Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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17 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 Information on corrosion control and prevention structure of the steel at the nanoscale to create a microstructure without carbides and secondary particles. Steel made with the nanotechnolog y process has a differ- ent microstructure and does not form these microgalvanic cells. During the cooling step in the alloy's fabrication pro- cess, a f ine, lath martensite microstruc- ture that resembles ply wood is formed, which provides the alloy with strength, ductility, toughness, and corrosion resis- tance; and the presence of carbides is almost eliminated, says Faza. This is pos- sible, he explains, because the alloy's low- carbon content reduces the excess carbon in the matrix that can combine with the chromium in the alloy to form chromium carbides that, in turn, reduce the alloy's corrosion resistance by depleting the chromium from the matrix. Additionally, the low content of other carbide-forming elements prevents the formation of secondary particles in the microstructure that can initiate micro- galvanic cells and galvanic corrosion. The low-carbon chromium steel alloy con- tains a maximum carbon content of 0.15%, ~9.5% chromium, and low amounts of other carbide-forming elements such as tungsten, molybdenum, vanadium, tita- nium, niobium, tantalum, and zirconium. The microcomposite has a minimum yield strength of 100 ksi (690 MPa) and minimum tensile strength of 150 ksi (1,030 MPa). The microstructure and chemical properties of the high-strength, low- carbon, chromium microcomposite steel delay corrosion initiation by as much as f ive times longer than for CS, as well as lower the corrosion rate once corrosion is initiated, which will extend the service life of the application without the need for overdesigning the size of the anchor rod for sacrif icial purposes, says Faza. He notes that experience has shown the microcomposite steel alloy to possess a chloride threshold level (the level where chlorides will destroy the steel's protec- tive f ilm) that is about four to f ive times higher than that for CS. "Any time there is an opportunity to reduce the amount of steel you're putting into the ground and still achieve the load- carrying capacity, that's always an advan- tage—not just for the supplier but the end user as well," says Printz. Contact Tom Printz, Williams Form Engineering—e-mail: tprintz@williamsform. com; and Salem Faza, MMFX—e-mail: salem. References 1 Global Statistics, Global Wind Energy Coun- cil , graphs (October 28, 2014). 2 Texas Wind Energy, American Wind Energy A s s o c i a t i o n , h t t p : / / w w w . a w e a . o r g / Resources/state.aspx?ItemNumber=5183 (October 28, 2014). 3 ASTM A1035/A1035M-11, "Standard Specifi- cation for Deformed and Plain, Low-Carbon, Chromium, Steel Bars for Concrete Rein- forcement" (West Conshohocken, PA: ASTM International). 4 ASTM A29/A29M-12e1, "Standard Specifica- tion for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought" (West Con- shohocken, PA: ASTM). 5 ASTM F436-11, "Standard Specification for H a rd e n e d S t e e l Wa s h e r s" ( We s t C o n - shohocken, PA: ASTM). 6 ASTM A47/A47M-99 (2014), "Standard Spec- ification for Ferritic Malleable Iron Castings" (West Conshohocken, PA: ASTM). 7 ASTM A536-84 (2014), "Standard Specifica- tion for Ductile Iron Castings" (West Con- shohocken, PA: ASTM).

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