Lawnmower blade steel?

DaQo'tah Forge · Aug 15, 2004

My brother's 6 year old son loves to come over to my shop and hit steel with me on the weekends.

This weekend he had with him some old lawnmower blades that he himself fished out of the junk pile when his dad was about to toss them away. He saved them just for me...

So I "HAVE" to use them, there is no way around this...

I have forged them down to the point where I could use the belt grinder and gave them a knife shape. I normalized them 2 times, I have fully Annealed them over night...and have finished all I needed to do before I Heat-treat the cutting edge to make it hard.

QUESTION:

Now I was going to use my O/A torch and heat just the cutting edge , then quench in quenching oil that was heated to 160..

Is that would you suggest?

Or should I use water?

indian george · Aug 15, 2004

This was from the Neo-Tribal website

When ready to harden (blade should have been normalized prior to this step) heat to non-magnetic and quench in oil. You can either quench just the point and edge, or the entire piece. The main thing is that once hard--temper immediately. Don't wait. An old metal worker once told me that a piece that is freshly quenched and not tempered soon thereafter would not be the same piece of steel the next day, implying that the delay somehow affected the steel. Son't know if that's true, but why take the chance?

1. If you quench just the edge and point, then clean off the blade enough to see metal, then bake in your kitchen oven at 375 for 3-3 1/2 hours, being sure to check it and turn it over every so often. You want to have the blade turn a nice color between straw yellow and bronze. You don't want it to get purple to blue color, so you may have to remove it if the colors are running. If you only hardened the edge and point, then you might be all set. Test cut with it (before mounting handles) and see if the blade chips out (too hard) or dulls easily (not hard enough.) You might have to adjust your oven temp up or down.

2. If you quenched the whole thing, then you can bake in the oven just like above, but then you need to take a hot piece of metal, or put a metal pipe (not galvanized) in your forge to rub the back of the blade over, or you can use a propane torch to draw a blue color to the back of the blade, ricasso and tang areas, leaving the cutting edge straw to bronze color. Keep a pail of cool water close by and the colors run quickly some times.

Again check out Tim LIvely's website, I believe he has a good article on heat treating.

Sandspur
Neo-Tribal Member
(1/16/01 6:50:27 pm)
Reply Re: lawnmower blades
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raker · Aug 15, 2004

DaQo'tah;
On lawn mower blades, I have heard that they will not harden because of the liability involved for the blade manufacturer. If the blade ever was hard enough to crack and fly off, killing or maiming someone, it would not be worth it. Better to sell you a soft blade and when it wears out, sell you another one.
To check if it will be suitable for a knife, harden a small piece and try to break it. If it breaks, it will make a knife, if not, it is scrap iron. This is what I teach in my knife class as every one wants to use something to make a knife and have no idea that it may not be possible. Always, when in doubt, check it out. It will save a lot of time and expense later on.
On heat treating it, play like it is a piece of 52100 steel but only temper it on the low end to start. As above, if it chips, raise the tempering temp til it flexes.

george tichbourne · Aug 16, 2004

I haven't found one yet that will throw a decent spark when I am sharpening it so I guess that for durability they are not hardenable material.

cwhittington · Aug 16, 2004

I have a bunch of mower blades and I've tested a few of them and each of them got brittle hard. Maybe I got lucky when I pulled them, or maybe they all came from older mowers, but they appeared normal. Perhaps some of the blades are made with high carbon but not hardened?

DaQo'tah Forge · Aug 16, 2004

Okay,,,,as I have to use the lawnmower blade to make this knife anyway,,,I will go ahead and treat it as if it was 52100 steel,,,and just hope for the best.

When I read a few comments here, I ran out to my shop and started my forge and did a heating/quench of the rest of the lawnmower blade that I did'nt use up.

I quenched in water.

I dont know if the blade is truly hard or not, BUT...but the file does skip just like you would expect to happen if it was hard.

The file digs into the part of the blade that didnt get quenched, and skips right over the part that did....so I think this is going to work...

raker · Aug 16, 2004

And now you know that it will harden and you won't waste all your time on something that won't. It is really an easy test to do and I have done it on several steels that were questionable.
How about a pic when you get it made?

Gwinnydapooh · Aug 17, 2004

Just because the manufacturer doesn't make it very hard doesn't at all mean that it's not carbon steel and won't take a temper if YOU harden and temper it!

As with all things, test it and you won't go wrong.