Cu-P合金化超低碳贝氏体钢的热塑性

Hot ductility of Cu-P alloyed ultra-low carbon bainitic steel

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 evaluate the hot ductility of newly developed ultra-low-carbon bainitic steel,tensile stress-strain behavior of the steel were studied by using thermal simulation testing technology.The fracture surfaces were observed by SEM.The results show that although Cu-P alloying reduces the strain at necking point,the reduction of area of the steel are still more than 60% in the temperature range of 750-1300 ℃.The good hot ductility of P-bearing steel is attributed to that trace boron in the steel effectively inhibits phosphorous segregation at grain boundary and decreases the transformation temperature of austenite to pro-eutectoid ferrite.Nb（C,N） precipitation induced by deformation leads to the decrease of ductility at 800-900 ℃.Considering the hot ductility and ultimate strength of ultra-low-carbon bainitic steel,it is suggested that continuous cast slab should be strongly cooled at the first cooling stage to decrease temperature below 1350 ℃ and weakly cooled at the second cooling stage to keep temperature above 800 ℃.