Improvement of fracture toughness of forging steels microalloyed with titanium by accelerated cooling after hot working

Impact Toughness and Tensile Properties Improvement through Microstructure Control in Hot Forged Nb-V Microalloyed Steel

“…It has been reported that, such particles can act as cleavage crack initiation points with a deleterious effect on impact energy. 9,35) As illustrated in Fig. 5, the engineering stress-strain curve, for specimen with 1 200°C reheating temperature and 0.3°C/s cooling rate, shows a sharp peak followed by a stress drop during necking accompanied with high postuniform strain.…”

“…24) In the acicular ferrite microstructure, refining the ferrite lath size, eliminating pearlite, minimizing the development of interlath carbides, and control of the amount and distribution of retained austenite are critical for the achievement of optimum strength and toughness properties. 7,9,25) In the present article the influence of thermomechanical process parameters on the above mentioned microstructural characteristics particularly with regard to the formation of acicular ferrite and the resultant mechanical properties of a Nb-V microalloyed steel is investigated. The overall objective of the study was the development of a forging process to produce high strength-high toughness (tensile strength Ͼ850 Mpa, impact energy at room temperature Ͼ30 J) microalloyed forged automotive safety parts such as axles, hubs and steering parts.…”

“…[2][3][4][5][6] The first generation of microalloyed steels (C-Mn-V steels) had ferrite-pearlite microstructures and the low toughness values were associated to the inherent cleavage fracture mode of pearlite. 2,[7][8][9][10] Therefore researches have been focused on eliminating or minimizing the amount of pearlite that can be formed during post forge cooling. 2,7,11) In recent years, the trend has been to modify the ferrite-pearlite microstructure with high impact toughness microstructures such as acicular ferrite through a judicious control of thermomechanical processing parameters.…”

Effect of titanium on the allotriomorphic ferrite transformation kinetics in medium carbon–manganese steels

“…The helium flow-rate during cooling is controlled by a proportional servovalve. These devices ensure an excellent efficiency 4 in controlling the temperature and holding time of isothermal treatments and also ensure fast cooling (200 Ks -1 ) in quenching processes. Dilatometric samples were austenitized in vacuum (1 Pa) at a constant rate of 5 ºC/s.…”

“…Recent works have demonstrated that medium carbon microalloyed forging steels with acicular ferrite microstructure can be manufactured at industrial scale [1][2][3][4][5]. The main interest of this microstructure lies in the good combination of mechanical properties that presents as compared with bainite and especially with ferritic-pearlitic microstructures.…”