| 高速列车用51CrV4钢弹簧材料的工艺、组织和性能研究 | |
| 朱林 | |
| Subtype | 硕士 |
| Thesis Advisor | 单以银 |
| 2010 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 北京 |
| Degree Discipline | 材料加工工程 |
| Keyword | 51crv4 Cct 奥氏体晶粒 热处理 沿晶断裂 |
| Abstract | "实验室以高速列车转向架用51CrV4钢弹簧材料为研究对象： 钢在850℃、950℃加热时，保温时间对晶粒尺寸的影响效果较小；加热温度是影响晶粒尺寸的决定因素，钢在800-900℃保温时，得到的晶粒其尺寸均在10μm以下，但 900℃保温时，钢的原奥氏体晶粒开始出现了混晶现象；950-1200℃保温时，奥氏体晶粒尺寸随着温度的提高呈线性增加。综合上述研究结果制定了该材料的淬火工艺：850℃保温60min油冷淬火。 当淬火试样在特定温度下回火时，其硬度在回火的初始阶段降低速度较快，当回火时间达到30min后硬度值逐渐趋于稳定。回火温度低于310℃时，由于淬火马氏体尚未分解，仍然保持较高的硬度、韧性也未得到改善，因此冲击断口上表现为沿晶断裂特征；当回火温度提高到310-410℃时，马氏体完全分解，钢的硬度和韧性均发生变化，但因碳化物分布在晶界和板条界上，不利于韧性的改善，此温度区间回火材料的韧性不随温度的增加而显著增加，其断口上依然具有沿晶断裂的特征；当回火温度提高到410℃以上时，由于碳化物的形态与分布发生较大的改变，材料的韧性随回火温度的提高而线性增加。另外对淬火试样的热膨胀曲线研究表明，在290℃~410℃之间热膨胀曲线发生了明显的改变，说明此钢的相结构在此温度范围内有较大的变化，这一现象与实验中大尺寸样品在此温度范围内回火所观察到的相组织结构和性能的变化有较好的对应关系。 对钢在310-510℃回火范围内的拉伸性能和部分回火温度下的冲击韧性进行了研究。结果表明该钢在460℃回火时具有较好的强度、硬度、塑韧性以及较好的低温性能。 测定了钢的相变临界温度，研究了加热速度对Ac1和Ac3影响，结果表明：51CrV4钢的Ac1和Ac3 分别为718℃、786℃；当以50℃/s升温时Ac1提高了约15℃，Ac3提高了约42℃。进一步对过冷奥氏体的连续冷却转变特性研究表明：随着冷却速度的提高，51CrV4钢先后得到珠光体、贝氏体、马氏体组织；试样的硬度随着冷却速度的提高快速增加，当冷却速度为10℃/s时，硬度达到稳定值，组织为完全的马氏体组织。结合测定的相变温度，绘制出了51CrV4钢的CCT曲线。" |
| Other Abstract | "A laboratorial scale melted 51CrV4 steel, with satisfactory chemical composition and low non-metallic inclusions content, was forged to rods with diameter of 42mm and studied in the present work. Phase transformation character of the experimental 51CrV4 steel was investigated. Ac1 and Ac3 were measured through thermodilatometric analysis, in which the steel was heated from room temperature to 1000℃ with a heating rate of 0.05℃/s. Heating rate could affect the starting and finishing temperatures of the phase transformation. Ac1 and Ac3 were respectively 15℃ and 42℃ higher when the heating rate was increased from 0.05℃/s to 50℃/s. Microstructure and microhardness of specimens with different cooling rate were studied. It was found that pearlite, bainite and martensite were obtained successively and the microhardness was improved when the cooling rate was higher. Full martensite microstructure could be obtained and the hardness kept unchanged when the cooling rate was 10℃/s or higher. Continuous cooling transformation (CCT) diagram of the steel was drawn through analyses of the cooling thermodilatometric curve, microstructure and micro-hardness. The effects of heating temperature and holding time on austenite grain size were investigated. The results showed that the austenite grain size in the 51CrV4 steel grew up only in the beginning of 30min when the steel was heated at 850℃ and 950℃, and became unchanged when the holding time was even longer at those temperatures. The size of austenite grain size in the 51CrV4 steel was 10μm or smaller when the steel was heated at 800-900℃, but it was in mixed grain sizes when heated at 900℃. The grain size grew up linearly with heating temperature at 950-1200℃. Based on the above results, the 51CrV4 steel should be heated at 850℃ for 60min and oil quenched in order to get better mechanical properties. The effects of tempering temperature and holding time on microstructure and mechanical properties of the 51CrV4 steel were investigated through analyses of the thermodilatometric curve, microstructure, hardness and impact toughness. The hardness of the quenched 51CrV4 steel dropped quickly at the beginning of 30min when the steel was tempered at 260℃, 360℃, 460℃ and 560℃, and became unchanged when tempered for longer time. Mechanical properties of the 51CrV4 steel were dependent on the tempering temperature, and the martensite in the quenched 51CrV4 steel could not decompose completely when tempered below 310℃, resulting in high hardness, low charpy hardness and no intergranular cracking on the fractographs. The hardness dropped remarkably and charpy toughness improved greattly when the steel was tempered at 310℃. The carbide distributed along grain and lath boundaries was harmful to the toughness. The charpy impact toughness was only slightly improved when the steel was tempered at 310-410℃. The carbides were changed both in morphology and distribution when tempering above 410℃, and the toughness was improved linearly with tempering temperature. The thermodilatometric curves were changed greatly at 310℃ and 410℃, which agrees with changes of the microstucture and toughness. Better tensile property, hardness, low temperature toughness could be obtained when the 51CrV4 steel was tempered at 460℃." |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/64232 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 朱林. 高速列车用51CrV4钢弹簧材料的工艺、组织和性能研究[D]. 北京. 中国科学院金属研究所,2010. |
| Files in This Item: | There are no files associated with this item. | |||||
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Edit Comment