Metal identification: How To Identify Metal Types

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Metal identification is crucial before welding because you must select the appropriate welding process, filler metal, and welding parameters.

You should be able to identify metals by their look, spark test, and other manual testing methods we’ll discuss soon.

At the bare minimum, a welder must recognize most commonly welded metals like mild steel, stainless steels, aluminum, titanium, and a few others.

Featured image for the Metal identification article

In this article, you will learn proper metal identification methods. It’s relatively simple once you get the just of it. So, let’s get started.

Metal Categories – Ferrous Metals and Nonferrous Metal

All metals are classified as ferrous metals and non-ferrous metals at the most basic level.

  • Ferrous metal contains iron. Some examples are carbon steel, cast iron, high-strength steel, gray cast iron, white iron, malleable cast iron, wrought iron, and numerous alloy steels.
  • Non-ferrous metal doesn’t contain iron at all. Commonly welded examples are titanium alloys, copper, aluminum, magnesium, lead, and nickel.

Traditional Metal Identification Methods

Since most individuals and welding shops don’t have expensive equipment to perform optical emission spectrometry, x-ray diffraction, or other modern metal testing methods, we will stick with the basics.

There are a few ways for metal identification you can perform almost anywhere, and they work very well. Those are spark testing, appearance test, magnet test, and hardness tests (this does require an impression machine).

Visual Inspection

Inspecting for color, scratch marks, chipped parts, and broken edges are the first place to start.

While we can’t conclude much from the color test, we can start classifying the metal.

  • Redish color – most likely copper
  • Gray, dark gray, black – most likely some kind of ferrous metal
  • Shiny gray, white – most likely some type of stainless steel, titanium, or aluminum
  • Gold – most likely brass or bronze
Image of a different metals and how can you visually inspect and differentiate them

Further, we need to examine the scratches, chipped parts, and broken edges. If we can see the inner metal’s texture, that can help us identify different metal alloys.

MetalColorColor and structure
Unfinished, undamaged surfaceFreshly ground or filed surfaceFreshly fractured surface
Low carbon steel like mild steelDark grayBright silvery graySoft, bright gray
High-carbon steelDark grayBright silvery grayLight gray
Stainless steelLight silvery grayBright silvery grayMedium gray
Cast iron, grayDull graySilvery grayCrystalline structure, dark gray
Cast iron, whiteDull graySilvery whiteCrystalline structure, silvery white
Malleable ironDull grayLight silvery grayFine crystalline structure, dark gray
Wrought ironLight grayLight silvery grayBright gray
LeadDark grayWhite, silvery, with a hint of blueCrystalline structure, light gray
NickelLustrous, silvery whiteBright silvery whiteOff-white
Monel metalsDark grayLight grayLight gray
AluminumLight grayWhiteFine crystalline structure, white
CopperReddish, brown, and green if oxidizedBright reddishBright red
Bronze and BrassReddish-yellow, gold-like, or brownishReddish-yellow to yellow-whiteRed to yellow

Spark Test Metal Identification

The most efficient way to achieve metal identification with limited resources is to perform a simple spark test. Take the metal and grind the metal surface using an angle grinder for two to three seconds.

As you become a more experienced metal worker, you’ll be able to identify almost all metals just by the visual spark testing technique. However, your angle grinder does need at least 4500 RPM and a relatively new grinding wheel with a coarse grit size.

image of a spark test

Ferrous metal like irons and steels produce orange to red sparks with distinctive patterns that an experienced eye can quickly identify.

Some metal doesn’t produce sparks at all. For example, aluminum won’t create sparks when ground. Combining this test with a visual inspection may help you identify if the part is aluminum. Just be careful when grinding aluminum with a regular grinding wheel. It can break because aluminum requires specialized grinding wheels that won’t load up with fine aluminum particles.

Magnet Test

Generally, iron and iron-containing metals like low carbon steel are magnetic, while nonferrous metals don’t respond to magnets. However, this is not always the case. Some stainless steels are non-magnetic too. For example, the austenitic stainless steel contains nickel, taking away magnetic properties. However, if these steels are cold worked, they could become magnetic again.

While there are many variables to consider, magnet testing is a helpful addition to other tests described above.

