METHOD FOR MAKING PRODUCTS OF ELECTROLYTIC CHROME Russian patent published in 2002 - IPC

FIELD: metallic materials produced by powder metallurgy processes for using in high-temperature technology as material obtaining high heat resistance, improved mechanical strength. SUBSTANCE: method for making products of chrome comprises steps of preparing chrome containing charge, shaping product in form, double-stage sintering of product in gaseous atmosphere. Novelty is shaping of product in form made of steel sheet with thickness (0.8-2)mm. Product is sintered in hydrogen atmosphere. At first stage product is sintered in form at temperature consisting almost 80% of melting temperature of steel sheet; at second stage product is sintered without form at mode with uniform increase of temperature up to 1250+-20C at hydrogen flowrate equal to (15-20) cub. m/h during 5-6 hours; soaking product at temperature 1450+-50C for time period no less than 5 hours; subsequently cooling it together with furnace in hydrogen atmosphere until temperature no more than 60C; using as charge, mixture of crushed electrolytic chrome with fraction size no more than 1 mm, crushed broken chrome products with fraction size no more than 1mm and chrome powder reduced at next relation of ingredients: crushed electrolytic chrome - (75.0-80.0); crushed broken material of chrome products - (5.0-10.0); powder of reduced chrome - (10-20). Products may be sintered at first stage with hydrogen flowrate no less than 10 cub.m/hour in mode providing uniform increase of temperature until 1200+-20C for 5-6 hours; soaked at temperature 1200+-20C for period no less than 3 hours and then cooled together with furnace in hydrogen atmosphere until temperature no more than 60C. At second stage several members of composite product or products may be sintered at one charging. Contact zones of members or products are poured over with zirconium. Steel surfaces of form being in contact with charge are coated at using solution of slaked lime in water with relation of ingredients (by volume) 4:1. Applied coating is dried in air or in drying chamber; then form is placed on vibration bed. Product is shaped at pouring into form mixed charge by batches not exceeding 20 kg up to upper edge of form. After each batch bed is subjected to vibration for period 30-60 s. After termination of first sintering stage, hydrogen supply is interrupted; furnace is deenergized for cooling it together with product until 20C. Then semifinished product is drawn out of furnace; outer and inner steel envelopes of product are removed and semifinished product is placed to furnace for second sintering. Charge mixture may include mixture of crushed electrolytic chrome with fraction size 40-160 micrometers and crushed broken material of chrome products with fraction size 40-60 micrometers. Method allows to make chrome crucibles whose strength is 3 times more than that of molybdenum crucibles and is higher by 1.7 times than that of crucibles made according to well known method. It is possible to lower labor consumptions for making such crucibles. Reduced cost price of material is provided due to multiple use in mixture of part of recovery broken material of crushed chrome products. EFFECT: enhanced strength of products, lowered labor consumption. 7 cl, 1 dwg, 2 tbl