and Mn contents on microstructure and mechanical properties of medium Mn steels was also studied. Fibrous microstructures with fine, alternate films of ferrite and martensite with retained austenite were obtained. The low-C, high-Mn steel showed a superior combination of yield strength, ductility and impact toughness due to finer microstructure and higher retained austenite fraction, as compared to high-C, low-Mn steel. Thus, the beneficial effect of Mn enrichment in stabilising retained austenite and improving mechanical properties by transformation induced plasticity effect becomes evident.
“…Considering only the HABs the effective grain size was also estimated following the ECD method [29]. The effective grain size defines the crystallographic unit (surrounded by HABs), over which cleavage crack propagates in an uninterrupted fashion [34]. Figure 6 IPF maps (ND-IPF) of all the investigated samples.…”
The strength–toughness combination of an ultra-low carbon, low alloyed ‘air-cooled’ steel has been enhanced by developing and refining the granular bainite (GB) structure. Suitable alloy design and thermo-mechanical treatment involving forging, austenitisation (950–1150°C) and air-cooling resulted in the formation of GB matrix along with small islands of martensite–austenite constituents and allotriomorphic ferrite grains. Microstructural characterisation and phase transformation behaviour were studied by scanning electron microscopy and electron backscattered diffraction analysis. The effect of microstructural parameters on the strength-impact toughness combination was investigated. The steel showed an exceptionally low yield ratio, which is beneficial for seismic resistance application. GRAPHICAL ABSTRACT
“…Steels for naval applications, such as submarines, offshore platforms, and shipbuilding structures, demand high strength with high impact toughness at subzero temperatures (such as between À80 and À40 °C) due to their complex dynamic loadings experienced during service. [1][2][3] Most of the well-known naval grade steels, including the HY-80, HY-100, and HY-130 steels and the Cu-bearing HSLA-80 and HSLA-100 steels, are quenched and tempered martensitic steels. [2,4] A tempered martensite structure ensures a good combination of strength and toughness due to the hierarchical microstructure of martensite, which refines the 'effective grain size' controlling both the strength and toughness.…”
The present investigation correlates the austenite reversion and its stability during intercritical annealing (IA) with the tensile and Charpy impact properties of a low‐C naval grade steel. The as‐received steel is subjected to water quenching after austenitization at 950 °C, followed by IA at 620, 650, and 680 °C for 2 h. DICTRA simulation is used to predict the austenite reversion kinetics during the IA. Incorporation of cementite phase in the simulation correlates well with the experimental dilatometry results on the austenite growth kinetics. DICTRA simulation predicts a continuous rise in the reverted austenite fraction with increasing IA temperature. However, the percentage of reverted austenite, that gets retained after the subsequent quenching, decreases with increasing annealing temperature due to the reduction of austenite stability at elevated IA temperature. In other words, the amount of fresh untempered martensite increases rapidly with increasing IA temperature. Consequently, the sample annealed at an intermediate temperature of 650 °C (IA650) shows the best combination of strength, elongation, and low‐temperature impact properties as compared to the IA620 and IA680 steels due to an optimum balance of mechanically stable austenite and relatively lower untempered martensite fractions.
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