Effect of Bainite Morphology on Mechanical Properties of the Mixed Bainite-martensite Microstructure in D6AC Steel

Effect of the Austempering Process on the Microstructure and Mechanical Properties of 27MnCrB5-2 Steel

“…Moreover, it is worth noting that the samples austempered at a low and medium temperature displayed higher impact toughness compared to Q&T toughness [6]. It is widely known that finer carbide and more uniform carbide distribution can increase bainite impact toughness, because coarser carbides can act as cleavage crack nucleation sites [1,4,17]. This assessment is confirmed by the impact test results that highlight the negative effect of a longer holding time at a higher austempering temperature on impact toughness due to significant carbide growth.…”

“…These results are in agreement with the microstructural modification developed in the steel subjected to different austempering cycles. A low austempering temperature leads to the development of a mixed bainitic-martensitic microstructure, where martensite clearly significantly enhances the steel strength due to its superior strength with respect to bainite [4]. Moreover, the development of both martensite and bainite from the prior austenite grains leads to smaller packets of martensite and bainite, and induces plastic constraints in the bainite [15].…”

“…Moreover, the development of both martensite and bainite from the prior austenite grains leads to smaller packets of martensite and bainite, and induces plastic constraints in the bainite [15]. The reduction in the packet size of both martensite and bainite, of which the boundaries act as high angle boundaries, and the increase in the dislocation density in bainite lead to a further increase in steel strength [4,6].…”

“…Several studies reported that the presence of a microstructure of lower bainite and martenisite provides a better combination of mechanical properties (especially strength and toughness), compared to both upper and lower bainite and mixed upper bainite-martensite [1,4,5].…”

Evaluation of hydrogen-Induced cracking resistance of the In625 laser coating system on a C-Mn steel substrate

“…In the area of the microhardness peak (HAZ), the original microstructure of the substrate is destroyed during the thermal cyle imposed by the laser depositing process. The final microstructure reveals to be a lower bainite structure as shown in Figure 4b and supported by literature (Abbaszadeh et al, 2012), demonstrating that this hardness is in the magnitude range of lower bainite. On the other hand, the martensite hardness level would be around 700HV for a similar C-Mn steel.…”