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What Is The Difference In HRC #s?
- Thread starter Doug#1
- Start date
HRC refers to hardness. I believe that a diamond bit is pressed into the tempered steel under a standard pressure and the depth it penetrates is measured. The higher the number, the harder it is. Different steels have different optimum Rockwell Hardnesses. M2 performs better at a higher hardness than ATS 34 for example.
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bandsidthe is right on all counts. There will be little practical difference between the Same steel at RC59-61 compared to RC60-62. The hardness of steels seems to be over emphasized by some companies. For the same steel, a higher RC number will probably correlate with greater wear resistance. But it is nearly useless to compare different types of steels. If the RC number is too high for a particular steel alloy, it will be very wear resistant, but also prone to edge chipping or complete blade failure with moderate lateral stresses. Have a look at this thread from a couple of months ago for more info: Higher RC = better edge holding?
Paracelsus
[This message has been edited by Paracelsus (edited 01-18-2001).]
Paracelsus
[This message has been edited by Paracelsus (edited 01-18-2001).]
Hi Doug#1, views on the difference(s) between HRC 59-61 and HRC 60-62 is rather subjective, varying from individuals to individuals. From material/mechanical engineering point of view, in almost all cases, there is a tradeoff between hardness and toughness. Generally, a steel with HRC 59-61 will have lower hardness than one with HRC 60-62. However, the former will have better toughness. It is necessary to state that verification of true comparative values can only be obtained using laboratory testing techniques like the charpy/izod impact tests. Hardness values of steel may not always be a true indication of its wear resistance. This is so because the conventional hardness ratings like HRC measures the macro-hardness of the steel surface. Micro-constituents like chromium carbide (very hard; exist as many fine particles in M2) within a steel structure requires micro-hardness gauging instruments to dtermine. Values obtained are closer to representing the wear resistance of a steel where these micro-constituents play a major role.
Kindly forgive me if i made any mistake(s) as my materials reference books are not with me at present. Hope the above is of help.
Kindly forgive me if i made any mistake(s) as my materials reference books are not with me at present. Hope the above is of help.
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I seriously doubt that there are very many people who can tell the difference between the two hardness ranges you mention. The Rc values in question are VERY hard.
Further, the Rc test measures only SURFACE hardness; thus, as the edge wears, the underlying alloy is uncovered; the hardness of this has not been measured. This accounts for the excellent edge holding of Talonite (r), which is a hard facing alloy; this means that the alloy uncovered as the edge wears is just as hard as the surface alloy.
However all other things being equal (and there a lot of things that are covered by that statement), a higher Rc will probably yield more edge holding. There are precious few data on this subject; perhaps the best data I have found are the Wayne Goddard Edge Holding Tests. You may peruse them here.
If you are interested in the methodology of the Rockwell scale, go here.
Click on technical data, then Rockwell Hardness.
Walt
[This message has been edited by Walt Welch (edited 01-18-2001).]
Further, the Rc test measures only SURFACE hardness; thus, as the edge wears, the underlying alloy is uncovered; the hardness of this has not been measured. This accounts for the excellent edge holding of Talonite (r), which is a hard facing alloy; this means that the alloy uncovered as the edge wears is just as hard as the surface alloy.
However all other things being equal (and there a lot of things that are covered by that statement), a higher Rc will probably yield more edge holding. There are precious few data on this subject; perhaps the best data I have found are the Wayne Goddard Edge Holding Tests. You may peruse them here.
If you are interested in the methodology of the Rockwell scale, go here.
Click on technical data, then Rockwell Hardness.
Walt
[This message has been edited by Walt Welch (edited 01-18-2001).]
Cliff Stamp
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- 17,562
Paracelsus:
CPM-3V has a change in impact toughness of over 100% from 58 to 62 RC. The adhesive wear resistance also changes significantly, a little more than 30%. Even small changes in RC like a point or two can significantly alter the material properties of a steel.
That being said, it is of importance to know how a steel is being heat treated than just the final RC. Are cryogenics being used, if so in what manner? Are multiple tempers being used? Are the blades heat treated in large batches? If so what QC checks are in place?
Anyway in general, a few points higher in RC usually means a slightly stronger, more wear resistant blade that has slightly reduced toughness and ductility. This means that it will resist impacting and wear better but is more likely to see brittle failure (chipping). There are exceptions to these general rules and across different steels they don't hold that well at all.
-Cliff
CPM-3V has a change in impact toughness of over 100% from 58 to 62 RC. The adhesive wear resistance also changes significantly, a little more than 30%. Even small changes in RC like a point or two can significantly alter the material properties of a steel.
That being said, it is of importance to know how a steel is being heat treated than just the final RC. Are cryogenics being used, if so in what manner? Are multiple tempers being used? Are the blades heat treated in large batches? If so what QC checks are in place?
Anyway in general, a few points higher in RC usually means a slightly stronger, more wear resistant blade that has slightly reduced toughness and ductility. This means that it will resist impacting and wear better but is more likely to see brittle failure (chipping). There are exceptions to these general rules and across different steels they don't hold that well at all.
-Cliff