Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
Lomic:
If the edge is badly deformed the cutting ability will be very low even if the V-carbides are freshly faced. At a low hardness the strength of the metal will be relatively low and thus the edge will roll and/or dent readily. Thus the push cutting ability will be very low because of the vastly increased cut resistance and as well the slicing ability will be shot as the carbides will not all cut on the same tract and very few will be perpendicular to the direction of the slice.
Rdrangerer, the grain structure can be blown in a steel in a number of ways. If you don't preheat the piece correctly, soak the steel too long, wait too long to temper it after hardning, etc., basically if you don't do everything the way you should.
As R.J. noted, the most complex high speed steels are much more difficult to heat treat because they are much more sensitive and even a small mistake like soaking for a couple of minutes too long can blow the grain size.
As for how grain size effects performance, this is something I would like clarifed as well. There are some things that I think I have a handle on but somethings that are a bit more muddled often because many references use the same term to mean very different things. So here goes :
A finer grain structure will result in a stronger metal. This is because as the grain size decreases the total surface area increases and the surface boundries of the grains are what impede internal movement and thus allow the metal to resist outside forces.
(Note there are lots of other factors which effect strength besides grain surface area.)
By pretty much the same effect, the impact toughness decreases as you decrease the grain structure because the metal no longer has the ability to absorb dynamic loads by internal movement. However the static toughness might actually increase as it depends directly on the strength and ductility. And while the ductility decreases the strength will increase.
So for example if you heat treat to say 52 RC as opposed to 58 RC you get a stronger steel. I think this is due in part to the smaller grain size at 58 RC. This would also fit with the fact that at softer RC's steels start to get very aggressive slicing due to the larger grain size.
However, this is where it gets a bit cloudy. For example if you do something wrong and it causes the grain size to increase you might not get a tougher steel nor an aggressive slicer because the carbide dispersion might be poor and if you have huge clumps of carbides you could get fractures easily as compared to small carbides dispersed throughout the steel and poor edge holding as the large carbides could readily break out from the edge.
Anyway, it would seem to me that as you decrease the grain size you get an edge that will remain crisp for longer periods of time and will push cut better as it will have greater wear resistance and strength. But for steels with larger grain sizes (D2) you get an edge which is more aggressive slicing. I don't think that sharpening will be readily effected except to the extent that which structure will take less damage and/or lose less metal from the edge.
R.J. (or anyone else), if I went off somewhere in the above, by all means correct it.
-Cliff
If the edge is badly deformed the cutting ability will be very low even if the V-carbides are freshly faced. At a low hardness the strength of the metal will be relatively low and thus the edge will roll and/or dent readily. Thus the push cutting ability will be very low because of the vastly increased cut resistance and as well the slicing ability will be shot as the carbides will not all cut on the same tract and very few will be perpendicular to the direction of the slice.
Rdrangerer, the grain structure can be blown in a steel in a number of ways. If you don't preheat the piece correctly, soak the steel too long, wait too long to temper it after hardning, etc., basically if you don't do everything the way you should.
As R.J. noted, the most complex high speed steels are much more difficult to heat treat because they are much more sensitive and even a small mistake like soaking for a couple of minutes too long can blow the grain size.
As for how grain size effects performance, this is something I would like clarifed as well. There are some things that I think I have a handle on but somethings that are a bit more muddled often because many references use the same term to mean very different things. So here goes :
A finer grain structure will result in a stronger metal. This is because as the grain size decreases the total surface area increases and the surface boundries of the grains are what impede internal movement and thus allow the metal to resist outside forces.
(Note there are lots of other factors which effect strength besides grain surface area.)
By pretty much the same effect, the impact toughness decreases as you decrease the grain structure because the metal no longer has the ability to absorb dynamic loads by internal movement. However the static toughness might actually increase as it depends directly on the strength and ductility. And while the ductility decreases the strength will increase.
So for example if you heat treat to say 52 RC as opposed to 58 RC you get a stronger steel. I think this is due in part to the smaller grain size at 58 RC. This would also fit with the fact that at softer RC's steels start to get very aggressive slicing due to the larger grain size.
However, this is where it gets a bit cloudy. For example if you do something wrong and it causes the grain size to increase you might not get a tougher steel nor an aggressive slicer because the carbide dispersion might be poor and if you have huge clumps of carbides you could get fractures easily as compared to small carbides dispersed throughout the steel and poor edge holding as the large carbides could readily break out from the edge.
Anyway, it would seem to me that as you decrease the grain size you get an edge that will remain crisp for longer periods of time and will push cut better as it will have greater wear resistance and strength. But for steels with larger grain sizes (D2) you get an edge which is more aggressive slicing. I don't think that sharpening will be readily effected except to the extent that which structure will take less damage and/or lose less metal from the edge.
R.J. (or anyone else), if I went off somewhere in the above, by all means correct it.
-Cliff
