Materials and Design 32(2011)2763-2770 Contents lists available at ScienceDirect Materials and design ELSEVIER journalhomepagewww.elsevier.com/locate/matdes Microstructure and mechanical properties of dissimilar materials joints between t92 martensitic and s304h austenitic steels Jian Cao, Yi Gong, Kai Zhu, Zhen-Guo Yang Xiao-Ming Luo, Fu-Ming Gu of Special Equipment Inspection Technical Research, Shanghai 200062, PR China ARTICLE O A BSTRACT Article history: In this paper, 192 martensitic steel and S304H austenitic steel were welded by gas tungsten arc welding (GTAW)process. Microstructural features and mechanical properties of T92 and S304H dis rials joints were investigated. The results showed that the part of the joints with relativel Available online 8 January 201 strength was T92 coarse-grained heat affected zone(CGHAZ), while the part of the joints which revealed elatively we hess was weld metal. The decrease of t strength in 192 CGHAZ parse ten martensite structure. Weak toughness of the joints was resulted from the coarse of the weld metal. however. the weld in transverse direction of the joints milar materials joints was provided higher tensile strength by the orientation distribution of grains compared with T92 CGHAZ. e 2011 Elsevier Ltd. All rights reserved. 1 Introduction tensitic steels[14-17. Thus, it is widely used for superheaters and reheaters which have the abominable service environment in us Increased heat efficiency and improved environmental protec- boilers. Normally, t92 steel can be used as pipes linking superheat- tion are always the innovative driving forces in the development ers and reheaters. In this case, the welding between T92 and S304H of ultra supercritical(USC) boilers for fossil power plants, whose steels will be necessary. steam temperature is up to 600C and pressure exceeds 27 MPa Until now, many researches have mainly focused on the proper Under this USC condition, the heat efficiency can rise to around ties of T92 and S304H steels. As for T92 and S304H dissimilar 45%, compared with the value as 41% of supercritical (SC)boilers. materials joints, however, there almost hasn't any report about However, with the increase of steam parameters, requirements it. Since T92/S304H dissimilar materials joints is obtained by using for the materials applied in the USc boilers components are melted filler material to join two steels, the melted filler material becoming higher. Thus, many new generation steels have been will re-crystal to form the weld metal part of the joints after weld- developed in recent years, including T92(9Cr05Mo2WVNb) ing. In addition, due to the effect of welding thermal cycles, not martensitic steel and S304H (18Cr9Ni3CuNbN)austenitic steel only the microstructure of T92 adjacent weld metal but also the T92 steel was developed by the Nippon Steel Corporation of microstructure of S304H adjacent weld metal will both change Japan 1 in the late 1990s by modifying chemical compositions during the welding process. Considering that the mechanical prop- pon T91(9Cr1MoVNb) for even more preferable mechanical erties of the joints are closely linked with its microstructure. Thus, properties at high temperatures. This steel has the manufacturers an in-depth insight into the structure-property relationships of designation as NF616(ASTM Stands A213)and contains 0.5% Mo, T92/S304H dissimilar materials joints may have great significan 88 W, as well as small additions of Nb, V and B Creep strength for both the dissimilar steels welding process between new gener f T92 at 600C increases about 10-20% compared with that of ation martensitic and austenitic steels, and the safety of the Usc T91 at 600C[2-13 S304H steel was developed by Sumitomo Me- boilers In our work, on the one hand, mechanical properties of tal Industries Ltd on the base of TP304H(OCr19Ni10. As a new T92/S304H dissimilar materials joints were carried out through type of austenitic steel, S304H possesses not only excellent resis- tensile and impact tests. On the other hand the microstructures tance to high-temperature corrosion and steam oxidation mainly across the entire joints were also investigated. What's more, the due to high Cr content, but also superior creep strength than mar- detailed mechanism governing the microstructural evolution of the joints during welding process was analyzed by means of the electron back-scattered diffraction(EBSD) technique, which was Corresponding author. Tel. +86 21 65642523: fax: +86 21 65103056 firstly used to study the process of grain structure development of dissimilar materials joints 0261-3069/s- see front matter o 2011 Elsevier Ltd. All rights reserved doi:10.1016 mates.201101.008Microstructure and mechanical properties of dissimilar materials joints between T92 martensitic and S304H austenitic steels Jian Cao a , Yi Gong a , Kai Zhu a , Zhen-Guo