式中: K 为相变塑性系数 ( 通过试验可以测得 ) ; f M 为马氏体的体积分数; Δf M 为马氏体体积分数增量; S ij 为应力张量.
2
有限元模型及计算案例
为了研究相变塑性对残余应力的影响,采用的 材料为低温相变材料,由于合金含量较多,该材料在 冷却过程中只发生奥氏体—马氏体相变. 为了方便 起见,采用了 TIG 重熔的焊接方法,有限元模型如 图 2 所示,试板尺寸为 200 mm × 200 mm × 5 mm,焊
图2 Fig. 2
有限元模型
Finite element mode
为定量考察相变塑性对焊接残余应力的影响, 计算了 4 个案例. Case A 不考虑相变; Case B 考虑
邓德安,等: 相变塑性对低温相变钢焊接接头残余应力计算精度的影响
第8 期
11
由于焊缝方向上的拘束度大,因此材料在冷却过程 中由奥氏体向马氏体转变时,由于体积膨胀抵消了 相变前形成的累积拉伸应力. 在计算模型中考虑了 在冷却过程中的过冷奥氏体屈服强度,因此材料冷 却到马氏体相变温度前由于受奥氏体的屈服极限的 限制形成的累积拉伸应力并不是很大,在体积膨胀 的作用下最终在焊缝和热影响区的应力就变成压缩 应力了. 仔细比较 Case B,Case C 和 Case D 可以发
图3 Fig. 3
现,三者之间还是有一定的差异. 在 Case B 中完全 忽略了相变塑性的影响,焊缝和热影响区的压应力
材料的屈服强度与温度的关系
Temperature-dependent yield strength
体积变化和屈服强度变化,但不考虑相变塑性; Case C 考虑体积变化、屈服强度变化和相变塑性; Case D 在 Case C 的基础上,人 为 将 相 变 系 数 ( K) 放 大 一 倍. 需要说明的是,目前还没有直接测量低温相变
平均值约为 - 180 MPa,而 Case C 和 Case D 在对应 位置的平均值分别为 - 150 和 - 110 MPa. Case D 中,由于人为扩大了相变塑性系数,计算得到的纵向 残余应力与 Case C 相比焊缝和热影响区的纵向压 缩应力值在整体上偏小些.
低碳钢钢管焊接变形[J]. 焊接学报,2006,27( 1) : 76 - 80. Deng Dean,Liang Wei,Luo Yu,et al. Prediction of welding de-
图 7 比较了 Case A,Case B,Case C 和 Case D 的中央断面上表面横向残余应力分布. 从图 7 可 知,在不考虑相变的情况下 ( Case A) ,焊缝和热影 响区的横向应力较小,而在考虑相变引起的体积变 化和屈服强度变化情况下( Case B) 焊缝及其附近的 横向残余应力明显增加. 在考虑相变塑性情况下, 上表面横向应力有所下降,且相变塑性系数越大,横 向应力值下降越多,这说明相变塑性也有减缓横向 残余应力在相变过程中的变化趋势的效果 .
formation in mild steel pipe using thermal elastic plastic finite element method[J]. Transactions of the China Welding Institution, 2006,27( 1) : 76 - 80. [3] 张增磊,史清宇,刘
园,等. 焊接数值模拟材料新模型的建
立及应用[J]. 焊接学报,2009,30( 2) : 45 - 48. Zhang Zhenglei,Shi Qingyu,Liu Yuan,et al. Establishment and application of material models for numerical simulation of welding process[J]. Transactions of the China Welding Institution,2009, 30( 2) : 45 - 48. [4] 邓德安,清岛祥一. 焊接顺序对厚板焊接残余应力分布的影 响[J]. 焊接学报,2012,33( 12) : 55 - 58. Dean Deng,Shoichi Kiyoshima. Influence of welding sequence on welding residual stress distribution in thick plate joint[J]. Transactions of the China Welding Institution,2012,33( 12) : 55 - 58. [5] 邓德安,清岛祥一. 退火温度对 SUS304 不锈钢焊接残余应力 计算精度的影响[J]. 金属学报,2014,50( 5) : 626 - 632. Dean Deng,Shoichi Kiyoshima. Influence of annealing temperature on calculation accuracy of welding residual stress in a SUS304 strainless steel joint[J]. Acta Metallurgica Sinica,2014,50( 5) : 626 - 632. [6] Deng Dean,Tong Yangang,Ma N,et al. Prediction of the residual welding stress in 2. 25Cr-1Mo steel by taking into account the effect of solid-state phase transformation[J]. Acta Metallurgica
图7 Fig. 7
中央断面上表面的横向残余应力分布
Transverse residual stress distributions on top sur-
Sinica ( English Letters) ,2013,26( 3) : 333 - 339. [7] Inoue T. Mechanics and characteristics of transformation plasticity and metallo-thermo-mechanics process simulation[J]. Engineering
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结
论
[8] Leblond J. Mathematical modeling of transformation plasticity in steels II: coupling with strain hardening phenomena[J]. International Journal of Plasticity,1986,5: 573 - 591.
( 1) 相变引起的体积变化和屈服强度变化对低 温相变材料的残余应力有明显的影响 .
