烧结锰钢碳氮共渗层结构的研究

INVESTIGATION ON THE STRUCTURE OF CARBONITRIDED LAYER IN SINTERED MANGANESE STEELS

用TEM研究了粉末烧结Fe—C系和Fe—Mn—C系合金碳氮共渗层的组织结构。结果表明,锰能增加烧结体的开口孔隙度,从而增加共渗层深度。经150℃回火,碳氮共渗马氏体中析出Fe_(18)N_2(α″)相,合金元素锰能显著增加Fe_(16)N_2(α″)相的弥散度。经300℃回火,碳氮共渗马氏体中析出Fe_3C,没有发现Fe_4N(γ′)相。

The structure of carbonitrided layer in sintered Fe-C and Fe-Mn-C alloys was studied by TEM observation. The results show that the element Mn can increase the open porosity in the sintered compacts and consequently increase its depth of carbonitrided layer.After tempering of both steels at 150℃, the Fe_(16)N_2(α″)phase was precipiteted from both the carbonitrided martensite matrix. The experimental results show that hhe element Mn can significantly increase the dispersity of precipitated phase in Fe-Mn-C alloy and the average thickness of dispersoid is about 60～7 and the length 500～600, while the thickness of dispersoid precipitated from the martensite of Fe-C alley is about 500 and the length 3000, which is one order larger than that from the martensite of Fe-Mn-C alloy. This illustrates that the Mn is favourable to the nucleation of dispersed phase Fe_(16)N_2 and restrAlNs its growth.When the carbon steel was tempered at 100～200℃ the stress would be relaxed and the εphase should be precipitated, but in this study, the Fe_(16)N_2 phase was precipitated from the martensite, and the εphase was not observed. These results show that the nitrogen atoms not only can interrupt the odering of carbon atoms in anstensite lattice, but also interrupt the partial crdering of carbon atoms in martensite phase, which leads to restrAlN the precipitation of εphase. It is shown that when the martensite is tempered below 200℃, the Fe_(16)N2 phase is precipitated as mentioned above, tempered at 200～290℃, the FeN phase(γ')is observed, tempered at higher than 300℃ only Fe_3C phase is observed.