调质态含Cu高强钢的强化机理及钢中Cu的析出行为
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摘要
对含Cu低合金高强度钢板淬火并经高温时效后,采用SEM、EBSD、HRTEM和APT等手段对其微观组织和纳米尺度Cu的析出相进行了表征,对其厚度截面的室温拉伸性能进行了测定,并对钢板厚度方向近表面和心部的强化机理进行了分析。结果表明,高温时效后钢中Cu的析出相尺寸在6～50 nm范围内,30 nm以内的为9R结构的短棒状或球状粒子,30 nm以上的为fcc结构的长棒状粒子,棒状粒子中微量的Mn、Ni在Cu粒子与基体界面上的偏聚更明显。在较高温度范围内进行时效后,钢的屈服强度随着时效温度的升高而呈大致线性下降趋势,钢的主要强化机制为细晶强化,其次为位错强化和析出强化,经计算,钢中每1%(质量分数)的Cu在过时效状态下能够产生约90 MPa的析出强化增量。钢板厚度截面存在强度差异,表面与心部强度相差约40 MPa,这主要是由于晶粒尺寸及位错密度差异所导致。
High strength low alloy(HSLA) steels are widely used in the construction of ship structures, oil pipelines, offshore platforms and so on because of their good strength, toughness and weldability. HSLA steel is generally designed with low carbon and Cu alloying. Tempered lath bainite or martensite and nano-precipitate phase of Cu can be obtained by quenching and ageing process after rolling to ensure the excellent matching of strength, low temperature toughness and weldability of HSLA steel. At present, increasing attention has been focused on the precipitation behavior and strengthening mechanism of Cu particles in HSLA steel which was aged at the peak hardness of ageing curve. However, in practical engineering applications, overageing heat treatment is generally used to make HSLA steel achieve a good match of strength and toughness. In this work, the microstructure and nano-sized Cu precipitates of an industrial production HSLA steel plate with thickness of 35 mm were characterized by SEM, EBSD, HRTEM and APT. Meanwhile, the strengthening mechanism of the tested steel was investigated. The results show that Cu precipitates in the tested steel processed by overageing are mainly in the range of 6～50 nm, Cu particles exhibiting short rod or spherical shape within 30 nm are 9 R structure,and other particles size larger than 30 nm exhibiting long rod or spherical shape are fcc structure. The segregation of trace Mn and Ni in rod particles on the interface between Cu particles and matrix is more obvious. After ageing at a higher temperature range, the yield strength of the tested steel decreases linearly with the increase of tempering temperature. The main strengthening mechanism of the HSLA steel is fine grain strengthening, followed by dislocation strengthening and precipitation strengthening. The calculated results show that every 1%Cu added in the tested steel can produce about 90 MPa precipitation strengthening increment under the condition of overageing heat treatment. The strength difference between the surface and the center of the tested steel plate is about 40 MPa, which is mainly due to the difference of grain size and dislocation density of steel.
High strength low alloy(HSLA) steels are widely used in the construction of ship structures, oil pipelines, offshore platforms and so on because of their good strength, toughness and weldability. HSLA steel is generally designed with low carbon and Cu alloying. Tempered lath bainite or martensite and nano-precipitate phase of Cu can be obtained by quenching and ageing process after rolling to ensure the excellent matching of strength, low temperature toughness and weldability of HSLA steel. At present, increasing attention has been focused on the precipitation behavior and strengthening mechanism of Cu particles in HSLA steel which was aged at the peak hardness of ageing curve. However, in practical engineering applications, overageing heat treatment is generally used to make HSLA steel achieve a good match of strength and toughness. In this work, the microstructure and nano-sized Cu precipitates of an industrial production HSLA steel plate with thickness of 35 mm were characterized by SEM, EBSD, HRTEM and APT. Meanwhile, the strengthening mechanism of the tested steel was investigated. The results show that Cu precipitates in the tested steel processed by overageing are mainly in the range of 6～50 nm, Cu particles exhibiting short rod or spherical shape within 30 nm are 9 R structure,and other particles size larger than 30 nm exhibiting long rod or spherical shape are fcc structure. The segregation of trace Mn and Ni in rod particles on the interface between Cu particles and matrix is more obvious. After ageing at a higher temperature range, the yield strength of the tested steel decreases linearly with the increase of tempering temperature. The main strengthening mechanism of the HSLA steel is fine grain strengthening, followed by dislocation strengthening and precipitation strengthening. The calculated results show that every 1%Cu added in the tested steel can produce about 90 MPa precipitation strengthening increment under the condition of overageing heat treatment. The strength difference between the surface and the center of the tested steel plate is about 40 MPa, which is mainly due to the difference of grain size and dislocation density of steel.
