In this study, the microstructures and mechanical properties of X70 pipeline steels produced with varying Mo contents, accelerated cooling rate and intermediate slab blank thickness are systematically investigated. Results showed that the microstructures and mechanical properties of the X70 pipeline steels were strongly affected by Mo addition. The pearlite and proeutectoid ferrite formation is obviously inhibited in containing-Mo steel and the acicular ferrite (AF) is obtained in a wide range of cooling rates. With the increasing the cooling rates, the AF constituent amount increases. The grains can be refined by increasing the thickness of intermediate slab for enhancing the cumulative reduction rates, and meanwhile increase the number density of precipitates. It was proved by simulation and industrial trials that the low-alloy X70 pipeline steels can be produced increasing cooling rates and the thickness of intermediate slab without strength and toughness degradation which also reduce alloy cost.

In this study, the effect of deformation amount distribution of X70 pipeline steel on the microstructure and mechanical properties in the austenite recrystallization temperature region are investigated. The results reveal that the austenite grain size is smaller and more uniform by increasing the last-pass rough rolling deformation amount in the austenite recrystallization region. An increase in the last-pass rough-rolling deformation amount can also improve the strength and low-temperature toughness. The deformation mechanism and microstructural evolution based on the last-pass in the austenite recrystallization temperature region are clarified. The final microstructure refinement effect of granular bainite and acicular ferrite attribute to the finer and more uniform original austenite grain size. The main strengthening mechanisms are grain boundary strengthening and dislocation strengthening. The high proportion of the high-angle grain boundary is significantly greater for improving the strength and toughness, which impedes dislocations to slip across grain boundaries.

利用热轧试验机组、Zeiss光学金相显微镜及透射电子显微镜(TEM)研究了在线固溶处理工艺及轧后待温时间对其组织和性能的影响.结果表明,在线固溶处理与离线固溶处理相比铁素体含量更高,屈服强度和抗拉强度较高,塑性和低温韧性降低较为明显,随着轧后待温时间的增加,锯齿状奥氏体含量逐渐降低,并最终转变为岛状奥氏体.TEM分析表明,在线固溶处理的铁素体相内分布大量位错.随着待温时间增加,铁素体和奥氏体的相界处有Cr2N相析出,造成钢板的塑性和耐蚀性能降低,考虑到脆性相析出数量及奥氏体形态演变,轧后钢板应快速入水.

In this study, the flow behaviour, and microstructure evolution of the SDSS2507 were systematically investigated via hot compressive tests. Subsequently, the hot processing map was constructed according to the obtained stress–strain curves and corresponding equations. Additionally, metallographic examinations of hot compressed specimens found that the softening mechanism of the ferrite and austenite is dynamic recovery (DRV) and dynamic recrystallisation (DRX), respectively. With increasing the strain rate, it promotes the DRX in austenite. Moreover, micro-cracks could initiate from the ferrite/austenite phase boundaries or grain boundaries within the ferrite due to the strong discrepancy of deformation coordination between the two phases or precipitation of Cr2N precipitates along the ferrite/austenite phase boundaries or ferrite grains at higher strain rate. Considering the hot processing map and microstructural evolution in SDSS2507, the optimum hot processing parameters for SDSS2507 are found to be in a low strain rate range of 0.1–3 s−1 with the temperature range of above 950°C.

通过热轧厂热轧和冷轧厂盐酸酸洗,试制了含钛和不含钛的两种热轧酸洗钢板.采用金相显微镜、透射电子显微镜和拉伸试验机研究了两种试制钢板的显微组织和性能.结果表明:两种钢板的显微组织均由铁素体和珠光体组成,其屈服强度达到400 MPa以上,抗拉强度高于500 MPa,断后伸长率大于30％.与不含钛的钢相比,含钛钢的晶粒细小,屈服强度和抗拉强度高,断后伸长率低,屈强比高.

在实验室条件下采用金相组织观察、力学性能测试等手段分析了试验钢的性能和组织.通过对普碳钢进行成分微调、控轧控冷工艺以及利用时效处理在鞍钢热连轧生产线上开发研制了抗拉强度达590 MPa的高强度车轮用钢,并进行了带合同工业试制,实现年生产量4万余t.

简要介绍了SAPH400热轧钢板的研制生产,并对开裂样件进行了缺陷分析.结果表明,钢板边部宏观"卷边"容易在后续变形时沿边部开裂.基体组织主要为贝氏体,降低了钢板的整体塑性,同样容易导致钢板在加工变形时开裂失效.

某汽车大梁用500L-Z钢在冲压过程中出现开裂.采用宏观检验、金相检验和扫描电镜检验对其冲压开裂的原因进行了分析.结果 表明:在冲压过程中,切边不平直处发生加工硬化导致开裂,而试样中间的珠光体偏析带也是产生裂纹的原因之一.