Investigation And Application Of Great Austenite-Bainite Ductile Cast Die

In the process of steel tube in periodic tube rolling plant, huge piercing die hold the balance of produce cost, produce efficiency and product quality. Piercing die is investigated in this paper with 2340mm length, 780mm maximal outer diameter, 436mm minimal inner diameter and 5t weight. The temperature on the inner wall of the piercing die is more than 600(C when it is working, and it also suffers invert stress. Therefore, fatigue crack is easy to formed on the inner wall of the piercing die, which will lead to the decline of the piercing die, the increase of produce cost, and the downgrade of steel tube quality.On the precondition of unchanging the process of piercing die, the failure reason of the Re- Mg-Mo ductile cast iron piercing die is analyzed in this paper, and improvement from both smelt cast and heat treatment is suggested.Piercing die is a big cast, and it needs rather long time to cast and crystal, is it is easy to form such defect as gray spot, shrinkage porosity, pinhole and segregation, which induces to the strength reducing and ductile declining of the piercing die. Thus, the casting effect of piercing die can be obviously improved by applying controlling composition, spheroidization + double-inoculation treatment and proper inoculant.Heat treatment brought forth as follow, austenized at 900(C for 3h and tempered at 400(C for 3h. Because of the great bulk of the piercing die, brine quench will cost much, so water + oil double quench process is adopted. Results from field test show: the metallographic structure of material heat treated is austenite- bainite, which promote the toughness and wearability.Field application shows: that the problem of not enough life in periodic tube rolling plant is settled on the whole with the application of austenite-bainite piercing die. This paper is carried out according to the production, new technology of modern material science is applied. Method is researched to gain austenite-bainite structure in producing great ductile cast tool or die in order to improve the mechanics. It is a representative case for other metallurgy corporation in applying proper economic methods to settle the technology, promote the product quality, reduce the produce cost, strengthen the competitive position according to own characteristics.