Dual-phase steel (DP steel) is a high-strength

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

that has a ferritic– martensitic microstructure. DP steels are produced from low or medium

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

s that are quenched from a temperature above A₁ but below A₃ determined from continuous cooling transformation diagram. This results in a

microstructure Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymer ...

consisting of a soft ferrite matrix containing islands of martensite as the secondary phase (martensite increases the

tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...

). Therefore, the overall behaviour of DP steels is governed by the volume fraction, morphology (size, aspect ratio, interconnectivity, etc.), the grain size and the carbon content. For achieving these microstructures, DP steels typically contain 0.06–0.15 wt.% C and 1.5-3% Mn (the former strengthens the martensite, and the latter causes solid solution strengthening in ferrite, while both stabilize the austenite), Cr & Mo (to retard pearlite or bainite formation), Si (to promote ferrite transformation), V and Nb (for precipitation strengthening and microstructure refinement). The desire to produce high strength steels with

formability Formability is the ability of a given metal workpiece to undergo plastic deformation without being damaged. The plastic deformation capacity of metallic materials, however, is limited to a certain extent, at which point, the material could experien ...

greater than

microalloyed steel Microalloyed steel is a type of alloy steel that contains small amounts of alloying elements (0.05 to 0.15%), including niobium, vanadium, titanium, molybdenum, zirconium, boron, and rare-earth metals. They are used to refine the grain microstructu ...

led to development of DP steels in 2007 by

Tata Steel Tata Steel Limited is an Indian multinational steel-making company headquartered in Mumbai, Maharashtra, with its primary operations based in Jamshedpur, Jharkhand. It is a subsidiary of the Tata Group. Formerly known as Tata Iron and Steel ...

. DP steels have high ultimate tensile strength (UTS, enabled by the martensite) combined with low initial yielding stress (provided by the ferrite phase), high early-stage strain hardening and macroscopically homogeneous plastic flow (enabled through the absence of Lüders effects). These features render DP steels ideal materials for automotive-related sheet forming operations. The steel melt is produced in an

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

top blowing process in the converter, and undergoes an alloy treatment in the secondary metallurgy phase. The product is

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

- killed steel, with high tensile strength achieved by the composition with

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. Their advantages are as follows: *Low

yield strength In materials science and engineering, the yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and w ...

*Low yield to tensile strength ratio (yield strength /

= 0.5) *High initial strain hardening rates *Good uniform elongation *A high strain rate sensitivity (the faster it is crushed the more energy it absorbs) *Good fatigue resistance Due to these properties DP steels are often used for automotive body panels, wheels, and bumpers.

References

Notes

Bibliography

*. * *. *. * . *{{Citation , last = Abid , first = Najmul H. , last2 = Abu Al-Rub , first2 = Rashid K. , last3 = Palazotto , first3 = Anthony N. , title = Computational Modeling of the Effect of Equiaxed Heterogeneous Microstructures on Strength and Ductility of Dual Phase Steels , publisher = Elsevier , journal = Computational Materials Science , year = 2015 , volume = 103 , pages= 20–37 , doi=10.1016/j.commatsci.2015.02.051. Steels Vehicle technology