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Lawn mower blade material, again

This post relates the "Steel for Knife making" post by "rider" to rec.crafts.metalworking on 8/31/06. The thread changed migrated from knives to lawn mower blades, so here I am.

Last week at a threshing show, a guy brought me a brand new mower blade to flatten and then to bend 2 or 3" of each end up at 90 degrees to make a hand pushed sod cutter. I have used and sharpened a lot of mower blades and have seen some past posts on this topic, but opinions and experiences seem to vary widely. Here's my most recent experience: I heated this blade to about 1900 degrees F and forged down the "wings". I let it cool until there was NO color in it all, then quenched it in water. It got hard as glass and shattered off about the same 2 inches that I quenched when I hit it with a hammer. To me, this said that the material was Not water hardening, but rather oil or air hardening stock. So, I reheated it gently,let it soak a few minutes and then slowly moved it from the fire to the coals a few inches away over a period of about 2 minutes, then let it cool to room temp for 10 minutes or so. The stock became soft enough to file easily. I conclude it had to be oil hardening (NOT air hardening), or I would not have been able to anneal it with the above process.

I believe that (if this blade is similar to the blades I use on my Cub Cadet mowers) these blades are left in the annealed condition after forming and sharpening so they don't shatter or crack in service.

Would they make good knives? Who the heck knows, if you don't know the exact analysis of the material. Why spend hours at the grinder or whatever to produce something that might or might not work. The parallel for me is in making blacksmithing tools. I have chosen 3 kinds of material (S1, S7 and W1) for my struck tools and I know how to work each and when to use them. Even worse to me, would be to use mystery metal for a tool that I was going to sell to someone else. When "mystery metal" works is in a "McGyver" situation where you have to do SOMETHING, right now, and getting the exact right stuff is out of the question.

Throwing away old mower blades, I remain Pete Stanaitis.

Reply to
spaco
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You didn't temper the blade after the first quench???

I've done this too, but it's really an experiment, and there isn't going to be much in the way of force in the blades.

Q: "Would they make good knives?"

A: Yes they do, but need to be oil quenched and tempered, otherwise they may shatter and not hold an edge.

Mind you there's a little cavete with this statement, buy brand name blades or use blades from mowers that have been cutting grass. The blades that cut grass, and the occasional rock will show wear that may or may not be acceptable... it's like choosing any mystery metal a little care in the choice makes the difference.

Q: "Why spend hours at the grinder or whatever to produce something that might or might not work?"

A: Well if you get good at recycling metal, you can turn trash into treasure, and it's fun to do I guess.

Personally I use a lot of old file blades and turn them into pattern welded items, or I use the material to make useful tools for myself... recycling again I guess. It depends on the items final use, and how much tollerance you can have.

However I also use a lot of Super 9 (which is a 5160 proprietry alloy) for larger blades. I don't heat treat these myself I leave these to the experts, who have space and the ability to control the process over a

3ft length of steel... and they can do it for a lot cheaper than I can. There isn't much tollerance for these items so an exact metal is necessary.

S: "Even worse to me, would be to use mystery metal for a tool that I was going to sell to someone else".

R: It would of course depend on the tool, and how you've made it. Eg. some low carbon steel for a body and some medium carbon for a face can make a really nice hammer, these metals can be sourced from scrap easily. OR a chosen mover blade can make a really nice camping knife or utility knife that would be a joy to own.

To sum up, if you choose your mystery metal with some care, and if you design with a tollerance then you can turn "junk" into something useful.

Less waste.

Regards Charles

spaco wrote:

Reply to
Chilla

No, I wanted to see how hard it would get without a fluid or rapid air quench.

Pete

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Chilla wrote:

Reply to
spaco

Well that does explain why it shattered, sounds like you're having fun though :-)

Regards Charles

spaco wrote:

Reply to
Chilla

First thing that jumped out at me was no discription of an "in between normalizing step". Pete did you really quench directly after it'd been exposed to a high forging temperature?

You know what I'm getting at... grain growth. :/

What about the spark-test results? :)

Spark testing can be "fun" too? ;)

Alvin in AZ

Reply to
alvinj

I did a spark test the other day and burnt a hole in my overalls :-( Charles

Reply to
Chilla

--------------------------------------------- I did not quench at all. The first time I heated it, I let it cool in room air until there was no color (below about 900 degrees F. Then I stuck it in water to cool it down so I could handle it.

When I got done forging it later, I "> I reheated it gently,let it soak a few minutes and then slowly moved it from the fire to the coals a few inches away over a period of about 2 minutes, then let it cool to room temp for 10 minutes or so." This would suffice as an anneal for water hardening and some oil hardening metals.

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I am not a big believer in spark testing. I know that bugs many people, but I don't think its definitive enough for a completely unknown material. It has its place where the user knows that the mystery metal has to be one of 3 or 4 known steels that have varying enough properties to make the test useful.

I have watched experts do it and then listened to several other observers saying they saw different things from what the expert said he saw and from each other. At a minimum, this means to me that you had better be an expert to trust your life or someone elses to the results.

Pete Stanaitis

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Reply to
spaco

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