LOW TEMPERATURE FORGING METHOD FOR LARGE-SIZED FORGING STEEL PRODUCT

摘要

PURPOSE:To refine a crystal grain and to increase the stiffness and fatigue strength of a large-sized forging steel product by forming the forging steel article after casting completion in bainite or martensite structure and by adding the work more than the constant rate within the range of the specific temp. at the time of elevation of temp. under heat treatment. CONSTITUTION:The structure of the forging steel product after completion of the forging is made a bainite or martensite by dropping the temp. thereof. Thereafter, the structure is made an austenite by raising the temp. gradually and the work =2% is added by a hammer B within the temp. range of 1,200 deg.C from the Ac3. In this case, numerous gamma uncleusi are caused from the sub-grain to refine the austenite crystal grain and to increase the stiffness and fatigue strength of the large-sized forging steel product. After the work, the refining is more promoted and stabilized and the large-sized forging steel product of high quality can be formed with high efficiency by holding or with the temp. up of the steel ingot while upto 1,200 deg.C from Ac3.