Easy Test Needed To Tell 4140 From Carbon Steel

[Linstrum]

In my shop and perhaps also in the field, I need an easy way to distinguish chrome-moly and chrome-moly-nickel steels (like 4130, 4140, and 4340) from the various grades of plain carbon steel. The problem is that the superficial characteristics of those steel groups are identical. For example, those families all make the same type of grinding sparks, are magnetic, all have the same dark silver color when polished, they all can be hardened and tempered by identical heat treatment methods, and their specific gravities fall in the same range. Where their big differences lie are in their strengths after heat treatment, which I don't have any good way of measuring, or for that matter, measuring in the field. I know about the alloy test kits but even the "cheap" ones sell for over $200. What resources are there that can help me with this problem? Thanks,-------Richard Linstrum

 

[FrancisEMoore]

In the early days of my training as an engineer, we used a cheap acid test for these types of analysis. Since you are asking to tell the difference between 4140 and 4130, I think you are trying to reach too far for a cheap test. I have a portabel OES that can tell the difference between those materials, but it is probably the only instrument that will do it, and it retailed for over $50,000 when I purchased it a couple of years ago. I would suggest you check into some acid tests and see how far you can get with them. XRF's will not be able to help you with carbon contents, and they retail for over $25,000.

Frank Moore, P.E.
Consulting Metallurgical Engineer
Kansas City Power and Light Co.

 

[weldmete]

If you can't afford a metal analyzer then you can either hire someone that has a metal analyzer to come out to your location and examine each piece of metal or you can cut off a small piece of metal from each plate, bar or pipe and send the samples to a test lab to be analyzed (be sure to identify the pieces you cut with the metal you cut it from). It just depends upon how many items you need to have analyzed. Once you have the metals analyzed you need to color code or stamp the different metals you have so you don't lose track of what you have. You need to identify the new metals you buy, as well, so you don't get into this predicament again.

 

[unclesyd]

The acid test mentioned is: A 1/1 solution of laboratory grade Hydrochloric Acid saturated with Sulfur Dioxide gas. Look for a purple spot. This is actually a test for Moly. There is a manufacurer of a chemical spot test for various elements in metal. I'll try to find a name. Also there is a spark test that I used while checking scrap for a foundry that works well with a little practice. Check known materials against a clean abrasive wheel. The Cr-Mo material will have a very defenitive "bud break" arrow at the tail of the spark.
This is old info:
Alloy 410
System Scientific Laborotories
Dumont, Nj

 

[GRoberts]

If you are only tring to distinguish between carbon steel and alloy steel, and not between the various grades of alloy steel, (i.e. between 4130 and 4140), then a portable hardness tester ought to do the trick for you.

 

[stanweld]

For 4130 and 4140, a spark test can be used. This takes considerable skill but can be quite effective. This method was used by Bethleham Steel back in the late 60s and early 70s. I date myself since I did some of this testing in the the 60s and was able to detect about .05% differences in Carbon content and was easily able to distinguish between 4130 and 4140.

 

[stanweld]

Beside spark testing and chemical spot checking, we also used eddy current testing to differentiate 4140 and 4340.
When portable XRF analyzers became available to us in 1971, that became the primary method to separate "mixed" alloy steels - except for carbon content.

 

[mdighe]

I had opportunity to work in the raw materials lab in a big overseas automotive manufacturer during my co-op. All this lab did was check the incoming raw forgings and casting.

I dont know the name of the instrument, but it involved striking an arg between the part and an electrode and looking at the spart through a set of lenses and prism. The spark had the characteristic wavelengths of light for the alloying elements. The eye piece also had a standard wavelength guide for the common alloying elements. All you did was match up the line spectrum with the standard.

It was very fast, easy, reliable and requierd no maintenance.

 

[NickE]

mdighe-- Sound like and optical emmission spectrometer w/o the intensity measuring part of the assembly. hmmm neato...



Nick
I love materials science!

 

[patdaly]

GRoberts, if he happened to have 4140 in the annealed stste, would not a portable hardness tester give a false reading?

 

[GRoberts]

Cheap and easy solutions are seldom foolproof. An "average" annealed 4140 (approx 190-210HB) would be slightly harder than an "average" carbon steel (hot rolled at least(approx 150-180HB)). I'm sure there would occasionally be an overlap. For this test to be effective, the user would need to know what ranges he expects the material to fall into and develop acceptance criteria for a "difinitive" result. It may or may not meet the needs of the original poster, but if it meets his needs, it would be quick and inexpensive.

 

[MOB1]

TO mdighe
THE INSTRUMENT IS CALLED A 'METASCOP' AND THE SPECTRUM IS VIEWED THROUGH AN EYEPIECE AND COMPARED WITH STANDARDS.