METHOD FOR MAKING HOT ROLLED SEAMLESS TUBES Russian patent published in 2001 - IPC

FIELD: processes for rolling metal products, mainly rolling tubes of cast iron with spheroidal graphite. SUBSTANCE: method comprises steps of casting hollow billet, heating it for rolling, rolling billet in tube rolling mill. Hollow billet is made by centrifugal casting from cast iron with spheroidal graphite at relation of outer diameter of billet to its inner diameter in range (1.05:1) - (1.7:1). Cast cooled billet is heated at rate no more than 70C/min up to temperature (830-950)C, soaked for 1-5 hours and then it is cooled until temperature (690-730)C at rate (2-10)C/min and further it is cooled at arbitrary rate until shop temperature. At rolling billet is heated up to (730-1100)C. Cast iron with spheroidal graphite for casting billet contains (mass%): carbon - (2.5-3.2), silicium - (1.5-2.5), magnesium - (0.02-0.05), sulfur - less than 0.01, phosphorus - less than 0.1, ferrum - the balance. EFFECT: enlarged assortment of tubes rolled of cast iron with spheroidized graphite having improved corrosion and fatigue resistance values in comparison with steel tubes. 3 cl