高强钢EQ70焊接接头CTOD韧性与微观组织的关系研究
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摘要
由于焊接结构向大型化、高强化、深水冰冷海域方向发展,对焊接接头的脆性断裂问题的研究显得非常迫切和重要。为了适应生产的需要,断裂力学不断提出一系列断裂韧性指标,CTOD作为断裂韧性的一个指标,其真实性和准确性是其他参量不能比的。然而以往的很多研究都是针对夏比冲击试验的结果和微观组织的关系展开的,对CTOD韧度与微观组织的关系的研究还未见有报道,随着CTOD评定准则的广泛使用,研究高强钢CTOD韧度与微观组织的关系是一项非常有意义的工作。
本文的研究依托国家工业和信息化部项目：《EQ56/EQ70焊接接头CTOD韧性机理与允许值研究》工信部装(2009)382号。采用相关性研究方法研究EQ70高强钢CTOD韧度和焊接工艺,即确定材料的韧性与某种组织结构或断口形貌相关,通过探索合适的焊接工艺设法并避免有害的组织结构,最终达到改善钢材韧性的目的。本文的工作主要包括以下几个内容：
1.本文结合EQ70高强钢的特点介绍了常见的微观组织结构,并对电子显微镜做了比较,证明扫描电子显微镜较适合于清晰分析焊接接头的组织和断口形貌。
2.本文通过CTOD试验方法测定了60mm厚的两种焊接工艺下EQ70高强钢焊接接头的韧度,试验结果表明采用焊接工艺B的焊缝处CTOD均值大于采用焊接工艺A的焊缝处CTOD均值,对应的熔合线的CTOD均值差别不大,但是两种焊接工艺下焊缝处的CTOD离散性都小于熔合线的CTOD离散性。
3.本文在CTOD试验的基础上做了金相试验,在高倍扫描电镜下分析了微观组织对海洋高强钢EQ70焊接接头韧性的影响,分析结果表明EQ70焊接接头粗晶区产生脆化的主要原因有两个：其一是粗晶区中的粒状贝氏体以M-A组元的形式分布在板条铁素体上,它的存在促进了在其边界裂纹的起裂,上贝氏体中粗大的碳化物也使强化作用减弱很容易萌生裂纹降低韧度。其二是粗晶区晶粒粗大导致韧性下降。本文比较分析两种焊接工艺下焊接接头微观组织的差异后,提出了改善焊接工艺的方法,适当降低焊接线能量可以提高焊接接头的韧度。
4.本文对CTOD允许值进行了讨论,为CTOD允许值的确定提供了建议。
Because of the welding structure developing to the large scale, the high strengthening, the deep and freezing water, the problem of brittle fracture of welded joints becomes particularly urgent and important. In order to adapt to the needs of the production, fracture mechanics continue to put forward a series of fracture toughness. CTOD as an indicator of fracture toughness, other parameters cannot be compared with whose authenticity and accuracy. However, many studies are carried out for the relationship of the Charpy impact test results and the microstructure. There is no report on relationship of CTOD toughness and microstructure. With the widespread use of the CTOD assessment criteria, the study on the relationship between the CTOD toughness and microstructure of high strength steel is a very meaningful work.
This paper relies on the national industry and information technology program "CTOD toughness mechanism and allowed values of EQ56/EQ70welding joints". Item number:Industry and informatization ministry <2009>,382. The EQ70high strength steel CTOD toughness and welding process were studied by correlation method. That is to determine the relationship between the toughness of the material and microstructure or fracture morphology, and explore the suitable welding process and try to avoid harmful microstructure, and ultimately achieve the goal of improving the toughness of steel. This work includes the following content:
1. This paper describes common microstructure combined with characteristics of high strength steel EQ70. Then electron microscopes were compared and Scanning electron microscope was proved more suited to analyze clearly the microstructure and fracture morphology at welded joints.
2. The toughness of welded joints for high strength steel EQ70with60mm thickness by two welding processes has been determined by CTOD test. The results showed that the CTOD average value at the weld by the welding process B is greater than the value at the weld by welding processes A. Corresponds to CTOD average value on the fusion line, there is not much difference. But the CTOD discrete nature at the weld is less than that on the fusion line by two welding processes.
3. Metallographic test was made on the basis of the CTOD test. Under the high-powered scanning electron microscope, the effect of microstructure on CTOD of welded joints for offshore high-strength steel has been analyzed. The results show that there are two reasons for the embrittlement of the EQ70CGHAZ. One is that the granular bainite in CGHAZ was distributed on the lath ferrite in the form of the M-A. It promotes the cracks crack in its boundary. The coarse carbides in the upper bainite weaken the strengthened effect, which make the cracks crack easily and reduce the toughness. The other is that coarse grains decrease the toughness. In this paper, the microstructure of different samples by two different welding processes has been compared and a method to improve the welding process has been put forward. Reduce the welding heat input appropriately can improve the toughness of welded joints.
