Environmentally Safe Lubricants for Sheet Forming and Cold Forging of Stainless Steel

Carried out under the "MUP2" Programme.
As an alternative to machining, bulk and sheet forming ("cold forging" and "deep drawing") of stainless steel has large potential in Danish industry. Due to the high flow stress and heavy strain hardening, however, the tribological conditions are very severe. A further problem is the large tendency of oxides on stainless steel to break down during plastic deformation of material causing direct metal-to-metal contact between workpiece and tool surface. The result of this is pick-up of workpiece material on the tool surface, and subsequent scoring of the workpiece surface when it passes such assemblies of pick-up. The purpose of the project is to develop new, inorganic lubricants for cold forging and methods for the necessary coating processes on stainless steel, and to develop alternatives to the commercially applied paraffin oils, which are undesireable from an environmental point of view. To achieve these goals basic research is carried out concerning reactions of the lubricants on the steel surface, phase transitions in the coatings under extreme pressure and high temperatures, as well as investigations of the various coating processes.
New tribologic tests are developed to make up a series of tests ranging from laboratory tests to full scale production tests. All new lubricants are evaluated with respect to their environmental safety.
A new type of lubricant for sheet forming of stainless steel has now been developed to the production test level. Furthermore, a new process for applying coatings of zinc-calcium phosphate on stainless steel based on the work carried out in an industrial Ph.D. project (Thomas Steenberg) has been further developed to the level of production test. These coatings are used in combination with sodium stearate as lubricants for cold forging.