Development of YP 960 and 1100 MPa Class Ultra High Strength Steel Plates with Excellent Toughness and High Resistance to Delayed Fracture for Construction and Industrial Machinery

摘要

Construction and industrial machinery has grown in size and is now being used in increasingly severe environments. These changes are fueling growing needs in the market for ultra high strength steel plates with excellent toughness. To meet these needs, JFE Steel has developed two new types of ultra high strength steel plate with excellent toughness for construction and industrial machinery: JFE-HYD~(R)960LE and JFE-HYD~(R)1100LE. The main characteristics of the material design applied to these new steels are refinement of the effective grain and enhancement of the uniform dispersion of fine cementite, which are achieved by ausforming and rapid heating and tempering. Ausforming is achieved by quenching the work-hardened austenite. The uniform dispersion of fine cementite, meanwhile, is realized by rapid heating and tempering using HOP~(R) (Heat-treatment On-line Process), the only technology of its kind in the world. Due to this material design, these newly developed steels have high resistance to delayed fracture as well as excellent low temperature toughness. The high resistance to delayed fracture is one of the most important characteristics to utilize these ultra high strength steels for industry. JFE-HYD960LE and JFE-HYD 1100LE also have excellent weldability due to the low carbon content and low carbon equivalent design. These steels are already in use in global industries and we expect the demand for them to grow as the needs for large construction and industrial machinery expand in the future.