Martensitic microstructure in quenched and tempered 17CrNiMo6 steel with the prior austenite grain size ranging from 6 μm to 199 μm has been characterized by optical metallography （OM）, scanning electron microsco...Martensitic microstructure in quenched and tempered 17CrNiMo6 steel with the prior austenite grain size ranging from 6 μm to 199 μm has been characterized by optical metallography （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The yield strength and the toughness of the steel with various prior austenite grain sizes were tested and correlated with microstructure characteristics. Results show that both the prior austenite grain size and the martensitic packet size in the 17CrNiMo6 steel follow a HalI-Petch relation with the yield strength. When the prior austenite grain size was refined from 199 μm to 6 μm , the yield strength increased by 235 MPa, while the Charpy U-notch impact energy at 77 K improved more than 8 times, indicating that microstructure refinement is more effective in improving the resistance to cleavage fracture than in increasing the strength. The fracture surfaces implied that the unit crack path for cleavage fracture is identified as being the packet.展开更多
文中对 P91 钢两类焊缝的拉伸、冲击、硬度,特别是断裂韧性进行了试验研究。结果表明:强度、硬度高,冲击韧性低的 R 焊缝具有低的断裂韧度,强度、硬度低,冲击韧性高的 D 焊缝具有高的断裂韧度;R 焊缝的低韧性主要与其晶粒粗大、网状晶...文中对 P91 钢两类焊缝的拉伸、冲击、硬度,特别是断裂韧性进行了试验研究。结果表明:强度、硬度高,冲击韧性低的 R 焊缝具有低的断裂韧度,强度、硬度低,冲击韧性高的 D 焊缝具有高的断裂韧度;R 焊缝的低韧性主要与其晶粒粗大、网状晶界及焊接过程中焊接线能量和电流偏大有关,而 D 焊缝的低强度与高的断裂韧度则与焊后二次回火时温度过高有关。对于 R 焊缝,用厚度 12mm 的三点弯曲(SEB)试样测得的条件 KIC(Kq)与厚度 25mm 的紧凑拉伸(CT)试样测得的有效 KIC基本一致。展开更多
Clean high carbon heavy rail steel was prepared by the process of vacuum induction furnace smelting,forging and rolling.Mechanisms of RE on the impact toughness and fracture toughness for clean high carbon steel were ...Clean high carbon heavy rail steel was prepared by the process of vacuum induction furnace smelting,forging and rolling.Mechanisms of RE on the impact toughness and fracture toughness for clean high carbon steel were investigated.In addition,the appropriate range of RE content for clean high carbon steel was determined.Both the austenite grain size and pearlite lamellar spacing decreased due to small amount of RE,consequently the impact toughness and fracture toughness were improved evidently.When the RE content exceeded a critical value,the pearlite lamellar spacing was increased,because RE was segregated on the austenite grain boundaries,damaged the orientation relationship of pearlite transformation,caused the disorder growth and morphology degenerating of pearlite.With the increasing of RE content,both the impact toughness and fracture toughness of clean high carbon steel were gradually increased at first and then decreased.It was found that when the RE content was between 0.0081% and 0.0088%,both the impact toughness and fracture toughness of clean high carbon heavy rail steel were the best.The maximum ballistic work was 21.2 J（20 ℃） and 12.2 J（-20 ℃）,respectively.The maximum plane-strain fracture toughness was 45.67 MPa·m1/2（20 ℃） and 37.04 MPa·m1/2（-20 ℃）,respectively.展开更多
文摘Martensitic microstructure in quenched and tempered 17CrNiMo6 steel with the prior austenite grain size ranging from 6 μm to 199 μm has been characterized by optical metallography （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The yield strength and the toughness of the steel with various prior austenite grain sizes were tested and correlated with microstructure characteristics. Results show that both the prior austenite grain size and the martensitic packet size in the 17CrNiMo6 steel follow a HalI-Petch relation with the yield strength. When the prior austenite grain size was refined from 199 μm to 6 μm , the yield strength increased by 235 MPa, while the Charpy U-notch impact energy at 77 K improved more than 8 times, indicating that microstructure refinement is more effective in improving the resistance to cleavage fracture than in increasing the strength. The fracture surfaces implied that the unit crack path for cleavage fracture is identified as being the packet.
文摘文中对 P91 钢两类焊缝的拉伸、冲击、硬度,特别是断裂韧性进行了试验研究。结果表明:强度、硬度高,冲击韧性低的 R 焊缝具有低的断裂韧度,强度、硬度低,冲击韧性高的 D 焊缝具有高的断裂韧度;R 焊缝的低韧性主要与其晶粒粗大、网状晶界及焊接过程中焊接线能量和电流偏大有关,而 D 焊缝的低强度与高的断裂韧度则与焊后二次回火时温度过高有关。对于 R 焊缝,用厚度 12mm 的三点弯曲(SEB)试样测得的条件 KIC(Kq)与厚度 25mm 的紧凑拉伸(CT)试样测得的有效 KIC基本一致。
文摘Clean high carbon heavy rail steel was prepared by the process of vacuum induction furnace smelting,forging and rolling.Mechanisms of RE on the impact toughness and fracture toughness for clean high carbon steel were investigated.In addition,the appropriate range of RE content for clean high carbon steel was determined.Both the austenite grain size and pearlite lamellar spacing decreased due to small amount of RE,consequently the impact toughness and fracture toughness were improved evidently.When the RE content exceeded a critical value,the pearlite lamellar spacing was increased,because RE was segregated on the austenite grain boundaries,damaged the orientation relationship of pearlite transformation,caused the disorder growth and morphology degenerating of pearlite.With the increasing of RE content,both the impact toughness and fracture toughness of clean high carbon steel were gradually increased at first and then decreased.It was found that when the RE content was between 0.0081% and 0.0088%,both the impact toughness and fracture toughness of clean high carbon heavy rail steel were the best.The maximum ballistic work was 21.2 J（20 ℃） and 12.2 J（-20 ℃）,respectively.The maximum plane-strain fracture toughness was 45.67 MPa·m1/2（20 ℃） and 37.04 MPa·m1/2（-20 ℃）,respectively.
