Limitations of tin-free steel

Tin free steel has been developed in Japan as an alternative to tinplate for packaging of food products and general line cans. Tin free steel is manufactured by electroplating cold-rolled steel plate with chromic acid.

Like tinplate, tin-free steel has good formability and strength but it is much cheaper than tinplate. Food cans, can ends, trays, bottle caps and closures can all be made from tin-free steel.

Disadvantages of tin-free steel
*Additional cost due to compulsory lacquering 
*Limitation on packing acid products
*Not suitable for soldering end seams
*Problems in welding
Limitations of tin-free steel

What are the advantages of tin-free steel?

Tin-free steel is steel that has been rendered electronically passive by means other than tinning. Steel rusts in the presence of oxygen and dissolves in food to impart undesirable colors and flavors.

Steel companies introduced tin-free steel in 1965. It is a cold-rolled sheet steel product that has been thinly coated with metallic chrome oxide by electrolytic deposition. By placing an inert layer on the surface of the same low-carbon used for electrolytic tin-plating, it is at least partially protected against oxidation and dissolution.

The advantages of tin-free steel
*The base layer of chromium acts as corrosion barrier
*Excellent formability & strength
*Prevents rustling and iron oxide pickup
*Tin-free steel has a chemically stable surface and suitable for attractive printing
*Ease of fabrication
*Good chemical and thermal resistance. This allows an attractive finishing and a shorter time to place in a tunnel oven when high temperature lacquers are used.
*Organic coating adhere well
*Resistance to internal pressure
*Resistant to stains produced by sulphurs
*Excellent shaping and beautiful appearance

Tin-free steel requires a coating of an organic material to provide complete corrosion resistance. Although the chrome/chrome oxide makes tin-free steel unsuitable for welding, it also makes tin-free steel excellent for the adhesion of coatings such as paints, lacquers and inks.

Tin-free steel also has good formability and strength, but it is much cheaper than tinplate.
What are the advantages of tin-free steel?

Tin-free steel

This material is produced by electronically coating mild steel plate with a chromium/chromium oxide film. By placing an inert layer on the surface of the same low-carbon steel used for electrolytic tin-plating, it is at least partially protected against oxidation and dissolution.

The chrome layer acts as corrosion barrier. The oxide layer recues chrome surface oxidation and covers discontinuities in the surface. The process was developed in Japan and one version, known as Hi-Top is being made in the United Kingdom.

The chromium/chromium oxide layer is even thinner than the thinnest tin coatings normally used, and must be lacquered before it can be used in the manufacture of containers.

The cost if tin-free steel is lower than of tinplate, but is increased by the necessity for lacquer coating.

Tin-free steel has found fairly wide usage, typically examples being daw-redraw containers and fixed ends for processed food cans.
Tin-free steel