对低碳钢在Ae3以上进行了单道次快速大形变量变形, 测定了材料在高温变形前后的室温拉伸曲线并观察其断口形貌。对结果的分析表明, 低碳钢在Ae3以上的温度发生形变诱导铁素体相变, 是形成超细晶粒(3 μm左右)的主要原因。应变速率大于0.1 s-1时, 可诱导形成铁素体晶粒, 且随着应变速率的提高铁素体分数增加而晶粒尺寸减小; 当应变速率大于10 s-1时铁素体分数达到饱和, 晶粒尺寸的变化不大。与先共析铁素体相比, 形变诱导铁素体的强度和硬度大大提高, 低碳钢Q235的屈服强度由250 MPa左右提高到510 MPa, 抗拉强度则达到615 MPa, 而形变诱导铁素体的塑性有所降低, 但仍保持较高的水平。
A series of tests of fast-single pass-heavy deformation in low carbon steel was carried out using Gleeble 3500 thermal-mechanical simulation machine at the temperature above Ae3. The mechanical property of material before and after deformation was tested, and the fracture morphology was observed. Results denote that the deformation induced ferrite transformation (DIFT) above Ae3 is responsible for the ultra-fine grain size (about 3 μm). DIF can be induced when strain rate was 0.1 s−1. With the raise of strain rate, ferrite fraction becomes larger and the grain size smaller until DIF is saturated at the strain rate of 10 s−1. Grain refinement through DIFT leads to an increase in strength and hardness. For low carbon steel Q235, the yield strength can be improved from 250 MPa to 510 MPa and the tensile strength arrives at 625 MPa, and the plasticity decreases slightly which will remains in high level.
参考文献
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