Effects of Oxides on Tensile and Charpy Impact Properties and Fracture Toughness in Heat Affected Zones of Oxide-Contain
- PDF / 4,973,958 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 65 Downloads / 208 Views
UCTION
WELDING is a critical process particularly for large-scale linepipes used for transporting crude oil or natural gas. Welding processes of linepipe steels are generally classified into the seam welding to make pipes from thick steel plates and girth welding to connect pipes.[1–3] During the course of welding, linepipe steels often meet with the problem of low toughness, because heat affected zones (HAZs) are formed in welded regions. According to welding thermal cycles, microstructures such as bainitic ferrite (BF) or martensite HYO KYUNG SUNG, Postdoctoral Research Associate, and SEOK SU SOHN, Research Assistant, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea. SANG YONG SHIN, Assistant Professor, is with the School of Materials Science and Engineering, University of Ulsan, Ulsan 680-749, Korea. KYUNG SHIK OH, Senior Principal Researcher, is with the Steelmaking Research Group, Technical Research Laboratories, POSCO, Pohang 790-785, Korea. SUNGHAK LEE, Professor, is with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, and also with the Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: shlee@postech. ac.kr Manuscript submitted September 3, 2012. Article published online April 12, 2014 3036—VOLUME 45A, JUNE 2014
having low toughness are readily formed in HAZs, while prior austenite grains are greatly grown.[4] In order to safely use linepipe steels under extreme conditions, thus, the formation of BF or martensite is prevented or minimized in HAZs, while the formation of acicular ferrite (AF) is promoted. Recently, oxide metallurgy, in which oxides having excellent high-temperature stability are favorably utilized, has been developed to improve the toughness of the HAZ.[5,6] Oxides act as ferrite nucleation sites at austenite grains during the welding, promote the formation of fine AF, and prevent the formation of coarse bainite or martensite.[7,8] Alloying elements such as Mg, Ti, and Al work effectively for oxide formation, and oxides formed by combining these alloying elements act as nucleation sites for fine AF during the austeniteferrite transformation.[9–12] Larger size and no. of oxides are more effective for the formation of AF.[13,14] Since welding thermal cycles and heat inputs greatly affect the formation of AF, various welding methods such as shielded metal arc welding and gas metal arc welding have been developed for reducing heat inputs and increasing welding speeds.[14,15] Thus, correlation studies between the size and no. of oxides, formation of AF, welding thermal cycles, and Charpy impact properties in oxide-containing steel HAZs should be understood to METALLURGICAL AND MATERIALS TRANSACTIONS A
improve the HAZ toughness and to achieve appropriate welding conditions. Though the oxide metallurgy is generally accepted for the toughness improvement, reasons why the toughness is affected by toughness testing conditions including specimen dimensi
Data Loading...
