METHOD OF THERMAL TREATMENT OF LARGE SIZE SLABS OUT OF GRAY PEARLITIC IRON Russian patent published in 2004 - IPC

FIELD: metallurgy; thermal treatment of large-size slabs out of gray pearlitic pig-iron.

SUBSTANCE: the invention is dealt with metallurgy, in particular, with a thermal treatment of large-size slabs out of gray pearlitic iron and may be used in production of cylinder cartridges for powerful ship diesel engines. Technical result of the invention is an increase of strength, hardness and wear resistance of the gray pearlitic iron formed in large-sized slabs. The method of thermal treatment of the large size slabs out of gray pearlitic iron provides for, that composition of the slabs contains the following elements in the ratio: C + 2 Si = 5.0 - 6.2 and 0.8 Cu + 4V = 0.8 - l. 7 (mass %); carbon 2.9 - 3.5; silicon 0.9 - 1.5; manganese 0.5-1.0; phosphorus 0.15- 0.5; chromium, nickel, molybdenum, titanium in the sum - 0.1- 0.8; vanadium - up to 0.32; boron - up to 0.04; copper - up to 1.55; sulfur - up to 0.1; iron - the rest. The thermal treatment is conducted in two cycles. The first cycle provides for the heating up to 550-580 ° and up to 820-860°С with speeds accordingly

80-100°С/hour and 130-180°С/hour. The temperature leveling of cross-sections takes no more than 25 minutes, accelerated refrigerating from 820 - 860°С to 470 - 520°С at a speed of 370-580°С/hour; in the second cycle - heating from 470-520 ° C up to 820-860°С with speed of 130-180°С/hour; alignment of temperature of cross-sections and refrigerating from 820-860°С up to 470-520°С on modes of the first cycle at final refrigerating up to 200-300°С with cooling rate of no more than 50°С/hour and further at random speed.

EFFECT: increase of strength, hardness and wear resistance of the gray pearlitic iron formed in large-sized slabs.

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