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Vanadium Carbide Layer Supported by Strong Substrate is tough, not brittle.Misconception - Tool builders and tool users know that all types of carbides are extremely hard. This fact leads many to think that carbide coatings on steels are very brittle and diminish the impact and fatigue strength of a substrate. This is not true. Fact - When you combine the excellent surface properties inherent in vanadium carbide and the high strength inherent in good substrate steels, you get outstanding surface properties (bulk toughness). This Is especially true of the vanadium carbide coating infused on tool steels by the Thermal Diffusion (TD) tool treatment process. During the TD treatment, the vanadium carbide layer adheres so strongly to the steel substrate surface that the carbide layer and substrate behave as one body. The TD Process is the only tool treatment process that ensures this high adhesion and performance. Figure 1a depicts the TD treated punch after 101,500 hits. It shows that steady wear of the vanadium carbide layer has started on the cutting edge and that the wear extends around to the side surface exposing the substrate at the cutting edge. The original vanadium carbide layer can still be seen at the center of the punch face. If the vanadium carbide layer had chipped off, neither the steady coating wear nor the smooth contour of the exposed cutting edge could be seen. Figure 1b depicts the uncoated punch after 16,100 hits. On the uncoated punch severe wear and chipping of the cutting edge are evident. In fact, the severe edge wear probably caused the chipping. The tests showed that the uncoated punch could take only about 1/6 of the hits the TD treated punch endured. Another advantage of using TD treated punches is that a high number of resharpenings is possible. TD treated punches incur smaller end damage during use and, thus, require less material removal at the cutting edge (Figure 1). TD also reduces side surface damage from galling. Smaller end damage and reduced galling mean less resharpening resulting in dramatically increased tool life. The advantages of TD hold true even when hard product materials such as stainless steel, spring steel, high strength steel as well as heavy gauge and double thickness materials are being punched. Even when working with these hard materials, TD increases the number of hits before and between regrinding(s) up to twenty times or more. Another example of the extreme toughness of the vanadium carbide layer is that TD treated steel does not fail under mechanical loading. In bending and fatigue tests, cracking of the vanadium layer prior to cracking of the fully hardened steel substrates is rarely observed. In fact, tool failure may not be caused by chipping of the vanadium carbide layer at all, but by chipping off of the substrate itself, especially if imperfectly hardened substrates or extremely brittle substrates were used. Be sure to use the right substrate for your application. When substrate steels with great toughness and adequate compressive strength are TD treated, you get high wear-resistant, tough tooling that withstands hit after hit. |
TD Center |
Test
results support the fact that VC coated tooling is tough, not brittle.
In the following test, a TD treated punch was compared to
an uncoated punch. Both punches were A2 steel, .133 inch (3.4 mm)
perforating punches. Both were used to perforate .125 inch (3.2
mm) thick carbon steel plate. Figure 1 shows the
cross sections of the punches.