What steel is lawnmower blades made of, and is it suitable for knives?

B

BluesHarp

Joined
Oct 14, 2007
Messages
40
Hi, fellow knife heads. I have been making knives for years, mostly from so-called "junk steel" because I have an unlimited supply of huge industrial sawblades that makes fantastic knives. I've gotten plenty of downers from other makers telling me to stick to "known" steel, but I guess I like making something useful out of used things. Especially free used things.

I have come across a whole pile of free lawnmower blades. All brand new, still painted. The challenge here is that there are some tricky twists and bends to these blades, so getting a good flat piece to work with is a challenge. I only do stock removal, so I won't be forging this metal. I haven't gotten yet to testing some of this metal. I was going to cut some test pieces of different sizes, and try heating up to non-magnetic and quenching in different materials: water, oil, brine, anti-freeze, etc. and then see how brittle it is. If it looks like the carbon content is high enough that my test pieces snap off clean in the vise, I'm going to go all out and make a knife then do cutting tests like crazy on it.

Anybody had experience with lawnmower blades? I read in a few places online that they might be 5160, which is suitable knife steel. Any other votes? Any experience?

I'll post my own results later.

Thanks.
 
Lawnmower blades are designed to be soft. If you had a hard mower blade hit a tree stump, it would shatter and throw shrapnel all over the yard. They are designed to bend rather than break. With that, my guess would be that lawnmower blades are made of whatever scrap the asian lawnmower blade plant could find. Of course you could do your own testing if you have nothing but time on your hands.

They do a great job at cutting grass, so that's what I'd let them do.
 
Lawnmower blades may be designed to be soft, but that doesn't mean they're made from mild steel or steel that won't harden. IMHO the only real way you'll ever know whether or not they're worth making a knife out of is to make a few, heat treat and temper them and see if they'll hold an edge. Of course, since you don't know what the steel is, you'll have to experiment with heat treating.

I think it's great that you use what's on hand or what you have access to. I think too many times we get caught up in the "use known steel or else" mindset and forget that knives have been made for centuries out of unknown steel. Plus sometimes it can be downright fun to use something unkown and find a way to make it work! Experimenting can be just as much fun as the actual making of the knife!
 
As long as you enjoy the process of testing the steel you have and don't mind spending the time to do it. Also, good known simple steel is really affordable and if you factor in your time, probably even cheaper than "junk steel". But if it's not a question of cost but more of recycling then more power to you.
 
If they don't get brittle using a water quench then from my reading it will be nigh on impossible to get them hard enough for a good knife blade. If you know who made the blades then you might be able to determine the composition. John Deere makes lawn mower blades suitable for knives. Also, if you use superquench you can get the some of the lower carbon blades harder than expected. At any rate any of the steel will make usable but not necessarily good 'chopper' blades.
 
Nothing wrong with using junk steel. I made hundreds of good knives from old saw blade steel years ago.

Some mower blades will harden, others wont. Personally, I'd stick with the saw steel and sell the mower blades as mower blades. :)
 
@:bluesharp Lawnmower blade are usually 1040/1045 steel. large grain and very soft so that they will crush instead of shatter. Never seen a knife out of a lawnmower blade much harder than 45-50RC (without adding carbon from sawdust). However it is certainly good practice before you get into tougher steels. There was a good thread on lawnmower blades in knife making in the Canadian Connection sub forum on here but i no longer see the CC.
 
Last edited:
Large grain so that it won't shatter? Adding carbon with sawdust?.......

Blues, you enjoy using recycled materials, so that is reason enough to keep using them. Folks have given some valid opinions on why doing otherwise might be a good idea, especially if you sell your finished knives. As far as your idea of quenching in antifreeze ~ DO NOT DO THIS.

Best
Steve
 
Thanks for all the replies! To Mudbug and others who keep an open mind about using "junk steel" for making knives, I say thank you twice. I've made hundreds of knives over 20 years. I'm a second-generation knifemaker, and my father taught me the attitude of using what's on hand to make something useful, and not be a snob about your materials. I don't consider myself a professional knifemaker, but I also think knifemaking is not a religion. Bringing up the topic of "junk steel" always gets everyone fired up and taking sides. For me, it's about learning. I think it's cool to find a piece of material (especially if it's free) and figure out what it's made of, and figure out if I can use it to make a useful tool. A very "famous" bladesmith told me 10 years ago that I could never make a good working knife out of concrete-cutting sawblades. He said they're mostly 4140 or who-knows-what, and no good for making a knife. Really? I've put in many hours experimenting with heat treating techniques, and finally hit on a process that works for me. I've tested my finished knives side by side with Gerber, Buck and Kershaw production knives, and I can beat most of them. With so-called junk steel. It's about learning how to make the right bevel, and use the right heat treatment. So I'm inclined to give lawnmower blades a try. No, you can't make a working knife out of just anything that calls itself steel, but my point is that you need to keep an open mind and give things a try. I've got nothing against you professionals who will only use "known" steel. Me, I like to experiment. I've got a garden full of tomatoes and peppers, and some people ask me why I waste so much sweat and time making my own salsa when I can buy it at the store. I tell them, "because now I know how to make salsa, and you don't". :)
 
swordmaster said:
....... large grain and very soft so that they will crush instead of shatter............. (reference to increasing hardness)- adding carbon from sawdust ..........
Click to expand...


