US 6,270,594 B1Granted

Composition and method for producing an alloy steel and a product therefrom for structural applications

AssigneeBethlehem Steel Corporation

InventorsRichard L. Bodnar, Yulin Shen

Life of this patent

Estimating the term…

Loading patent…

Abstract

A method of making a high strength low-alloy steel includes the steps of casting an alloy steel into a cast form, hot rolling the cast form into a partially rolled form, and control rolling the partially rolled form to a rolled product. The controlled rolling is discontinued at a discontinue rolling temperature and is then acceleratedly cooled to a finish cooling temperature. The alloy steel uses a low silicon, carbon niobium, vanadium, titanium-containing steel composition. Silicon is less than 0.04% by weight, vanadium is between 0.05 and 0.10% by weight, niobium is between 0.06 and 0.14% by weight, titanium is between 0.006 and 0.02% by weight, and carbon is between 0.06 and 0.14% by weight. The controlled chemistry, controlled rolling, and accelerated cooling allows the discontinue rolling temperature to be high, thereby improving rolling productivity. The low-carbon alloy chemistry results in improvements in castability, formability, and weldability.

Claims23

Dependent claims

In a method of making a rolled product by casting an alloy steel into a cast form, hot rolling the cast form into a partially rolled product, control rolling the partially rolled product into a rolled product, discontinuing control rolling at a discontinue rolling temperature, and air cooling the rolled product from the discontinue rolling temperature to ambient temperature, an improved method of making a rolled product the steps of the improved method comprising:

a) providing a cast form having a thickness (t1) and an alloy steel composition consisting essentially of, in weight percent:
less than 0.04% silicon;
between 1.00 and 2.00% manganese;
between 0.006 and 0.020% titanium;
up to 0.012% nitrogen;
between about 0.005 and 0.080% aluminum;
between about 0.05 and 0.10% vanadium;
between about 0.01 and 0.05% niobium;
and
between about 0.06 and 0.14% carbon;
the balance iron and incidental impurities;
b) hot rolling said cast form within a first rolling temperature range and reducing said cast form to a partially rolled product having a thickness (t2);
c) control rolling said partially rolled product form in a second rolling temperature range and reducing said thickness t2 to make a rolled product having a thickness (t4), the control rolling to thickness t4 being finished at a finish rolling temperature ranging between about 1490° F. to about 1675° F.;
and
d) accelerated cooling said rolled product having said thickness t4 to a finish cooling temperature (FCT),
e) wherein the rolled product has a yield strength of at least 65 ksi and a tensile strength of at least 80 ksi.

13 more elements

a) providing a cast form having a thickness (t1) and an alloy steel composition consisting essentially of, in weight percent:
less than 0.04% silicon;
between 1.00 and 2.00% manganese;
between 0.006 and 0.020% titanium;
up to 0.012% nitrogen;
between about 0.005 and 0.080% aluminum;
between about 0.05 and 0. 10% vanadium;
between about 0.03 and 0.05% niobium;
and
between about 0.06 and 0.14% carbon;
the balance iron and incidental impurities;
b) hot rolling said cast form within a first rolling temperature range and reducing said cast form to a partially rolled product having a thickness (t2);
c) control rolling said partially rolled product form in a second rolling temperature range and reducing said thickness t2 to make a rolled product having a thickness (t4);
and
d) accelerated cooling said rolled product having said thickness t4 to a finish cooling temperature (FCT).

12 more elements

Dependencies are inferred from the claim text.