EXPANDABLE HIGH-STRENGTH STEEL MATERIAL AND EXPANDED HIGH-STRENGTH STEEL PIPE HAVING SUPERIOR EXPANDABILITY AND COLLAPSE RESISTANCE, AND METHODS FOR MANUFACTURING THEREOF

摘要

There are provided an expandable high-strength steel material and an expanded high-strength steel pipe having excellent expandability and collapse resistance, and methods for manufacturing the expandable high-strength steel material and the expanded high-strength steel pipe. The expandable high-strength steel material including, by weight, manganese (Mn): 12% to 18%, carbon (C): 0.3% to 0.6%, and a balance of iron (Fe) and inevitable impurities, wherein the carbon (C) and the manganese (Mn) satisfy the following condition: 23 = 35.5C + Mn = 38. Before being expanded, the expandable high-strength steel material has an austenite single phase microstructure, and after being expanded, the expandable high-strength steel material has a microstructure including 5 area% to 50 area% martensite and 50 area% to 95 area% austenite.