When you are selecting a metal to use in fabrication, to perform a mechanical repair, or even to determine if the metal is weldable, you must be able to identify its underlying type. Some field metal identification tests can be used to identify a piece of metal.
It is necessary to know metal composition to produce a satisfactory weld. Metal workers and Welders must be able to determine various metal products so that proper work methods may be applied. For equipment, drawings (MWOs) should be available. They must be examined to determine the metal to be used, and any heat treatment if required.
After some practice, the welder or metal worker will learn that certain parts of equipment or machines are forgings, others are cast iron, other and so on.
- 1 Common Metal Testing Methods
- 1.1 Metal Identification Testing Order
- 1.2 Summary Metal Identification Chart
- 1.3 Surface Appearance Metal Test
- 1.4 Metal Filing Test
- 1.5 Metal Spark Test
- 1.5.1 What is a spark test?
- 1.5.2 Do Not Use Spark Testing on Nonferrous Metals
- 1.5.3 Studying The Spark
- 1.6 Magnetic Tests
- 1.7 Non-magnetic Metals
- 1.8 Metal Chisel, Fracture or Chip Tests
- 1.9 Aluminum and Magnesium Test
- 1.10 Metal Flame or Torch Test
- 1.11 Hardness Tests
- 1.12 Chemical Analysis
- 1.13 Steel Bar Color Coding
- 1.14 Free Additional Reading on Metal ID
- 1.15 References
Common Metal Testing Methods
There are seven tests commonly used to identify metals. Each is summarized below. Use tests along with information on the mechanical and physical properties of each metal.
These tests are as follows:
- surface appearance
- spark test
- chip test
- magnet test
- torch test
- chemical test
- hardness test
Metal Identification Testing Order
When conducting a metal identification test, we suggest performing tests in the order outlined in these metal identification charts, starting with the easiest to execute:
If the metal is not magnetic follow the following test sequence
For slightly magnetic metals go down this test sequence
For magnetic metals follow this test sequence
Summary Metal Identification Chart
Use this metal identification chart to quickly identify methods that can be used for scrap metal identification or other metal ID requirements.
Surface Appearance Metal Test
Sometimes you can identify a metal simply by its surface appearance. The table below indicates the surface colors of some of the more common metals.
The appearance test includes such factors as appearance and color of un-machined and machined surfaces.
Role of Shape and Form
Shape and form give certain clues as to metal identity. The form can be descriptive; for example, shape includes such things as cast engine blocks, automobile bumpers, reinforcing rods, angle irons or I-beams, pipe fittings pipes.
Consider the form and how the part is made. Castings will have signs of parting mold lines, cold rolled or extruded surfaces or hot rolled wrought material. As an example is a piece of pipe is cast, it could be cast iron or wrought iron, which would typically be composed of steel.
Color As A Clue in Metal Identification Methods
A strong clue in metal identification is color. It can differentiate precious metals, magnesium, aluminum, brass, and copper. If there are signs of oxidation, remove it via scraping to reveal the color of the unoxidized surface. Scraping aids in the identification of copper, magnesium, and lead. Rust or oxidation on steel is a sign that can be used to differentiate corrosion resisting steels from plain carbon steels.
Fractured surfaces or filed metal surfaces can also provide clues. Working with a metal sometimes leaves distinctive marks that can help with identification.
- Malleable iron and cast iron can have sand mold evidence.
- High carbon steel reveals rolling or forging marks
- Low-carbon steel shows forging marks
Role of Surface Feel and Examination
The surface feel can provide additional indications of metal type. For example, stainless steel is rough when not finished, and metals such as Monel, nickel, bronze, brass, copper and wrought iron are smooth. Lead has a velvety appearance and is smooth.
Limitations of a surface examination are that you often do not have the information needed to classify the metal.
Metals such as malleable iron and cast iron often show evidence of sand mold.
Surface Color vs. Other Tests
When the metal surface does not provide enough information for identification other tests can be used. Tests that are simple to perform in any shop include:
- magnetic tests
- spark tests
- chip test
- magnetic tests
Metal Filing Test
Metal Spark Test
A metal spark test is useful for identifying the type of metal and in the case of steel, determining its relative carbon content. Spark tests use sparks given off when holding metal against a grinding wheel as a way of classifying iron and steel.
