Patent ID: 6673171
Filing Date: 2004-01-06
Classification: C21D

Abstract:
A method for producing a medium carbon hot-rolled steel strip having enhanced uniform elongation at room temperature, said method comprising:a) providing a steel slab having a composition in weight percent consisting of carbon 0.30/0.70, manganese 0.75/2.0, silicon up to 1.0 max., total aluminum 0.020/0.10, the balance iron and incidental impurities; b) hot-rolling said steel slab to strip with a hot roll finishing temperature within the range of 839Â° C. (1542Â° F.) to 773Â° C. (1424Â° F.); c) coiling the hot rolled steel strip; d) box annealing the hot rolled coil at a temperature no greater than the A1 temperature, said temperature being within a range of A1 to 677Â° C. (1250Â° F.), said temperature and the time at temperature being effective to transform substantially all of the carbides in the microstructure to spheroidized form and so that essentially none of the carbides are transformed to graphite, said hot rolled and box annealed coil having a minimum uniform elongation of at least 15% and a lower yield strength within a range of about 50 ksi to about 60 ksi.