Lee Hung-Chi, Chen Tai-Cheng, Chen Wen-Han, Tsay Leu-Wen
Department of Optoelectronics and Materials Technology, National Taiwan Ocean University, Keelung 202301, Taiwan.
Department of Material Research, National Atomic Research Institute, Taoyuan 325207, Taiwan.
Materials (Basel). 2025 Sep 2;18(17):4121. doi: 10.3390/ma18174121.
This study evaluated the fatigue performance of nitrided H13 steel with and without a compound layer (CL), using two nitrogen potentials (K = 0.8, designated as LN, and K = 2.0, designated as HN). Fine particle peening (FPP) was applied prior to gas nitriding to introduce a refined microstructure and compressive residual stress (CRS) in the peened zone. After gas nitriding at 540 °C for 8 h, the refined structure remained on the outermost layer of all samples, regardless of the nitrogen potential. A CL primarily composed of FeN formed on the external surface of the HN sample, whereas the LN sample remained free of CL. A higher K promoted CL formation and slightly increased the case depth in the HN sample compared to the LN sample. Fatigue cracks initiated at the external surface of the H13 steel substrate (SB). Overall, the LN and HN samples exhibited similar residual stress fields and, consequently, comparable fatigue performance. In the high-cycle fatigue regime, fatigue cracks originated from subsurface inclusions, resulting in significantly improved fatigue strength and life for both the LN and HN samples compared to the SB sample. Under cyclic stresses at or above 1100 MPa, the crack initiation site in the HN sample tended to shift from subsurface inclusions to the external surface. Throughout the fatigue tests, no multi-cracking or spalling of the CL was observed in the HN sample, regardless of the cyclic stress.
本研究评估了有和没有化合物层（CL）的渗氮H13钢的疲劳性能，采用了两种氮势（K = 0.8，记为LN，以及K = 2.0，记为HN）。在气体渗氮之前进行细颗粒喷丸（FPP），以在喷丸区域引入细化的微观结构和压缩残余应力（CRS）。在540°C下进行8小时气体渗氮后，无论氮势如何，所有样品的最外层都保留了细化结构。在HN样品的外表面形成了主要由FeN组成的CL，而LN样品没有CL。较高的K促进了CL的形成，并且与LN样品相比，HN样品的渗层深度略有增加。疲劳裂纹在H13钢基体（SB）的外表面萌生。总体而言，LN和HN样品表现出相似的残余应力场，因此疲劳性能相当。在高周疲劳 regime 下，疲劳裂纹源自亚表面夹杂物，与SB样品相比，LN和HN样品的疲劳强度和寿命均显著提高。在1100 MPa及以上的循环应力下，HN样品中的裂纹萌生位置倾向于从亚表面夹杂物转移到外表面。在整个疲劳试验过程中，无论循环应力如何，在HN样品中均未观察到CL的多裂纹或剥落现象。