What is a spark test?
The test involves holding a sample lightly against a grindstone or abrasive wheel. Take note and visually inspecting the spark color, shape and length, a metalworker can with accuracy identify the metals.
While the test is fast and extremely convenient, it does not replace chemical metal analysis. It is a quick method for sorting metals where the spark characteristics are known such as when sorting mixed steels.
When metal is held lightly against a grinding wheel, the different kinds of steel and iron produce sparks that vary in color, shape, and length.
Carrier Line Definition
This test is particularly useful when identifying cast steel or cast iron scrap metal. These metals create give off small particles of the metal which are torn off quickly, becoming red-hot. As they shoot off the abrasive wheel, they follow what is called a carrier line or trajectory.
When examining a “carrier line” look at the spark length, stream, and color.
One advantage of the spark test is that it can be used with all types and stages of metals, including finished parts, machined forgings and bar stock in racks.
When using the spark test on steel, some steels have the same carbon content but differing alloying elements, such as the difference between unalloyed and low alloyed steel. Steel has different types of alloys that can affect the characteristics of the bursts in the spark picture, the bursts themselves and the carrier lines. Alloys can accelerate or slow the carbon spark or make carrier lines darker or lighter.
For example, the metal Molybdenum looks like an orange-colored, detached spearhead at the end of the carrier line. When working with nickel, it can suppress the carbon burst effect. That said, the nickel spark can be identified by brilliant white light in tiny blocks. The carbon burst is contained by silicon even more than the nickel. Silicon causes the carrier line to end in a white flash of light abruptly.
Do Not Use Spark Testing on Nonferrous Metals
Conducting a spark test is not helpful for identifying nonferrous metals such as nickel-base alloys, aluminum, and copper. These metals do not show significant spark stream. That said, this method can be used to differentiate between nonferrous and ferrous metals.
How To Conduct a Spark Test
You can use either a portable or stationary grinder for spark testing. In either case, the speed on the outer rim of the wheel should not be less than 5,00 feet per minute (1,525 m) to get a good spark stream. The abrasive wheel should be very hard and kept clean to produce a true spark rather than a coarse spark.
Use a grinding wheel that has a hardness to last for some time, but soft enough to maintain a free cutting edge. Conduct spark tests in little light to make it easier to see the spark color. As a recommendation, use standard metal samples when comparing sparks with test patterns.
- When holding the metal piece, position it so that the stream of sparks moves across your line of vision. Steadily hold the metal park still and then touch the high-speed grinder wheel to the metal with enough pressure to create a spark stream that is horizontal and about 12 inches (30.48cm) long. The spark stream should be at a right angle to your line of vision. Be careful not to have too much wheel pressure pressing against the metal since increased pressure raises the spark stream temperature. Increased pressure also makes it appear as if the metal has a higher percentage of carbon content.All aspects of the spark stream (near the wheel, mid-stream, incandescent particles at the end of the stream, are noted as part of the identification process. Through trial and error, you will get a feel for the right amount of pressure to apply to the project, without changing grinder wheel speed, to get an accurate spark stream.
- When looking at the spark stream, observe 1/3 of the way from the tail end. Watch how the sparks cross your line of vision. Attempt to form an image of an individual spark. Once your do this, then look at the entire spark stream.
Studying The Spark
The spark resulting from the test should be directed downward and studied. Spark length, color, activity, and shape relate to characteristics of the material being tested. The spark stream has specific items which can be identified.
What are spark test carrier lines?
Carrier lines are straight lines of sparks. They are usually continuous and sold. They may divide into three short forks or lines at the end of the carrier line.
What are the types of spark streams?
A sprig is a spark stream that divides into more lines at the end of the stream. They occur in different locations on the carrier line. These sprigs are called either fan bursts or stars. At times, a carrier line slightly enlarges for a short length, continues, and then enlarges for a short period. When you see heavier portions at the end of the carrier line, they are called buds or spear points.
- If there is a presence of high sulfur levels, it results in thicker areas in the carrier lines. These thick areas are called spearheads.
- Cast iron metal has extremely short streams
- Most alloy steels and low-carbon steels have relatively long streams.
- Steels usually have white to yellow color sparks
- Cast irons are reddish to straw yellow
- Sparks in long streaks that have a tendency to burst into a sparkler effect are seen with .0.15 percent carbon steel.
