保护气成分对1000MPa级高强熔敷金属组织特征的影响
|
摘要
通过附带EDS的FEGSEM、EBSD、TEM等实验方法,研究了保护气成分(Ar+5%CO_2、Ar+10%CO_2、Ar+20%CO_2、Ar+30%CO_2,体积分数)对1000 MPa级高强熔敷金属组织特征的影响,阐明了保护气成分对组织转变的影响机制。结果表明,随着保护气中CO_2含量增加,1000 MPa级熔敷金属强度略有下降,而冲击韧性先升高后降低。不同保护气熔敷金属均由马氏体/贝氏体混合组织及板条间残余奥氏体组成。随着保护气中CO_2含量增加,熔敷金属中贝氏体相变体积分数为50%时的温度(B_(50))与马氏体相变开始温度(M_s)相变温度区间增大,适宜贝氏体形核的夹杂物数量增多,随贝氏体含量(体积分数)由8%增加到29.6%,其形核位置从原始奥氏体晶界向原始奥氏体晶界及晶内夹杂物处共同形核转变,熔敷金属组织形貌由"平行状"向"交织状"转变,分割细化组织,有利于高强熔敷金属强韧性的改善。
In recent years, high and ultra-high strength steels have been developed and used in light-weight constructions such as the structural members of mobile equipment in order to reduce weight and fabrication costs and to enhance the performance. Welding of steels with yield strength of more than 900 MPa is particularly challenging because of the toughness requirements for the weld metal, which calls for welding consumables of high strength and good toughness. Weld metals have been produced for a variety of welding methods with yield strength up to or above 1000 MPa, but their impact toughness remained only at medium yield strengths. Proper microstructure is the key to meeting this requirement,and its final microstructure depends on the chemical composition and cooling rate. For the deposited metal produced by gas metal arc welding(GMAW), the composition is dependent on the welding wire and shielding gas. The cooling rate of the weld metal is controlled by a combination of heat input and heat extraction. It is known that the addition of CO_2 to argon based shielding gas is effective for improvement of productivity in GMAW welding of steel. Through the chemical reaction in the welding arc, CO_2 in the shielding gas can affect the chemical composition of the weld metal, and its microstructure. The 1000 MPa grade deposited metals was welded with GMAW, and the effects of shielding gas composition(Ar+(5%～30%)CO_2,volume fraction) on the general compositional and microstructural characteristics of deposited metals, including nonmetallic inclusions, were experimentally characterized with SEM, EBSD and TEM. The microstructure of the deposited metals is mainly composed of martensite and bainite. With the increase of CO_2 content(5%～30%), the strength of the deposited metals decrease slightly and the impact toughness increases first and then decreases. Meanwhile, the transformation range(B_(50)-M_s) of the deposited metal increases, the bainite content increases(8%～29.6%) with the quantity of inclusions that are suitable for bainite nucleation increases, and the nucleation position changes from the original austenite grain boundary to the common nucleation on the original austenite grain boundary and inclusions within the grain. At the same time, the microstructure morphology of the deposited metal changes from parallel to intertexture, which presented an intersected configuration and microstructure refinement.
In recent years, high and ultra-high strength steels have been developed and used in light-weight constructions such as the structural members of mobile equipment in order to reduce weight and fabrication costs and to enhance the performance. Welding of steels with yield strength of more than 900 MPa is particularly challenging because of the toughness requirements for the weld metal, which calls for welding consumables of high strength and good toughness. Weld metals have been produced for a variety of welding methods with yield strength up to or above 1000 MPa, but their impact toughness remained only at medium yield strengths. Proper microstructure is the key to meeting this requirement,and its final microstructure depends on the chemical composition and cooling rate. For the deposited metal produced by gas metal arc welding(GMAW), the composition is dependent on the welding wire and shielding gas. The cooling rate of the weld metal is controlled by a combination of heat input and heat extraction. It is known that the addition of CO_2 to argon based shielding gas is effective for improvement of productivity in GMAW welding of steel. Through the chemical reaction in the welding arc, CO_2 in the shielding gas can affect the chemical composition of the weld metal, and its microstructure. The 1000 MPa grade deposited metals was welded with GMAW, and the effects of shielding gas composition(Ar+(5%～30%)CO_2,volume fraction) on the general compositional and microstructural characteristics of deposited metals, including nonmetallic inclusions, were experimentally characterized with SEM, EBSD and TEM. The microstructure of the deposited metals is mainly composed of martensite and bainite. With the increase of CO_2 content(5%～30%), the strength of the deposited metals decrease slightly and the impact toughness increases first and then decreases. Meanwhile, the transformation range(B_(50)-M_s) of the deposited metal increases, the bainite content increases(8%～29.6%) with the quantity of inclusions that are suitable for bainite nucleation increases, and the nucleation position changes from the original austenite grain boundary to the common nucleation on the original austenite grain boundary and inclusions within the grain. At the same time, the microstructure morphology of the deposited metal changes from parallel to intertexture, which presented an intersected configuration and microstructure refinement.
