Effect of sulfur content on the microstructure and toughness of simulated Heat-Affected zone in Ti-Killed steels
- PDF / 2,387,863 Bytes
- 10 Pages / 597.28 x 785 pts Page_size
- 38 Downloads / 191 Views
I.
INTRODUCTION
IN recent years, the increasing demand for energy resources has pushed energy exploration activities into more climatically hostile regions o f the world. To meet the stringent safety requirements for welded steel structures in these regions, the steels must have high strength, excellent low-temperature toughness, and good weldability. In addition, high heat input welding processes have been extensively used in ship building and construction industries to increase welding efficiency and save labor costs. E1'2'31These processes, however, usually cause the deterioration o f toughness o f the heat-affected zone (HAZ) because o f their longer duration at higher temperatures. Increasing efforts have been devoted to developing high strength steels which can retain excellent low-temperature toughness o f H A Z even after high heat input welding. It is well known that the toughness o f weld metal can be improved by increasing intragranular acicular ferrite (IAF) in the microstructure, and oxide inclusions are generally considered as effective nuclei for the formation o f I A F . 14-9] This concept has recently been applied to produce titanium oxide-bearing steels w h i c h can fulfill the properties requirement for high heat input w e l d ing. I~°-~61 In the authors' previous w o r k s , the influence o f killing practice and chemical composition on the inclusion phases and HAZ toughness were investigated, l~3-~61 The volume fraction o f IAF was found to increase as the n u m b e r density o f Ti-oxide dominant inclusions increased. E14,161 However, the presence o f Ti-oxide dominant inclusions are always accompanied by MnS.t~3'~5] JYE-LONG LEE, Associate Scientist, and YEONG-TSUEN PAN, Engineer, are with the Steel and Aluminum Research and Development Department, China Steel Corporation, Kaohsiung, Taiwan, Republic of China. Manuscript submitted August 1 1 , 1992. METALLURGICAL TRANSACTIONS A
These observations have cast doubt as to whether Tioxide inclusion itself o r the complex compound Tioxysulphide is responsible for the increase o f IAF. Concerning the influence o f sulfur on the formation o f IAF, Evans1~Tifound that increasing the sulfur content in the weld metal leads to a decrease in the amount o f IAF. Devillers e t al.i~8] have proposed that the coating o f MnS on oxide will reduce the nucleation potential o f IAF. On the contrary, St-Laurent and L'Esperance 1~gl found that increasing sulfur in the inclusions is associated with an increase in IAF. Yamamoto e t a l . H21 and Ueshima e t a l .12°1 have postulated that the precipitation of MnS on Ti-oxide causes a depletion o f manganese around inclusions. This local chemical variation leads to an increase in transformation temperature, thereby promoting the formation of IAF. In order to clarify the preceding controversy, this investigation studied the specific influence o f sulfur on the characteristics o f inclusions in Ti-killed steels. The role o f MnS in the formation o f IAF and the modification o f H A Z toughness were also investigated.
Data Loading...
