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Corrosion Behavior

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Duplex Stainless Steels: Part One

Duplex stainless steels represent a specialized family of corrosion-resistant alloys featuring a unique microstructure combining austenitic and ferritic grains. These materials contain 18-28% chromium and 4.5-8% nickel, providing properties intermediate between austenitic and ferritic stainless steels. The duplex structure offers exceptional stress corrosion cracking resistance, high strength, and superior chloride attack resistance while maintaining good weldability and formability.

Duplex Stainless Steels: Part Two

Duplex stainless steels (DSS) are widely used in chemical, petrochemical, cellulose and nuclear plants around the world. Because of their fine austenitic-ferritic microstructure they offer an excellent combination of mechanical and corrosion resistance properties.

Galvanic Corrosion

Galvanic processes occur between different metals and between different areas of the same metal in the water environment. Water is an electrolyte, a poorly conductive one at the low dissolved solids content of fresh waters, and a highly conductive one at the high dissolved solids content of sea water.
When two different metals are immersed in an electrolyte and connected through a metallic path, current will flow. Oxidation occurs at the anode and reduction (normally oxygen reduction) occurs at the cathode.

Heat-Resisting Alloys

Heat-resisting alloys useful at temperatures above 1200oF are based on iron, on nickel and on cobalt and contain elements that form precipitates that harden the matrix after solution treating and aging. Structural stability and resistance to oxidation and corrosion at elevated temperatures are required of these alloys.

Heat-resisting steels

Steels are now used for a wide variety of conditions entailing heat and corrosion under both static and dynamic stresses, such as aero engine valves, furnace conveyers, retorts, oil cracking units and gas turbines. Three important properties are necessary in material used at elevated temperatures:
1. Resistance to oxidation and to scaling.
2. Retention of strength at the working temperature.
3. Structural stability as regards carbide precipitation, spheroidisation, sigma formation and temper embrittlement.

High Temperature Corrosion: Part One

High-temperature corrosion is a form of corrosion that does not require the presence of a liquid electrolyte.
Strictly speaking, high-temperature oxidation is only one type of high-temperature corrosion, but it is the most important high-temperature corrosion reaction.