Session: 5. Properties of metals

Total Time: 1 hour

Objectives:

* To determine the type/grade of available junk steel
* To discuss the properties and characteristics of various grades of steel
* To identify potential uses of available steel

Resources:

* Attachment 5-A, "Identifying and Testing Scrap Metal"
* Andrews, "Carbon Content of Steel for Different Uses," page 127
* Weygers, "Steel for Blacksmith," page 15

Materials:

A variety of junk steel salvaged from wrecked autos and rail cars; e.g., leaf springs, coil springs,
axles, torsion bars, linkage rods, push rods, valves, rail tie, plate, rail spikes, rail section, side or
bed plate from rail car, sill from rail car, etc.

Procedures:

Step 1. (10 minutes)
Explain the objectives and distribute Attachment 5-A, "Identifying and Testing Scrap Metal." Ask the group to read it.

Step 2. (15 minutes)
Select a piece of junk steel and demonstrate how to identify its type and properties.

Step 3. (15 minutes)
Have participants divide into four groups and select, identify, and describe the properties of an item of junk steel.

Step 4. (10 minutes)
Reconvene the groups and have them report on their junk item.

Step 5. (10 minutes)
Have participants examine the chart on Page 4 of the Attachment and identify potential uses of the scrap items listed.

Attachment 5-A

IDENTIFYING AND TESTING SCRAP METAL

Identification

A variety of unknown types of steel are encountered when working with scrap metal. Several simple tests exist which the blacksmith may use to identify these unknowns. Because of logistics, it may not be possible to perform all of the tests, but with one or two of these tests and some experience, one can learn to recognize useful metal at a glance.

There are several types of "steel" that (for the most part) we will not be dealing with in the context of these classes. They are: cast steel, cast iron, high alley steels, and stainless steel.

The other common metals found in scrap that we will not deal with are copper and aluminum; we will use brass for brazing.

The types of steel that we are looking for may be divided, for the sake of simplicity, into three categories: low carbon, medium carbon, and high carbon steel. The percentage of carbon present determines the major properties (i.e., hardness, fusibility, toughness). Only the medium and high carbon steel; are temperable.

Low Carbon: contains about .05-.30% carbon and of the three, because of the relative low cost of production, it is used extensively. Some sources of low carbon scrap are car bodies, some types of rebar, old nails, bolts, panels on railroad cars, railroad spikes, some types of angle iron, rolled pipe, some types of wire, nails, straps, hinges, tanks, drums, etc. It is manufactured in rolled bars, and the most common ones are round, flat or square bars of ¼ - 1". It is NOT temperable but may be forge welded.

Medium Carbon: contains roughly .30-.60% carbon. It is a harder material (harder to work and harder to find), and may be tempered. It is the most available temperable scrap metal. Some sources are springs, axles, torsion bars, gearshift bars, shock absorber bars, and, in general, anything that must stand up to a higher degree of stress and strain. It will not bend easily like mild steel. It is also used where tempering is required (e.g., auto/truck axles, auto/rail car springs, leaf springs, steering columns).

High Carbon: contains roughly .60-1.5% carbon, and usually has an alloy present. It is much harder than medium carbon, but is available in scrap sometimes as old pneumatic drill bits, old bulldozer blades, milling cutters, metal saws, cutting dies, threading dies, and files.

Testing

Spark Test: Hold a piece of the material in question against a high-speed grinder and closely observe the sparks given off. Generally, the brighter and more explosive the spark, the greater the carbon content of the steel in question. Try known pieces and study their relationships.

Sound Test: If the piece is small enough, lightly toss it onto a concrete floor or stone. Listen for the sound, and compare the sound to known pieces.

Cold Chisel Test: Using a sharp cold chisel and light blows, attempt to cut the beginning of a curl from the material in question, noticing the following points:

- Does the material cut easily or does it resist?
- If it resists, does it nick the chisel blade?

Again, compare a known material with the piece in question.

File Test: This test is fairly self-explanatory. Using a file, test the surface for hardness. This also reveals the color of unoxidized metal.

Hardening Test: Take the piece in question and heat its tip to light cherry or dark orange and quench it in water. Test it with a file, and note:

- Does the file slide over it like glass?
- Do the teeth bite slightly, or is there no difference between the hardened part and the rest of the piece?

Again, if in question, test against a known piece.

Previous Use: One of the most important clues in determining the type of steel in question (whether tempered or not) is to be found in its previous use. If a piece of steel would have needed to be exceptionally tough, tempered, and/or abrasive-resistant to perform Its function (e.g., torsion bar, spring, pneumatic bit), then we can assume with greater certainty that it is some type of medium to high carbon steel.

TEMPER TEST

If an untested spring is to be used for tool making, it is advisable and practical to perform the temper test.

Temper test

Flatten evenly a 4" section.

Perform the water quench (heat reserve method) on the end, quenching before the colors run the entire length of the piece.

Strike with hammer.

Critical color is determined by where the break occurs in relation to the patina. Tools from this spring should then be tempered at the color/temperature prior to the critical color.

SCRAP METAL IDENTIFICATION - A. Atkeison