Almost 7 years after former Nickel Institute Director Dr David Jenkinson's 2006 Technical Bulletin, ASSDA's technical expert, Dr Graham Sussex, revisits the CrMn grades of stainless steel.

BACKGROUND

Almost all of the stainless steels in use have 16% chromium or more and have nickel or other additions to make them austenitic and hence formable, tough and readily weldable. However, the formal definition of a stainless steel is that it is an iron- and carbon-based alloy with more than 10.5% chromium. Historically, the corrosion mitigation industry regarded alloys with more than 12% chromium as stainless steels mainly because those alloys did not corrode in mild environments. Because of the perceived problem of high initial price when using stainless steels, alloys that are ‘barely’ stainless (and with low nickel to boot) are more competitive with painted or galvanised carbon steel than higher alloys.

Stainless steel can provide excellent service underground. It is stronger than polymers and copper and its resistance to chlorides and acidic acids is significantly better than carbon or galvanised steels.

The greatest challenge we face is the control of our own success. With 7 billion people on earth, all with an insatiable appetite for a high standard of living, the newest dimension of materials competition is sustainability.

If a job requires greater corrosion resistance than grade 304 can provide, grade 316 is the 'next step up'. Grade 316 has virtually the same mechanical, physical and fabrication characteristics as 304 with better corrosion resistance, particularly to pitting corrosion in chloride environments.

Stainless steels are now cheaper than ever, but there is still room to minimise costs (see Table 1), which will improve the bottom line for individual companies, projects and the industry as a whole.

The common austenitic grades of stainless steel, 304 and 316, are also available with controlled low or high carbon contents, know as "L" and "H" variants, with particular applications.

Reasons for using stainless steel threaded fasteners are the same as those for selecting other stainless steel components - generally resistance to corrosive or high temperature environments. In addition to the obvious benefits in improved aesthetics and longevity however, there can be significant cost savings if the joint will require disassembly and reassembly.

The Workhorse of Hydrometallurgy

Posted 17 May 200

Stainless steel has earned a reputation as the material of choice for the mining and hydrometallurgical industries. This article discusses suitable grades and applications and the emerging opportunities for stainless steel in these industries.

Stainless steels are widely used in the food industries, including wine production, because of their corrosion resistance and ease of cleaning which result in negligible product contamination.

Principles of Mig Welding

According to the AWS Welding Handbook volume 2, MIG welding is "an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool. The process is used with shielding from an externally supplied gas and without the application of pressure". The wire is usually supplied in spools and fed through to the welding arc by an electric feed motor, with no manual control ofthe wire feeding process ie semiautomatic.

Accurate specification of a surface finish is vital for extracting maximum functionality and durability from stainless steel components. Read Part 2. Read Part 3.

Quick and easy tips for keeping that shine

Retaining a sparkling finish on stainless steel surfaces is just a matter of a few simple steps. And you don't need expensive products or special equipment - ordinary household cleaners are usually all that's required. You just need to bear in mind a few easy DOs and DON'Ts...

The last issue of Australian Stainless contained an overview of coated abrasives and guidelines for achieving the desired surface finish. This technical series continues with a comparison of grit size and hardness. Read Part 1. Read Part 3.

Our three-part series on coated abrasives concludes with information on choosing the correct abrasive product for the desired finish. Read Part 1. Read Part 2.

Posted 1 July 2003

Stainless steel combines structural strength with corrosion resistance to form a superior construction material which additionally supports a range of aesthetically pleasing finishes.

Successfully using stainless steel depends on environment, grade selected, surface finish, the expectations of the customer and the maintenance specified.

Stainless steels provide robust solutions, but in harsh or borderline environments with high expectations for durability, surface finish will have a substantial impact on performance. Surface finishes can be applied mechanically (usually with abrasives) and chemically.

Understanding how chemical and mechanical treatments will affect the characteristics of the surface and will enable the best possible outcome for the client and the structure. Chemical treatment can be used to improve the corrosion performance of the steel, and hence its appearance in service.

For many years there has not been a Standard to cover the low pressure stainless steel cast pipe fittings commonly used in Australia and other countries around the world.

A crevice is a narrow gap between a piece of metal and another piece of metal or tightly adhering material like plastic or a film of bacterial growth.

Many metals and alloys are susceptible to crevice corrosion, but in stainless steel, crevices are the first and most common place for corrosive attack to begin. With a little understanding, crevice corrosion can either be avoided or minimised.

The visual performance of outdoor stainless steel depends on five interrelated factors:

• Surface finish - smooth and clean and free of crevices.
• Grade selection - appropriate for environment.
• Good design - rain washing and uniform draining.
• Maintenance program - regular cleaning.
• End user expectations.