目的 针对316L奥氏体不锈钢表面耐磨性能不足而限制其在阀门密封副及滑动副中的应用问题,采用盐浴氮碳共渗（QPQ）处理,系统研究氰酸根质量分数、共渗温度及共渗时间对渗层组织演化、耐磨性能及耐蚀性能的影响规律。方法 采用正交试验设计,以氰酸根质量分数、共渗温度和共渗时间为影响因素,利用SEM、EDS及XRD分析渗层组织、元素分布及相组成,结合显微硬度、摩擦磨损及质量分数为3.5%的NaCl溶液动电位极化试验评价综合性能,并采用极差分析和方差分析评价各工艺因素对磨损性能的影响。结果 QPQ处理后,所有试样表面硬度均提高至1 100HV0.3以上,其中试样6#磨损体积最低（仅为2.087× 10⁶ μm³）,降至316L基体的1/3~1/4。极差分析和方差分析均表明,共渗时间对磨损性能影响最显著,其次为共渗温度和氰酸根质量分数（C>B>A,P<0.05）。高氰酸根质量分数及长时间共渗导致渗层内部形成大量龟裂网络状微裂纹。电化学测试表明,高温QPQ处理降低了316L不锈钢在Cl^-介质中的耐蚀性,腐蚀主要沿氧化膜龟裂网络及渗层裂纹扩展,试样7#形成大量团聚状铁氧化物腐蚀产物,并伴随局部Cr富集。结论 QPQ处理能够显著提高316L不锈钢表面耐磨性能,但耐磨性与耐蚀性之间存在一定权衡关系。渗层结构完整性是决定材料综合性能的关键因素。综合比较9组试验结果,A2B3C1（氰酸根质量分数为36.2%~38.2%、580 ℃、2 h）获得最低磨损量及相对较优的耐蚀性能,为本研究试验范围内的综合最优工艺参数,可为316L不锈钢阀门关键零部件QPQ工艺优化提供理论依据和工程参考。

The optimization of salt bath nitrocarburizing followed by post-oxidation (Quench-Polish-Quench, QPQ) for austenitic stainless steels remains challenging because improvements in wear resistance are frequently accompanied by deterioration in corrosion resistance. In particular, the coupled effects of cyanate concentration, nitrocarburizing temperature, and treatment duration on the evolution of the modified layer and the corresponding wear-corrosion balance have not been systematically clarified. In this work, a three-factor, three-level orthogonal experimental design (L9) was employed to quantitatively investigate the effect of QPQ processing parameters on the microstructure, phase constitution, hardness, tribological behavior, and electrochemical corrosion performance of 316L stainless steel. The objective was to identify the governing factors controlling comprehensive surface performance and establish an optimized processing window for valve sealing components operating in mildly corrosive environments.
QPQ-treated specimens were characterized through scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), surface roughness measurements, and microhardness testing. Tribological behavior was evaluated by reciprocating sliding wear tests against Al₂O₃ balls under a maximum Hertzian contact pressure of approximately 1.23 GPa, while corrosion behavior was assessed by potentiodynamic polarization in 3.5wt.% NaCl solution. Range analysis and analysis of variance (ANOVA) were further employed to quantify the statistical significance of each processing parameter on wear resistance.
All QPQ-treated specimens developed a typical gradient structure consisting of an outer oxide film, a compound layer, and a diffusion layer, with total modified-layer thicknesses ranging from 41.33 to 74.58 μm. Cross-sectional SEM observations combined with EDS line scanning revealed the formation of a continuous oxygen-enriched surface oxide approximately 7 μm thick. XRD analysis confirmed that the modified layer consisted primarily of Fe₃O₄, ε-Fe_2-3N, γ′-Fe₄N and CrN phases. Nitrogen supersaturation induced the formation of expanded austenite together with lattice expansion and residual compressive stresses, whereas prolonged treatment at elevated temperature promoted partial decomposition of expanded austenite and precipitation of CrN.
The QPQ treatment remarkably enhanced surface hardness. All treated specimens exhibited hardness values exceeding 1 100 HV_0.3, while the maximum hardness reached 1 275.09HV0.3, approximately 4.7 times that of the untreated substrate. Although the average friction coefficients remained within a relatively narrow range (0.58-0.69), the wear volume varied dramatically among different processing conditions. The minimum wear volume, 2.087×10⁶ μm³, was obtained for specimen 6, corresponding to a reduction of 67%-75% compared with untreated 316L. In contrast, specimen 7 exhibited the largest wear volume (1.345×10⁸ μm³), nearly two orders of magnitude higher than specimen 6 despite maintaining a relatively high hardness.
Microstructural observations revealed that this abnormal wear behavior originated from the degradation of modified-layer integrity rather than insufficient hardness. Under the combined condition of high cyanate concentration (38.2wt.%-40.2wt.%) and prolonged nitrocarburizing (4 h), numerous interconnected microcracks developed within the compound layer and propagated preferentially along grain boundaries. These defects acted as stress concentration sites during cyclic Hertzian contact, initiating local spallation. Detached hard fragments subsequently participated in three-body abrasion, accelerating abrasive wear and fatigue-induced delamination, thereby causing a drastic increase in material loss. Correspondingly, SEM examination of worn surfaces demonstrated that specimen 6 exhibited only shallow grooves characterized by mild abrasive wear, whereas specimen 7 presented extensive spallation pits, debris accumulation, and severe material removal.
Electrochemical measurements indicated that high-temperature QPQ treatment generally reduced the corrosion resistance of 316L stainless steel in chloride-containing environments. Compared with the untreated substrate, all QPQ-treated specimens exhibited higher corrosion current densities and lower polarization resistance. Corrosion morphology demonstrated that chloride ions preferentially penetrated through the crack network within the oxide film and subsequently propagated along subsurface microcracks. For specimen 6, corrosion was mainly confined to the crack intersections where fine Fe-rich oxide particles accumulated, while the oxide layer remained largely intact. In contrast, specimen 7 showed extensive agglomerated iron oxide corrosion products together with localized chromium-enriched regions. EDS analysis suggested that these chromium-rich areas resulted primarily from preferential dissolution of iron rather than the formation of a continuous protective Cr₂O₃ film. Consequently, the cracked oxide layer gradually lost its protective capability, allowing localized corrosion to continuously propagate into the modified layer.
Statistical analyses demonstrated excellent agreement between range analysis and ANOVA. Nitrocarburizing time was identified as the most influential parameter affecting wear resistance, followed by nitrocarburizing temperature and cyanate concentration (C>B>A, P< 0.05). Although the theoretical optimum predicted by range analysis was A₁B₃C₁, the experimentally verified optimum within the investigated parameter space was A₂B₃C₁, corresponding to a cyanate concentration of 36.2wt.%-38.2wt.%, a nitrocarburizing temperature of 580 ℃, and a treatment duration of 2 h. This condition simultaneously achieved the highest hardness, the lowest wear volume, and relatively superior corrosion resistance among all tested specimens.
These findings demonstrate that the comprehensive performance of QPQ-treated 316L stainless steel is governed primarily by the structural integrity of the modified layer rather than hardness alone. Excessive nitrocarburizing promotes crack formation within the compound layer, which simultaneously accelerates tribological failure and chloride-induced corrosion. The optimized QPQ processing parameters established in this work provide a practical strategy for balancing wear resistance and corrosion resistance in 316L stainless steel and offer valuable guidance for the surface engineering of critical valve sealing components operating under combined sliding and mildly corrosive service conditions.