High-strength steel excellent in weldability and process for production thereof

• Main Authors: Soshiroda, Tetsuo, Hoshika, Tetsuji
• Format: Patent
• Language: English
• Published: 24.04.2012

2 The present invention provides a high-strength steel material capable of suppressing formation of blowholes during welding even if the strength thereof is improved by nitriding, and a method of manufacturing such a high-strength steel material by using a low rolling force. A high-strength steel of the present invention contains 0.05% (percent by mass unless otherwise specified in describing chemical composition) or below C, 1% or below Si, 1.5% or below Mn, 0.05% or below P, 0.05% or below S, 0.05% or below Al, 0.02 to 0.3% Ti, and 0.020% or below N. The high-strength steel material has metallographic structure of a single phase of ferrite and contains Ti nitride grains having a maximum size of 20 nm or below and coherently precipitated in a density of 250 grains/μmor above. In the high-strength steel material, the ratio of the number of Ti nitride grains having a maximum size of 6 nm or below to that of Ti nitride grains having a maximum size of 20 nm or below is 80% or above.