| 摘要 |
<p>A high strength and high ductility low carbon steel product having a tensile strength of 800 MPa or more, a homogeneous elongation of 5 % or more, and an elongation at break of 20 % or more which is produced by a method comprising subjecting an ordinary low carbon steel or an ordinary low carbon steel added with B in an amount being 0.01 % or less and effective for accelerating martensitic transformation to working and heat treatment to prepare a product having roughened austenite crystal grains and then to cooling with water, to provide a steel product having a martensite phase in an amount of 90 % or more, and subjecting the steel product to a low strain working, specifically a cold rolling at a total rolling reduction of 20 % or more and less than 80 %, and to a low temperature annealing at 500 ° C to 600 ° C, to thereby form a hyperfine crystal grain ferrite structure having an average grain diameter of 1.0 µm or less; and a method for producing the steel product.</p> |
