Multi-Factor Impact on Stainless Steel Crankshaft Fatigue Strength

The Effect of Casting Shrinkage on Crankshaft Fatigue Strength Previous research has reported that a certain factory experienced a large number of crankshaft fractures. Upon visual inspection of the crankshaft, it was determined that the primary cause of the fractures was casting shrinkage at the connecting rod journal position, which was visible to the naked eye. The cause was analyzed as follows: under conditions where cold steel supply was problematic, the cold steel used for shrinkage compensation was omitted during crankshaft molding. After reinstating the chill steel casting process, the casting shrinkage issues in the crankshaft were successfully resolved. This demonstrates that casting shrinkage has a significant impact on the fatigue strength of crankshafts.

The Effect of Black Banding and Gray Spots on Crankshaft Fatigue Strength Under conventional process conditions, the fracture surfaces of stainless steel crankshafts typically exhibit a gray or silver-gray color, and the crankshaft body as well as the tensile test specimens should also exhibit similar characteristics. For black banding issues, they are primarily formed due to the influence of gray spots on the reciprocating motion of the crankshaft journal during fatigue testing, while the formation of gray spots is mainly influenced by silicon segregation in the molten steel. During fatigue testing of a batch of stainless steel crankshafts, abnormal black layers and gray spots were observed on the crankshaft cross-section. Although this issue is relatively rare in stainless steel crankshafts, it still constitutes a form of internal defect. The presence of this issue adversely affects the fatigue strength of the crankshaft, and crankshafts with black bands or gray spots may develop fatigue cracks prematurely during normal use, leading to a decrease in fatigue strength.

Analysis of the Influence of Heat Treatment Processes on the Fatigue Strength of stainless steel Crankshafts

Effects of Normalizing and Medium-Frequency Quenching Processes on Crankshaft Fatigue Strength Previous studies have shown that for stainless steel crankshafts, high-temperature normalizing treatment can eliminate free carbides, thereby adjusting the morphology of ferrite and pearlite in the matrix and their relative proportions. This process enhances the comprehensive mechanical properties of the stainless steel crankshaft, thereby improving its fatigue strength. Additionally, during the manufacturing process of stainless steel crankshafts, medium-frequency quenching treatment can form a hardened layer of a certain depth on the surface of the crankshaft, which is significant for improving its wear resistance. However, some studies suggest that under traditional non-rounded corner quenching processes, an unbalanced and opposing stress relationship may form at the interface between the quenched and non-quenched zones of the crankshaft, adversely affecting fatigue strength. Therefore, when introducing medium-frequency quenching processes, it is advisable to opt for rounded corner quenching processes to achieve satisfactory treatment results.

Effect of isothermal quenching process on crankshaft fatigue strength In the production process of stainless steel crankshafts, the application of isothermal quenching can enable the crankshaft to obtain a primary bainite phase, while also forming a certain amount of martensite and retained austenite structures, resulting in high strength and toughness levels in mechanical properties. According to existing research reports, the issue of insufficient fatigue strength in stainless steel crankshafts caused by deviations in chemical composition has been addressed by applying isothermal quenching, thereby resolving quality issues in the heat treatment of crankshafts. The application of isothermal quenching not only improves the fatigue strength of stainless steel crankshafts but also significantly enhances their wear resistance, thereby effectively extending their service life and yielding tangible comprehensive benefits.

The Effect of Oxygen Nitriding on Crankshaft Fatigue Strength From a chemical processing perspective, in the manufacturing process of stainless steel crankshafts, oxygen nitriding treatment can create a compound layer with high nitrogen content on the crankshaft surface, while also forming a saturated oxygen diffusion layer. Due to the influence of oxygen and nitrogen diffusion, the chemical composition of the surface layer of the stainless steel crankshaft changes, and the corresponding microstructure shows a significant improvement trend. The overall wear resistance and fatigue performance of the crankshaft are effectively improved. It is important to note that for stainless steel crankshafts treated with oxygen-nitriding, the improvement in fatigue resistance is significantly influenced by the diffusion level of the oxide layer. Rapid cooling after nitriding, forming a saturated solid solution in the diffusion layer, or generating high residual compressive stress can all enhance fatigue strength. It is precisely because the oxygen-nitriding process enables the formation of a deeper diffusion layer on the crankshaft surface that it holds significant importance and value in extending the service life of steel casting components.