I work in a chemical plant, and routinely have to cut into industrial insulation to inspect the equipment behind it. Tin snips are good but they leave a jagged cut. A knife leaves a much cleaner cut. I'm looking for a steel that will give me the most cuts in between sharpening. Currently I use a Cold Steel American Lawman (AUS8), a Buck csar-t (ATS-34), and a ZT 0561(Elmax). I love the lawman's thinner hollow grind blade. Maybe I should pick up the CTS XHP version.
From what I've read, my two best options are m390 and m4. what do you guys think?
I would be cutting through one to two layers of thin sheet metal and whatever material is insulating. Sometimes it's hard sheetrock material and sometimes it's a pumice type material. Any steel can do this. I'm looking for longevity.
Thanks
OP, since I thought your question was a good one and I'm always interested in learning I copied your question and posted it in another forum to see what was said. Here is an answer given by someone who's fairly well educated in this kind of stuff:
Lets take a look at what we need, to start :
Impact toughness is of no benefit here as the knife isn't going to take any impact, corrosion resistance also isn't an issue and thus we don't need high impact toughness or corrosion resistance. Now what do we need/want? A steel which has high strength and wear resistance to reduce rolling/deformation and wear. As there is metal being cut, a high adhesive wear resistance is desired.
Now you might be inclined to say that you need chip resistance however because there is no strict demand for a very high cutting ability, the chip resistance can be obtained simply by adjusting the edge geometry so that it has enough stability so that the apex will not suffer carbide tear out.
The last thing is that the required sharpness is really low. Gypsum board and sheet metal can be, and in fact typically are cut with blades so dull they won't pass many sharpness tests that are typically discussed. Even fibreglass insulation can be cut with very dull blades.
Now what does all of this mean, look for :
-a very high hardness in ideally a HSS (as it is very easy to get high martensite fraction)
-a very high carbide fraction
and then adjust the edge to ensure it doesn't chip and is the minimal apex and edge angle and then minimize the edge thickness and then primary grind as this will enhance performance strongly.
A few candidates would be - M4 as a readily available steel or ideally something like Maxamet or 121REX. If you have access to a custom maker you could get a very decent knife even from something as simple as 1095 at 67 HRC. Alvin Johnson used to do comparisons of 1095/67 HRC on exactly that type of work (trimming metal) and noting how strongly it would out perform something like ATS-34/60+ HRC by Paul Bos.
The critical part is however to adjust the edge so that it doesn't chip and has the minimal configuration. This has an even bigger influence than the steel.
