voestapine eifeler Coatings is the leading provider of the highest quality PVD coatings in North America. With the demands put on the forging industry of today, taking advantage of eifeler PVD coatings will go a long way in satisfying those demands. Duplex-TIGRAL – A proven AlCrTiN high temperature coating voestalpine eifeler Coatings developed this high performance PVD coating for very high resistance against oxidation and abrasion. Benefits are: high hardness and wear resistance, superior abrasion and erosion resistance, corrosion resistance from alloying attack, high oxidation temperature and thermal stability and improved coefficient of friction. When an increase in production, extended tool life, less down time, and higher tool performance are requirements, then voestalpine eifeler Coatings is your solution provider.
CROSAL – The newest generation of AlCrN coating
This innovative AlCrN-based high-performance coating was specially developed for use at high temperatures, up to 2012°F (1100°C). Locally high to very high temperatures occur in many forging processes. Our innovative CROSAL® coating meets all the necessary demands to the highest degree: high hot hardness, high resistance to oxidation and high adhesive strength.
In hot forging a heated up billet is pressed between a die set to a nearly finished product. Large numbers of solid metal parts are produced in aluminum alloys, copper alloys, steel or superalloys where irregular shapes need to be combined with good mechanical properties. The main methods of impression die forging are drop or hammer forging and press forging.
Typical die failures
Hot forging dies are exposed to severe mechanical and thermal cyclic loading, which puts high demands on the die material. Thus, there are some phenomena which restrict die life.
- Wear: Wear occurs when the work material plus oxide scale glide at high velocity relative to the impression surface under the action of high pressure. It is most pronounced at convex radii and in the flash land. Wear is increased drastically if the forging temperature is reduced.
- Gross cracking: Gross cracking may occur during a single cycle or, as in most cases, over a number of cycles; in the latter instance, the crack growth proceeds via a high-stress fatigue mechanism. Gross cracking is more frequent in hammer blocks than in press tooling, because of the greater degree of impact.
- Plastic deformation: This occurs when the die steel is locally subjected to stresses in excess of the yield strength. Plastic deformation is quite common at small convex radii, or when long thin tooling components, e.g. punches, are subjected to high bending stresses.
- Thermal fatigue cracking: This results if the surface of the impression is subjected to excessive temperature changes during the forging cycle. Such temperature changes create cyclic, thermal stresses and strains at the die surface, which eventually lead to cracking via a low-cycle fatigue mechanism (heat checking).
Die material properties
The properties profile required for tool steel in forging dies depends to some extent on the type of forging operation, on the work material and on the size of the part, depth of impression etc. However, a number of general characteristics will always be required in all forging operations. The particular die damage mechanism to which resistance is conferred by the various properties are given in parentheses.
- Sufficient hardness and ability to retain this at elevated temperatures – temper resistance (wear, plastic deformation, thermal fatigue cracking).
- Enhanced level of hot tensile strength and hot hardness (wear, plastic deformation, thermal fatigue cracking).
- Good toughness and ductility at low and elevated temperatures (gross cracking, thermal shock cracking, thermal fatigue cracking).
- It is important that the die steel exhibits adequate toughness/ductility in all directions.
- Adequate level of fatigue resistance (gross cracking).
- Sufficient hardenability (retention of wear resistance, etc., if the die is re-sunk)