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More than Stainless

More than Stainless: Your Guide to Steel Types & Grades Have you ever wondered about the metals that J&J Trailers uses to build your trailer or custom steel fabrications? Chances are that many of the items you purchase from us are made from steel.

The World Steel Association reports more than 3,500 grades of steel alone. That’s an amazing variety!

So Why the Variation? The simple answer is that steel is produced according to its intended application. Depending on the chemical properties that factor into the production, the result can vary widely; hence, the need for a grading system. The Canadian Institute of Steel Construction, or CISC, divides steel into 4 broad categories:

  • Carbon-based steel
  • Alloy steel
  • Tool steel
  • Stainless steel
Your steel sink or set of chef knives belong to the latter two categories; conversely, most auto parts and electric motors are made from alloy steel. Again, it all depends on the final application.

Steel Basics If you ask a machinist about the most important factor in steel fabrication, you'll probably hear the word “carbon.” But why does carbon matter so much?

Let’s use the World Trade Center as an example. The WTC in New York City has been under a great deal of scrutiny ever since 9/11. Metal fabricators have wondered about the grades of steel used in its construction, and whether or not a different grade might have kept the building from its tragic collapse.

Multiple steel grades factored into the WTC’s construction. One of the most common was A36, which reportedly holds up to 36,000 pounds of pressure per square inch before it starts to bend. Of course, the building also contained steel grades whose strengths went all the way to 100,000 pounds of pressure per square inch.

All in all, the World Trade Center used more than 200,000 tons of steel in its construction. As to the question of whether different steel grades would have kept the structure intact, the jury is still out. What matters here are the steel grades and carbon levels within the steel. The lower the carbon, the weaker the steel.

Carbon-Based Steel Did you know that carbon-based steel accounts for more than 90% of total steel production in the world? If you delve into the myriad of applications out there, you’ll likely find carbon steel as the main construction element. Carbon-based steels contain trace alloys, and falls into 3 basic sub-categories:

  • Low or mild carbon steel (up to .3% carbon; generally light-duty bolts, tire-rods or pins can be made from low-grade carbon steel)
  • Medium carbon steel (between .3% and .6% carbon; this grade can be heat treated and made into such things as kingpins or small shafts)
  • High carbon steel (more than .6% carbon; may be used in bearing steels or drill rods, to name just two applications)
Here’s where steel grading comes in. Carbon is such a critical element that the entire steel grading system is based on it. The last 2 digits of a steel grade (for example, the A36 grade mentioned above) express the average carbon percent by weight. So we can assume the A36 grade implies a carbon weight of .36%.

Alloy-Based Steel When we speak of alloyed steel, we’re talking about steel that contains alloy elements such as silicon, nickel, manganese, copper, chromium, aluminum or titanium.

The proportion of these alloys in the mix is as important to the application as carbon is to carbon-based steels, directly impacting product strength, weld-capability, corrosion-resistance and other factors.

As already mentioned above, the most common applications for alloyed steels are auto parts, generators, electric motors and pipelines.

Tool Steel Tool steel is made today for at least 2 main reasons: to increase durability and to increase heat resistance in the tool. To that end, this type of steel generally contains various quantities of tungsten, cobalt, molybdenum and/or vanadium. The carbon content generally falls between .7% and 1.5%, allowing for superior durability.

Because tool steel is known for its peculiar hardness and abrasion resistance, it's also a big part of repeated-stress tools like stamping dies, quarrying tools, cutting machinery and some knives.

The CISC grades list a letter (A for air-hardened, H for hot-working, S for shock-resistant and so forth), then a double digit number to indicate carbon percentage. The higher the number, the harder the steel.

Stainless Steel Where does the “stainless” part factor into stainless steel? If you understand that many steels are not rust-proof, then you may see the distinction. Because stainless steel adds a mix of chromium as its main alloy, this element alone makes the steel nearly 200 times more corrosion resistant than, say, low-carbon (mild) steel. That makes stainless steel incredibly useful in multiple fields, particularly for food-based industries and medical equipment. These are 3 basic categories of stainless steel:

  • Ferritic - This is a magnetic stainless steel that contains such alloys as titanium, molybdenum, aluminum and/or trace amounts of carbon and nickel along with the requisite chromium.
  • Austenitic - This category of stainless is non-magnetic, and is the type most commonly used in piping or kitchen equipment.
  • Martensitic - Because this is both a magnetic stainless steel and heat-treatable steel, it's one of the strongest of the stainless steels. It's most commonly used in cutting tools and dental or surgical equipment.

The next time you use a tool or contemplate the strength of your trailer, you'll have a better idea as to its steel composition.

For more information, be sure to contact our expert staff at J&J Trailers!