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本文叙述热轧条件对于几种碳素钢的奥氏体晶粒度和其机械性能的影响;同时对于压下的积累作用以及奥氏体晶粒大小对于热轧特征如塑性、变形阻力和冲击靱性的影响亦作了探讨。 研究结果示:原始奥氏体晶粒较粗大的轧件,除了随冷却速度的降低而晶粒变粗的一般趋势外,沿出现了不均匀的长晶粒、带状组织和魏氏组织;合碳较高(0.66％C)的钢材则随着冷却速度的不同而出现了索氏体、珠光体和铁素体。 随着奥氏体晶粒的加大,屈伏强度σ_s和低温(-20℃)冲击靱性α_k有显著的降低。轧制后的冷却速度(同一的奥氏体晶粒度)对于断面减缩率ψ的影响不大,但是随着冷却速度的提高,σ_s、σ_b和高低温冲击靱性a_k都有所提高。 在1050℃轧制不同含碳量的钢材时,均出现了发生粗大奥氏体晶粒的临界加工量区域(介于0—10％之间),不过在同一热轧条件和临界加工量范围内,从各钢种获得的最大奥氏体晶粒度有相当大的差别,其中以40号钢有最小的晶粒度(约21/2号),而钢三有最大的晶粒度(约0号),保温时间对40号钢的晶粒度的影响最小,而对钢三的晶粒席的影响最大。 在各钢种中,压下的积累均相当显著,而影响轧件的奥氏体晶粒度以最后一次的压下量起较大的作用。如果最后一次的压下量在临界数值内(钢三为5—15％之间

A study has been made on the effects of hot working conditions on the austenitic grainsize and mechanical properties of carbon steels. At the same time, the cumulative effect ofsuccessive reductions and the effect of austenitic grain size on such hot working characteristics asplasticity, resistance to deformation and the impact values have also been investigated. Thefollowing are the results obtained. Specimens having coarse austenitic grain size, besides the general tendency of giving greatergrain size with the increase in cooling speed, also give nonuniform long grains, banded structuresand widmanstatten structures. Specimens having higher carbon contents (0.66％C) give sorbitic,pearlitic and ferritic structures with different cooling speeds. With the increase in the austenitic grain size, there is a notable lowering in the yield pointand the impact values at—20℃. Tensile tests with specimens having the same austenitic grainsize show that the cooling speed after rolling has little effect on the reduction in area, but withthe increase in cooling speed there is a raise in the yield point, the ultimate strength and theimpact values at room temperature and at—20℃. When steels with different carbon contents are rolled at 1050℃, there appears a criticalreduction range between 0 and 10％, in which the austenitic grains become coarse. However,under the same hot working conditions and within the same critical reduction range, there is alarge difference in the largest grain size obtained with different carbon steels. The soaking timehas also different effects on different steels. In all steels investigated, there is a marked cumulative effect of reduction, but the reductionin the last hot working operation has the greatest effect on the austenitic grain size. Hence it isimportant to avoid critical reduction in the last rolling pass. Specimens from carbon steels having No. 0 and No. 8 grain sizes respectively show littledifference in their hot working characteristics: at 900℃, the difference in impact values betweenthese two specimens amounts only to 8％, the difference in the resistance to deformation to 3％and the difference in the critical reduction in height at fracture in the impact compression testamounts only to 2％.