氮含量对无镍奥氏体不锈钢平衡相转变的影响

Effects of nitrogen content on phase transformation behavior of nickel-free austenitic stainless steels

高氮铬锰奥氏体不锈钢有着极为广泛的应用前景,然而氮含量对其相转变的影响尚不十分清晰。设计并冶炼了氮质量分数为0.02%~1.20%的试验钢,对各钢的平衡相转变进行了热力学计算,对δ铁素体和Cr2N的形貌进行了观察。结果表明,钢中δ铁素体的最大析出量随着氮含量的升高而降低,当氮质量分数超过1.05%后,无δ铁素体析出。获得了试验钢加热时δ铁素体的析出温度与氮含量的关系式。随着氮含量的升高,试验钢在冷却时Cr2N的析出温度逐渐升高,并获得了其定量关系式。在GN04钢中,1 200℃等温2h后的δ铁素体主要沿三叉晶界分布。Cr2N析出优先在晶界形成,然后朝着晶内发展。在相同等温条件下,试验钢中Cr2N的析出量随着氮含量的升高而增大,且层片间距随之减小。

High nitrogen nickel-free austenitic stainless steels have wide application prospects in many fields.However,the effects of nitrogen mass fraction on phase transitions are still unclear yet.High nitrogen nickel-free austenitic stainless steels with nitrogen mass fraction from 0.02%to 1.20% were designed and melted.And the thermodynamic calculation of equilibrium phase transition of steels was carried out,the morphology of δ ferrite and Cr2 N was observed.The results showed that the maximum precipitation ofδferrite was decreased with nitrogen mass fraction increase,but when nitrogen mass fraction beyond 1.05%,there was no δ ferrite found.The relations between the precipitation temperature of δ ferrite and nitrogen mass fraction during the steel heating process were obtained.With the increase of nitrogen mass fraction,the precipitation temperature of Cr2 N when steels were cooling increased gradually,and its quantitative relationship was obtained.In GN04 steel,the δ ferrite after 1 200 ℃ is othermal heat treatment in 2 hwas mainly distributed along the trigeminal grain boundary.The precipitation of Cr2 N was formed firstly on grain boundary and then spread in crystal.It also increased with nitrogen mass fraction increase in the same isothermal heat treatment,but layer spacing decreased.