- Carbon tool steel exhibits pronounced bursting
- 1.00% Carbon Steel shows minute and brilliant sparklers or explosions. As the carbon content increases, the intensity of bursting increases.
Proficiency in Spark Testing Ferrous Metals
If you are interested in becoming proficient as a spark tester of ferrous metals, collect several types of metals for practice. Prepare the metals so that they are the same shape and size so that this alone doesn’t indicate the identity. Put a unique number on an each sample. Then create a list of names with the corresponding numbers.
Then, test each sample, recording the name after you do the test. Repeat until you get good enough to identify each sample.
Abrasive Wheel Safety
Never use an abrasive wheel that is out of balance or cracked because the vibration can cause the wheel to break or shatter. A shattering wheel can be dangerous to anyone standing in the area.
Before using, always check the wheel for cracks and secure mounting.
Be sure that any new grinding wheel is sized correctly. As the size of the wheel radius increases, the rim speed increases, despite the face that the motor rpm is the same. If using an oversized wheel, there is a risk that the speed at the rim (peripheral speed) and any centrifugal force becomes so great, that the wheel comes apart. Only use a grinding wheel that is designed for use at a specific RPM.
To protect against a wheel that shatters, place guards on grinders as protection. DO NOT use a grinder when the guards are missing.
Stand to one side when activating the grinder. Stay out of line with the wheel to protect against a wheel that bursts.
Never put sideways pressure on the abrasive wheel or overload a grinder unless it is expressly built to withstand such use.
Always wear a face shield or safety goggles when using the grinder. Ensure that the tool rest (the device that helps the operator hold the work) is adjusted to the minimum clearance for the wheel. Move the work across the wheel face to prolong wheel life. Moving the work minimizes grooving and any wheel dressing.
When working with a grinding wheel, keep fingers clear of the wheel. Also, watch for any loose clothing or rags that can become entangled in the wheel.
When using an abrasive wheel, do not wear gloves.
Never hold metal with tongs while grinding.
Never grind nonferrous metals on a wheel intended for ferrous metals because such misuse clogs the pores of the abrasive material. This buildup of metal may cause it fly apart after becoming unbalanced.
Grinding Wheel Care
Recondition frequently to keep the grinding wheel in good condition. The process for cleaning the periphery of the wheel is called dressing. The dressing process involves breaking away any dull abrasive grains to create a smooth wheel surface.
The wheel dresser is used for dressing grinding wheels on bench and pedestal grinders.
Magnets are frequently used for metal identification. Ferrous iron-based alloys are magnetic, while nonferrous metal is non-magnetic.
Using a small pocket magnet a test can be performed where with experience, it is possible to distinguish between a material that is slightly magnetic with one that has a strong magnetic pull.
The nonmagnetic materials are easily recognized.
Magnetic metal identification tests are not 100-percent accurate because some stainless steels are nonmagnetic. In this instance, there is no substitute for experience.
There are three major groups of stainless steel:
- Martensitic: contain 11.5% to 18% chromium and up to 1.2% carbon, sometimes some nickel
- Ferritic: contain 10.5% to 27% chromium and are nickel-free
- Austenitic: contain 16% to 26% chromium and up to 35% nickel – highest corrosion resistance. These steels have good weldability (do not heat before welding.) The most common type of Austenitic steel is 304 grade or 18/8 (18% chromium and 8% nickel.) Used in food processing, dairy, and aircraft industries.
If a metal clings to a magnet, it means that it is ferritic. It is stainless steel, low-alloyed or unalloyed steel or normal steel. Note that stainless steel has poor weldability while low alloy or unalloyed steel has high weldability. Ferritic steels are in architectural and auto trim applications. It has less anticorrosion applications and is not hardenable by heat treatment.
Strongly magnetic materials include:
- Types of Steel
- Carbon steel
- Low-alloy steel
- Martensitic stainless steels
- Pure nickel
- Iron alloy
Slightly magnetic reactions are from metals that include:
- High-nickel alloys
- Stainless steel of the 18 chrome 8 nickel type when cold worked, such as in a seamless tube.