I can't send swordmaster a PM or email, so all I can do is note that the quoted information is not metallurgically sound.
Please understand I am not trying to start an argument, but I have no other way of letting you know that I greatly disagree with this info. Any further discussion should be in a different thread or off the forum by email/PM.



As to the question from Bluesharp -
Lawn mower blades are made to bend not break. Hardness isn't an attribute in the steel that is desirable....so they don't use steel that has that trait. It is usually low carbon and has toughening alloys, like nickel, chromium, and molybdenum.

Here is a post I made a while back on the subject:
........ Lawn mower blades are low carbon high alloy steel that has high impact resistance and toughness. Hardness is a bad thing in a mower blade, so they don't make the steel hardenable to more than the mid 40's.
There are specialty blades for industrial mowers made in tool steel ( very expensive), but 99.9% of all the blades you will come by will be a nickle/chrome alloy with about 45 points of carbon. ........

Use this search engine to search for old threads on BF. If you enter "Lawn Mower Blades" you will get dozens of threads and hundreds of posts.......all saying that lawn mower blades won't work.
http://www.google.com/cse/home?cx=011197018607028182644:qfobr3dlcra




As far as lawn mower blades being used for knives goes, they are not going to make any kind of a good knife. I would compare a knife made of mild steel from Home Depot and a lawn mower blade as being about equivalent in quality. Maybe different steels, but the same end result.

By quenching in brine or water the steel can be hardened to some degree, but the hardness will be low, and the blades may be brittle.
If you were a forging knifemaker, there could be some reason to try using then for forging practice, but as a stock removal material, there is no sensible reason to make a knife from a lawn mower blade at all.

If you are wedded to the idea of using this stack of blades, cut off the end of one and send it to a metal testing lab for analysis. Then you will know what steel it is and how to HT it. You could test the steel at home with 100 tests, and still would not know what it is.



Please do not quench in antifreeze.
 
Last edited:
As someone who has made a few knives from lawnmower blades (and just about everything else), I can say there is a lot of variation in ht and alloy. At least you have some that are probably the same, and also not full of unseen cracks.

I don't like to sell my blades when I don't know what they are made of... but I still like to make some now and then out of re-purposed steel. So, I say have fun but don't expect anyone to be able to definitively tell you what they are made of or how to ht...

psst but I would start by treating it as 1045 and if you have ht you can flatten the silly things out too...

Oh and lawnmower blades might be designed to cut grass, which imo puts them in tameshigiri territory for cutting grass mats... but as mentioned above they might be designed for not breaking, very different design parameters... now you have me wanting to make an S7 lawnmower blade... I have lawnmower blades made of handcrafted knives!?:p
 
wnease said:
Oh and lawnmower blades might be designed to cut grass, which imo puts them in tameshigiri territory for cutting grass mats... but as mentioned above they might be designed for not breaking, very different design parameters... now you have me wanting to make an S7 lawnmower blade... I have lawnmower blades made of handcrafted knives!?:p
Click to expand...

I believe that cutting individual blades of grass at thousands of RPM vs. tightly woven strands of grass (or grass like substance) rolled into a relatively dense cylinder are two different things.

I can "cut" grass with a broom handle if I swing it fast enough. At the same speed, a rolled grass matt wouldn't be phased.

That being said, I can make my lawn mower blades shaving sharp (and have several times in the past), but that doesn't mean the edge will last very long. Very similar to a custom knife I once received that was made from a "band saw blade" by a reputable maker who had performed his own heat treat and testing, and made dozens (if not not hundreds) of blades. Out of the package, the knife had a perfect edge, and was hair popping sharp. I made about a dozen cuts through some rope and cardboard before the blade would barely "saw" through a piece of paracord.
 
Lawnmower blade steel is not suitable for knives, you have stated that you will not accept advice to that accord, so be it. Do not quench in antifreeze, it has toxic vapors, if you want to make super quench it is brine with dish soap

-page
 
You must log in or register to reply here.
Back
Top