METHOD FOR MAKING ELONGATED CONVERSION LARGE- AND MEAN- DIAMETER TUBES OF CENTRIFUGALLY CAST HOLLOW BILLETS AND ELECTROSLAG REFINING INGOTS OF STEELS FOR TELESCOPIC SYSTEMS (PERISCOPES OF SUBMARINES) Russian patent published in 2005 - IPC

FIELD: rolled stock production, namely manufacture of elongated conversion large- and mean-diameter tubes of centrifugally cast hollow billets and ingots of electroslag refining of steels 08X10H20T2 and 08X10H16T2 for telescopic systems of periscopes of submarines while providing values of impact viscosity KCU more than 100 J/cm².

SUBSTANCE: method comprises steps of producing centrifugally cast billets, heating them till ductile temperature, rolling in pilger mill to thick-wall tubes with allowance for mechanical working, subjecting tubes to heat treatment. In pilger mill conversion hot rolled tubes are rolled while taking into account 1 - 3 rerolling procedures in cold rolling mills depending upon type of billet and dimension of ready product (length, diameter, wall thickness). Conversion hot rolled tubes are rolled to intermediate and final sizes in cold rolling mills at elongation value μ = 1.2 - 1.55. Centrifugally cast hollow billets and drilled ingots of electroslag refining are soaked on grates of furnace without tilting them at 950 -1000°C for 180 - 300 min of homogenization depending upon diameter and wall thickness. Then centrifugally cast billets are uniformly heated up to 1150 -1200°C at heating rate 2.3 - 2.5° C/min at tilting in periods of 15 - 20 min at total period of heating 8 - 11 hours. Ingots of electroslag refining are heated up to 1200 -1250°C at heating rate 1.8 - 2.0°C/min while tilting them in 20 - 25 min for total heating period 9.5 - 12.5 hours. Large-size billets and ingots are heated for more long periods. Centrifugally cast hollow billets are rolled in pilger mill to hot rolled conversion tubes while taking into account 2 - 3 next rerolling of them in cold rolling mills. Sleeves pierced of ingots are rolled in pilger mill to conversion hot rolled conversion tubes while taking into account 1 - 2 rerolling processes in cold rolling mills. Ingots with diameter up to 500 mm are pierced in skew rolling mill to sleeve at one piercing operation with elongation value μ = 1.2 - 1.4. Ingots with diameter 540 mm and more are pierced at two piercing operations with elongation value μ₁ = 1.2 -1.4 and μ₂ = 1.1 - 1.3 respectively. Conversion elongated cold rolled tubes after rolling them to intermediate size are subjected to austenitization in mode providing temperature of furnace space at time moment of charging in range 1000 - 1100°C, heating according to power of furnace up to 1050 ± 15°C, soaking at such temperature for 1 min per 1 mm of tube wall thickness and cooling in air. Conversion elongated cold rolled tubes of ready size after rolling and austenitization are subjected to heat treatment - tempering in mode providing charging at 700 - 730°C; heating according to power of furnace; soaking at temperature 685 ± 15°C for 5 - 5.5 h; cooling in air.

EFFECT: strict geometry size of diameter and thickness of walls of elongated conversion tubes, lowered metal consumption, enhanced operational reliability of ready products.

8 cl, 2 tbl