STRONG AND TOUGH FAIL-SAFE STEEL WITH ULTRA-FINE ELONGATED GRAIN STRUCTURE

摘要

A strong 1800 MPa class steel with an ultrafine elongated grain structure and a strong <110>// RD fiber deformation texture was fabricated by multi-pass caliber rolling at 773 K, and a V-notch Charpy impact and static three point bending tests were conducted. The strength-toughness balance of the developed steel was remarkably improved compared with conventionally quenched and tempered steel with a martensitic structure. The developed steel showed enhanced toughness in impact energy at ambient temperature of about 10 times than that of the conventional steel as well as inverse temperature dependence of the impact energy from 333 K to 213 K. The static fracture toughness of the developed steel was about 40 times higher than that of the conventional steel. The microstructural design that improves the toughness in ultrahigh strength steels is clarified. For the toughness design in ultrafine grained steels, it is essential to understand the spatial distribution of weak sites such as {100} cleavage planes and boundaries of elongated grains.