引文
[1]Seo J S,Lee C,Kim H J.Influence of oxygen content on microstructure and inclusion characteristics of bainitic weld metals[J].ISIJ Int.,2013,53:279
[2]Yu S F,Qian B N,Guo X M.Microstructure of ULCB deposited metal and effect of carbon and oxygen contents on mechanical property[J].Acta Metall.Sin.,2005,41:1082(于少飞,钱百年,国旭明.ULCB熔敷金属组织与碳、氧含量对力学性能的影响[J].金属学报,2005,41:1082)
[3]Gouda M,Takahashi M,Ikeuchi K.Microstructures of gas metal arc weld metal of 950 MPa class steel[J].Sci.Technol.Weld.Join.,2005,10:369
[4]LePera F S.Improved etching technique to emphasize martensite and bainite in high-strength dual-phase steel[J].JOM,1980,32(3):38
[5]Keehan E,Karlsson L,Andrén H O,et al.New developments with C-Mn-Ni high strength steel weld metals,Part A-Microstructure[J].Weld.J.,2006,85:200S
[6]Keehan E,Karlsson L,Andrén H O,et al.New developments with C-Mn-Ni high strength steel weld metals,Part B-Mechanical properties[J].Weld.J.,2006,85:218S
[7]An T B,Tian Z L,Shan J G,et al.Effect of shielding gas on microstructure and performance of 1000 MPa grade deposited metals[J].Acta Metall.Sin.,2015,51:1489(安同邦,田志凌,单际国等.保护气对1000 MPa级熔敷金属组织及力学性能的影响[J].金属学报,2015,51:1489)
[8]St-Laurent S,L'Espérance G.Effects of chemistry,density and size distribution of inclusions on the nucleation of acicular ferrite of C-Mn steel shielded-metal-arc-welding weldments[J].Mater.Sci.Eng.,1992,A149:203
[9]Girault E,Jacques P,Harlet P,et al.Metallographic methods for revealing the multiphase microstructure of TRIP-assisted steels[J].Mater.Charact.,1998,40:111
[10]Peng Y,Peng X N,Zhang X M,et al.Microstructure and mechanical properties of GMAW weld metal of 890 MPa class steel[J].J.Iron Steel Res.Int.,2014,21:539
[11]Luo Z J,Wang L P,Wang M,et al.Effect of lath martensite/bainite microstructure on strength and toughness of a low carbon martensite steel[J].Trans.Mater.Heat Treat.,2012,33(2):85(罗志俊,王丽萍,王猛等.板条M/B组织对低碳马氏体钢强韧性的影响[J].材料热处理学报,2012,33(2):85)
[12]Steven W,Haynes A G.The temperature of formation of martensite and bainite in low-alloy steels,some effects of chemical composition[J].J.Iron.Steel.Inst.,1956,183:349
[13]Gadallah R,Fahmy R,Khalifa T,et al.Metallographic methods for revealing the multiphase microstructure of TRIP-assisted steels[J].Mater.Charact.,1998,40:111
[14]Yang C L,Lin S B.Fundamentals of Arc Welding[M].Harbin:Harbin Institute of Technology Press,2003:1(杨春利,林三宝.电弧焊基础[M].哈尔滨:哈尔滨工业大学出版社,2003:1)
[15]Zhang J C,Wang G R,Shi Y H,et al.Application of mixed gas in gas metal arc welding[J].Weld.Pipe Tube,2006,29(3):46(张建春,王国荣,石永华等.混合气体在熔化极气体保护焊中的应用[J].焊管,2006,29(3):46)
[16]Keehan E,Karlsson L,Marimuthu M,et al.High strength steel weld metals:Developments with Ni and Mn[A].Proceedings of the 7th International Welding Symposium[C].Kobe:Japan Welding Society,2001:797
[17]Keehan E.Microstructure and properties of novel high strength steel weld metals[J].Weld.Res.Abroad,2006,52:1
[18]Peng X N,Peng Y,Tian Z L,et al.Effect of Ni on the microstructure evolution of Cr-Ni-Mo series high strength weld metal[J].Trans.China Weld.Inst.,2014,35(9):32(彭杏娜,彭云,田志凌等.Ni元素对Cr-Ni-Mo系高强焊缝组织演化的影响[J].焊接学报,2014,35(9):32)
[19]Singh S B,Bhadeshia H K D H.Estimation of bainite platethickness in low-alloy steels[J].Mater.Sci.Eng.,1998,A245:72
[20]Chang L C,Bhadeshia H K D H.Microstructure of lower bainite formed at large undercoolings below bainite start temperature[J].Mater.Sci.Technol.,1996,12:233
[21]Pak J H,Bhadeshia H K D H,Karlsson L,et al.Coalesced bainite by isothermal transformation of reheated weld metal[J].Sci.Technol.Weld.Join.,2008,13:593
