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气体氮化热处理工艺在我国应用比较广泛。气体氮化用的氮化罐一般采用奥氏体不锈钢制造,个别工厂因不锈钢材料供应困难,只能用低碳钢制造。众所周知,不论用不锈钢还是用低碳钢制造的氮化罐,都存在着随着使用时间的延长,氮化罐不断老化的现象。只不过不锈钢的表面有着稳定的钝化膜,妨碍氮的渗入,氮化罐的老化比较慢一些,而用低碳钢制成的氮化罐的老化较为明显。随着氮化罐不断老化,氨气的分解率相应地增大,为保持一定的氨分解率,就要增大氨气流量。一般资料介绍,只认为氨气流量增大,会浪费液氨和易造成漏气等疵病,致于氨气流量的增大对氮化质量的影响很少有研究报导。我们在多年生产实践中,曾出现过周期性的发生氮化裂纹。为分析和解决氮化裂纹产生的原因,我们曾对液氨的质量、干燥剂、调整氮化工艺参数等方面都做过试验,均未见效。进一步对氨气流量的增大与产生氮化裂纹之间是否存在着一定关系结合生产进行试验。本文主要讨论随着氮化罐老化,为保持氨分解不变,使氨气流量增大对氮化裂纹产生的影响。在这里需指出,氨的含水量也会影响氨气分解率的稳定,本文不讨论含水量的影响。
Nitrogen gas heat treatment process is widely used in our country. Nitriding cans for gas nitriding are generally made of austenitic stainless steel. Due to the difficult supply of stainless steel in individual factories, it can only be made of mild steel. As we all know, regardless of stainless steel or made of low-carbon steel nitride tank, there is the use of time as the tank aging nitriding phenomenon. However, the stainless steel surface has a stable passivation film, hindering the infiltration of nitrogen, nitriding tank aging slower, while the nitriding tank made of mild steel aging more obvious. With the aging of the nitriding tank, the decomposition rate of ammonia increases correspondingly, in order to maintain a certain ammonia decomposition rate, it is necessary to increase the ammonia flow. General information, only that ammonia flow increases, liquid ammonia will be wasted and easy to cause flaws and other flaws, resulting in increased ammonia flow on the quality of nitriding rarely been reported. In our many years of production practice, there have been periodic occurrence of nitrided cracks. In order to analyze and solve the causes of nitrided cracks, we have done tests on the quality of liquid ammonia, desiccant, adjustment of nitriding process parameters, etc., and none of them has been effective. Further tests on whether there is a certain relationship between the increase of ammonia flow rate and the occurrence of nitrided cracks in combination with production. In this paper, with the nitriding tank aging, in order to maintain the same ammonia decomposition, the ammonia flow increased the impact of nitrided cracks. It should be pointed out here that the moisture content of ammonia will also affect the stability of ammonia decomposition rate, this article does not discuss the impact of water content.