How to identify a steel?

[zaebis]

Ok I was just milling a belt pulley (steel) from a car. I needed to carve its center piece to be left on the shaft and discard everything else. I setup for what I thought would be 1018 parameters and started to cut a circle (CNC mill). WIth a bit of whining it got the job done but I was close to breaking an end mill (on engaging). Anyways the cut revealed bare metal color (pulley was painted) and rather ugly cut surface (I was expecting shiny as they always come out with 1018). The color of the bare metal was gray and the surface was grainy / notchy.

Long story short; how does one IDs steel params for cutting when no info is available? Are there any tricks of the trade to do that?

[wildwestpat]

Suggest you make it a rule to start with a modest feed rate rather than assume you have a free cutting mild steel to deal with. Your description fits with cast iron (gray, grainy / notchy). If you had removed the paint you might have found other clues that the pulley was a casting - rough sand cast finish and possibly the remanents of flash lines or fetteling by rough grinding away of the flash lines. Also cast parts often have a makers number cast into the surface at some point that is not going to be machined away. Your observation of high load on engaging the cutter would also point to cast iron as there is a skin on the cast iron that is much tougher to cut through and tipped tools are good.

Also cast iron generates swarf which is dull grey and is more akin to fragments than long curls.

Rough test should also include:-

Can it take a center punch mark easily?

Can it be drilled - is the swarf continuous or is it broken up like coarse powder?

Can it be nicked with a hand file or does the file skate over the surface? The harder the steel the more it will resist marking by the file. Try this with known mild steel 1018 to establish a reference.

Is it magnetic? Obvious but some of the stainless steels are much less magnetic than 1018. Again compare with 1018 so that you can compare in the future.


Hope this helps.

[Fegenbush]

The previous post has great information. However, if you absolutely must know the composition of the material prior to machining, PMI is the way to go. Positive Material Identification. It uses a 'gun' to touch the surface of the material and determine its exact material makeup. Your local scrap place is likely to have one and they may do a test for you. I say may because many are protective of their equipment, as it costs anywhere from $20,000 to $50,000.

PMI in conjunction with a hardness test will tell you anything you want to know about a material. It is very useful if you have exotic alloys that you're working with that require a nice surface finish.

Hope this helps,

Fegenbush