Nonmagnetic materials include:
- Copper-base alloys
- Aluminum-based alloys
- Zinc-base alloys
- Annealed 18 chrome and 8 nickel stainless
- Precious metals
- Austenitic stainless steel
Metal Chisel, Fracture or Chip Tests
Several metals can be identified by examining chips produced with a hammer or chisel or the surface of a broken part. The only tools required are a cold chisel and a banner. Use the cold chisel to hammer on the edge or corner of the material.
Once chiseled, the surface will reveal the base metal color without oxidation. This is true for magnesium, lead, and copper. In some cases, an indication of the structure is the roughness or coarseness of the broken surface.
The ease or difficulty of chipping the metal part also indicates the level of ductility. If a metal piece bends easily without breaking it is one of the more ductile metals. It is one of the brittle metals if it breaks quickly with little or no bending.
A simple test used to identify an unknown piece of metal is the chip test. The chip test is made by removing a small amount of material from the test piece with a sharp, cold chisel.
The material removed varies from a continuous strip to small, broken fragments. The chip may have smooth, sharp edges; it may be coarse-grained or fine-grained, or it may have saw-like edges.
Chip size is a critical input in metal identification. The ease with which the chipping happens is considered since it indicates metal hardness. A chip will break apart if it is a brittle material and for a continuous chip, it means the metal is ductile.
Metals With Continuous Chips (easily chipped and the chips do not tend to break apart)
- Mild steel
- Malleable iron
Brittle Chips: small broken fragments
- Gray cast iron
Chips Hard to Obtain: because of metal hardness, but can be continuous
- High-carbon steel
The information in the table below can aid in metal identification using this test.
Aluminum and Magnesium Test
To test for the presence of aluminum and magnesium perform the following steps:
- Wash with clean water and wait 5 minutes. If you see the following colors, it indicates the presence of the indicated metals:
- Drip on the clean area one to two drops of 20% caustic soda (NaOH) solution.
- Clean an area of the metal.Black: Al + Cu (copper), Ni (Nickel) or Zn (Zinc)
Grey/Brown: AL + Si (silicon, over 2%)
White: Pure Aluminum
No color change: Magnesium (Mg)
Metal Flame or Torch Test
Using an oxyacetylene torch, a welder can identify various metals by studying how the puddle of slag and molten metal looks and how fast the metal melts during heating.
When a sharp corner of a white metal part is heated, the rate of melting can be an indication of its identity.
Hardness quality is complex and requires a review of the metal’s physical qualities.
It is most often defined regarding the method used for its measurement and usually, means indentation resistance. Hardness may be related to wear resistance since one measure is scratch resistance. The word “hardness” is sometimes used to refer to the temper or stiffness of wrought products because tensile strength is related to the indentation hardness of the metal. The cutting characteristic of metal, when used as a tool, is sometimes called its hardness, but with experience, you will see how the various indications of hardness are not the same.
The following describes the processes for the performance of various hardness tests.
The file test is a less precise test of hardness. The file test is a method of determining the hardness of a piece of material by trying to cut into it with the corner edge of a file. The hardness is indicated by the file bite. This is the oldest and one of the simplest methods of checking hardness; it will give results ranging from quite soft to glass hardness. The principal objection to the use of the file test is that no accurate record of results can be maintained as numerical data.
The table below summarizes the reaction to filing the relative Brinell hardness, and the possible type of steel.
Rockwell Hardness Test
The Rockwell Hardness Test uses as Rockwell hardness testing machine to measure the impression depth when using a known load to make by a hard test point. Soft metals will result in a deeper impression and low hardness numbers. It is more difficult to make an impression using hard metals, resulting in higher hardness numbers.
A dial indicates the hardness number. In this test, a 1/16″ steel ball for softer metals or a 120° diamond cone for hard metals is pressed into the surface by a deadweight acting through several levels. The dial gage indicates hardness using the Rockwell “B” and “C” scales. The Rockwell number will be higher, the harder the piece. As an example, you will not see a reading of more than 30 to 35 on the Rockwell “C” scale for machinable steel. At the same time, you will see a reading of 63 to 65 for a hardened speed cutter. A “C” scale and a diamond point are needed when doing a hard steel test. If testing nonferrous metal, use a “B” scale and a steel ball.
Brinell Hardness Test
The Brinell test is similar to the Rockwell test. The difference between Rockwell and Brinell is that the Brinell test looks at the area of the impression. The test is conducted by forcing a hardened ball 10mm in diameter into the surface of the metal being tested.
