Metallurgical phase transition reveals pattern in new decorative steel
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Metallurgical phase transition reveals pattern in new decorative steel
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new type of decorative steel has been formed using a process that differs from that used to generate ancient or modern patterned steels. The metal exhibits an almost infinite variety of threedimensional (3D) patterns, thus enabling bladesmiths and jewelers to create unique knives and jewelry. More than 2000 years ago, sword makers valued a patterned steel called Damascus steel for its hardness and ability to hold a sharp edge. However, the process used to make Damascus steel was lost around the mid-18th century. Modern metallurgical engineers have attempted to reproduce Damascus steel in the lab, discovering that aggregates of iron carbide created the wavy patterns in the material. However, the methods that were used to form the original Damascus steels remain under debate. Early swordsmiths and modern knifemakers have created patterned steels by first forging layers of different metals, commonly iron and steel, together to make a solid billet. They then repeatedly folded and reforged the billet, creating a layered material that revealed the contrasting colors of each component. Modern knifemakers use the patterned steel to enhance the aesthetic appeal of their custom knives. As recently described in the Journal of Alloys and Compounds (doi:10.1016/j.jallcom.2016.08.327), Ly n n A . B o a t n e r o f O a k R i d g e
a National Laboratory and his colleagues have discovered a new type of patterned steel. This advance was made accidentally, while working with single crystals of steel containing 70 wt% iron, 15 wt% nickel, and 15 wt% chromium. Instead of heating the material, as they had in past research, the researchers decided to cool the metal b by plunging it into liquid nitrogen. When they removed the metal, they noticed a 3D pattern that extended throughout the material. At very cold temperatures, this steel undergoes a phase transition from the austenitic phase, a face-centered-cubic crystal structure, to the martensitic phase, a tetragonal body(a) A custom knife made with a new type of decorative steel. centered crystal. As the material Credit: Lynn A. Boatner. (b) Optical interference-contrast miwarms to room temperature, crograph showing the symmetry of the (111) face of a cryosingle-crystal 70 wt%Fe-15 wt%Ni-15%wt%Cr only certain domains return to quenched alloy. Credit: Journal of Alloys and Compounds. the original austenitic phase. The remaining martensitic phase creates the raised 3D pattern. The pattern in the steel reveals the they desire, then they smooth and polish symmetry of the crystallographic oriit, and finally plunge it in liquid nitrogen. entation of the austenitic phase. Cutting Polishing the metal after cooling it would the material along the (111) face of the remove the raised pattern. austenitic phase generates a triangular Jeffrey Wadsworth, president and pattern after cooling, while a rectangular CEO of Battelle Memorial Institute, pattern reveals the twofold symmetry of has researched the metallurgy of both the (
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