20CrMnTi钢齿轮疲劳寿命研究

Research on Fatigue Life of 20CrMnTi Steel Gear

齿轮是推土机等工程机械的常用重要传动件,使用中其失效主要由疲劳所致。为了弄清这类齿轮疲劳失效的原因,提高齿轮的疲劳寿命,制作了试验用20CrMnTi钢齿轮,对其渗碳至1.8~2.4 mm和2.4~3.0 mm两种深度,炉冷至840℃油淬,随后再次加热至840℃油淬,180℃回火。采用MTS Landmark250KN型电液伺服试验机对齿轮进行了动态压缩试验,采用电子显微镜观察齿轮的疲劳断口形貌。结果表明,渗碳层越深,齿轮的疲劳寿命越高,疲劳断口可分为裂纹源区、裂纹扩展区和瞬断区三部分,距表面100~200μm处有少量产生裂纹源的微孔洞。此外,齿轮表面的机加工缺陷也易导致裂纹源的形成。

Gear is an important transmission part commonly used in such engineering machinery as bulldozers and the others, and its failure in service is attributed to primarily fatigue. For the purpose of discovering the reason why gear fails due to fatigue, the gears for test were made from 20CrMnTi steel, and carburized to two depths of 1.8 to 2.4 mm and 2.4 to 3.0 mm, furnace-cooled to 840℃ and oil-quenched, then again heated to 840℃ and oilquenched, and tempered at 180℃. Subsequently, the gears were subjected to dynamic compression test by using MTS Landmark250KN electro-hydraulic servo testing machine until the gear tooth fractured, and fatigue fracture of the gear was examined by SEM. The results indicated that the deeper carburized layer, the higher fatigue life of the gear exhibited, and that the fatigue fracture might divided into three positions such as crack initiation area, crack propagation area, and suddenly fractured area, and a small amount of micro-voids where crack will be initiated were present in 100 to 200 μm below the surface of the gear. Furthermore, defect originating from machining is easy to cause crack to be initiated in the gear.