引文
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[23]Wang W.Precipitation and structural evolution of copper-rich Nano phases in reactor pressure vessel model steels[D].Shanghai:Shanghai University,2011(王伟.反应堆压力容器模拟钢中富Cu相的析出及晶体结构演化研究[D].上海:上海大学,2011)
[24]Xu G,Chu D F,Cai L L,et al.Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel[J].Acta Metall.Sin.,2011,47:905(徐刚,楚大锋,蔡琳玲等.RPV模拟钢中纳米富Cu相的析出和结构演化研究[J].金属学报,2011,47:905)
[25]Zhang Z Y,Li Z D,Yong Q L,et al.Precipitation behavior of carbide during heating process in Nb and Nb-Mo micro-alloyed steels[J].Acta Metall.Sin.,2015,51:315(张正延,李昭东,雍岐龙等.升温过程中Nb和Nb-Mo微合金化钢中碳化物的析出行为研究[J].金属学报,2015,51:315)
[26]Yong Q L,Ma M T,Wu B R.Micraoalloyed Steel--Physical and Mechanical Metallurgy[M].Beijing:China Machine Press,1989:22(雍岐龙,马鸣图,吴宝榕.微合金钢--物理和力学冶金[M].北京:机械工业出版社,1989:22)
[27]Yong Q L.Secondary Phase in Steels[M].Beijing:Metallurgical Industry Press,2006:361(雍岐龙.钢铁材料中的第二相[M].北京:冶金工业出版社,2006:361)
[28]Zhang Z Y,Sun X J,Yong Q L,et al.Precipitation behavior of nanometer-sized carbides in Nb-Mo microalloyed high strengh steel and its strengthening mechanism[J].Acta Metall.Sin.,2016,52:410(张正延,孙新军,雍岐龙等.Nb-Mo微合金高强钢强化机理及其纳米级碳化物析出行为[J].金属学报,2016,52:410)
[2]Yang J B,Yamashita T,Sano N,et al.Simulation of competitive Cu precipitation in steel during non-isothermal aging[J].Mater.Sci.Eng.,2008,A487:128
[3]Ghosh S K,Haldar A,Chattopadhyay P P.Effect of pre-strain on the ageing behavior of directly quenched copper containing microalloyed steel[J].Mater.Charact.,2008,59:1227
[4]Shi X B,Yan W,Wang W,et al.Novel Cu-bearing high-strength pipeline steels with excellent resistance to hydrogen-induced cracking[J].Mater.Des.,2016,92:300
[5]Liu D S,Cheng B G,Chen Y Y.Fine Microstructure and toughness of low carbon copper containing ultra high strength NV-F690heavy steel plate[J].Acta Metall.Sin.,2012,48:334(刘东升,程丙贵,陈圆圆.低C含Cu NV-F690特厚钢板的精细组织和强韧性[J].金属学报,2012,48:334)
[6]Yu X M,Zhao S J.Study on Cu precipitate of the low C high strength steel containing Cu and Ni during isochronal tempering[J].Acta Metall.Sin.,2013,49:569(余锡模,赵世金.含Cu和Ni低碳高强度钢等时回火析出富Cu相的研究[J].金属学报,2013,49:569)
[7]Wen Y R,Hirata A,Zhang Z W,et al.Microstructure characterization of Cu-rich nanoprecipitates in a Fe-2.5Cu-1.5Mn-4.0Ni-1.0Al multicomponent ferritic alloy[J].Acta Mater.,2013,61:2133
[8]Isheim D,Kolli R P,Fine M E,et al.An atom-probe tomographic study of the temporal evolution of the nanostructure of Fe-Cu based high-strength low-carbon steels[J].Scr.Mater.,2006,55:35
[9]Sun M X,Zhang W N,Liu Z Y,et al.Direct observations on the crystal structure evolution of nano Cu-precipitates in an extremely low carbon steel[J].Mater.Lett.,2017,187:49
[10]Chi C Y,Yu H Y,Dong J X,et al.The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe-Cr-Ni type austenitic heat resistant steel for USC power plant application[J].Prog.Nat.Sci.Mater.Int.,2012,22:175
[11]Liu Q D,Gu J F,Liu W Q.On the role of Ni in Cu precipitation in multicomponent steels[J].Metall.Mater.Trans.,2013,44A:4434
[12]Kapoor M,Isheim D,Ghosh G,et al.Aging characteristics and mechanical properties of 1600 MPa body-centered cubic Cu and B2-Ni Al precipitation-strengthened ferritic steel[J].Acta Mater.,2014,73:56