Yang a,⇑ , Xiao-Ming Luo b , Fu-Ming Gu b aDepartment of Materials Science, Fudan University, Shanghai 200433, PR China b Shanghai Institute of Special Equipment Inspection & Technical Research, Shanghai 200062, PR China article info Article history: Received 8 September 2010 Accepted 4 January 2011 Available online 8 January 2011 Keywords: Microstructure Mechanical properties Dissimilar materials joints abstract In this paper, T92 martensitic steel and S304H austenitic steel were welded by gas tungsten arc welding (GTAW) process. Microstructural features and mechanical properties of T92 and S304H dissimilar mate￾rials joints were investigated. The results showed that the part of the joints with relatively weak tensile strength was T92 coarse-grained heat affected zone (CGHAZ), while the part of the joints which revealed relatively weak toughness was weld metal. The decrease of tensile strength in T92 CGHAZ was due to its coarse tempered martensite structure. Weak toughness of the joints was resulted from the coarse dendritic austenite of the weld metal. However, the weld metal in transverse direction of the joints was provided higher tensile strength by the orientation distribution of grains compared with T92 CGHAZ. 2011 Elsevier Ltd. All rights reserved. 1. Introduction Increased heat efficiency and improved environmental protec￾tion are always the innovative driving forces in the development of ultra supercritical (USC) boilers for fossil power plants, whose steam temperature is up to 600 C and pressure exceeds 27 MPa. Under this USC condition, the heat efficiency can rise to around 45%, compared with the value as 41% of supercritical (SC) boilers. However, with the increase of steam parameters, requirements for the materials applied in the USC boilers components are becoming higher. Thus, many new generation steels have been developed in recent years, including T92 (9Cr0.5Mo2WVNb) martensitic steel and S304H (18Cr9Ni3CuNbN) austenitic steel. T92 steel was developed by the Nippon Steel Corporation of Japan [1] in the late 1990s by modifying chemical compositions upon T91 (9Cr1MoVNb) for even more preferable mechanical properties at high temperatures. This steel has the manufacturer’s designation as NF616 (ASTM Stands A213) and contains 0.5% Mo, 1.8% W, as well as small additions of Nb, V and B. Creep strength of T92 at 600 C increases about 10–20% compared with that of T91 at 600 C [2–13]. S304H steel was developed by Sumitomo Me￾tal Industries Ltd on the base of TP304H (0Cr19Ni10). As a new type of austenitic steel, S304H possesses not only excellent resis￾tance to high-temperature corrosion and steam oxidation mainly due to high Cr content, but also superior creep strength than mar￾tensitic steels [14–17]. Thus, it is widely used for superheaters and reheaters, which have the abominable service environment in USC boilers. Normally, T92 steel can be used as pipes linking superheat￾ers and reheaters. In this case, the welding between T92 and S304H steels will be necessary. Until now, many researches have mainly focused on the proper￾ties of T92 and S304H steels. As for T92 and S304H dissimilar materials joints, however, there almost hasn’t any report about it. Since T92/S304H dissimilar materials joints is obtained by using melted filler material to join two steels, the melted filler material will re-crystal to form the weld metal part of the joints after weld￾ing. In addition, due to the effect of welding thermal cycles, not only the microstructure of T92 adjacent weld metal but also the microstructure of S304H adjacent weld metal will both change during the welding process. Considering that the mechanical prop￾erties of the joints are closely linked with its microstructure. Thus, an in-depth insight into the structure–property relationships of T92/S304H dissimilar materials joints may have great significances for both the dissimilar steels welding process between new gener￾ation martensitic and austenitic steels, and the safety of the USC boilers. In our work, on the one hand, mechanical properties of T92/S304H dissimilar materials joints were carried out through tensile and impact tests. On the other hand, the microstructures across the entire joints were also investigated. What’s more, the detailed mechanism governing the microstructural evolution of the joints during welding process was analyzed by means of the electron back-scattered diffraction (EBSD) technique, which was firstly used to study the process of grain structure development of dissimilar materials joints. 0261-3069/$ - see front matter 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.01.008 ⇑ Corresponding author. Tel.: +86 21 65642523; fax: +86 21 65103056. E-mail address: zgyang@fudan.edu.cn (Z.-G. Yang). Materials and Design 32 (2011) 2763–2770 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes