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利用Formaster-F全自动相变测量装置对超低碳微合金钢进行不同冷却速度的热处理,采用金相显微镜观察试验钢的微观组织,采用450SVD数显维氏硬度计测量试验钢的维氏硬度。结果表明,当冷却速度<1℃/s时,试验钢的显微组织均为多边形铁素体,维氏硬度平均最大值为177.0 HV5;当冷却速度达到3℃/s时出现准多边形铁素体,维氏硬度平均值为187.3 HV5;当冷却速度达到5℃/s时钢的显微组织中出现粒状贝氏体,此时维氏硬度平均值为193.3 HV5;20℃/s时出现贝氏体铁素体,准多边形铁素体消失,维氏硬度平均值为221.6 HV5;当冷却速度达到50℃/s时钢中出现马氏体,显微组织为三相组织即粒状贝氏体+贝氏体铁素体+马氏体,维氏硬度平均值达到224.0 HV5;冷却速度达到165℃/s后,钢中的显微组织仍为三相组织,此时试验钢的平均维氏硬度值达到本试验的最大值263.3 HV5。在所有的冷速下,试样中均未发现珠光体。
Using Formaster-F automatic phase change measuring device, the ultra-low carbon microalloyed steel was heat-treated at different cooling rates. The microstructure of the test steel was observed with a metallurgical microscope. The Vickers hardness of the test steel was measured with a 450SVD digital Vickers hardness tester . The results show that when the cooling rate is less than 1 ℃ / s, the microstructure of the test steel is polygonal ferrite. The average maximum Vickers hardness is 177.0 HV5. When the cooling rate reaches 3 ℃ / s, The mean Vickers hardness is 187.3 HV5. When the cooling rate reaches 5 ℃ / s, granular bainite appears in the microstructure of the steel, meanwhile the mean value of Vickers hardness is 193.3 HV5. When the cooling rate reaches 20 ℃ / s, Martensite and quasi-polygonal ferrite disappeared and the average Vickers hardness was 221.6 HV5. When the cooling rate reached 50 ℃ / s, martensite appeared in the steel and the microstructure was three-phase structure, ie, granular bainite + Bainitic ferrite + martensite, Vickers hardness average reached 224.0 HV5; cooling rate reached 165 ℃ / s, the microstructure of the steel is still three-phase structure, the test steel average Vickers The hardness value reached the maximum of 263.3 HV5 in this test. No pearlite was found in the sample at all cooling rates.