4. The CTOD allowed value was discussed in this paper, which provides a suggestion for determining the allowed value.
本文的研究依托国家工业和信息化部项目：《EQ56/EQ70焊接接头CTOD韧性机理与允许值研究》工信部装(2009)382号。采用相关性研究方法研究EQ70高强钢CTOD韧度和焊接工艺,即确定材料的韧性与某种组织结构或断口形貌相关,通过探索合适的焊接工艺设法并避免有害的组织结构,最终达到改善钢材韧性的目的。本文的工作主要包括以下几个内容：
1.本文结合EQ70高强钢的特点介绍了常见的微观组织结构,并对电子显微镜做了比较,证明扫描电子显微镜较适合于清晰分析焊接接头的组织和断口形貌。
2.本文通过CTOD试验方法测定了60mm厚的两种焊接工艺下EQ70高强钢焊接接头的韧度,试验结果表明采用焊接工艺B的焊缝处CTOD均值大于采用焊接工艺A的焊缝处CTOD均值,对应的熔合线的CTOD均值差别不大,但是两种焊接工艺下焊缝处的CTOD离散性都小于熔合线的CTOD离散性。
3.本文在CTOD试验的基础上做了金相试验,在高倍扫描电镜下分析了微观组织对海洋高强钢EQ70焊接接头韧性的影响,分析结果表明EQ70焊接接头粗晶区产生脆化的主要原因有两个：其一是粗晶区中的粒状贝氏体以M-A组元的形式分布在板条铁素体上,它的存在促进了在其边界裂纹的起裂,上贝氏体中粗大的碳化物也使强化作用减弱很容易萌生裂纹降低韧度。其二是粗晶区晶粒粗大导致韧性下降。本文比较分析两种焊接工艺下焊接接头微观组织的差异后,提出了改善焊接工艺的方法,适当降低焊接线能量可以提高焊接接头的韧度。
4.本文对CTOD允许值进行了讨论,为CTOD允许值的确定提供了建议。
Because of the welding structure developing to the large scale, the high strengthening, the deep and freezing water, the problem of brittle fracture of welded joints becomes particularly urgent and important. In order to adapt to the needs of the production, fracture mechanics continue to put forward a series of fracture toughness. CTOD as an indicator of fracture toughness, other parameters cannot be compared with whose authenticity and accuracy. However, many studies are carried out for the relationship of the Charpy impact test results and the microstructure. There is no report on relationship of CTOD toughness and microstructure. With the widespread use of the CTOD assessment criteria, the study on the relationship between the CTOD toughness and microstructure of high strength steel is a very meaningful work.
This paper relies on the national industry and information technology program "CTOD toughness mechanism and allowed values of EQ56/EQ70welding joints". Item number:Industry and informatization ministry <2009>,382. The EQ70high strength steel CTOD toughness and welding process were studied by correlation method. That is to determine the relationship between the toughness of the material and microstructure or fracture morphology, and explore the suitable welding process and try to avoid harmful microstructure, and ultimately achieve the goal of improving the toughness of steel. This work includes the following content:
1. This paper describes common microstructure combined with characteristics of high strength steel EQ70. Then electron microscopes were compared and Scanning electron microscope was proved more suited to analyze clearly the microstructure and fracture morphology at welded joints.
2. The toughness of welded joints for high strength steel EQ70with60mm thickness by two welding processes has been determined by CTOD test. The results showed that the CTOD average value at the weld by the welding process B is greater than the value at the weld by welding processes A. Corresponds to CTOD average value on the fusion line, there is not much difference. But the CTOD discrete nature at the weld is less than that on the fusion line by two welding processes.
3. Metallographic test was made on the basis of the CTOD test. Under the high-powered scanning electron microscope, the effect of microstructure on CTOD of welded joints for offshore high-strength steel has been analyzed. The results show that there are two reasons for the embrittlement of the EQ70CGHAZ. One is that the granular bainite in CGHAZ was distributed on the lath ferrite in the form of the M-A. It promotes the cracks crack in its boundary. The coarse carbides in the upper bainite weaken the strengthened effect, which make the cracks crack easily and reduce the toughness. The other is that coarse grains decrease the toughness. In this paper, the microstructure of different samples by two different welding processes has been compared and a method to improve the welding process has been put forward. Reduce the welding heat input appropriately can improve the toughness of welded joints.
4. The CTOD allowed value was discussed in this paper, which provides a suggestion for determining the allowed value.
引文
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[2]陈伯蠡.焊接工程缺欠分析与对策[M].北京机械工业出版社,2006.
