Tech Talk
What is vanadium carbide coating?
Carbide coatings on tool steels are often regarded as brittle, diminishing the impact and fatigue strength of the substrate. However, tests run by the Arvin TD Center, Columbus, Ind., show that when vanadium carbide (VC) coatings are combined with the high strength inherent with good substrate steels, the result is a tough tool with long tool life. In fact, VC coatings have extended the life and performance of dies, punches, core pins, and tooling as much as 503.
The Arvin TD Center is a supplier of the Thermal Diffusion (TD) vanadium carbide coating. Arvin tests show that VC treated tooling can increase the number of times a punch can be resharpened, while improving tool performance - even with hard product and heavy gauge materials.
The TD Process is a high temperature tool treatment that diffuses a nonporous metallurgically bonded vanadium-carbide layer into and onto a tooling substrate. The VC layer adheres so strongly to the steel surface that the carbide layer and substrate behave as one body. The VC layer is 0.0001 to 0.0006-in. thick and has a hardness of 3,200 to 3,800 on the Vickers hardness scale.
Because the VC is diffused into and onto the tool substrate, TD significantly reduces galling, wear, seizure, and corrosion, while providing superior peel and adhesion strength. The TD Process is effective with air-hardened cold and hot working die steels such as A2, D2, and H13, high speed steels, and cemented carbides. The steels should have a 0.3% or greater carbon content.
In one test, a TD treated punch was compared to an uncoated punch. Both punches were A2 steel, 0.133-in. perforating punches. Both were used to perforate 0.125 in.-thick carbon steel plate. Researchers examined the TD treated punch after 101,500 hits. They found that steady wear of the vanadium carbide layer had started on the cutting edge and that the wear extended around to the side surface exposing the substrate at the cutting edge. The original vanadium carbide layer could still be seen at the center of the punch face.
After only 16,100 hits, the uncoated punch had severe wear and chipping of the cutting edge. The tests showed that the uncoated punch could take only about 1/6 of the hits the TD treated punch endured.
Another advantage of the TD/VC coating 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. TD also reduces side surface damage from galling. Smaller end damage and reduced galling mean less resharpening, which results in dramatically increased tool life.
VC-treated tooling also performs better even when hard product materials, such as stainless steel, spring steel, and high strength steel, as well as heavy gauge and double thickness materials, are punched. When working with these hard materials, TD increases the number of hits before and between regrinding up to 203 or more.
Another example of the extreme toughness of the vanadium carbide is that TD-treated steel does not fail under mechanical loading. In bending and fatigue tests, researchers rarely observed cracking of the vanadium carbide layer prior to cracking of the fully hardened steel substrates. Indeed, 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 are used.
