Effect of coiling temperature on the structure and properties of thermo-mechanically rolled S700MC steel

The boron-free S700MC steel is usually produced by exploiting the properties of a ferrite-bainite mixed microstructure formed coiling strips at temperature about 450?C, i.e.below bainite starting temperature. With aim further enhancing mechanical 6 to 10 mm thick strips, industrial tests were carried out 600?C promote formation structure ferrite and carbides, which also acceptable for this type steel. Unexpectedly, composed martensite was obtained. Compared ferritic-bainitic grade, new characterized slight decrease yield point but an increase ultimate tensile strength no less than 80 MPa, with transition from quasi-discontinuous clearly continuous yielding behaviour. Accordingly, ratio decreases 0.90 0.75 impact energy 35 J 60 two gauge levels, respectively. behaviour coiled high explained as direct consequence dual phase hard interspersed in soft matrix. presence so-called incomplete reaction. partial transformation into after long time required coil cool down stabilize untransformed austenite due carbon enrichment making lower temperatures impossible.