Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： 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- 3 ensures this kind of ultra- high strength steel a remarkable weight reduction effect of 16.6%.
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology submitted time 2018-06-28 Cooperative journals: 《干旱区研究》
Abstract： 以古尔班通古特沙漠南缘莫索湾为研究区，选取植被盖度依次为10%、15%的固定半固定沙丘以及植被盖度为30%的固定沙丘作为典型样地，用典范排序（CCA）的方法对该地区样方、环境因子与物种多度之间进行对应分析，用典型相关分析的方法对各样地物种多样性与地形因子、土壤理化因子之间进行相关分析。结果表明：物种与环境因子之间存在显著的相关关系，前4轴可以解释物种总变异的84.4%，土壤砂粒是影响物种分布一个较为敏感的指示性因子，物种大量分布在土壤砂粒所在的排序轴上；受地形影响较大的物种有硬萼软紫草、黄花珀菊、砂蓝刺头、刺沙蓬；受土壤有机质、土壤水分、土壤pH影响显著的物种有齿稃草、角果藜、黄耆、尖喙牦牛儿苗。不同指标体系的典型相关分析结果表明：地形与物种多样性因子之间第1 对典范相关系数为0.54，土壤理化因子与物种多样性的第一对典范系数分别为0.93、0.96,第二对典范系数分别为0.79、0.80,存在着显著的相关关系。地形因子中，坡向主要影响物种丰富度指数Simpson；土壤理化因子中，砂粒和土壤有机质主要影响优势度指数Shannon,土壤含水量和pH主要影响均匀度指数Pielou。该区域物种分布状态是由地形和土壤因子共同作用。
Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Basic Disciplines of Agriculture submitted time 2017-11-10 Cooperative journals: 《中国生态农业学报》
Abstract：为探究古尔班通古特沙漠南缘莫索湾地区33 年来人工梭梭林群落(依靠天然降水)的生态特征, 本文对两种造林技术(积雪-客沙造林和秋灌造林)人工梭梭林地梭梭的长势、草本植物、土壤水分进行了调查和监测。结果表明: ①积雪-客沙造林和秋灌造林梭梭至今生长良好, 目前植株高度和冠幅均大于2 m 和2 m2, 当年新生枝条长度均大于20 cm; 初始造林梭梭存活率较高, 分别为40%和63%; 经过自然更新, 现有密度均有所提高, 人工林形成异龄复层混交林, 林下生长有不同优势种的草本植物; 土壤含水量均>2.00%, 能够满足梭梭生长。②由于两种造林技术的土地处理方式和初期水分供给量不同, 导致两种林地梭梭生长、林下草本植物盖度和多样性以及天然更新梭梭植株数量均有很大差异, 整体秋灌造林地的状况优于积雪-客沙造林地。③两种造林技术对于当地生态条件均有很好的适应性, 虽然积雪客沙造林密度相对较低, 但优于自然植被状况, 且造林成本低;秋灌造林密度较大, 天然更新植株数量较多, 但造林成本高, 后期生长较缓慢, 需要采取一定的人工措施调整密度。综上可知, 积雪-客沙造林和秋灌造林梭梭目前生长均较稳定, 后者对该区生态条件适应性更强。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：通过腐蚀磨损试验研究了下贝氏体球墨铸铁材料的腐蚀磨粒磨损行为，分析了影响腐蚀磨损失重率的主要因素。采用SEM和TEM对磨损表面特性进行了分析；根据磨损表层纵剖面的显微硬度研究了材料表层在腐蚀磨损过程中的形变硬化效应；结合下贝氏体球墨铸铁的电化学行为研究了载荷对耐腐蚀性能的影响。结果表明：下贝氏体球墨铸铁的腐蚀磨损机理为化学腐蚀失重和犁沟式磨粒磨损。载荷的提高对表面粗糙度、材料表面与磨粒之间的摩擦力以及磨粒压入材料表面的深度有显著的影响，从而导致磨粒磨损失重率显著上升；并且，较高的载荷作用下，材料表面出现分层组织和条带状石墨，形成局部微型原电池，促使腐蚀速率提高，同时分层组织的疲劳断裂也将促使失重率进一步提升；不过，载荷的增加使得基体中残留奥氏体内部出现大量位错的缠结，促进材料表面硬化，这在一定程度上提高了材料的耐磨性能。当载荷从10 N增至200 N时，腐蚀磨损失重率从0.16 g/(cm2?h)增至0.42 g/(cm2?h）；当粗糙度Ra值由0.12 μm增大到5.2 μm时，腐蚀电流从0.56 mA上升至5.62 mA。另外，下贝氏体球墨铸铁的腐蚀磨损失重曲线可分为三个阶段，分别为磨损初期的点接触加速磨损阶段、磨损中期的面接触稳定磨损阶段、磨损后期的疲劳磨损失稳阶段。
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