The art of testing steel

"STEEL is steel", some will say. “So why try? But have you never heard of nickel steel, tungsten steel or cobalt steel? There are some very important differences.

To illustrate: high-speed trains run on tracks that can really be penalized. They must be able to withstand extreme wear. It requires special steel containing 12 to 15% manganese.

There are even housewives chosen for steel! You don't want a guy. Polished cookware with up to 12% chromium and maybe nickel is not just "steel". It is made of stainless steel. And there are many kinds of stainless steel; For example, some are modified to be more resistant to corrosion than others.

Thousands of people who work in workshops and factories know that each product manufactured requires a specific type of steel. There are different types. So how can you identify the right one? In general, just looking at metal is not enough to tell. Does the worker have to send a sample to a laboratory for chemical analysis? It would be very expensive and take a long time. Obviously, there has to be a more practical way.

A color coding system

Steel fabricators mark the ends of steel bars produced in use by color. Matching color tables are provided to inform the user exactly which steel alloy to select from the basket.

As you may know, an alloy is created when two or more metals are melted. For example, copper and zinc together form the brass alloy. In addition to iron, alloy steels also contain several elements. They can be added to make the steel harder or more corrosion resistant or flexible, etc. Keep in mind that a combination of steel and chrome (possibly with a little nickel) is needed to make lightweight stainless steel pans.

What if we have different types of steel bars on hand and the color coded tips are cut or the color chart cannot be found? Courage, all is not lost.

Spark tests reveal the unknown

There is a way to find out what kind of steel you have on hand. This can be done by spark testing, an ancient art recently developed in modern industrial science. With this technology, you can determine not only the chemical composition of the metal, but also the properties that are removed from the steel by decarbonization and heat treatment.

Sparks are created when a piece of metal hits a grinding wheel. Fast, non-destructive and accurate spark tests detect the presence of most alloying elements in metal. A high speed portable grinder is used. The 6.3cm long wheel can reach 15,000-20,000 RPM without breaking. The impeller should be cleaned before anyone starts the spark test. Otherwise, you may already have steel particles that will give deceptive results.

The constant pressure between the wheel and the steel sample is very important. This pressure must be sufficient to generate a spark current about two meters long. "But," you ask, "what does he do to create sparks?"

Well, those sparks reveal the unknown to the discerning eye. In the flow of sparks, each element creates its own pattern and color. The quantity of an element present in steel is determined by observing the frequency of its characteristic spark. It is therefore possible to detect the presence of elements such as carbon, manganese, silicon, nickel, chromium, molybdenum, tungsten, copper, aluminum, titanium, vanadium and colombium. Therefore, an experienced spark tester can select the manganese steel needed to make durable railway tracks.

There are two general categories of steel: common carbon steels and alloy steels.

Ordinary carbon steel

Let's see when a piece of carbon steel is firmly placed against a high speed wheel. The general appearance of the spark will help determine if it is carbon steel or carbon steel. The low carbon content produces long and narrow fluxes, while the high carbon steels have short and wide fluxes.

We must also pay attention to the carrier lines, that is, the individual paths that make up the spark current. These are made up of small particles of steel which are removed from the steel rod by rubbing the wheel. The heat created by pulling on a particle and the friction created by moving it through the air causes the particle to glow. Well, every little piece of steel looks like a little meteor moving through space!

Because low carbon steel is soft, the larger parts will come loose from the steering wheel. Therefore, the individual guides are wider and due to the mass effect, they glow more than the small particles of harder and more brittle carbon-rich steel.

The type of blast and the shape near the end of the guides will more precisely determine the carbon content of the steel. Shoots vary in size, shape, form, intensity and distance from the wheel. A low carbon content results in fewer hairpin chips, while a high carbon content gives a lot of star chips. A look at the attached illustration shows some of the differences just mentioned.

As the carbon content increases, the density of the spark increases. This is seen in the middle of the stream. These differences can be seen in the attached illustration. Keep in mind, however, that the correct pressure of the steel sample against the wheel is extremely important in assessing the density.

Alloy Steel Spark Test

When testing sparks in alloy steels, special factors must be considered, as each element and the percentage of each element present in the steel create individual spark properties and color effects.

One factor that can be described as the individual brand of each item is its characteristics. The higher the content of the alloying element in steel, the more pronounced properties the element has in the spark current. For example, suppose you are testing an unknown steel and looking for an "arrowhead" at the end of each major conveyor belt. This means that the steel contains molybdenum. The presence of vanadium is indicated by an inverted umbrella at the end of each guide line.

Color is another factor. The general rule of thumb is that easily oxidizable elements make the spark flow brighter, while those that resist oxidation tend to darken the flow. Most carbon steels are light yellow. Alloy steel mainly produces a dirty yellow color. High-speed tungsten steel generates a flow of dark red or orange sparks.

From this brief discussion, it can be seen that spark testing is an important industrial art and is very helpful in identifying mixed and unknown types of steel. You may never become such a brilliant artist, but it's good to know that others have developed these skills. Think about it the next time you use the stainless steel frying pan set or go on a cog on smooth steel straps.