摘要
本文对570℃×5h软氮化后的40Gr钢试样再进行650～850℃不同温度加热急冷处理,然后分别对各试样进行金相、电子金相和力学性能试验。试验结果表明,经过软氮化后的中炭铬钢在650℃加热30分钟铁的氮化物开始分解,在750℃加热15分钟时氮化物层基本分解完毕。ε相先在和α(或γ)相相界面上分解,然后在ε相的相界面分解,析出的氮原子向深层扩散,这些和低炭钢的试验结果相同,钢含碳量的提高和少量的铬含碳量对ε相的分解过程影响不大。 由于钢加热时表面层ε相的分解和氮原子向深层扩散,中炭钢软氮化再加热淬火后可获得含氮的针状隐晶马氏体组织。本文在试验结果基础上提出了最佳的软氮化复合处理工艺。
A medium cabon low alloy steel 40Cr was nitrocarburized at 570℃ for 5h,and then reheated and quenched for different tempertauresin the range of 650-850℃. The structures of the specimens were studied by optical and electron microscopy, and some mechanicalproperties were also tested. The results show that when reheat at 650℃ for 30 min,the iron nitrides start to decompose,and finishes at a 750℃ X 15 min reheat. The ε phase decomposes preferentially at its phase boundaries with the α or γ phase, then at its laryer boundary. The decomposed nitrogen atoms diffuse inward to the core. These results are inaccord with that obtained from low carbon steel specimens. The increase of carbon content and a low content of chromium in the steel do not much affect the decomposition process.Because reheating causes the decomposition of e phase at the surface and the inward diffusion of nitrogen atoms,fine acicular nitrogen ?containing martensitic structure can be obtained after reheating and quenching of the nitrocarburized medium carbon steel. Optimum treating parameters for the blend heat treatment are proposed.
