Heavy wall steel material having superior weldability and method for producing the same

Abstract

A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 μm or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm 2 and uniform ferrite grains 2 μm or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction.

1 . A heavy wall steel material having superior weldability, which is a steel material having a diameter or a side 5 mm or more in length and which comprises oxides 1 μm or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm 2  and uniform ferrite grains 2 μm or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction. 
     
     
         2 . A method for producing a heavy wall steel material having superior weldability, which comprises allowing Ti—Mn—Si complex oxides crystals 1 μm or less in particle diameter to form in a texture obtained from a molten steel and uniformly dispersing them at a dispersion density of from 10,000 to 100,000 particles/mm 2 , rolling the resulting steel material through a hole profile in the temperature range of 400° C. or higher but not higher than the Ac3 transformation point, and subjecting it to a recrystallization treatment to form uniform ferrite grains 2 μm or less in grain diameter over the plane making a right angle with respect to the rolling direction, thereby obtaining a heavy wall steel material having superior weldability and having a diameter or a side 5 mm or more in length, wherein the molten steel contains:
 carbon (C) at an amount corresponding to a quantity such that carbides account for 20% by volume or less in the resulting material; 
 silicon (Si) accounting for 0.8% by weight or less; 
 manganese (Mn) accounting for from 0.05 to 3.0% by weight; 
 titanium (Ti) which forms oxides, accounting for 0.3% by weight; and 
 balance iron (Fe) together with unavoidable impurities. 
 
     
     
         3 . A method for producing a heavy wall steel material having superior weldability as claimed in  claim 2 , wherein the method comprises undercooling the molten steel by placing it inside an oxide slag, thereby allowing oxide crystals 1 μm or less in particle diameter to form in the texture and uniformly dispersing them at a dispersion density of from 10,000 to 100,000 particles/mm 2 . 
     
     
         4 . (canceled)