For soft materials such as brass and copper, the ball has an applied pressure of 500 kilograms. The pressure changes to 3,000 kilograms for materials like steel and iron. With an applied load, a small microscope is used to measure the diameter of the impression.
The metal hardness number is determined by dividing the load that was applied by the impression area. This is then compared to the division results in a hardness conversion table. The table indicates the metal number.
With this process, the hardness is measured by the height of rebound of a diamond pointed hammer after it has been dropped through a guiding glass tube onto the test piece and the rebound checked on a scale. The harder the material used, the greater the rebound of the hammer because the rebound is directly proportional to the resilience or springiness of the test piece. The height of the rebound is recorded on a gage.
Since the scleroscope is portable, it can be carried to the work enabling tests to be performed on a large section of metal too heavy to be carried to the work bench. The indentations made by this test are very slight.
Vickers Hardness Test
The Brinell hardness method is similar to the Vickers hardness testing method. The penetrator used in the Brinell test is a round steel ball while a Vickers machine relies on a diamond pyramid. The impression made by this penetrator is a dark square on a light background. This type of impression is easier to measure than the circular impression. One key advantage if that the diamond point doesn’t deform like when using a steel ball.
Some metals can be identified using a chemical test. These test can be performed right in the metal shop. Chemical analysis is used to identify metals using a system developed by the Society of Automotive Engineers (SAE.)
Monel vs. Iconel Identification
Inconel can be distinguished from monel with one drop of nitric acid applied to the surface. It will turn blue- green on Monel but will show no reaction on Inconel.
Stainless Steel Identification
A few drops of a 45% phosphoric acid will bubble on low-chromium stainless steels.
Magnesium vs. Aluminum Identification
Aluminum can be differentiated from Magnesium by using silver nitrate, which will leave a black deposit on magnesium, but not on aluminum.
Numerical Index System
One of the most widely known steel numbering systems for steel specifications and compositions is the one established by the Society of Automotive Engineers (SAE), known as SAE designations. The specifications were originally intended for use in the automotive industry; however, their use has spread into all industries where steel and its alloys are used. As the title implies, this is a numerical system used to identify the compositions of the SAE steels. With only a few exceptions, plain steels and steel alloys are identified by a four-digit numbering system. With this procedure, shop drawings use numbers and blueprints to partially describe the composition of the materials referred to in the drawings.
Numbers use 4 or 5 digital codes for ferrous metals.
- First digit: Type of alloy (e.g.; 1 = steel)
- Second and third digits indicate the main alloy in whole percentage numbers.
- The last two or three numbers is the carbon content in hundredths of 1 percent.
To provide a better understanding of the SAE system, assume that a shop drawing indicates the use of 2340 steel. The primary alloying element or type of steel is the first digit to which it belongs; in this case, a nickel alloy. In the simple alloy steels, the second digit indicates the approximate percentage of the predominant alloying element (3 percent nickel).
The last two digits always indicate the carbon content in points, or hundredths of 1 percent (i.e., 0.40 hundredths of 1 percent carbon). From this explanation, it can be seen that a 2340 designation indicates a nickel steel of approximately 3 percent nickel and 0.40 hundredths of percent carbon.
Steel Bar Color Coding
A color code established by the Bureau of Standards of the United States Department of Commerce for making steel bars. Markings are applied by painting the ends of metal bars.
The work of preparing this color code was undertaken initially at the request of the National Association of Purchasing Agents.
- Solid colors: usually mean carbon steel
- Twin colors: designate alloy and free-cutting
Free Additional Reading on Metal ID
Metal Identification Test Sequence: Free PDF with a recommended testing sequence for magnetic, slightly magnetic and non-magnetic metals.
“Metal Tests: How to Identify Metals for Welding” . N.p., n.d. Web. 18 Feb. 2017
“SPARK TEST – tpub.com.” I N.p., n.d. Web. 18 Feb. 2017
“Fundamentals of Professional Welding – Free-Ed.Net.” . N.p., n.d. Web. 18 Feb. 2017
“MECHANICAL PROPERTIES OF METALS AND ALLOYS ” . N.p., n.d. Web. 18 Feb. 2017