Hardness Test

A few hardness testing methods are used for metal identification but let’s stick to the two most popular:

  • The Rockwell method requires a Rockwell hardness testing machine that measures the depth of indentation made by the machine’s cone-shaped point.
  • The Brinell hardness test requires a similar machine, unsurprisingly called the Brinell hardness testing machine. However, unlike the Rockwell test, the Brinell hardness test measures the area of a hardened ball’s impression into the metal under a 3,000kg load. If the impressed area is large, it means that the metal is softer and belongs to soft metals, but if the indentation is slight, it belongs to hard metals.
MaterialBrinell hardness number
Lead5.0
Pure aluminum15
Copper35
Soft brass60
Hardened aluminum75
Mild steel130
Annealed chisel steel235
White cast iron415
Nitrated surface 750
Glass1550
Rhenium diboride4600

Identifying Common Metals

Let’s stop talking abstractly and apply the common metal identification methods to typical metals welders, and other metal workers need to identify daily.

Carbon Steel

It’s relatively easy to identify low-carbon steel, but beginners may have some trouble with it. This is a prevalent metal used almost everywhere, and it’s the most commonly welded material thanks to its excellent mechanical properties.

image of mild steel rebar
The most basic example of mild steel is the reinforcement rebar.
image of flat bar high carbon steel
Example of high carbon steel flat bars.

Carbon steel is made by melting iron ore and adding carbon to it to create different grades of carbon steel.

  • Low carbon steel, or mild steel, is used in almost all industries. It is ductile, malleable, relatively strong, easy to weld, and inexpensive. The carbon content is approximately 0.05–0.30%.
  • Medium carbon steel balances ductility and strength. It is often used in the automotive industry, and for large parts, thanks to its good wear resistance. The carbon content is approximately 0.3–0.5%.
  • High carbon steel is very strong but brittle, so it is difficult to weld without adequate post welding heat treatment. It is used for springs, specialized parts, tools, etc. The carbon ranges from 0.6% to 2%.
  • Cast iron has a carbon percentage above 2% and is not technically steel. It is a very brittle material but extremely strong. Still, due to very poor ductility, it can’t be welded without particular precaution and experience.

All carbon steels are magnetic, rust quickly, heavy and dense, and have a relatively uniform dark, dull color. But, when ground, you will see a shiny metallic surface appearance.

Carbon steel responds well to a spark test:

  • Low carbon steel creates a long stream of sparks with a “finger burst” pattern.
  • Medium to high carbon steel has a shorter stream of sparks with a more pronounced burst pattern. The sparks flare up at a wider angle as they go off the grinding point.
  • Cast iron creates the shortest stream of sparks, and the sparks don’t explode as much. They are narrower, and sometimes there are very few sparks coming off.

Stainless Steel

Stainless steel is carbon steel but with a minimum of 10% chromium which prevents corrosion and gives it its silvery shiny look. However, not every stainless steel is the same. There are tens of different grades, so if welding stainless steel, ensure you know exactly what type you are working with; it’s a very sensitive metal.

There are four different stainless steel categories, and it’s impossible to tell them apart visually. But, the magnet testing is helpful to determine if your stainless steel part is austenitic. If it’s magnetic, the piece is likely ferritic or martensitic stainless steel.

image of a stainless steel kitchen sink
The most basic example of stainless steel is your typical kitchen sink.
This is an excellent video demonstrating how austenitic stainless steel reacts to magnets and ferritic does not.
  • Ferritic stainless steel contains a minimal amount of carbon. It’s soft, ductile, and has limited corrosion resistance. So, if you doubt that the corroded steel you have is stainless, it is possible with ferritic type. It is magnetic, so that can add to verification.
  • Martensitic stainless steel has exceptionally high strength, poor ductility, and low fracture resistance. You can try to bend it, and if it breaks, that can be a sign that your SS is martensitic. It is often used for cutlery, aerospace applications, and medical devices.
  • Austenitic stainless steel is non-magnetic, have superior corrosion resistance, and is the most commonly used stainless steel. These are your typical 300 and 400 SS grades.
  • Duplex stainless steel is a bland of three alloys: molybdenum, nickel, and chromium. It’s tougher than ferritic SS and has a better stress corrosion cracking resistance than austenitic SS.

To learn how to weld stainless steel, refer to our separate article where we covered it in detail. Additionally, you should understand how different mechanical treatment affects the finishing surface of stainless steel.

Galvanized Steel

Galvanized steel is zinc-coated steel. This coating provides corrosion protection and gives it a unique, consistent shiny gray color making this metal identification fairly simple.

