Alloy Artifacts

Exploring Ingenuity in Iron ...

Introduction

Since the term "alloy steel" is used very frequently on this site, we thought that some of our readers might be interested in learning more about the alloys used for tool making. We've divided the material here into two sections, the first covering the industry standard alloys commonly used for tools, and the second with information gathered by testing the alloy content of actual production tools.

Standard Alloys for Tool Making

Table 1 below lists some of the AISI standard alloy steels used for making tools. The AISI number is a commonly used reference for steels and can be used to find more information about the alloy.

The chemical elements in the alloys are listed by their standard abbreviations, in particular carbon (C), manganese (Mn), chromium (Cr), nickel (Ni), molybdenum (Mo), and vanadium (V). Some additional elements are reported, including phosphorus (P), sulfur (S), and silicon (Si). Phosphorus and sulfur are usually regarded as impurities whose content must be strictly controlled.

Alloy Analysis Using X-Ray Fluorescence

X-Ray Fluorescence (XRF) is a technique widely used for measuring the metallic element content of steel alloys and other substances. The testing is non-destructive, quick, and inexpensive, making it ideal for checking the content of various alloys.

Principles of X-Ray Fluorescence

The basic principle of X-ray fluorescence (XRF) is based on the fact that most of the chemical elements (including all of the metals) will emit radiation when excited with sufficiently energetic X-rays. This secondary radiation (termed fluorescence) is emitted at precisely defined wavelengths (or energies) characteristic of each specific element, and is generally in the X-ray spectrum as well. Thus the most basic XRF analyzer would consist of a source of X-rays and a detector capable of determining the wavelength and intensity of the emitted radiation.

For more information, the Wikipedia article X-Ray Fluorescence[External Link] provides an excellent introduction.

Measured Composition for Tools

We were able to have a small number of tools tested on an X-ray fluorescence (XRF) analyzer and have reported the test results in Table 2 below. The XRF machine used for the analysis was set up for measuring the specific metal content of scrap metal and did not report the carbon content, as this was not relevant for the application.

The items tested were actual finished tools that can be seen elsewhere on this site. As finished tools, several of the examples retained at least partial chrome or nickel finishes, which has resulted in skewed measurements for chromium and nickel content in some cases. The suspiciously high readings have been noted with an asterisk (*) in the table.

Anyone wishing to do comparable testing on their own tools would be well advised to select examples that are unfinished, whether originally or courtesy of extensive rust, or that have been ground down such that the finish is no longer present in some areas. XRF testers generally look at only a small spot, so if the finish is missing from that area, the results should indicate the base metal.

Discussion of Results

[Pending arrival of round-tuits]

References and Resources

Information on particular alloy steels was obtained from Machinery's Handbook, Revised 21st Edition, published in 1979 (and many other editions) by Industrial Press Inc. (New York). This tome of 2,400+ pages is a standard reference for machinists, mechanical engineers, and anyone needing information on machine shop practice.

The interested reader will find numerous online articles on XRF available via a Google search. A good starting point is the Wikipedia article X-Ray Fluorescence[External Link], which provides an excellent background on the physics of fluorescence, as well as a discussion of the applications and links to manufacturers of XRF analyzers.

Another good reference on XRF is available at Geochemical Instrumentation and Analysis[External Link].