Taking the powder metallurgical process even further are new developments in antigalling tool steels. These steels have taken the concept of a lubricious coating and brought it to the powder stage of manufacture. Nitrogen is diffused throughout the tool steel cross-section in the form of nitrides.
The inherent low coefficient of friction creates a result that minimizes the use of external coatings in applications where adhesive wear or sticking has been a major issue. One example is Vancron 40, which contains fine and uniformly distributed vanadium nitrides with a hardness of 2800 HV. While most P/M steels obtain their characteristics through the introduction of increasing amounts of MC type carbides, this grade has more than 20 percent MN in the form of vanadium nitrides.
This material has been used in plastic mold tooling areas such as interlocks, bushings and lifters—where tool steels of dissimilar hardness ranges have been required in order to minimize adhesive wear. It has also been used in place of bronzes where pressures are high and the metal is too soft to resist the loading of the application. It will improve performance where coatings do not hold up and galling is the result.
Due to its internal lubricity, it is actually easier to machine than many other P/M steels. If left uncoated, it can be polished to achieve very high finishes, and refurbished (repolished) should some pickup occur. In addition, it can achieve 62 HRC through high-temperature tempering, so that it can be high temperature processed (under 950ºF) without loss of properties.
An example of where this grade has been successfully used is when Vancron 40 was substituted for bushings and lifters in a detergent closure mold. The previous bushing material was a bronze alloy, which had heavy scoring due to high loads.
The bushing was replaced with the antigalling tool steel, which worked well. No scoring was noted on the steel; however, as the pressures were still high, galling continued to take place on the mating lifters. The previous lifter material was a mold quality S7 at 54-56 HRC. Coating the S7 with a PVD coating did not improve the situation, as the lifters only lasted two days before pickup, even with the coating. A secondary attempt was made at coating the lifters with a diamond-like coating. This lasted a few weeks. The antigalling steel was substituted and experienced no further scoring or scuffing.
very useful information, Nitrogenated tool steel is mainly used for the slider and lifter in a mold
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