伍翠兰++田磊++洪悦++王津++陈兴岩

摘要：工业纯铁（厚度为1 mm）经580 ℃气体渗氮4 h后进行不同方式（油淬， 炉冷）的冷却，然后对油淬的试样进行自然时效和100～220 ℃的人工时效.采用X射线衍射仪、扫描电镜、透射电镜、维氏显微硬度计和拉伸疲劳实验机等研究了不同热处理条件下渗氮层的微观组织结构和力学性能.结果表明：渗氮试样完全由化合物层和扩散层组成，冷却方式不改变化合物层的厚度和最外层的相结构，却显著影响扩散层的微观组织和力学性能.油淬试样的扩散层在自然时效过程中形成大量的氮原子团簇从而产生了自然时效强化；人工时效可以控制油淬试样扩散层中析出相的种类和数量，低温时效的析出相主要为α′′Fe16N2相，较高温度时效的析出相主要为γ′Fe4N相；自然时效样品具有很高的硬度和强度，人工时效样品的硬度和强度随时效温度的升高而降低，较高温度时效有助于提高延伸率；化合物层对渗氮层的强度没有很大影响，但却显著降低了渗氮层的拉伸疲劳强度.

关键词：气体渗氮；微观组织；力学性能；时效析出；相变

中图分类号：TG113；TG161；TG156.8 文献标识码：AThe Effect of Cooling Methods and Subsequent Ageing on the

Nitrided Layer of Pureiron by Gas Nitriding at 580 ℃

WU Cuilan， TIAN Lei， HONG Yue， WANG Jin， CHEN Xingyan

（College of Materials Science and Engineering， Hunan Univ， Changsha， Hunan410082， China）Abstract：A pure iron （1 mm in thickness） was gas nitrided at 580 ℃ for 4h， followed by oil quenching or furnace cooling. The oilquenched samples were first naturally aged （NA）， and then artificially aged between 100 ℃and 140 ℃. The microstructural examinations and property characterization were investigated using Xray di？ractometer， scanning electron microscope， transmission electron microscope， Vickers hardness tester and fatigue tester. It was found that the nitrided samples consisted of compound layers （CLs） and diffusion layers （DLs）. The cooling method did not change the thickness of the CLs and the phase constitutes of the upper-most layer， but had remarkable effect on the microstructure and mechanical property of the DLs. A great quantity of richN clusters precipitated from the oilquenched DLs after natural ageing for 200h， and the oilquenched DLs had a great natural ageing strengthening phenomenon. During artificial ageing （AA）， the type and number of precipitates could be controlled by the ageing temperature and ageing time. The main precipitates are the α″Fe16N2 during lower temperature ageing while it is the γ′Fe4N at higher temperature ageing. The NA samples could get very high hardness and strength. The hardness and strength of the AA samples decreased with the increase of ageing temperature. The high temperature ageing greatly improves the elongation of the oilquenched samples. The CLs had little effect on the tensile stress of the nitrided samples， but greatly decreased the fatigue strength under the tensile.

Key words：gas nitriding； microstructure； mechanical properties； precipitation； phase transformation

渗氮是一种金属表面强化的化学热处理技术，被广泛应用于钢铁、钛合金及铝合金等金属材料的表面强化处理[1-5].渗氮能显著提高工件的表面硬度、耐磨性和耐腐蚀性等[3，6-7].气体渗氮是指向加热到某一温度范围并密封的炉罐中渗氮，使氮原子渗入到工件表面的处理.气体渗氮相对离子……