冷却速度对超低碳微合金钢组织和性能的影响

Effect of cooling rate on microstructure and mechanical properties of ultra-low carbon micro-alloyed steel

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。

Heat treatment experiment was carried out on an ultra-low carbon micro alloyed steel with different cooling rate by means of Formaster-F automatic phase transformation measurement device. The microstrueture and hardness were tested by metallographic microscope and 450SYD digital Vickers hardometer. Results show that microstructure of the tested steel is polygonal ferrite and the maximum average hardness is 177.0 HV5 when the cooling rate is less than 1 ℃/s; some quasi-polygonal ferritc appears and the average hardness is 197.3 HV5 when the cooling rate reaches 3 ℃/s; some granular bainite exists and the average hardness is 193.3 HV5 when the cooling rate reaches 5 ℃/s; some bainite ferrite appears and quasi-polygonal ferrite disappears when the cooling rate reaches 20 ℃/s, and the average hardness is 221.6 HV5; when the cooling speed is up to 50 ℃/s, some martensite appears, and the microstructure is composed of granular bainite, bainite ferrite and martensite, and the average hardness is 224 HV5; when the cooling rate reaches 165 ℃/s, the microstructure is still composed of granular bainite, bainite ferrite and martensite, and the average hardness is 263.3 HV5. Under all of the cooling rate, pearlite does not appear in all the specimens.