You should never weld galvanized steel without adequate protection like PAPR systems. Additionally, you must use proper welding fume extraction systems or have sufficient ventilation. Welding galvanized steel releases extremely hazardous fumes that lead to poisoning and severe symptoms.

So, it is necessary to first remove the zinc coating by grinding it off. The produced dust contains zinc and should not be inhaled. It is best to grind the zinc coating outside while wearing adequate respiratory protection.

image of galvanized steel
Example of galvanized steel. Keep in mind that the galvanization texture may be different depending on the zinc coating process. It can vary from bright silvery gray to dark flaked gray. Image credits: coremarkmetals.com

There aren’t any easy methods to test if the steel you have is galvanized or painted. So, if you are unsure, you should take every precaution before welding it.

Aluminum

An inexperienced welder may mistake aluminum for stainless steel. But it’s easy to exclude SS as an option.

Aluminum is very light, doesn’t make any sparks when ground with an angle grinder, it’s not ferrous, so it’s non-magnetic, it doesn’t rust, but it does create a dull oxide layer, and underneath it is a very shiny silvery aluminum.

image of aluminum bars

Aluminum is soft, ductile, malleable, and relatively strong. So, it’s often used in industries where strength is required, but the low weight is paramount, like aerospace and automotive industries. If you wish to learn more about welding aluminum read our full guide.

Titanium

Titanium is easy to mistake for aluminum because it’s lightweight and has a similar silver color. It has an incredible strength-to-weight ratio, but it’s not often used due to its high cost. Plus, welding titanium is challenging, so its application is limited.

However, it is often used in the petrochemical industry or when maximum strength is required for pressure tanks and vessels. It is also found in high-end vehicles (especially motorcycles) and the aerospace and medical industry. It’s a non-toxic metal, so replacement hips and medical screws are often made out of titanium.

image of titanium pipe

Unlike aluminum, titanium does create sparks when using a grinding wheel on its surface. But unlike carbon steel, its sparks are much more yellow and sometimes almost white. You can immediately tell there is a massive difference in spark test color, which is a dead giveaway that the metal may be titanium. If it’s not magnetic, has a whiteish spark stream, its lightweight, then it’s not stainless, carbon steel, or aluminum, leaving only one option—titanium.

Copper

Copper is relatively easy to identify visually. Its characteristic red color is easy to tell. Plus, it’s a non-magnetic metal. So, if you come across a painted copper metal, performing a magnet test may be your first step.

Once you conclude that it’s not a ferrous material, you can grind some paint off and scratch into its surface.

As soon as you see the red copper color, there isn’t much more to it.

image of copper pipes

Brass

image of brass fittings

Brass has a distinct shiny gold color, but in time it becomes slightly dull as oil and grease build upon it. Valves, fittings, and inlets are made of brass thanks to its excellent fit properties and its resistance to static electricity and sparks. Brass is an alloy of copper and zinc, and it’s a softer metal than bronze.

Bronze

image of bronze metal

Bronze is an alloy of copper and tin. Sometimes it’s challenging to tell bronze from brass. But, bronze has a slightly more reddish color while brass is much more gold-like. This is a soft metal often used in interior decoration, but it’s also possible to find it in the marine industry. For example, ship propellers and fittings may be made of bronze.

Lead

image of lead

Lead is a very toxic metal, and welding lead requires honoring all safety measures. To learn how to weld lead, read our full article on the topic. Lead has a dark gray, almost black color, and it’s an extraordinarily dense and soft, malleable metal. It is often used in the medical field as protection against X-rays and other radiation forms.

Conclusion

It’s often difficult to tell metals apart unless you take many metal properties into consideration, which is the best way of metal identification. Unless you are looking at copper, it takes analyzing various metal characteristics like appearance test, weight, shine, observing the spark stream, and magnet behavior.

So, don’t just rely on one aspect to identify the metal. As you gain more experience, metal identification will become second nature, especially with common metals like carbon steel, stainless, and aluminum. But, there are also modern metal identification methods like laser induced breakdown spectrometer and unlike popular traditional testing methods, we discussed here, modern metal testing methods are far more conclusive.

Resources:

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Adam Mason

Welder by trade for a decade and more. Now also a web designer and a blog owner. Doing product reviews and writing blogs about welding trade and perks and minuses of being a welder.

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