[3]苗张木,王振宇.厚钢板焊接接头韧性CTOD试验评定技术及应用[J].宽厚板.2006,12(6),23-28.
[4]曹兴华.Q390低合金高强钢焊接性研究[D].南京理工大学硕士学位论文.2010.
[5]吕奎清.高强钢焊接的现状和发展[2011-09-19].http://www.doc88.com/p-69691678744.htm-1.
[6]Enda Keehan. Effect of Microstructure on Mechanical Properties of High Strength Steel Weld Metals. Ph.D dissertation. Dept. of Physics, Chalmers University of Technology and Goteborg University. Goteborg, Sweden,2004.
[7]徐宏伟.国外汽车川先进高强度钢板及其标准综述[J].冶金标准化与质量,2007,2(44),8-13.
[8]陈立人,张冠军.国内外钢科技的新进展与石油机械用钢研究[J].石油机械.2005,33(12),50-54.
[9]苗张木.厚钢板焊接接头韧度CTOD评定研究[D].武汉理工大学博士学位论文,2005.
[10]罗继相,王志海.金属工艺学.湖北：武汉理工大学出版社.2009.2.
[11]H.K.D.H. Bhadeshia, L.-E. Svensson, B. Gretoft, J. Mater. Sci.,21,3947,1986.
[12]L.E. Svensson:Control of microstructure and properties in steel arc welds[M],CRC Press, Inc.,1994
[13]D. J. Widgery, Deoxidation practice and the toughness of mild steel weld metal, Ph. D. thesis, University of Cambridge,1974.
[14]M. Lord, Design and modelling of ultra - High Strength Steel Weld Deposits, Ph. D. Thesis, Materials Science and Metallurgy, University of Cambridge, U.K.,1999.
[15]Z.Zhang, R.A. Farrar, Columnar grain development in C-Mn-Ni low-alloy weld metals and the influence of nickel, J. Material. Science.,30:pp.5581-5588,1995
[16]K. Easterling, Introduction to the Physical Metallurgy of Welding[M], Butterworths & Co Ltd.,1983.
[17]R.W.K. Honeycombe & H.K.D.K. Bhadeshia, Steel Microstructure and Properties, 2nd Ed., Edward Arnold, London[M],1995.
[18]E.S. Davenport and E.C. Bain, Trans. Met. Soc. A.I.M.E. 90, 117, 1930.
[19]Kathleen Mills, Joseph R D, James D D. Metals Handbook Vol 12 Fractography. 9th ed, Ohio:ASM,1987.12-26.
[20]H.K.D.H Bhadeshia, Bainite in Steels[M], The institute of materials, London,1992
[21]H.K.D.H. Bhadeshia, Some phase transformations is steel[J]. Material Science and Technology,1999.15:p.22-29
[22]G.V. Smith and R.F. Mehl, Trans. AIME,150,211-226,1942.
[23]Charlie R Brooks, Ashok Choudhury. Failure analysis of engineering materials. New York:McGraw2Hill,2002.129-187.
[24]Henry G, Horstmann D. Macrofractography and microfractography. Beijing:China Machine Press,1990.5-45.
[25]H.K.D.H. Bhadeshia and J.W. Christian, Proc. of the Int. Conf. on Bainite,ASMI, Chicago, USA,1998.
[26]J. W. Christian, The Strength of Martensite, Chapter 5, Strengthening methods in crystals, A. Kelly and R. B. Nicholson[M], (Edits), Applied Science Publishers Ltd., London,1971.
[27]P. G. Winchell and M. Cohen, Trans., ASM,55,347,1962.
[28]邢继彬,孙新军,刘清友,等.X80管线钢热影响区ICHAZ组织性能.科技创新导报.2010.No15.63-64.
[29]吴立新,方玉.现代扫描电镜的发展及其在材料科学中的应用[J].武钢技术.2005,43(6).36-40
[30]Joesph Goldstein, Dale Newbury, David Joy, et al.Scanning Electron Microscopy and X-Ray Microanalysis[M],3rd. Edit., Plenum Publishers, New York,2003.
[31]陈世朴.金属电子显微分析[M].北京：机械工业出版社,1992.
[32]潘春旭.复合零部件异种金属焊接接头显微结构特征及其转变机理研究[D].武汉科技大学博十学位论文.1998
[33]British Standard Institution.BS7448:Part2:Method for Determination of KIC、Critical CTOD and Critical J Values of Welds in Metallic Materials[S]. London:British Standard Institution, 1997.
[34]DET NORSKE VERITAS. Offshore Standard DNV-OS-C401-2008:Fabrication and Testing of Offshore Structures. [S]
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