Effect of Annealing on Microstructure and Hardness of Ultra-high Strength Low Alloy Bainitic Steel
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摘要: 针对国内某钢厂生产的低合金超高强度贝氏体钢设计了3种不同锻后冷却+等温退火软化工艺,利用扫描电镜观察不同退火工艺下试验钢的显微组织,并采用布氏硬度计测试其硬度。结果表明:锻后空冷+亚温球化退火工艺下材料显微组织为回火托氏体,碳化物呈断续状或短片状,硬度(HB)为270;而锻后空冷+等温球化退火工艺下显微组织仍为回火托氏体,碳化物则呈粗大条状,硬度(HB)为290;试验钢经锻后炉冷+亚温球化退火工艺处理后,其显微组织转变为回火索氏体,钢中的M-A岛分解,碳化物球化并聚集长大,铁素体发生回复,材料硬度(HB)大幅降低至245,满足切屑加工性能要求。Abstract: Three different annealing processes regarding forge cooling and isothermal softening were designed for ultra-high strength low alloy bainite steel produced by a domestic steel plant. The microstructure of the samples under different annealing processes was observed by scanning electron microscope,and the hardness was measured by a Brinell hardness tester. The results show that the microstructure of the materials under air cooling +sub-thermal spheroidization annealing is composed of tempered tortolite,where the carbides are intermittent or patchy,and hardness is 270 HB. The microstructure under air cooling +isothermal spheroidization annealing is still composed of tempered tortolite,where the carbides are thick strips,and hardness is 290 HB. The microstructure under furnace cooling +sub-thermal spheroidization annealing is composed of tempered sostenite,where the M-A islands are decomposed,the carbides are spheroidized and aggregated,and the ferrite is recovered. Hardness of steel with the later process is significantly reduced to 245 HB,which is appropriate for cutting performance.
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Key words:
- bainite steel /
- annealing /
- microstructure /
- carbide /
- hardness
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