Study On Microstructure And Mechanical Properties Of New Aluminum Hot Work Die

With the rapid development of processing technology and economy in our country, the demand for research and development of new hot work die steel which has high performance, long life and low cost become more and more urgent. Casting die and extrusion die are used repeatedly in high temperature condition, so the mold materials should have good resistance to tempering softening. At present,1.2367 (0.4C-Cr5-Mo3-V) is high hot strength hot work die steel, which is widely used at home and abroad. It is improved on the basis of H13 by alloy composition optimization of lower silicon and higher molybdenum. In order to futher improve red hardness and thermal strength of 1.2367 steel, increase the service life of the mold and reduce cost, raise the competitiveness of products in the market, optimization of alloy composition by adding aluminum element on the basis of 1.2367 steel. In general, aluminum is an important alloying element for enhance the red hardness and thermal stability of high speed steel and the price of aluminum is cheap. So research of aluminum has certain practical significance and economic benefits in hot work die steel 1.2367 steel.In this paper, micro structure transformation law of annealing, quenching, tempering and the different mechanical properties between 1.2367 steel and 1.2367A1 steel were investigated by calculating and analyzing methods of Thermo-Calc, Formastor-F â…¡ dilatometer, OM, SEM, EDS, TEM, hardness testing, tensile and impact test and so on. The main conclusions are as follows:1) The types of equilibrium phases of the steel are not changed by the addition of aluminum, but critical point AC3, Ac1, Ms temperature are increased and temperature range for transformation from ferrite to austenite is extended. Also the solution temperature of alloy carbides are increased. The whole of CCT curve left shift.2) By addition of aluminum, the effective grain size is refined, alloy carbides precipitation and dispersion distribution during tempering are improved, overall hardness during tempering is increased, the secondary hardening peak during tempering is increased, the tempering stability of steel is enhanced. Moreover, tensile strength is increased, at last achieved the effect of add cobalt.3) Because of the content of nitrogen and oxygen in the steel was not considered in the previous period, the total amount and kinds of non-metallic inclusions in steel are increased, cause of aluminum-containing inclusions and primary carbides segregated on the segregation band, impact toughness and tensile ductility of tested steel are reduced, after the addition of aluminum.