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: Materials Science >> Materials Science (General) submitted time 2017-11-21 Cooperative journals: 《金属学报》
Abstract：以9Cr18合金为研究对象，分别对9Cr18热轧态材料及半固态坯料进行触变压缩实验。通过OM和SEM研究了其在加热、半固态及变形冷却后的显微组织演变规律，分析了其压缩过程的固液流动特性和应力-应变关系。研究表明，半固态坯料制备是保证材料发挥半固态变形特性的必备流程，坯料加热至半固态温度能够保证固液三维均匀分布，充分发挥液相流动特性。仅通过对轧态材料加热至半固态温度区间会导致液相沿原带状组织区域熔化析出，固液分布不均匀。热轧态材料带状熔化致使液相不能形成三维连通，液相流动只能在不同部位的若干区域进行，变形主要通过固相颗粒塑性变形完成，进入最后阶段变形抗力上升。半固态坯料变形过程中固液相分布均匀，当变形进行至触变阶段，液相由于受到向外侧压力梯度作用，在固相间隙中流动，固相颗粒予以协调，发生宏观固液分离，从而使变形抗力随之下降。9Cr18合金在半固态温度区间成形过程中表现出不同于传统热处理的组织演变规律。半固态温度范围内奥氏体溶解合金元素的能力较传统奥氏体化 (1050 ℃)极大提高，从而提高了奥氏体在快速冷却过程中的稳定性，在冷却后得到过饱和的亚稳奥氏体组织。半固态独特的组织演变过程为材料组织性能控制提供一种新的可能，可以据此设计满足特殊要求的热处理工艺。
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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