低碳双相钢断口分析

通过不同温度亚温淬火及回火,在15~#钢中得到了不同体积百分比及不同强度比的铁素体马氏体双相组织,并从拉伸断口和冲击断口分析研究了这些组织对钢的力学性能及断裂过程的影响。

低碳双相钢的二次淬火工艺研究

研究了２０ＳｉＭｎＴｉ钢经过不同热处理工艺处理，分析随亚温淬火温度的变化，材料的组织和力学性能的变化规律．热处理可以使材料得到良好的强塑性配合．其抗拉强度达到 ９５０ＭＰａ，屈服强度达到 ９２０ ＭＰａ，伸长率为２０％，断面收缩率为５３．４％．

低碳双相钢的形变强化研究

通过亚温淬火热处理获得双相组织，在此基础上，对试样进行冷拉形变复合强化处理．结果表明，１５５ｉＭｎＴｉ钢经热处理后，强度明显提高，塑性也好；在复合强化后，强度进一步提高，而塑性仍保持较好．

超高强低碳Si-Mn冷轧双相钢的回火组织和力学性能研究

将Fe-0.12C-0.45Si-1.80Mn-0.25Cr钢轧硬材在临界区加热保温后水冷,获得抗拉强度超过1100 MPa的铁素体＋马氏体双相钢.研究了不同温度回火后,该双相钢组织和力学性能的变化.结果表明,低碳Si-Mn冷轧双相钢随着回火温度的提高,强度逐渐下降而伸长率增加.在200～300 ℃回火,强度性能下降不多但伸长率大大提高,而且屈强比低,有利于获得较好的综合性能（抗拉强度大于1000 MPa,总伸长率接近14%）.在回火温度超过300 ℃时,马氏体岛内孪晶晶界变得模糊,回火温度达到600 ℃时,马氏体岛分解比较完全,分解为粗大渗碳体球化颗粒.超过300 ℃回火后,应力应变曲线出现不连续屈服,而且随着回火温度增加屈服平台逐渐伸长.

热处理对低碳硅-铌双相钢组织与性能的影响

研究了不同的热处理工艺对低碳硅-铌双相钢的显微组织、力学性能及冷拔性能的影响。结果表明,试验钢采用临界区淬火和双重淬火两种制度,可在830℃到960℃较宽的温度范围内获得铁素体+马氏体的双相组织,纤维状双相组织或铁素体边界马氏体双相组织同样具有理想的强韧性配合。经300℃充分回火,可消除时效对性能的影响。其钢丝的拉拔率达90%以上,具有良好的成形性及耐磨性能。

In-situ investigation on the fatigue crack propagation behavior in ferrite-pearlite and dual-phase ferrite-bainite low carbon steels

The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel.This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy(SEM),electron backscattering diffraction(EBSD) and fatigue fractography analysis.Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite,and that the cracks in ferrite-bainite steel were "locked" in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous.Moreover,the fatigue fracture surface analysis and the coincidence site lattice(CSL) obtained by EBSD indicated that low-CSL grain boundaries in ferrite-bainite steel distributed more uniformly,which has a more significant effect on the resistance of crack propagation.It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.