Patent GB-744024-A (GB)
Title: Improved method for producing shaping dies and dies so produced
IPC: C22C29/00
Filed: 1953-09-25
Abstract: 744,024. Making dies; powder metallurgy. SINTERCAST CORPORATION OF AMERICA. Sept. 25, 1953 [Sept. 30, 1952], No. 26509/53. Classes 83 (2) and 83 (4). A method of making a die, more particularly for the extrusion of hot metal, comprises sintering a powder compact containing 40-80 per cent by volume of titanium carbide in the presence of a matrix-forming heatresistant metal at a temperature above the melting point of the latter and in a vacuum of at least 2500 microns of mercury for a time sufficient for the metal to completely wet the carbide and form a continuous matrix having dispersed therethrough fine particles of a precipitate and isolated carbide particles and particle aggregates. Preferably the carbide powder is pre-sintered in the presence of a small amount of the binder metal and then fully sintered and heat treated in the presence of the remainder in liquid form. Alternatively, the whole of the binder may be included in the original compact. The titanium carbide powder preferably contains about 18 per cent combined carbon and 2-5 per cent graphitic carbon and may contain up to 5 per cent each of silicon carbide or boron carbide and up to 10 per cent each of the carbides of chromium, vanadium, molybdenum, tungsten, zirconium or hafnium, the total amount of such added carbides not exceeding 25 per cent by volume. Suitable matrix-forming alloys include those known under the Registered Trade Marks " Nichrome " V, "Inconel," " Hastelloy " C, " Stellite " 31 and various high-speed and stainless steels. In one example, titanium carbide powder of 325 mesh is heat treated for one hour at 1900‹ C. and the agglomerate crushed, passed through a 140 mesh sieve and mixed with 10 per cent by weight of nickel carbonyl of 325 mesh for 24 hours in a stainless steel ball mill. This mixture was wetted with acetone, compacted at 10 tons per square inch and pre-sintered in hydrogen for ¢ to 1 hour at 1200‹ C. The resulting mass was machined to the form shown in Fig. 2 and sintered again at 1600-1700‹ C. for 3 hours in a vacuum increasing from 500 to 50 microns of mercury. Further machining reduced the mass to the form shown in Fig. 3, a depression 5 being formed in a barrier 3 which is 0.2 inch thick. The porous body was then heated in vacuo for two hours at 1500 C. in contact with an alloy comprising 80 per cent nickel, 14 per cent chromium, 6 per cent iron, which infiltrated the skeleton and dissolved the necessary amount of titanium carbide to attain equilibrium. The resulting die body was then machined and lapped to the final form, Fig. 4, and shrink fitted into an alloy steel casing. Alternatively the blank was machined to the form of Fig. 3 after the first pre-sintering step. In another example, a titanium carbide powder mixture containing 10 per cent cobalt was hot pressed in the annular cavity of a mould, the temperature being kept at 1600‹ C. for 75 minutes while a pressure of 200 pounds per square inch was exerted on the compact. The resulting skeleton was removed from the mould, again sintered and infiltrated with an alloy of cobalt 69 per cent, chromium, 25 per cent and molybdenum 6 per cent for 195 minutes at 1525‹ C. The die was finishmachined and ground. In a modification, the cobalt was replaced by nickel in the original powder mixture and the infiltrating alloy comprised nickel 58 per cent, molybdenum 17 per cent, chromium 15 per cent, tungsten 5 per cent and iron 5 per cent. Specification 735,668 is referred to.