[22]Keehan E.Effect of microstructure on mechanical properties of high strength steel weld metals[D].G?teborg:Chalmers University of Technology,2004
[2]Yu S F,Qian B N,Guo X M.Microstructure of ULCB deposited metal and effect of carbon and oxygen contents on mechanical property[J].Acta Metall.Sin.,2005,41:1082(于少飞,钱百年,国旭明.ULCB熔敷金属组织与碳、氧含量对力学性能的影响[J].金属学报,2005,41:1082)
[3]Gouda M,Takahashi M,Ikeuchi K.Microstructures of gas metal arc weld metal of 950 MPa class steel[J].Sci.Technol.Weld.Join.,2005,10:369
[4]LePera F S.Improved etching technique to emphasize martensite and bainite in high-strength dual-phase steel[J].JOM,1980,32(3):38
[5]Keehan E,Karlsson L,Andrén H O,et al.New developments with C-Mn-Ni high strength steel weld metals,Part A-Microstructure[J].Weld.J.,2006,85:200S
[6]Keehan E,Karlsson L,Andrén H O,et al.New developments with C-Mn-Ni high strength steel weld metals,Part B-Mechanical properties[J].Weld.J.,2006,85:218S
[7]An T B,Tian Z L,Shan J G,et al.Effect of shielding gas on microstructure and performance of 1000 MPa grade deposited metals[J].Acta Metall.Sin.,2015,51:1489(安同邦,田志凌,单际国等.保护气对1000 MPa级熔敷金属组织及力学性能的影响[J].金属学报,2015,51:1489)
[8]St-Laurent S,L'Espérance G.Effects of chemistry,density and size distribution of inclusions on the nucleation of acicular ferrite of C-Mn steel shielded-metal-arc-welding weldments[J].Mater.Sci.Eng.,1992,A149:203
[9]Girault E,Jacques P,Harlet P,et al.Metallographic methods for revealing the multiphase microstructure of TRIP-assisted steels[J].Mater.Charact.,1998,40:111
[10]Peng Y,Peng X N,Zhang X M,et al.Microstructure and mechanical properties of GMAW weld metal of 890 MPa class steel[J].J.Iron Steel Res.Int.,2014,21:539
[11]Luo Z J,Wang L P,Wang M,et al.Effect of lath martensite/bainite microstructure on strength and toughness of a low carbon martensite steel[J].Trans.Mater.Heat Treat.,2012,33(2):85(罗志俊,王丽萍,王猛等.板条M/B组织对低碳马氏体钢强韧性的影响[J].材料热处理学报,2012,33(2):85)
[12]Steven W,Haynes A G.The temperature of formation of martensite and bainite in low-alloy steels,some effects of chemical composition[J].J.Iron.Steel.Inst.,1956,183:349
[13]Gadallah R,Fahmy R,Khalifa T,et al.Metallographic methods for revealing the multiphase microstructure of TRIP-assisted steels[J].Mater.Charact.,1998,40:111
[14]Yang C L,Lin S B.Fundamentals of Arc Welding[M].Harbin:Harbin Institute of Technology Press,2003:1(杨春利,林三宝.电弧焊基础[M].哈尔滨:哈尔滨工业大学出版社,2003:1)
[15]Zhang J C,Wang G R,Shi Y H,et al.Application of mixed gas in gas metal arc welding[J].Weld.Pipe Tube,2006,29(3):46(张建春,王国荣,石永华等.混合气体在熔化极气体保护焊中的应用[J].焊管,2006,29(3):46)
[16]Keehan E,Karlsson L,Marimuthu M,et al.High strength steel weld metals:Developments with Ni and Mn[A].Proceedings of the 7th International Welding Symposium[C].Kobe:Japan Welding Society,2001:797
[17]Keehan E.Microstructure and properties of novel high strength steel weld metals[J].Weld.Res.Abroad,2006,52:1
[18]Peng X N,Peng Y,Tian Z L,et al.Effect of Ni on the microstructure evolution of Cr-Ni-Mo series high strength weld metal[J].Trans.China Weld.Inst.,2014,35(9):32(彭杏娜,彭云,田志凌等.Ni元素对Cr-Ni-Mo系高强焊缝组织演化的影响[J].焊接学报,2014,35(9):32)
[19]Singh S B,Bhadeshia H K D H.Estimation of bainite platethickness in low-alloy steels[J].Mater.Sci.Eng.,1998,A245:72
[20]Chang L C,Bhadeshia H K D H.Microstructure of lower bainite formed at large undercoolings below bainite start temperature[J].Mater.Sci.Technol.,1996,12:233
[21]Pak J H,Bhadeshia H K D H,Karlsson L,et al.Coalesced bainite by isothermal transformation of reheated weld metal[J].Sci.Technol.Weld.Join.,2008,13:593
[22]Keehan E.Effect of microstructure on mechanical properties of high strength steel weld metals[D].G?teborg:Chalmers University of Technology,2004