研究了两种V含量(0.15%、0.28%)的中碳非调质钢37Mn Si VS在不同奥氏体化加热温度和不同保温时间下的奥氏体晶粒长大规律。结果表明,随着加热温度的升高,实验钢的奥氏体晶粒近似呈指数形式长大;随保温时间的延长,实验钢的奥氏体晶粒呈抛物线形式长大。V含量的增加使得奥氏体晶粒细化,且出现急剧长大的温度升高,但V含量的增加对等温长大指数的影响较小。利用实测数据并结合晶粒长大动力学理论,并引入V含量作为变量,模拟得到了能够预测不同V含量的37Mn Si VS钢的奥氏体晶粒长大的数学模型。
Single compression tests were carried out with a Gleeble-3800 thermal simulator to investigate hot deform- ation behavior of two vanadium-microalloyed medium-carbon steels for fracture splitting connecting rod. The tests were performed to a total true strain of 0.92 at true strain rates ranging from 10-2 to 10 s-1 and deformation temper- ature of 900--1 150 ℃, The results show that hot deformation behavior of the tested steels is similar to that of con- ventional medium-carbon microalloyed steels and dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate. The austenite deformation resistance and activation energy of deformation increase with increasing vanadium content from 0.15% to 0. 28% and thus the starting time of dynamic recrystallization was delayed. Finer recrystallized austenite grain could he obtained at higher strain rate, lower deformation temperature and higher vanadium content. TEM observation of the specimens quenched just before and after deformation reveals that vanadium is mainly in dissolved solute condition in austenite and thus affects the dynamic recrystallization behavior of the tested steels mainly through solute-drag effect.
The fracture splitting property of medium carbon steel 37MnSiS microalloyed with V up to 0. 45% was investigated by using simulated fracture splitting test,for the development of new crackable medium carbon steel to manufacture high performance connecting rod. Conventional high carbon steel C70S6 was used for comparison. The results show that the volume fraction of both ferrite and V-rich M（ C,N） particles increases,and the pearlite interlamellar spacing decreases with increasing V content,which in turn results in gradual increase of strength and decrease of ductility and impact energy. The fracture splitting property of the tested steel could be improved significantly due to the increase of V content mainly through the precipitation hardening mechanism of fine M（ C,N） precipitates. The fraction of brittle cleavage fracture in the crack initiation area increases noticeably with increasing V content and full brittle cleavage fracture surface could be obtained when V content was increased to 0. 45%. It is concluded that medium carbon steel with V content higher than about 0. 28% possesses not only comparable or even higher mechanical properties with those of conventional steel C70S6,but also excellent fracture splitting property,and therefore,is more suitable to fabricate high performance fracture splitting connecting rod.
