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为考察新型超低碳贝氏体钢连铸坯的热塑性,利用热模拟实验技术研究了Cu-P合金化超低碳贝氏体钢在750～1350℃温度范围的拉伸应力-应变行为,热塑性和拉伸断口的变化,分析了产生这些变化的原因和磷对热塑性的影响机理。结果表明:Cu-P合金化使超低碳贝氏体钢高温拉伸时发生颈缩的应变量减小,但在750～1300℃温区的断面收缩率均达到60%以上。钢中微量硼有效抑制磷在奥氏体晶界的偏聚以及降低先共析铁素体的相变温度是高磷钢保持良好热塑性的主要原因。在800～900℃热塑性的下降与形变诱发Nb(C,N)粒子析出有关。根据热塑性和抗拉强度的变化规律,建议连铸坯在一冷区采取强冷,使表面温度迅速降低到1350℃以下,在二冷区采取弱冷,温度保持在800℃以上,从而使连铸坯始终具有较高的热塑性。
In order to investigate the thermoplasticity of the new ultra-low carbon bainitic steel slab, the tensile stress-strain behavior of Cu-P alloyed ultra-low carbon bainitic steel at 750 ~ 1350 ℃ was studied by means of thermal simulation experiment. Thermoplastic and tensile fracture changes, analysis of the reasons for these changes and the impact of phosphorus on the thermoplastic mechanism. The results show that the Cu-P alloying reduces the amount of strain in the neck when ultra-low carbon bainitic steel is drawn at high temperature, but the reduction of area in the temperature range of 750-1300 ℃ reaches more than 60%. Trace boron in steel can effectively inhibit the segregation of phosphorus in the austenite grain boundaries and reduce the phase transition temperature of pro-eutectoid ferrite is the main reason for high-phosphorus steel to maintain good thermoplasticity. The decrease of thermoplasticity at 800-900 ℃ is related to the precipitation of Nb (C, N) particles induced by deformation. According to the change rule of thermoplasticity and tensile strength, it is suggested that the slab adopt strong cooling in a cold zone, so that the surface temperature can be rapidly reduced to below 1350 ℃, weak cooling in the second cooling zone and temperature above 800 ℃, The slab always has a high thermoplastic.