I am having a tough time with it. It mostly looks the same to me. I tried several pieces of steel, at least one of them should have been high carbon (axle shaft) but I couldn't tell the difference between it and a piece of ordinary bar stock, a piece of angle, or even a piece of rebar. I grabbed a Craftsman wrench, I couldn't really see any difference. Wouldn't a Craftsman wrench be high carbon steel?  Tonight I did some searching and learned a bench grinder is better to use for spark testing than a hand held, which is what I was using yesterday. I'll try that next, (only get shop time on the weekends) and maybe make it darker in the shop? Any pointers would be appreciated.

A dark shop and a bench grinder help. More carbon makes more stars, but alloys such as Chromium  and Nickle inhibit the stars. Chromium makes a more red spark, Manganese is more white and adds stars.

Wrenches and axles are medium carbon, because you want them tough, not hard. Spark testing is tougher now with today's alloys. Better for scrap testing is look at the item, and use it for a similar use after forging. Axles-pry bar, hammer head, punch, etc...  A file will be high carbon. 

Not all files are high carbon, most of the old files made in the U.S. are though. The ones coming from China are only case hardened.

build you a set of "known" samples and then you can do 1:1 compares of the sparks and so dial in a bit closer.

What's weird is when HSS, cast iron and wrought iron may look pretty similar but are very different in composition and use!

Hi bigb,

You're trying pretty similar sparking stuff. If you want to work with scrap try to compare these: 1. piece of smaller angle iron - sure structural mild steel. 2. piece of leaf spring - almost sure 5160 type medium carbon low alloy. 3. piece of ball bearing - almost sure 52100, 1.0% high carbon steel. 

Also I use an angle grinder with the thinnest cutting disc. Works for me. But I gave up to try identify steels this way elsewhere than in my own shop.

Bests:

Gergely

Thanks for all the suggestions, Gergely what you said makes perfect sense. I have some big roller bearings and I really need to get to the scrap yard this Saturday and pick up some leaf springs.

16 hours ago, ThomasPowers said:

build you a set of "known" samples and then you can do 1:1 compares of the sparks and so dial in a bit closer.

Yup, it's the only way, and practice!

I have trouble grinding the metal and studying the spark at the same time. I have someone take a pic of the sparks while I'm grinding, then I study the pics.

Maybe this will help

that is quite helpful Jim. also I think it was Thomas who suggested having a had full of known steels to compare with mystery steel to determine what it is.  thanks much. 

11 hours ago, MotoMike said:

I think it was Thomas who suggested having a had full of known steels to compare with mystery steel to determine what it is. 

Even if you don't know the precise composition of your "known" steel, comparing the sparks of your test piece with those from a chunk of structural steel, a flea market cold chisel, and an automotive coil spring will put you roughly in the right ballpark.

I found a more resolute copy of the above image.

 

I save and label a test coupon   from every new known alloy I get for future reference but JHCC is right a piece of structural steel, a cold chisel, and a piece of spring steel will give you some idea of what you're dealing with. You can also do a break test if you plan on hardening the mystery steel. Search bamsite heat.pdf and you'll find a pretty good PDF explaining it that you can download for free.

Pnut

And be wary of "Junkyard Steel Charts" as they are often based on Steel Manufacturers' suggestions and not what is actually used in the real world!

Thank you, pnut, for that PDF recommendation.  I will have to do some experimenting with that information.

I have been using coil springs, fork lift tine and sucker rod for tooling.

One thing I have learned via cutting various different alloys for 25+ years is this:  The softer the material the more disc it will eat.  I don't know why, but a bearing race will not eat up a cutting disc as fast as a chunk of re bar. 

 

  Oh, and thanx for the PDF that was good reading. :D

 

 Actually small angle can be bed frame which is mostly med-high carbon.