【作者】 周玉华；

【导师】 樊新民； 单以银；

【作者基本信息】 南京理工大学 ， 材料学， 2010， 硕士

【摘要】 本文以四种成分均符合欧标要求的高速列车用弹簧钢51CrV4为研究对象,重点研究钢中夹杂物对其力学性能的影响。通过控制钢中Al、S、O等杂质元素的含量,制备具有不同夹杂物类型和数量的四种钢。利用Formastor-F热膨胀仪测试钢的CCT曲线,研究钢的相变特性；依据标准DIN 50602对钢中的夹杂物类型及等级予以评定；测试了钢的冲击、拉伸、硬度等常规力学性能,利用超声波疲劳试验机测试其中夹杂物含量与类型均不同的两种钢的疲劳性能。相变特性研究结果表明：1#钢的Ac3为754℃,Ac1为714℃；2#钢的Ac3为750℃,AC1为715℃；3#钢的Ac3为780℃,Ac1为720℃；JK钢的Ac3为766℃,Ac1为669℃；当以高于5℃／s的冷却速度冷却时,四种钢得到的组织主要为马氏体；当升温速度从0.05℃／s提高到50℃／s时,四种钢的Ac3、Ac1均有所升高。常规力学性能测试研究表明：夹杂物等级在K3=62.5以内,随着夹杂物含量的增高,硬度值呈下降趋势；硫化物夹杂的含量对51CrV4钢的拉伸性能影响不明显；随着形貌为细长链状的夹杂的含量的增加,51CrV4钢的冲击性能呈下降趋势。超声疲劳研究结果表明：JK钢存在传统的疲劳极限,为675MPa,而1#钢则不存在。经推算,1#钢的疲劳极限为432.4MPa,可见JK钢的疲劳极限明显高于1#钢。JK钢中的硬质夹杂物尺寸小于其临界夹杂物尺寸4.05μm,故其疲劳断裂起源于表面基体；1#钢中的氧化物夹杂平均尺寸为51.7μm,远大于其夹杂物临界尺寸4.13μm,故其疲劳断裂起源于夹杂物；JK钢中的硫化物夹杂含量高于1#钢中的,两种钢均未出现沿硫化物夹杂起裂的疲劳断口,可见,硫化物夹杂的含量对钢的疲劳极限影响不大。更多还原

【Abstract】 In this paper, four kinds of 51CrV4 whose components are in line with the European standard requirements were as the object of study. Effect of the inclusions in steel to the mechanical properties of steel was studied. By controlling the contents of impurity elements such as Al, S, O, steels with different types and contents of inclusions were produced. Phase transformation character of the four kinds of 51CrV4 was investigated. CCT curves were measured by using the equipment of Formastor-F. According to European standard DIN 50602, the types and grades of inclusion were assessed. The conventional mechanical properties of four steels were tested, such as impact, tensile, hardness. The fatigue properties of two steels in which the types and contents are both different were measured by using the Shimadazu USF-2000 ultrasonic fatigue test machine.The results of phase transformation character show that the Ac3 and Ac1 of 1# steel are respectively 754℃and 714℃; the Ac3 and Ac1 of 2# steel are respectively 750℃and 715℃; the Ac3 and Ac1 of 3# steel are respectively 780℃and 720℃; the Ac3 and Ac1 of 1# steel are respectively 766℃and 669℃. When the cooling rate is faster than 5℃/s, the microstructure of four steels are all martensite. The Ar3 and Arl are all increased when the heating rate increases from 0.05℃/s up to 50℃/sThe results of conventional mechanical properties testing show that when the content of inclusion is under the K3=62.5, the hardness value decline with the content of inclusions increased. The tensile properties has nothing to do with the content of sulfide inclusion; With the content of inclusion which is thin and long increased, the impact properties of the material of 51CrV4 decreased.The results of Utlrasonic fatigue testing show that the traditional fatigue limit of JK exist, and its value is 675MPa, but that of 1# does not. Under the projection, the fatigue limit of 1# is 432.4MPa. It’s obvious that the fatigue limit of JK is higher than that of 1#. Because the size of hard inclusion of JK is smaller than its critical size of 4.05μm, the origin of fatigue fracture is in surface matrix. But the size of the oxide inclusion of 1# is much large than its critical size of 4.13μm, so the origin of fatigue fracture is the inclusions; The content of sulfide in JK is higher than that in 1#, but there’s no fatigue fracture in which the origin is the sulfide inclusion, so it shows the fatigue limit does not depend on the content of sulfide.更多还原