TUBE STOCK OUT OF MICRO ALLOYED BORON CONTAINING STEEL Russian patent published in 2008 - IPC C21D8/10 C22C38/32 C22C38/60 

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to production of hot rolled tube stock with diameter from 80 to 180 mm. To facilitate minimal level of anisotropy of mechanical properties and low tendency to temper brittleness the stock is made out of steel, containing wt %: carbon 0.19-0.23, manganese 0.40-0.90, silicon 0.15-0.30, chromium 0.005-0.60, boron 0.001-0.003, titanium 0.02-0.04, aluminium 0.020-0.040, niobium 0.005-0.02, nitrogen 0.005-0.010, arsenic 0.0001-0.03, tin 0.0001-0.02, lead 0.0001-0.01, zinc 0.0001-0.005, iron and impurities: nickel - not more, than 0.10%, copper not more, than 0.10%, phosphorus not more, than 0.015%, sulphur not more, than 0.012% at a ratio: (As+Sn+Pb+5×Zn) ≤0,07; N/(Ti+0,5Al+10B)≤.0.21. The stock is made continuous cast, hot rolled and thermo refined, it has ferrite-pearlite structure, the dimension of the actual grain 6-9 points, macrostructure for central porosity, pointed non-uniformity, liquation square, subshrinking liquation not more, than 2 points for each kind, liquation strips - not more, than 1 point, non metallic inclusions of pointed sulphides, pointed oxides, stripped oxides, fragile silicates, plastic silicates, non deformed silicates for each kind of not more, than 4.0 points, tensile strength 560-950 N/mm², yield point is not more, than 420^{N/mm2, specific elongation is not less, than 20%, contraction ratio not less, than 45%, impact resilience not less, than 30 J/cm2. Hardenability into water - cut-off diameter D_c-off - 29 mm2, hardness in the point 6 mm at end hardening 40 HRC.}

EFFECT: providing minimal level of anisotropy of mechanical properties and low tendency to temper brittleness of stock.

4 cl, 2 ex