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Corrosion Special Topical Papers

Stainless Steels and Alloys: Why They Resist Corrosion
and How They Fail
*

Dr. Jianhai Qiu
School of Materials Engineering
Nanyang Technological University
Nanyang Avenue, Singapore 639797

 

ABSTRACT

This paper discusses the corrosion resistance properties of stainless steels with a focus on why stainless steels resist corrosion and how they fail under service conditions. It is hoped that the discussions would help designers, specifiers, engineers and maintenance personnels understand the corrosion resistance characteristics of stainless steels and hence aid their specification, design, selection, evaluation and efficient applications.

Introduction

Stainless steels are a family of special grade of iron-based alloys that contain at least 11% of chromium in their composition. As their names suggest, stainless steels can retain the "stainless" appearance as opposed to the rusty look of common carbon or mild steels. Car manufacturers often coat steel car body with 6 or more layers of metallic and non-metallic (paint) coatings to protect the substrate steel. Many of us have the experience that deep scratched car body, if not touched up promptly, would become rusty at scratched areas. If the car body is made of stainless steel [1], protective coatings become unnecessary and scratches on the stainless steel car body would not lead to rust stain formation. This is because stainless steels have remarkable resistance to atmospheric corrosion.

The photo showed a 1936 Deluxe Ford Sedan with a bare (not coated) stainless steel body. Other non-stainless steel components such as brake, clutch, gears and the engines had to be replaced three or more times, the surface condition of stainless steel body (after about 60 year's atmospheric exposure) is essentially the same as when the car left the assembly line.

 

 

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