Larrin
Gold Member
- Joined
- Jan 17, 2004
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It's true that in general if you want a smaller carbide size you should move to a grade with less wear resistance, however having as much toughness as possible while maintaining extremely great wear resistance is always a good thing.
I mentioned earlier the patent for 3V modified with niobium for finer carbide size: http://www.freepatentsonline.com/y2008/0078475.html Apparently though both Niobium and Vanadium form MC carbides, they are formed independently in casting, so you can have the same volume of carbides but a smaller average size. With the PM process, just like conventional casting, the greater the volume of carbide you have the larger the size, which is why 10V has a greater carbide size than 3V, 10V has ~17% carbide volume and 3V has ~5%, both only have vanadium carbides. Also, this is why the carbides are larger in CPM-154 than in S30V, though they have similar carbide volumes (17.5% vs. 14.5%), CPM-154 has only M7C3 carbides while S30V has 10.5% M7C3 and 4% MC. Since the M7C3 and MC carbides form relatively independently the average size is smaller in S30V than in CPM-154. However, the reason they are designated M7C3 is because it is not only Cr7C3, there is going to be some vanadium and molybdenum in some or all of the M7C3 carbides. If for example S30V modified with niobium now had 5% VC, 5% NbC, and 5% M7C3 carbide than that would be three carbides forming independently during casting (in powder form of course), which could mean a smaller average size, and therefore greater toughness and edge stability. And of course, this would mean 10% MC carbide (from VC and NbC) as opposed to the original 4% MC, which would increase wear resistance. Of course these are just example numbers to make my point, I have no idea what the real numbers would be. The difference in carbide size will likely be smaller in an S30V modification than in the 3V modified with niobium, but there is still a possibility of reduction.
It is true in the case of S110V that the major improvement over S90V is in corrosion resistance, and the carbide size isn't noticeably different, however the carbide volume is slightly greater in S110V than S90V. In the S110V patent there are abrasive wear numbers given, S110V does seem to have slightly greater abrasion resistance, but abrasive wear is primarily a test of the carbide volume and hardness. The crossed-cylinder wear test shows greatly the differences in MC carbide content, which is strangely missing in the patent since it is a favorite of Crucible's. They also of course raised the molybdenum content, as well as increased the maximum hardness attainable. Overall they seem to have matched or come close to the toughness of S90V (based solely on the carbide volume) while increasing the maximum hardness, wear resistance, and corrosion resistance, which is quite impressive.
For the record, I think S30V has considerably greater toughness than S90V, around 30-50% greater.
I mentioned earlier the patent for 3V modified with niobium for finer carbide size: http://www.freepatentsonline.com/y2008/0078475.html Apparently though both Niobium and Vanadium form MC carbides, they are formed independently in casting, so you can have the same volume of carbides but a smaller average size. With the PM process, just like conventional casting, the greater the volume of carbide you have the larger the size, which is why 10V has a greater carbide size than 3V, 10V has ~17% carbide volume and 3V has ~5%, both only have vanadium carbides. Also, this is why the carbides are larger in CPM-154 than in S30V, though they have similar carbide volumes (17.5% vs. 14.5%), CPM-154 has only M7C3 carbides while S30V has 10.5% M7C3 and 4% MC. Since the M7C3 and MC carbides form relatively independently the average size is smaller in S30V than in CPM-154. However, the reason they are designated M7C3 is because it is not only Cr7C3, there is going to be some vanadium and molybdenum in some or all of the M7C3 carbides. If for example S30V modified with niobium now had 5% VC, 5% NbC, and 5% M7C3 carbide than that would be three carbides forming independently during casting (in powder form of course), which could mean a smaller average size, and therefore greater toughness and edge stability. And of course, this would mean 10% MC carbide (from VC and NbC) as opposed to the original 4% MC, which would increase wear resistance. Of course these are just example numbers to make my point, I have no idea what the real numbers would be. The difference in carbide size will likely be smaller in an S30V modification than in the 3V modified with niobium, but there is still a possibility of reduction.
It is true in the case of S110V that the major improvement over S90V is in corrosion resistance, and the carbide size isn't noticeably different, however the carbide volume is slightly greater in S110V than S90V. In the S110V patent there are abrasive wear numbers given, S110V does seem to have slightly greater abrasion resistance, but abrasive wear is primarily a test of the carbide volume and hardness. The crossed-cylinder wear test shows greatly the differences in MC carbide content, which is strangely missing in the patent since it is a favorite of Crucible's. They also of course raised the molybdenum content, as well as increased the maximum hardness attainable. Overall they seem to have matched or come close to the toughness of S90V (based solely on the carbide volume) while increasing the maximum hardness, wear resistance, and corrosion resistance, which is quite impressive.
For the record, I think S30V has considerably greater toughness than S90V, around 30-50% greater.
