退火温度对冷轧Fe-Mn-Al-C低密度钢性能的影响

Effect of Annealing Temperature on Properties of Cold Rolled Fe-Mn-Al-C Low Density Steel

在850-1050℃范围内系统分析了冷轧Fe-Mn-Al-C钢的力学性能、金相组织、XRD图谱以及断裂行为,研究其在退火过程中奥氏体、铁素体、碳化物与力学性能的转变规律。结果表明,在850℃退火处理后冷轧Fe-Mn-Al-C钢的组织为奥氏体+带状d-铁素体+a-铁素体+k碳化物,晶间网状铁素体和较高的碳化物含量使钢板具有较高的强度但是塑性极差,发生解理断裂;在900-1050℃钢板的基体为奥氏体组织,a-铁素体含量下降,而带状d-铁素体破碎呈不连续岛状分布;当d-铁素体长大程度超过奥氏体组织时,铁素体含量增大,XRD峰值升高;退火组织的转变导致抗拉强度随温度的升高而下降,断后伸长率提高;在1000℃时强塑积达到最高值,得到强度与韧性的良好组合,抗拉强度为1003.1 MPa,断后伸长率为41.28%,强塑积为41.41 GPa·%。为了使冷轧Fe-Mn-Al-C钢具有良好的强韧性,退火温度不可低于950℃。同时,Fe-Mn-Al-C钢的测量密度为6.55 g·cm-3,减重效果显著,达到16.6%。

Effect of annealing treatment in a temperature range of 850-1050℃ on the evolution of microstructure involved with austenite, ferrite and carbides etc., as well as the mechanical properties and fracture behavior was studied for a cold rolled Fe-Mn-Al-C low density steel. The results show that the experimental steel annealed at 850℃ exhibits a complex microstructure consisted of austenite, banded dferrite, a-ferrite and small amount of carbides; there also existed intercrystalline network of ferrite and carbides which resulted in higher strength and poor plasticity, thus the steel becomes susceptible to cleavage fracture; the steel annealed at 900- 1050℃ consisted of recrystallized austenite as matrix, in which the volume fraction of a- ferrite decreased with the increasing temperature, while the band like d- ferrite was crushed into islets and distributed in the matrix discontinuously; as the growth of d-ferrite was more obvious than that of austenite, larger volume fraction of ferrite did occur, which resulted in high intensity of X-ray diffraction peaks of ferrite; the microstructure evolution during annealing lead to decrease of tensile strength and increase of total elongation with the increasing temperature; the experimental steel annealed at 1000℃ exhibits excellent combination of strength and ductility: i.e. tensile strength 1003.1 MPa,total elongation 41.28% and product of strength with ductility 41.4 GPa·%. Therefore, to acquire the optimal combination of strength and ductility, the cold-rolled Fe-Mn-Al-C steel should be annealed at temperatures above 950℃. Furthermore, the measured density of 6.55 g·cm- 3ensures this kind of ultra- high strength steel a remarkable weight reduction effect of 16.6%.