Microstructure evolution of 022Cr25Ni7Mo4N duplex stainless steel during isothermal treatment
FENG Han1, WANG Bao-shun2, WU Xiao-han1, WANG Man2, NAI Qi-liang2, SONG Zhi-gang1
1. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China;
2. Special Materials Research Institute, Zhejiang Jiuli Hi-Tech Metals Co., Ltd., Huzhou 313028, Zhejiang, China
Abstract：The microstructure evolution of 022Cr25Ni7Mo4N duplex stainless steel after isothermal treatment for 2-20 h at 1100℃ was studied. The morphology evolution of austenite grain was observed and the grain size was quantitatively characterized. The change of element content in austenite and ferrite phase was measured. The effect of microstructure evolution on the anisotropy of volume fraction of ferrite phase and low temperature impact toughness of test steels was analysed subsequently. The results show that with the increase of holding time, there is obvious accumulation, growth and coarsening of austenite grain, accompanied by significant changes in grain morphology. The volume fraction of rod-like crystal grains with a/b value above 4.0 dropped from nearly 20% to below 5%, and that of equiaxed grains with a/b value between 1.0 and 1.9 increases significantly, while the number of grains with size above 20 μm increases rapidly. The prolongation of the holding time makes molybdenum and chromium elements diffuse and enrich to the ferrite phase further, which leads to the increase of pitting resistance equivalent number (PREN) value in ferrite phase. The significant decrease in the volume fraction of slender rod-like austenite crystallites is the primary reason for the improvement in anisotropy of austenite volume fraction and the increase of low temperature impact toughness of test steel.
[1] HAGHDADI N,CIZEK P,HODGSON P D,et al.Effect of ferrite-to-austenite phase transformation path on the interface crystallographic character distributions in a duplex stainless steel[J].Acta Materialia,2018,145:196-209.
[2] SUN Y H,ZHAO Y,LI X B,et al.Effects of heating and cooling rates on δ↔γ phase transformations in duplex stainless steel by in situ observation[J].Ironmaking & Steelmaking,2019,46(3):277-284.
[3] 吴玖.双相不锈钢[M].北京:冶金工业出版社,1999:22-24. WU J.Duplex stainless steel[M].Beijing:Metallurgical Industry Press,1999:22-24.
[4] KANG D H,LEE H W.Study of the correlation between pitting corrosion and the component ratio of the dual phase in duplex stainless steel welds[J].Corrosion Science,2013,74(4):396-407.
[5] 吴忠忠,宋志刚,郑文杰,等.固溶温度对00Cr25Ni7Mo4N超级双相不锈钢显微组织及耐点蚀性能的影响[J].金属热处理,2007,32(8):50-54. WU Z Z,SONG Z G,ZHENG W J,et al.Effect of solution temperature on microstructure and pitting corrosion resistance property of super duplex stainless steel 00Cr25Ni7Mo4N[J].Heat Treatment of Metals,2007,32(8):50-54.
[6] MISHRA M K,BALASUNDAR I,RAO A G,et al.On the high temperature deformation behavior of 2507 super duplex stainless steel[J].Journal of Materials Engineering and Performance,2017,26(2):802-812.
[7] MA M,DING H,MISRA R D K,et al.A study on precipitation kinetics of sigma phase in a hot-rolled super duplex stainless steel during isothermal aging based on the Johnson-Mehl-Avrami model[J].Ironmaking & Steelmaking,2017,44(4):311-318.
[8] ZHANG B,JIANG Z,LI H,et al.Precipitation behavior and phase transformation of hyper duplex stainless steel UNS S32707 at nose temperature[J].Materials Characterization,2017,129:31-39.
[9] PETTERSSON N,WESSMAN S,HERTZMAN S,et al.High-temperature phase equilibria of duplex stainless steels assessed with a novel in-situ neutron scattering approach[J].Metallurgical and Materials Transactions A,2017,48(4):1562-1571.
[10] WARREN A D,HARNIMAN R L,GUO Z,et al.Quantification of sigma-phase evolution in thermally aged 2205 duplex stainless steel[J].Journal of Materials Science,2016,51(2):694-707.
[11] 白于良,杨银辉,曹建春,等.Mn对22%Cr双相不锈钢700℃时效σ相及韧性的影响[J].材料工程,2017,45(5):71-79. BAI Y L,YANG Y H,CAO J C,et al.Effect of Mn on σ phase and toughness of 22%Cr duplex stainless steel by aging treatment at 700℃[J].Journal of Materials Engineering,2017,45(5):71-79.
[12] 宋志刚,王宝顺,丰涵,等.S32750双相不锈钢冲击韧性影响因素探讨[C]//第六届中国国际双相不锈钢大会论文集.北京:中国特钢企业协会,2018:1-7. SONG Z G,WANG B S,FENG H,et al.Discussion about influencing factors on impact toughness of duplex stainless steels[C]//6th China International Duplex Stainless Steel Conference.Beijing:CSSC,2018:1-7.
[13] WANG S,ZHANG M,WU H,et al.Study on the dynamic recrystallization model and mechanism of nuclear grade 316LN austenitic stainless steel[J].Materials Characterization,2016,118:92-101.
[14] LEE T H,SUH H Y,HAN S K.Effect of a heat treatment on the precipitation behavior and tensile properties of alloy 690 steam generator tubes[J].Journal of Nuclear Materials,2016,479:85-92.
[15] 韩大尉,孙文儒,于连旭,等.Mo含量对IN718合金组织和力学性能的影响[J].航空材料学报,2018,38(4):64-74. HAN D W,SUN W R,YU L X,et al.Effect of Mo content on microstructure and mechanical properties of IN718 alloy[J].Journal of Aeronautical Materials,2018,38(4):64-74.
[16] MAKI T,FURUHARA T,TSUZAKI K.Microstructure development by thermomechanical processing in duplex stainless steel[J].ISIJ International,2001,41(6):571-579.
[17] 王佳,马勤,张红霞,等.σ相的析出对双相不锈钢晶粒的影响[J].热加工工艺,2009,38(18):41-43. WANG J,MA Q,ZHANG H X,et al.Influence of sigma phase precipitate on grain size of duplex stainless steel[J].Hot Working Technology,2009,38(18):41-43.
[18] 丰涵,宋志刚,郑文杰,等.一种双相不锈钢的侵蚀剂以及侵蚀方法:CN201810237545.2[P].2018-08-21. FENG H,SONG Z G,ZHENG W J,et al.An erosion agent and erosion method for duplex stainless steel:CN201810237545.2[P].2018-08-21.
[19] 徐洲,赵连城.金属固态相变原理[M].北京:科学出版社,2004:11-25. XU Z,ZHAO L C.Principle of metal solid phase transition[M].Beijing:Science Press,2004:11-25.
[20] AHMED M Z,BHATTACHARJEE P P.Microstructure,texture,and tensile properties of a severely warm-rolled and annealed duplex stainless steel[J]. Steel Research International,2016,87(4):472-483.
[21] 许婷,方晓英,朱言利,等.双相不锈钢中奥氏体沉淀相的晶粒取向及界面特征分布[J].材料工程,2018,46(2):34-40. XU T,FANG X Y,ZHU Y L,et al.Grain orientation and interface character distribution during austenite precipitation phase in duplex stainless steel[J].Journal of Materials Engineering,2018,46(2):34-40.
2020, Vol. 48 
