METHOD OF MAKING TUBULAR BLANKS FOR FORMING HEXAHEDRAL COVER TUBES OF LOW- DUCTILE NICKEL- FREE BORON-CONTAINING STEEL

FIELD: tube production, namely process for making hexahedral cover tubes of low-ductile nickel-free boron-containing steel, possibly manufacture of seamless hot rolled tube-blanks in tube rolling plants with pilger mills. SUBSTANCE: method of making tubular blanks for forming hexahedral cover tubes of low-ductile nickel-free steel with boron content 1.3-1.8% comprises steps of melting steel by vacuum-arc, vacuum induction, vacuum induction with subsequent vacuum-arc refining and plasma refining to ingots for further forging them to rod-blanks and mechanically working them; heating blanks until ductility temperature; piercing in first piercing mill to sleeves; piercing in second piercing mill to sleeves; rolling in automatic rolling mill during three passes with reduction; sizing in sizing mill to tubes at predetermined temperature; drilling in ingots central opening; heating them until ductility temperature; piercing in piercing mill to sleeves; rolling sleeves in pilger mill to tube-blanks; cooling blanks; repairing them if necessary and cutting by two equal parts - blanks; again heating blanks until ductility temperature and piercing in piercing mill to sleeves; then rolling in pilger mill to tube and straightening them in straightening machine at predetermined temperature while using heating temperature of rolling process. EFFECT: elimination of operations for forging ingots to rods, elimination of transporting blanks along path Russia-Ukraine-Russia, lowered factor of metal consumption at ingot-tube blank conversion, reduced cost of ready products - hexahedral steel tubes.