无镍含氮18Cr奥氏体不锈钢中相平衡的热力学计算

Thermodynamic calculation of the equilibrium phase-regions in the nickle-free 18Cr austenitic stainless steels containing nitrogen

利用ThermoCalc软件和相关数据库对不同Mn含量(质量分数,以下均同)及添加少量(质量分数,以下均同)Mo和C时,Fe-18Cr-Mn-Mo-C-N合金系在压力为100 kPa条件下随N含量(质量分数,以下均同)变化的垂直截面相图进行了计算.结果发现,当不添加Mo和C时,Mn含量从0增加到12%时,γ/(α+γ)相边界向左侧移动;随着Mn含量的继续增加,γ/(α+γ)相边界又向右侧移动.γ/(Cr2N+γ)、γ/(σ+γ)和γ/(N2+γ)相边界一直向右侧移动.γ/(Cr2N+γ+gas)相平衡时的γ相中氮含量随着Mn的添加也逐渐增加,即由0%Mn时的0.85%N变为22%Mn时的1.69%N,N在γ相中的固溶度提高近一倍.在18%Mn的合金中含有0.02%C时,奥氏体区的范围没有发生明显的变化,但存在M23C6化合物;当继续添加2%Mo时,γ/(α+γ)相边界向右侧移动,而且不但存在M23C6化合物还有M6C化合物.Fe-18Cr-18Mn-0.5N钢的奥氏体化温度及Cr2N相析出温度与此合金系的热力学计算结果基本一致,表明这些计算结果对Fe-18Cr-Mn-Mo-C-N合金系的成分设计及热处理工艺有重要参考价值.

The vertical sections of Fe-18Cr-Mn-N multicomponent system with the additions of a little molybdenum and carbon,varying as nitrogen and manganese contents,have been calculated by the ThermoCalc software and thermodynamic database under the atmosphere of 100 kPa.It is shown that the γ/（α＋γ） phase boundary moves to the left with increasing Mn content from 0 to 12 wt.% first,and then shifts to the right with further increasing Mn content when the alloy system contains neither molybdenum or carbon.The γ/（Cr2N＋γ）,γ/（σ＋γ） and γ/（N2＋γ） phase boundaries always shift to the right with increasing the Mn content.When the γ/（Cr2N＋γ＋gas） phases are in the equilibrium,the content of nitrogen in the γ phase increases with increasing the Mn content.i.e.,the nitrogen content increases from 0.85 wt.% to 1.69 wt.% when the Mn content increases from 0 to 22 wt.%,the solubility of N in the γ phase increases by one time.The γ phase region always changes little with the addition of 0.02 wt.%C into the 18 wt.%Mn alloy,but the M23C6 carbide exists.If the 2 wt.%Mo is added together with carbon,γ/（α＋γ） phase boundary shifts toward the right,and both M6C carbide and M23C6 carbide appear.The calculation is consistent with the experimental data on the austenitizing temperature and precipitation temperature of Cr2N phase in the Fe-18Cr-18Mn-0.5N alloy,and thus it suggests that the thermodynaic calculation be powerful in alloy design and processings of Fe-18Cr-Mn-Mo-C-N system.