作者简介:
( 2) 与体积膨胀和屈服强度变化相比较,相变 塑性对焊接残余应力的影响要小些,但它可减缓相
110 余篇. Email: deandeng@ cqu. edu. cn
邓德安,男,1968 年出生,博士,教授,博士研究生导
师. 主要从事焊接数值模拟和金属材料焊接方面的研究. 发表论文
2014,Vol. 35,No. 8
TRANSACTIONS OF THE CHINA WELDING INSTITUTION
Ⅰ
MAIN TOPICS,ABSTRACTS & KEY WORDS Effect of welding methods on impact toughness of ultra-low carbon martensitic stainless steel welding wire deposited metal DU Bing1,2 ,SUN Fenglian1 ,XU Yujun2 ,LI Xi2 aoyu ,L Xiaochun2 ,QIN Jian2 ( 1. College of Material Science and Engineering,Harbin University of Science and Technology, Harbin 150001,China; 2. Harbin Welding Institute,Harbin 150028,China) . pp 1 - 4 Abstract: As for the low impact toughness of weld metal for large hydro-turbine runner,effect of welding methods and gas content on impact toughness of ultra-low carbon martensitic stainless steel welding wire deposited metal is investigated. The results show that the Laser-MIG hybrid welding in addition to TIG welding can greatly improve the impact toughness. TIG can be used for weld repairs of stainless steel runner. Laser -MIG welding could promete the using in the group welding of laminas, vanes and band. The impact toughness decreased with the increase of C,[O]and [N]content of deposited metal,and [O] is the major factor. Spherical oxide inclusion can generate crack in deposited metal with high [O] condition,and decrease crack initiation and expansion energy. Key words: martensitic stainless steel; welding method; impact toughness; hydro-turbine runner Dynamic stability analysis of soft-switching resonant process and optimization of PWM control waveform ZHU Zhim1, 2 1 1 ing ,YANG Zhongyu ,XIA Zhuliang ,TANG Yingying1 ( 1. Department of Mechanical Engineering, Tsinghua University, Beijing 100084,China; 2. Key Lab. for Advanced Materials Processing Technology,Ministry of Education,Tsinghua University,Beijing 100084,China) . pp 5 - 8 Abstract: Based on the decoupled analysis of soft-switching resonant process in phase-shift controlled full- bridge power converter,a“1-2-1”cosine mode PWM control waveform is proposed,which is aimed at dealing with the process of power-start and frequently violent dynamic change on welding arc load. According to the generating principle of digital PWM control waveform in DSP,a phase-shift PWM control waveform with " 1-2-1" cosine mode is designed,and its control effect is verified experimentally. The results show that,by using this phase-shift PWM mode to control full-bridge power converter,it can not only meet the requirement of effective duty cycle in PWM control pulse with regard to the power output characteristics,but also guarantee the dynamic stability in soft-switching resonant process of leading-leg parallel resonant network and transformer primary side serial resonant network,so that the soft-switching state of power devices will be maintained in the process of power-start and frequently violent dynamic change on welding arc load. Key words: control waveform optimization; phase-shift palse width modulation control; soft-switching resonance; full-
bridge converter Influence of TRIP on calculated results of residual stress in a low temperature transformation steel joint DENG 1 2 2 Dean ,MURAKAWA Hidekazu ,MA Ningxu ( 1. College of Materials Science and Engineering, Chongqing University, Chongqing 400045,China; 2. Joining and Welding Research Institute,Osaka University,Osaka 567-0047,Japan) . pp 9 - 12 Abstract: In this study,a computational approach based on JWRIAN software was developed to predict welding residual stress in low temperature transformation ( LTT) steel joint with considering solid-state phase transformation. The main objective was to clarify the influences of volume change,yield strength variation and transformation induced plasticity ( TRIP) on the welding residual stress by means of the developed numerical method. Numerical results indicate that both volume change and yield strength variation during austenite-martensite have significant influences on the formation of welding residual stress in the LTT steel joint. In addition,TRIP also has somewhat influence on the welding residual stress,and it can relax the change tendency of both longitudinal and transverse stresses during phase transformation to some extent. Key words: solid-state phase transformation; numerical simulation; residual stress; transformation induced plasticity Fiber laser-assisted TIG welding weld characteristics and influencing factors YIN Yan1 ,TA Jinguo1 ,WANG Zhan1 chong ,ZHANG Ruihua1,2 ( 1. Key Laboratory of Non-ferrous Metal Alloys,Lanzhou University of Technology,Ministry of Education,Lanzhou 730050,China; 2. China Iron & Steel Research Institute Group,Beijing 100081,China) . pp 13 - 16 Abstract: On the base of active welding method,laser aided activating TIG welding was proposed. At first,the surface of weld was melted by the mini power laser protected by oxygen. Then the conventional TIG was used to cover the weld,which achieved the target of the weld with deeper penetration and narrower width. The results show that with the increase of welding current,the penetration and width of weld melted and unmelted by laser increased,but the penetration of weld melted increased faster. The increase of welding speed led to decrease of penetration and width. With increase of power laser,the penetration increased,but width decreased. With the increase of pre-melting speed,the penetration increased first and then decreased,the width decreased and then increased. The weld,its penetration increased significantly and appearance was good,was gained by optimum parameters. Thus laser aided activating TIG welding was developed as a novel active welding method. Key words: activating TIG welding; laser; oxygen; penetration increase