中温时效对022Cr21Ni2Mn5N钢析出行为及冲击韧性的影响

采用Thermo-Calc软件对022Cr21Ni2Mn5N双相不锈钢的近平衡态析出相进行了计算分析。采用光学显微镜、透射电镜、物理化学相分析方法对经中温时效处理后试验钢第二相的析出温度、种类、数量和位置进行了观察和研究,并分析了第二相析出行为对钢的冲击韧性的影响机理。结果表明:022Cr21Ni2Mn5N双相不锈钢在600~700℃中温时效时的析出相主要为六方结构的Cr_2N相和面心立方结构的M_(23)C_6相,未见σ相析出。中温时效时,受制于该钢较低的C含量,M_(23)C_6相析出位置仅局限于相界、晶界处。该钢较高的N含量促进钢中Cr_2N相析出,并在相界、晶界和铁素体晶内均有发现。时效初期M_(23)C_6和Cr_2N均具有较高的析出速度,时效时间继续延长析出量增长放缓。时效处理时间和温度直接影响钢的冲击性能:时效初期第二相的快速析出导致钢的冲击功急剧下降;时效足够长时间,第二相析出量达到饱和,钢的冲击功趋于稳定值;并且600℃长时时效时,钢的冲击功值达到最小。

Effect of mid-temperature aging on precipitation and impact toughness of 022Cr21Ni2Mn5N duplex stainless steel

The near equilibrium phases of 022Cr21Ni2Mn5N duplex stainless steel were calculated by Thermo-Calc software.The precipitation evolution during aging of the tested steel was investigated by OM,TEM and physico-chemical phase analysis,and type,morphology,distribution and precipitation temperature of the second phase were studied.The effect mechanism of precipitation on the impact energy of tested steel was discussed.The results show that Cr2 N phase in hexagonal structure and M23 C6 phase in face-centred cubic structure are the major phases precipitated in 022Cr21Ni2Mn5N duplex stainless steel at 600-700℃.However,theσphase is never found.Due to the lower carbon content of tested steel,the M23 C6 and Cr2 N particles precipitate only alongα/γinterfaces and grain boundary of ferrite phase.The Cr2 N particles precipitate also in ferrite phase grain benefited from the higher nitrogen content.The growth speed of M23 C6 and Cr2 N precipitation is very high during early aging and decreases gradually with the aging holding time increasing.The impact energy of specimens are strongly influenced by the aging temperatures and holding times.The impact energy of specimen decreases sharply during the early aging due to the high coarsening rate of precipitated phases.The amount of precipitations increase and the impact energy falls down with the aging time increasing until to an equilibration value.The impact energy of specimen aging at 600℃is confirmed to be the lowest.