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The Basics of Ferrous Metallurgy

102 Articles

Martensitic High Nitrogen Stainless Steels for Aerospace Cryogenic Bearing Applications

Martensitic high nitrogen stainless steels demonstrate exceptional properties including high strength, superior ductility, excellent corrosion resistance, and reduced grain boundary sensitization, making them ideal for critical aerospace applications. This research investigates the development and characterization of nitrogen-bearing martensitic stainless steels as alternatives to conventional AISI 420 and X105CrMo17 (AISI 440C) steels.

Medium Manganese Steels: Part One

Medium manganese steels represent a breakthrough third-generation advanced high-strength steel (AHSS) technology that addresses the limitations of previous generations while maintaining exceptional mechanical properties. These steels, containing 4-12 wt% manganese, exhibit transformation-induced plasticity (TRIP) or twinning-induced plasticity (TWIP) mechanisms depending on retained austenite stability.

Metallography: Part One

Microstructural examinations and visual evaluations of fracture surfaces provide an invaluable insight into the mechanism of component and assembly failures.
Typically, the metallography process uses sample specimens removed and mounted in bakelite plastic. The specimens are then ground to a fine finish with sandpaper and then polished to a mirror finish with diamond or alumina polishing materials.

Metallography: Part Three

The purpose of the coarse grinding stage is to generate the initial flat surface necessary for the subsequent grinding and polishing steps. As a result of sectioning and grinding, the material may get cold worked to a considerable depth with a resultant transition zone of deformed material between the surface and the undistorted metal.
Each stage of metallographic sample preparation must be carefully performed; the entire process is designed to produce a scratch free surface by employing a series of successively finer abrasives.

Metallography: Part Two

The technique for preparing metal sections can be divided into two groups, those processes involving the use of emery papers and coarse abrasives (grinding) and the subsequent operations using fine abrasives (polishing treatments).
Compression-type molding is commonly applied to encase specimens in 1 to 1.5 inch diameter plugs of a hardened polymer.

Microstructures in Austenitic Stainless Steels

Austenitic stainless steels undergo significant microstructural changes during exposure to elevated temperatures, with both short-term and long-term transformations affecting their properties. Initially, M23C6 carbides form during brief heat exposure, while extended aging leads to intermetallic phase precipitation and carbide dissolution. These transformations substantially influence both mechanical performance and corrosion resistance.