Improvement of reheat-cracking susceptibility and microstructure of T23 steel
ZHOU Ren-yuan1, ZHU Li-hui1, LI Shi-xian1, ZHAI Guo-li2
1. School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China;
2. Central Research Institute, Baoshan Iron and Steel Co., Ltd., Shanghai 201900, China
Abstract:The high reheat-cracking susceptibility of T23 severely endangers the safety of Ultra-super critical power plants. In order to decrease the reheat-cracking susceptibility of T23,the mass percent of elements such as C and W was optimized. The simulated coarse-grained heat-affected zone (CGHAZ) in T23 and modified T23 was produced via thermal simulation of welding,and the reheat-cracking susceptibility was evaluated by isothermal slow strain rate tensile test on Gleeble. The microstructure of CGHAZ in T23 and modified T23 was investigated by optical microscope (OM),scanning electron microscope (SEM) and transmission electron microscope (TEM). The effect of microstructure on the reheat-cracking susceptibility of modified T23 was discussed. The result shows that the reheat-cracking susceptibility of modified T23 is greatly decreased,and the mechanical properties meet the requirements of ASME specification. Compared with T23,there are less intergranular M23C6 precipitates and intragranular MX particles in modified T23. At the same time,the mass percent of C and W in the grain interiors is decreased in modified T23. Therefore,the difference between intergranular and intragranular strength is small in modified T23,leading to the improved reheat-cracking susceptibility. In addition,smaller grains and fewer M-A constituents in modified T23 help to decrease the reheat-cracking susceptibility. The decreased number of M23C6 at grain boundaries slows down the micro-void connection and crack propagation. The composition of modified T23 steel can provide reference for further improving the reheat-cracking susceptibility of T23 steel.
[1] 赵钦新,朱丽慧. 超临界锅炉耐热钢研究[M]. 北京:机械工业出版社,2010. (ZHAO Qin-xin,ZHU Li-hui. Research on Heat Resistant Steel for Supercritical Boiler[M]. Beijing:China Machine Press,2010.)
[2] Masuyama F,Koyoyama T. Development of a tungsten strengthened low alloy steel with improved weldability[J]. Boiler Manufacturing,1996(4):30.
[3] 瓦卢瑞克·曼内斯曼钢管公司. T23/T24管材手册——水冷壁和过热器用新材料[C]//超(超)临界锅炉用钢及焊接技术论文集. 苏州:超(超)临界锅炉用钢及焊接技术协作网,2005:305. (Vallourec and Mannemann Tubes Co.,Ltd. T23/T24 pipe handbook—New materials for water wall and Superheater[C]//Proceedings of Steel and Welding Technology for (Ultra) Supercritical Boiler. Suzhou:Steel and Welding Technology for (Ultra) Supercritical Boiler Collaboration Network,2005:305.)
[4] Komai N,Masuyama F,Ishihara I,et al. Development and application of 2.25Cr-1.6W (HCM2S) steel large diameter and thick section pipe[C]//Advanced Heat Resistant Steel for Power Generation Conference Proceedings. San Sebastian:The Electric Power Research Institute,1998:96.
[5] Park K,Kim S,Chang J,et al. Post-weld heat treatment cracking susceptibility of T23 weld metals for fossil fuel applications[J]. Materials and Design,2012(34):699.
[6] Strader K,Alexandrov B T,Lippold J C. Stress-Relief Cracking in Simulated-Coarse-Grained Heat Affected Zone of a Creep-Resistant Steel[M]. Cracking Phenomena in Welds IV. Switzerland:Springer International Publishing,2016.
[7] Chang J C,Heo N H,Lee C H. Intergranular cracking susceptibility of 2.25Cr1.3W and 9Cr1MoVNb weld metals at elevated temperatures[J]. Metals and Materials International,2010,16(6):981.
[8] Heo N H,Chang J C,Yoo K B,et al. The mechanism of elevated temperature intergranular cracking in heat-resistant alloys[J]. Mater Science and Engineering A,2011(528):2678.
[9] LI Y,WANG X,WANG J Q,et al. Stress-relief cracking mechanism in simulated coarse-grained heat-affected zone of T23 steel[J]. Journal of Materials Processing Technology,2019(266):73.
[10] Norton S J. Development of a Gleeble Based Test for Post Weld Heat Treatment Cracking in Nickel Alloys[D]. Ohio State:The Ohio State University,2002.
[11] 李夕强,王学,杨超,等. 预热和焊后热处理对T23钢接头力学性能的影响[J]. 中国电力,2016,49(2):1.(LI Xi-qiang,WANG Xue,YANG Chao,et al. Effects of preheating and post-weld heat treatment on the mechanical properties of T23 steel weldment[J]. Electric Power,2016,49(2):1.)
[12] 方鸿生,白秉哲,邓海金,等. 粒状贝氏体组织形态、精细结构及相变[J]. 金属热处理学报,1982(2):79.(FANG Hong-sheng,BAI Bing-zhe,DENG Hai-jin,et al. The morphology,fine structure and transformation mechanism of granular bainite[J]. Transactions of Metal Heat Treatment,1982(2):79.)
[13] 金玉静. T23钢粗晶热影响区再热裂纹敏感性研究[D]. 上海:上海交通大学,2015.(JIN Yu-jing. Study on the Susceptibility to Reheat-Cracking in the CGHAZ of T23 Steel[D]. Shanghai:Shanghai Jiaotong University,2015.)