HIGH-STRENGTH, THICK-WALLED, SEAMLESS STAINLESS STEEL PIPES AND METHOD FOR MANUFACTURING THEREOF

摘要

A high-strength heavy-walled stainless steel seamless tube or pipe with a wall thickness central portion having excellent yield strength and low-temperature toughness and a method for manufacturing the same are provided. The high-strength heavy-walled stainless steel seamless tube or pipe exhibiting excellent low-temperature toughness is characterized by having a chemical composition containing Cr: 15.5% to 18.0% and a steel microstructure containing a ferritic phase and a martensitic phase, wherein the maximum value of the areas of the ferrite grains in the steel microstructures in a circumferential direction cross-section and an L direction (rolling direction) cross-section of the steel tube or pipe is 3,000 µm 2 or less and the content of ferrite grains having areas of 800 µm 2 or less is 50% or more on an area fraction basis, where when adjacent ferrite grains are present in the steel microstructure and the crystal misorientation between one ferrite grain and the other ferrite grain is 15° or more, the adjacent grains are assumed to be grains different from each other.