齿轮钢中残余元素的影响研究

发布时间：2018-07-09 10:31

本文选题：锡 + 铜　；参考：《北京科技大学》2015年博士论文

【摘要】：针对西钢齿轮钢20CrMnTi中Sn等残余元素含量高,生产过程中易产生开裂以及表面缺陷、产品组织及淬透性不稳定等问题,本文对20CrMnTi钢中Sn等残余元素的影响进行了较为系统的研究；首次开展残余元素Sn对20CrMnTi钢组织转变及性能包括力学、冲击、淬透性及疲劳性能等方面的系统研究；同时对Sn等残余元素危害20CrMnTi钢热塑性的机理、改善热塑性的方法、高温氧化行为以及对热塑性改善后的20CrMnTi钢组织转变及淬透性进行了研究。主要结论如下：本研究中,随着Sn含量的增加,马氏体转变临界冷速降低,珠光体转变区域变宽,0.049%的Sn使得Ac3升高了15℃,马氏体形成温度降低13℃。冷速均控制在0.2-1℃/s左右时可获得均匀的铁素体+珠光体组织。Sn含量小于0.049%时,随着Sn含量的增加,抗拉强度和屈服强度有所提高,对面缩率和断后伸长率的影响不大,拉伸断口皆为韧窝状断裂,冲击性能降低,冲击断口皆为准解理断裂。对淬透性和疲劳性能无明显影响。 Sn、Cu恶化20CrMnTi钢的热塑性的主要机理是：①Sn的晶界偏聚,降低20CrMnTi钢的晶界能,弱化晶粒间聚合力,加速晶界微孔的形成和长大以及Sn能阻碍20CrMnTi钢动态再结晶的发生；②硫化铜析出相于晶界析出,促进微孔的形成和裂纹聚合以及Cu能阻碍动态再结晶的发生。随着Sn含量、Cu当量的增加,20CrMnTi钢的热塑性明显降低,热脆性区变宽,在热脆性区内,热塑性先降低后升高,且均在750℃出现塑性谷底。先共析铁素体于奥氏体晶界析出导致塑性谷底的产生,因为铁素体的屈服强度低于奥氏体的屈服强度,在拉伸过程中产生应力集中,恶化热塑性。20CrMnTi钢的临界Sn含量为0.021%、临界Cu当量为0.15。 B和稀土Y能够显著改善含锡20CrMnTi钢的热塑性。随着B/Y含量的增加,热脆性区变小,塑性谷底变浅且均向低温区移动,热塑性逐渐提高,其主要机理是钢中添加B/Y能够抑制Sn的晶界偏聚,增加晶间聚合力,阻碍奥氏体-铁素体转变,防止铁素体在奥氏体晶界析出,增加晶界滑移阻力,加快动态再结晶的发生以及抑制杂质元素S的晶界偏聚,同时B还能促进铁素体于晶内形核,软化奥氏体,提高奥氏体的变形能力,从而改善含锡20CrMnTi钢热塑性。本研究中,添加92ppmB/0.05%Y对含锡20CrMnTi钢热塑性改善效果最佳。高温氧化行为研究发现,含锡20CrMnTi钢在1150℃及1250℃时于空气中氧化1h,因为Sn在基体中具有较大的溶解度和扩散系数,在氧化层/基体界面均未发现富Sn相的存在。当铜锡共存时,1150℃空气中氧化1h,因Cu的扩散系数较小且Sn能降低Cu在奥氏体中的溶解度,所以在氧化层/基体界面发现富Cu相存在；在1250℃氧化时,则因界面处富Cu相的富集量小于消耗量,氧化层/基体界面未发现富Cu相。氧化层分为三层,最外层为Fe2O3层,中间为Fe3O4层,最内层为FeO层。对不同Si含量的含铜、锡钢的高温氧化行为研究发现,Si能降低氧化速率,进而降低氧化层/基体界面处富Cu液相的量,减少晶界渗入；同时,增大内氧化程度,增加氧化层/基体界面粗糙度,促进界面处富Cu液相向氧化层中迁移,进一步减少界面处富Cu液相的量,抑制热脆的产生。添加92ppmB的含锡20CrMnTi钢Ac3温度为844℃,因此,淬火加热温度应选择温度范围为874℃～894℃。冷速控制在0.2～1℃/s左右时可获得均匀的铁素体+珠光体组织。当冷速为3℃/s时,组织主要为粒状贝氏体+马氏体混合组织,同时有极少量的铁素体存在；当冷速大于10℃/s时,钢中全为马氏体组织。B能够提高含锡20CrMnTi钢的淬透性,B含量由15ppm增加到90ppm时,淬透性虽略有变化,但总体差别不大。
[Abstract]:In view of the high content of Sn and other residual elements in the 20CrMnTi steel gear steel, it is easy to produce cracking and surface defects in the process of production and the instability of product and hardenability. The influence of the residual elements such as Sn in 20CrMnTi steel is systematically studied in this paper. The transformation and performance package of the residual element Sn on the microstructure of 20CrMnTi steel for the first time is carried out. The systematic research on mechanics, impact, hardenability and fatigue properties, and the mechanism of Sn and other residual elements to harm the thermal plasticity of 20CrMnTi steel, the method of improving the thermal plasticity, the oxidation behavior at high temperature, and the transformation and hardenability of the 20CrMnTi steel after the improvement of thermoplasticity are studied. The main conclusions are as follows:
In this study, with the increase of Sn content, the critical cooling speed of martensitic transformation is reduced and the pearlite transition region broadens. The 0.049% Sn makes Ac3 rise 15 degrees C, and the martensite formation temperature decreases by 13. When the cold speed is controlled at 0.2-1 C /s, the.Sn content of the homogeneous ferrite + pearlite fabric is less than 0.049%, with the increase of the Sn content. The tensile strength and yield strength are improved, and the effect on the shrinkage and the elongation at the post break is not significant. The tensile fracture is a dimple fracture, the impact property is reduced, and the impact fracture is all quasi cleavage fracture. It has no obvious effect on the hardenability and fatigue properties.
The main mechanism of Sn, Cu to deteriorate the thermal plasticity of 20CrMnTi steel is: (1) the grain boundary segregation of Sn, reducing the grain boundary energy of 20CrMnTi steel, weakening the polymerization force between grain, accelerating the formation and growth of the grain boundary micropores, and hindering the occurrence of dynamic recrystallization of the 20CrMnTi steel, and the precipitation of copper sulfide precipitates at grain boundaries to promote the formation of micropores and the polymerization of cracks. And Cu can impede the occurrence of dynamic recrystallization. With the increase of Sn content and Cu equivalent, the thermal plasticity of 20CrMnTi steel decreases obviously, and the thermal brittleness area becomes wider. In the thermal brittleness region, the thermal plasticity decreases first and then increases, and the plastic valley bottom appears at 750 degrees. The strength is lower than the yield strength of austenite, and the stress concentration is produced during the tensile process. The critical Sn content of the thermoplastic.20CrMnTi steel is 0.021%, and the critical Cu equivalent is 0.15.
