METHOD FOR MAKING HOT DEFORMED AND CONVERSION MEAN- AND LARGE-DIAMETER TUBES OF CORROSION RESISTANT HARD-TO-FORM STEELS AND ALLOYS IN TUBE ROLLING AGGREGATE WITH PILGER MILLS Russian patent published in 2005 - IPC

FIELD: rolled tube production processes and equipment, namely manufacture of hot deformed mean- and large-diameter tubes of corrosion resistant hard-to-form steels and alloys, possibly making tubes in tube rolling aggregates with pilger mills.

SUBSTANCE: method comprises steps of drilling electroslag-refining ingots or billets with diameter 380-500 mm; holding them on grates of furnace at temperature 500-550°C for 70-95 min depending upon diameter of blank; heating up to temperature 1120 - 1140°C at rate 1.4 - 1.5 °C/min; piercing billets for forming sleeves at revolution number of rolling rolls 25 - 40 rev/min on mandrel with diameter providing reduction degree in pilger mill no less than 25 mm; realizing first piercing of electroslag-refining ingots or billets with diameter 460-600 mm in piercing mill at elongation degree 1.2 -1.4 and at revolution number of rolling rolls 15 -25 rev/min; realizing second and next (if necessary) piercing or expanding processes at diameter fit no more than 5.0%, elongation degree 1.4 -1,75 and revolution number of rolls 25 - 50 rev/min; seasoning cold sleeves after their first piercing with diameter 460-600 mm at relation D/S = 3.0 -4.5 on grates at temperature 400-500°C for 50 - 70 min depending upon sleeve diameter and wall thickness; heating sleeves until yielding temperature 1100 - 1260°C at rate 1.6 - 1.8°C/min depending upon kind of steel; uniformly heating sleeves with temperature 600 - 800 C after piercing mill until yielding temperature 1100 - 1260°C at rate 1.7 - 2.0°C/min; before discharging sleeves out of furnace keeping them for 45 -60 min at plasticity temperature while tilting sleeves in 10-15 min by angle 180є. Process of piercing sleeves that begins from gripping ingots or billets until their complete fitting onto mandrel is realized at decreased revolution number of rolling rolls from 25 until 15 rev/min. Stable piercing process is performed is realized at 15 -20 rev/min. At outlet of sleeve revolution number of rolls is increased up to 35 -40 rev/min. Piercing (expanding) process beginning from gripping sleeve until complete fitting of it onto mandrel is realized at decreased revolution number of rolling rolls from 50 until 20 rev/min. Stable expanding process is realized 20-25 rev/min. At outlet of sleeve revolution number of rolls is increased up to 45 - 50. Tubes are rolled in pilger mill at elongation degree μ = 3.0 - 5.0. Invention provides possibility for making high quality hot deformed tubes of large and mean diameters from corrosion resistant hard-to-form steels and alloys in tube rolling aggregates with pilger mills.

EFFECT: reduced metal consumption factor at conversion of electroslag-refining ingot to hot rolled tube, lowered cost of tubes.

5 cl, 1 tbl