 Keyword Ausformed bainaite / High weldability / HT60 class / Reducing pre-heating / High toughness / TMCP AFB Steel Plates (Advanced HT570, HT610class) AFB (Ausformed Bainite) Steel Plate was developed in response to requests from users that included (1) shortening delivery time, (2) reducing pre-heating, and (3) increasing toughness to make HT610-class steel plate with low carbon content by TMCP technology. The AFB steel plate is highly evaluated in that it is broadly applied to bridges, tanks, etc. It won "the 23rd Japan Institute of Metals' Prize for Technical Development " in 2000, and then, "the 34th Ichimura Prize for Industry and Contribution." Furthermore, it received "the Kihara Prize for Encouragement for Fiscal 2002." Feature 1. Shortened delivery time due to TMCP application According to the conventional QT (quenching & tempering) process, reheating is conducted twice after rolling, while if TMCP is applied, rolling and subsequent cooling are controlled in principle without reheating, resulting in shortening the manufacturing process. Feature 2. Reduced preheating and improved mechanical performance The conventional QT process used heat treatment to increase tensile strength. The resulting level of tensile strength depended on the chemical composition of the steel and on the heat treatment temperature. In contrast, the tensile strength of AFB steel depends on conditions of TMCP  (indicated by a circle in the figure).The greatest advantage of AFB steel is that it combines both high tensile strength and low-temperature toughness. These are the effects of the hyperfine bainite structure that is produced by first using precisely controlled rolling (controlled for temperature and rolling reduction) to create an Ausformed (deformed austenite) structure, and then performing controlled water cooling. Compared to other substances that possess the same level of tensile strength as QT process steel, this new type of steel allows the reduced use of hardening elements such as carbon (C), which adversely affect weldability. This means less preheating is needed and also improves toughness in heat-affected zone (HAZ). |
||
Mechanism of strengthening |
 |
Improvement in toughness |