B and rare-earth Y can significantly improve the thermal plasticity of tin containing 20CrMnTi steel. With the increase of B/Y content, the thermal brittleness area becomes smaller, the plastic bottom of the grain becomes shallow and is moving to the low temperature zone, and the thermal plasticity increases gradually. The main mechanism is that the addition of B/Y in steel can inhibit the grain boundary segregation of Sn, increase the intergranular polymerization force, obstruct the transformation of austenite ferrite and prevent ferrite. The body is precipitated in the austenite grain boundary, increasing the sliding resistance of grain boundary, accelerating the occurrence of dynamic recrystallization and inhibiting the segregation of the grain boundary of the impurity element S. At the same time, B can also promote the nucleation of the ferrite, soften the austenite, improve the deformability of the austenite, and improve the thermal plasticity of the tin containing 20CrMnTi steel. In this study, 92ppmB/0.05%Y is added to the 20Cr containing tin. The thermo plastic improvement effect of MnTi steel is the best.
The study of oxidation behavior at high temperature found that the 20CrMnTi steel containing tin oxide was oxidized at 1150 and 1250 C in the air, because Sn had large solubility and diffusion coefficient in the matrix, and no rich Sn phase was found in the oxidation layer / matrix interface. When copper and tin coexisted, 1H was oxygenated in the air at 1150 C, because the diffusion coefficient of Cu was small and Sn could reduce Cu in the Austria. The solubility of the Cu phase is found in the oxidation layer / matrix interface; at 1250 C, the enrichment of the rich Cu phase at the interface is less than the consumption, and the rich Cu phase is not found in the oxidation layer / matrix interface. The oxidation layer is divided into three layers, the most outer layer is Fe2O3 layer, the middle is Fe3O4 layer, and the most inner layer is FeO layer. The copper and tin with different Si content The study of high temperature oxidation behavior of steel shows that Si can reduce the oxidation rate, then reduce the amount of Cu liquid rich in the oxidation layer / matrix interface, reduce the infiltration of grain boundary, and increase the degree of internal oxidation, increase the roughness of the oxidation layer / matrix interface, promote the migration of the rich Cu liquid to the oxidation layer at the interface, and further reduce the amount of the rich Cu liquid phase at the interface, and restrain the amount of the rich liquid phase at the interface. The production of heat and brittleness.
The temperature of Ac3 containing tin 20CrMnTi steel added with 92ppmB is 844 C. Therefore, the temperature range of quenching should be selected from 874 to 894 C. The uniform ferrite + pearlite structure can be obtained when the cooling rate is about 0.2 ~ 1 C /s. When the cooling rate is 3 /s, the microstructure is mainly granular bainite + martensite and a very small amount of iron. When the cooling speed is more than 10 /s, the martensitic.B can improve the hardenability of the stannous 20CrMnTi steel, while the B content is increased from 15ppm to 90ppm, although the hardenability changes slightly, but the overall difference is not significant.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

【参考文献】