化学成分对轧制复合基层用低合金钢力学性能的影响

由于复合板加工工艺的特殊性,要求对基板用低合金钢进行相应的化学成分设计。通过稳定化热处理,研究了化学成分对化学成分不同的三种低合金钢力学性能的影响。结果表明,在稳定化热处理过程中,Ni、Cu、V等元素的加入,使得细小的原始奥氏体晶粒内部发生马氏体相变而形成簇状组织。因此,低合金钢的强度提高,低温韧性也提高。

600MPa级磁轭用钢循环载荷下的温度变化与疲劳极限评定

基于循环载荷下试样表面温度的变化规律,研究了600 MPa级磁轭用钢的循环变形行为,并对其疲劳极限进行了评定。结果表明:在静载荷和循环载荷下600 MPa级磁轭用钢的表面温度均呈规律性变化,循环载荷下更易产生不可逆变形。根据不同应力水平下温度稳定值的拐点确定出600 MPa级磁轭用钢的疲劳极限为277 MPa,而根据S-N曲线测定的疲劳极限为270 MPa,两者相差2.5%,说明根据试样表面温度变化规律能准确评定600 MPa级磁轭用钢的疲劳极限。

Variations in the Microstructure and Properties of Mn-Ti Multiple-phase Steel with High Strength under Different Tempering Temperatures

There are few relevant researches on coils by tempering,and the variations of microstructure and properties of steel coil during the tempering process also remain unclear.By using thermo-mechanical control process（TMCP）technology,Mn-Ti typical HSLA steel coils with yield strength of 920 MPa are produced on the 2250 hot rolling production line.Then,the samples are taken from the coils and tempered at the temperatures of 220℃,350℃,and 620℃respectively.After tempering the strength,ductility and toughness of samples are tested,and meanwhile microstructures are investigated.Precipitates initially emerge inside the ferrite laths and the density of the dislocation drops.Then,the lath-shaped ferrites begin to gather,and the retained austenite films start to decompose.Finally,the retained austenite films are completely decomposed into coarse and short rod-shape precipitates composed of C and Ti compounds.The yield strength increases with increasing tempering temperature due to the pinning effect of the precipitates,and the dislocation density decreases.The yield strength is highest when the steel is tempered at 220℃because of pinning of the precipitates to dislocations.The total elongation increases in all samples because of the development of ferrites during tempering.The tensile strength and impact absorbed energy decline because the effect of impeding crack propagation weakens as the retained austenite films completely decompose and the precipitates coarsen.This paper clarifies the influence of different tempering temperatures on phase transformation characteristics and process of Mn-Ti typical multiphase steels,as well as its resulting performance variation rules.

铌微合金对1GPa级热轧双相钢组织及性能影响

为了研究微合金元素铌对热轧双相钢组织和性能的影响,采用相同的工艺制备了含铌和不含铌2种热轧双相钢。通过光学显微镜(OM)、透射电镜(TEM)、X射线衍射仪(XRD)及电子背散射衍射(EBSD)等方法表征了组织变化规律,并分析了铌对双相钢力学性能影响及试验钢的强化机制。结果表明:2种双相钢显微组织均为铁素体和马氏体,铌钢中马氏体体积分数更高;由于铌抑制动态再结晶,无铌钢晶粒以等轴状为主,而铌钢晶粒更细,晶粒呈长条状。铌钢的抗拉强度为1306 MPa,屈服强度为1269 MPa,硬度为40HRC,冲击功为66.5 J,伸长率为12%。位错强化是试验钢的主要强化机制,占总强度40%以上,铌微合金使得试验钢析出强化增量从69 MPa(7%)增加到277 MPa(22%)、位错强化增量从480 MPa(51%)增加到539 MPa(42%)和细晶强化增量从143 MPa(15%)增加到219 MPa(17%),从而导致铌钢强度增高。