【作者】 王飞；

【导师】 刘日平；

【作者基本信息】 燕山大学 ， 材料学， 2022， 博士

【摘要】 传统钢铁已经难以满足当今日益苛刻的服役环境,因此亟需一种耐蚀、轻质、高强等优点集于一身的材料。目前备受关注的Fe-Mn-Al-C系低密度钢的研究还不完善,尚有许多问题需要解决,如:组织和性能随成分、热处理和变形条件的变化规律仍需要进行全面的探讨。本文以Fe-Mn-Al-C系低密度钢为基础,通过微合金化、改善变形和热处理工艺等手段优化其相组成及组织结构,从而获得综合力学性能优异,耐腐蚀性能出众的低密度钢。在实验室研究阶段使用真空电弧熔炼炉制备了一系列以微合金元素Ti含量为单一变量的低密度钢合金铸锭,研究了Ti含量的变化对低密度钢组织和力学性能的影响。添加Ti对材料力学性能的提升幅度明显。随着Ti含量的增加,低密度钢的屈服强度和抗拉强度呈上升趋势,其平均晶粒尺寸呈下降趋势。在添加重量百分数为0.3%的微合金元素Ti即可形成Ti C阻止晶界的长大,同时阻止了位错的滑移,从而提高强度。当添加0.6%Ti（wt.%）时,低密度钢的屈服强度达1031.8±11.9 MPa,抗拉强度达1158.6±20.6 MPa,断后延伸率为24.0±1.1%。相比于未添加Ti的样品,0.6%Ti低密度钢的强度提升明显。在实验室研究遴选最优力学性能0.6%Ti低密度钢的基础上,使用真空感应熔炼炉等工业生产设备获得了0.6%Ti低密度钢并设计了不同工艺的热变形处理。低密度钢的平均晶粒尺寸随轧制温度的降低而减小,同时,其屈服强度和抗拉强度随轧制温度的降低呈上升的趋势。在本试验中,当轧制温度为950℃时,0.6%Ti低密度钢展现出最优异的综合力学性能,屈服强度为841.4±12.9 MPa,抗拉强度为1008.2±18.7 MPa,断后延伸率为49.5±2.6%。因此,对于0.6%Ti低密度钢来讲,950℃为最优轧制温度。研究了退火温度和冷却方式对变形量为30%的冷轧态0.6%Ti低密度钢组织和力学性能的影响。样品经冷轧后引入大量位错,随着退火温度的升高,位错密度呈现下降的趋势,未进行退火处理样品的位错密度为5.61×10¹⁵ m^-2,而在550℃水冷至室温样品的位错密度为3.51×10¹⁴ m^-2,与未进行退火处理样品相比降低了一个数量级。此外,随着退火温度的升高,0.6%Ti低密度钢的屈服强度和抗拉强度呈下降的趋势,而断后延伸率呈明显上升的趋势,经450℃退火处理的空冷样品表现出最优综合力学性能,其屈服强度为1270.3±10.7 MPa,抗拉强度为1318.7±17.3 MPa,断后延伸率为19.5±1.2%。与未进行退火处理样品相比,其屈服强度仅下降9.3%,而断后延伸率增加达192.8%。在不同温度下经热轧处理0.6%Ti低密度钢的全浸失重试验以及电化学试验结果表明,随着轧制温度上升,低密度钢的耐蚀性提高。除此之外,由于在低密度钢中Cr和Al的存在,导致样品表面形成一层氧化膜,阻止了腐蚀介质对材料基体的腐蚀。在本文中还讨论了低密度钢的腐蚀机制,丰富了Fe-Mn-Al-C系低密度钢的相关研究,为低密度钢在工业上的应用提供了理论基础。更多还原

【Abstract】 Traditional steel has hardly met today’s increasingly harsh service environment,so a material that combines corrosion resistance,light weight and high strength is urgently needed.At present,the research on Fe-Mn-Al-C series low-density steel has attracted much attention,while it is not perfect and there are still many problems to be solved,such as:the variation law of structure and properties with composition,heat treatment and deformation conditions still needs to be comprehensively discussed.In this thesis,based on Fe-Mn-Al-C series low-density steel,the phase composition and microstructure of low-density steel were optimized by means of micro-alloying process,improvement on deformation and heat treatment process,so as to obtain the low-density steel with excellent comprehensive mechanical properties and outstanding corrosion resistance.In the laboratory research stage,a series of low-density steels with the content of Ti as a single variable were prepared using a vacuum arc melting furnace.The effects of Ti content on the microstructure and mechanical properties of the low-density steel were studied.The mechanical properties of the steels have been significantly enhanced by incorporating Ti.With the increase of Ti content,the YS and UTS of the low-density steel both showed upward trends,while its average grain size showed a downward trend.The incorporation of 0.3%Ti（wt.%）can form Ti C,prevent the growth of grain boundaries and prevent the slip of dislocations,thereby enhancing the strength.When 0.6%Ti（wt.%）was incorporated,the YS of the low-density steel reached 1031.8±11.9 MPa;the UTS reached1158.6±20.6 MPa and the TE was 24.0±1.1%.Compared with the samples without Ti,the low-density steel containing 0.6%Ti had a significantly enhanced strength.On the research basis of selecting the 0.6%Ti low-density steel with the best mechanical properties in the laboratory,the 0.6%Ti low-density steel was obtained by using industrial manufacturing equipment such as vacuum induction melting furnaces and the heat deformation treatments with different processes were designed.The average grain size of the low-density steel decreased with the decrease in rolling temperature,while its YS and UTS both showed upward trends.In this test,when the rolling temperature was 950℃,the0.6%Ti low-density steel exhibited the most excellent comprehensive mechanical properties with the YS of 841.4±12.9 MPa,the UTS of 1008.2±18.7 MPa and the TE of49.5±2.6%.Therefore,for the 0.6%Ti low-density steel,950℃was the optimal rolling temperature.This thesis studied the effects of annealing temperature and cooling method on the microstructure and mechanical properties of cold-rolled 0.6%Ti low-density steel with a deformation of 30%.A large number of dislocations were introduced into the samples after a cold rolling.With the increase in annealing temperature,the dislocation density tended to decrease.The dislocation density of the sample without annealing treatment was 5.61×10¹⁵m^-2,while the sample water-cooled to room temperature from 550℃was 3.51×10¹⁴ m^-2,one order of magnitude lower than that without annealing treatment.In addition,with the increase in annealing temperature,the YS and UTS of the 0.6%Ti low-density steel both showed downward trends,while the elongation after fracture increased significantly.The air-cooled samples annealed at 450℃showed the best comprehensive mechanical properties with the YS of 1270.3±10.7 MPa,the UTS of 1318.7±17.3 MPa and the TE of19.5±1.2%.Compared with the samples without annealing treatment,the YS decreased by only 9.3%,while the elongation after fracture increased by 192.8%.The total immersion weight loss test and electrochemical test of the 0.6%Ti low-density steel hot-rolled at different temperatures showed that the corrosion resistance of the low-density steel increased with the increase in rolling temperature.In addition,the presence of Cr and Al in the low-density steel formed an oxide film on the sample’s surface,which prevented the corrosion of matrix caused by the corrosive medium.In this thesis,the corrosion mechanism of the low-density steel was also discussed,which enriched the related studies on the Fe-Mn-Al-C series low-density steel and would provide a theoretical basis for the industrial applications of the low-density steel.更多还原