目的 Q235钢作为一种常用工业钢材，被广泛用于各类机械零件加工，但其在实际服役工况中经常因磨损导致零件失效。为了增强该类零件的耐磨性，延长其服役寿命，采用层流等离子体表面强化技术增强Q235零件表面抗磨损性能。方法 首先，基于自制的层流等离子体表面强化系统，采用单因素控制变量法，探索了不同工作电流(90~120 A)和不同淬火距离(40~70 mm)对Q235钢表面耐磨性和硬度的影响规律。然后，通过金相显微镜、扫描电子显微镜、维氏硬度测试仪、超景深3D显微镜和白光干涉仪等，对硬化前后的微观组织、硬度和耐磨性进行表征与分析。结果 深入揭示了层流等离子体表面淬火强化Q235钢的硬化机理，Q235钢表面淬硬区具有致密的板条状马氏体组织;在其他参数不变的情况下，硬化的深度、宽度、硬度、耐磨损性能随着工作电流的增加而增加，随着淬火距离的减少而增加。Q235钢表面淬硬层深度可达1.58 mm，相比基体而言，表面硬度提升了63%，摩擦因数下降了0.108~0.234，磨损率下降39%以上。结论 层流等离子体表面硬化能有效提高Q235钢的硬度和耐磨性能，有助于延长Q235工件的服役寿命;同时，工件的耐磨性和硬度与工作电流呈正相关，与淬火距离呈负相关。

Due to its comprehensive performance, easy processing, low cost, etc., Q235 steel has been widely used to manufacture various metal parts in the industrial fields. However, parts made of Q235 steel always fail due to part wear and tear, which limit the service life of these parts. For prolonging the service life of the parts made of Q235 steel, various surface hardening methods have been used to improve their surface qualities. As a novel surface hardening method, a home-made laminar plasma surface hardening method was used to harden the surface of Q235 steel for improving its wear resistance and hardness. Firstly, based on the home-made laminar plasma surface hardening system, the influences of the arc currents (90- 120 A) and the quenching distances (40-70 mm) on the surface wear resistance and hardness of Q235 steel were investigated by single factor control variable method. Then, the microstructure, hardness and wear resistance of Q235 steel before and after hardening were characterized and analyzed by metallographic microscope, scanning electron microscope (SEM), Vickers hardness tester, ultra depth of field, ultra-depth-of-field microscopic 3D workstation and white light interferometer to reveal the surface hardening mechanism of Q235 steel. The following experimental results were shown. The cross section of the hardened sample could be divided into three parts:hardened zone, heat affected zone and substrate, in which the hardened layer shaped as a "crescent"; the hardened zone was composed of dense lath martensite structure, while the heat affected zone was composed of residual austenite, martensite, ferrite and cementite. When the quenching distance and other parameters were constant, the depth, width, hardness and wear resistance of the hardened zone increased with the increase of the arc current. When the arc current and other parameters were constant, the depth, width, hardness and wear resistance of the hardened zone decreased with the quenching distance. In addition, when the arc current and quenching distance exceeded a certain value (I≥120 A or d≤50 mm), the surface of the substrate would be micro-fused, which would affect the topography and quality of the hardened zone. Besides, the corresponding hardness near the microfusion zone was lower than the hardened zone. More importantly, when the quenching distance was too large (d≥70 mm), the hardness and wear resistance of the hardening zone were sharply reduced:the maximum hardness of the hardened zone decreased from 265HV0.2 to about 232HV0.2 and the wear rate of the hardened zone increased from 1.62×10?5 mm3/(N.m) to 3.46×10?5 mm3/(N.m). Thus, the hardening quality of the substrate could be influenced by the quenching distance obviously. Overall, the maximum hardening depth of Q235 was 1.58 mm. The surface hardness increased by about 63%, and the friction coefficient and the wear rate reduced by about 0.108-0.234 and at least 39% respectively. Under dry friction conditions, the wear mechanism of the substrate was mainly abrasive wear, while the wear mechanism of the hardened zone was mainly abrasive wear and adhesive wear. Besides, the wear resistance and hardness of the pats were positively correlated with the working current, and negatively correlated with the quenching distance. Therefore, laminar plasma can be used as a new heat source to strengthen Q235 workpieces to improve surface wear resistance and hardness for prolonging their service life.