High-tension high-toughness steel having excellent resistance to delayed fracture and method for producing the same

Claim 1

A high tensile tension high-toughness steel excellent in resistance to delayed fracture, having a tempered martensitic structure obtained by quenching and tempering and having a tensile strength of at least 100 kg/mm 2 and consisting essentially, by weight, of 0.15 to 0.50% of C, up to 1.50% of Si, 0.20 to 1.50% of Mn, up to 2.00% of Cr, 0.0005 to 0.0030% of B, 0.005 to 0.10% of acid-soluble Al, up to 0.010% of P, up to 0.0020% of N, 0.010 to 0.050% of Ti and the balance iron and inevitable impurities.

Claim 5

A method for producing a high-tension high-toughness steel excellent in resistance to delayed fracture, and having a tensile strength of at least 100 Kg/mm 2 comprising the steps of preparing a steel consisting essentially, by weight, of 0.15 to 0.50% of C, up to 1.50% of Si, 0.20 to 1.50% of Mn, up to 2.00% of Cr, 0.0005 to 0.0030% of B, 0.005 to 0.10% of acid-soluble Al, up to 0.010% of P, up to 0.0020% of N, 0.010 to 0.050% of Ti and the balance iron and inevitable impurities, austenitizing said steel at a temperature of not lower than A 3 transformation point, quenching the thus austenitized steel in water, oil or a salt bath, and tempering the thus quenched steel at a temperature of not higher than A 1 transformation point.

Claim 6

A method for producing a high-tension high-toughness steel excellent in resistance to delayed fracture, and having a tensile strength of at least 100 Kg/mm 2 comprising the steps of preparing a steel consisting essentially, by weight, of 0.15 to 0.50% of C, up to 1.50% of Si, 0.20 to 1.50% of Mn, up to 2.00% of Cr, 0.0005 to 0.0030% of B, 0.005 to 0.10% of acid-soluble Al, up to 0.010% of P, up to 0.0020% of N, 0.010 to 0.050% of Ti and the balance iron and inevitable impurities, austenitizing said steel at a temperature of not lower than A 3 transformation point, quenching the thus austenitized steel in water, oil or a salt bath, and tempering the thus quenched steel at a temperature of not higher than A 1 transformation point.

Claim 7

A method for producing a high-tension high-toughness steel excellent in resistance to delayed fracture, and having a tensile strength of at least 100 kg/mm 2 comprising the steps of preparing a steel consisting essentially, by weight, of 0.15 to 0.50% of C, up to 1.50% of Si, 0.20 to 1.50% of Mn, up to 2.00% of Cr, 0.0005 to 0.0030% of B, 0.005 to 0.10% of acid-soluble Al, up to 0.010% of P, up to 0.0020% of N, 0.010 to 0.050% of Ti and at least one member selected form the group consisting of up to 0.50% of Mo, up to 0.20% of V, up to 0.10% of Nb and up to 0.50% of Cu, the balance being iron and inevitable impurities, austenitizing said steel at a temperature of not lower than A 3 transformation point, quenching the thus quenched steel in water, oil or a salt bath, and tempering the quenched steel at a temperature of not higher than A 1 transformation point.

Claim 8

A method for producing a high-tension high-toughness steel excellent in resistance to delayed fracture, and having a tensile strength of at least 100 kg/mm 2 comprising the steps of preparing a steel consisting essentially, by weight, of 0.15 to 0.50% of C, up to 1.50% of Si, 0.20 to 1.50% of Mn, up to 2.00% of Cr, 0.0005 to 0.0030% of B, 0.005 to 0.10% of acid-soluble Al, up to 0.010% of P, up to 0.0020% of N, 0.010 to 0.050% of Ti and at least one member selected form the group consisting of up to 0.50% of Mo, up to 0.20% of V, up to 0.10% of Nb and up to 0.50% of Cu, the balance being iron and inevitable impurities, austenitizing said steel at a temperature of not lower than A 3 transformation point, quenching the thus quenched steel in water, oil or a salt bath, and tempering the quenched steel at a temperature of not higher than A 1 transformation point.