BAM research project on the corrosion behaviour of stainless steel

The problem: corrosion due to incorrect processing
In principle, stainless steels should always be corrosion-proof. They can be found in many, often safety-related, areas of daily life and business, from skyscrapers and cars to factories. It is still possible, however, for stainless steel to rust, especially if it has not been properly processed – and this can have hazardous and expensive consequences. The reason for this, in most cases, is damage to the protective chromium oxide layer (passive film) that coats the stainless steel and protects its surface from corrosion. Grinding is often the last processing step before the passive film develops. If errors are made here, corrosion is preordained.

Joint project between industry and science
BAM recognised this problem in the stainless steel processing industry and, in 2016, initiated the research project "Optimisation of industrial corundum grinding processes to ensure the corrosion resistance of stainless steels". VSM was signed up as the partner for technical implementation. In the VSM Technical Center in Hanover, samples were ground before being stored under test conditions, and the corrosion behaviour of the steel samples was then investigated. In addition to BAM and VSM, the other parties involved were representatives of the steel industry, steel processing companies, abrasives manufacturers, universities and TÜV Süd (German technical safety inspectorate).

Results: fine grain sizes offer the best protection / grinding sequences and a clean surface are important
In November, the test results from the two-year research project were presented. The project showed that different types of grain, such as silicon carbide and aluminium oxide, offered hardly any special benefits with regard to corrosion protection. The constituents of abrasives, such as iron oxide and other active substances, had no influence on the corrosion behaviour either. It was found, however, that grinding with long-term abrasives can produce problematic surfaces. Under critical conditions, the inherent breaking out of the grain and the plating on of residual chippings can cause spots. "The finer and cleaner the surface finish, the better the corrosion protection", summarises Detlef Rother of VSM, who is also Chairman of the project support committee. "It is vitally important to strictly follow the correct grinding sequence – working from course to fine grain sizes. A final processing step using a non-woven abrasive is also beneficial."

Expansion of expertise and successful cooperation
New findings, which will certainly change the processes of steel working and processing companies – and which further expand VSM’s expertise in the optimal grinding and corrosion protection of stainless steels.

This project sees the continuation of a decade of traditional and successful cooperation between VSM and BAM. They have already completed various research projects together, one of which resulted in the familiar KorroPad, a quick and cost-effective test for stainless steel surfaces.

About BAM
BAM ensures safety in technology and chemistry. BAM (Bundesanstalt für Materialforschung und -prüfung) is a federal institute with responsibility to the German Federal Ministry for Economic Affairs and Energy. It tests, researches and advises to protect people, the environment and material goods. The technical safety of products and processes is central to all activities in chemistry, materials science, and materials engineering.