[13]Zhou B X,Wang J A,Liu Q D,et al.Effect of nickel alloying element on the precipitation of Cu-rich clusters in RPV model steel[J].Mater.China,2011,30(5):1(周邦新,王均安,刘庆东等.Ni对RPV模拟钢中富Cu原子团簇析出的影响[J].中国材料进展,2011,30(5):1)
[14]Mulholland M D,Seidman D N.Nanoscale co-precipitation and mechanical properties of a high-strength low-carbon steel[J].Acta Mater.,2011,59:1881
[15]Zhang C,Enomoto M.Study of the influence of alloying elements on Cu precipitation in steel by non-classical nucleation theory[J].Acta Mater.,2006,54:4183
[16]Kapoor M,Isheim D,Vaynman S,et al.Effects of increased alloying element content on Ni Al-type precipitate formation,loading rate sensitivity,and ductility of Cu-and Ni Al-precipitationstrengthened ferritic steels[J].Acta Mater.,2016,104:166
[17]Jiao Z B,Luan J H,Zhang Z W,et al.Synergistic effects of Cu and Ni on nanoscale precipitation and mechanical properties of high-strength steels[J].Acta Mater.,2013,61:5996
[18]Isheim D,Gagliano M S,Fine M E,et al.Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale[J].Acta Mater.,2006,54:841
[19]Jiao Z B,Luan J H,Miller M K,et al.Precipitation mechanism and mechanical properties of an ultra-high strength steel hardened by nanoscale Ni Al and Cu particles[J].Acta Mater.,2015,97:58
[20]Pan J S,Tong J M,Tian M B.Fundamentals of Material Science[M].Beijing:Tsinghua University Press,2011:660(潘金生,仝健民,田民波.材料科学基础[M].北京:清华大学出版社,2011:660)
[21]Zhang Z Y,Sun X J,Li Z D,et al.Effect of nanometer-sized carbides and grain boundary density on performance of Fe-C-Mo-M(M=Nb,V,or Ti)fire resistant steels[J].Chin.J.Mater.Res.,2015,29:269(张正延,孙新军,李昭东等.纳米级碳化物及小角界面密度对Fe-C-Mo-M(M=Nb、V或Ti)系钢耐火性的影响[J].材料研究学报,2015,29:269)
[22]Zhang Z Y,Chai F,Luo X B,et al.Method for measuring dislocation density of steel through electron back-scattered diffraction(EBSD)[P].Chin Pat,CN201810254056,2018(张正延,柴锋,罗小兵等.一种利用EBSD测量钢中位错密度的方法[P].中国专利,CN201810254056,2018)
[23]Wang W.Precipitation and structural evolution of copper-rich Nano phases in reactor pressure vessel model steels[D].Shanghai:Shanghai University,2011(王伟.反应堆压力容器模拟钢中富Cu相的析出及晶体结构演化研究[D].上海:上海大学,2011)
[24]Xu G,Chu D F,Cai L L,et al.Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel[J].Acta Metall.Sin.,2011,47:905(徐刚,楚大锋,蔡琳玲等.RPV模拟钢中纳米富Cu相的析出和结构演化研究[J].金属学报,2011,47:905)
[25]Zhang Z Y,Li Z D,Yong Q L,et al.Precipitation behavior of carbide during heating process in Nb and Nb-Mo micro-alloyed steels[J].Acta Metall.Sin.,2015,51:315(张正延,李昭东,雍岐龙等.升温过程中Nb和Nb-Mo微合金化钢中碳化物的析出行为研究[J].金属学报,2015,51:315)
[26]Yong Q L,Ma M T,Wu B R.Micraoalloyed Steel--Physical and Mechanical Metallurgy[M].Beijing:China Machine Press,1989:22(雍岐龙,马鸣图,吴宝榕.微合金钢--物理和力学冶金[M].北京:机械工业出版社,1989:22)
[27]Yong Q L.Secondary Phase in Steels[M].Beijing:Metallurgical Industry Press,2006:361(雍岐龙.钢铁材料中的第二相[M].北京:冶金工业出版社,2006:361)
[28]Zhang Z Y,Sun X J,Yong Q L,et al.Precipitation behavior of nanometer-sized carbides in Nb-Mo microalloyed high strengh steel and its strengthening mechanism[J].Acta Metall.Sin.,2016,52:410(张正延,孙新军,雍岐龙等.Nb-Mo微合金高强钢强化机理及其纳米级碳化物析出行为[J].金属学报,2016,52:410)
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