Go into any machine shop and you’ll get the same story. The wrong steel was used. I guess they wanted to try welding a spring grade that cracked when heated. Or maybe you chose some high carbon alloy for your deep draw application, but it cracked as press completed its cycle.
Fact is: Steel isn’t a monolith. It’s a vast family of materials where each has its own place and its own limitations. Knowing the difference between steel grades are what determines whether a part lasts for decades or fails on assembly line.
Why You Must Pick the Right Steel
This chart does a nice job of breaking that down and demonstrating that real key to performance is carbon content. Strength and hardness increase predictably with increasing carbon levels following a rising arc. This is where most folks go astray. Stronger is better, right? Not so much. Every small improvement in hardness has a direct impact on the loss of ductility and weldability.
The industry workhorse are low carbon steel, such as 1018 or A36 grades. These are easy to form and forgiving, and they’re also happy to see an arc. Jump up a bit further into medium ranges and we start talking gears and axles. We’ve got decent strength here. However, we has to be careful about welding these parts; preheating is required to avoid cracking.
Keep going upward into high carbon territory, springs, knives, etc., and weldability are pretty well gone. Those pieces is joined mechanically, or with extreme caution. At all. Instead, they’re joined mechanically, or with great care. This makes all the difference.
Match the material to the application, don’t apply the application to the material. But then there are the new rules regarding corrosion.
Chromium makes it stainless: “If you get down below about ten and a half percent chromium, you’re not getting stainless anymore,” says the infographic. “You just got yourself some regular old steel.” The infographic also explains the four primary microstructures in stainless, and how each should be treated different.
Most familiar are austenitic grades, such as 304 and 316, which is extremely weldable and nonmagnetic, making them most popular. These are used in chemical tanks and other places where food processing occur.
The remaining grades, ferritic and martensitic, are harder and more magnetic, but they’re trickier to work with. A hybrid called duplex stainless combines both microstructures. This provide double the strength of typical austenitic grades. You will see this used offshore, where extreme pressure meets extreme corrosion.
Tool steels have a place all their own over in the rugged corner of the chart. Tool steels are made to make tools out of other stuff. These might be a cutting tool, a mold, or a die. Something that can stand up to heat and wear and tear. Things like M2 or D2 steel is really hard. They often are well into the sixties on the Rockwell C scale. They also does not weld without being annealed first.
Try striking an arc on some cold tool steel and I bet it breaks right there. There is no warning. No nothing. You learn the lesson of metallurgy quicklyy and at a high cost.
The shop floor has another handy workaround too. You have some stainless? Need to know what type? Just give it the old magnet test. Austenitic stainless doesn’t stick; Martensitic and ferritic do. That’s it. It takes five seconds of time, but you may face hours of heartache down the road if you discover you’re attempting to weld a material that requires a particular low-hydrogen welding procedure.
Always read the mill cert. The grade stamp means nothing. What matters is the chemistry behind it.
In short, this all boils down to choosing between different steel types. Yes, you want it strong, but you want it to be formed too. Yes, you want it resistant to corrosion but maybe at the cost of toughness. And the chart is your guide to these choices.
You are reminding us that there’s no such thing as one best steel. You must use only the correct steel for the particular application: load, manufacturing process, or environmental conditions. It’s the difference between guesswork and engineering. This happen once you understand the structure, the alloying elements, and the carbon content.
Next time you pick up that bar of steel, don’t wonder what it is you’re holding. Ask yourself what it is supposed to do. What it’s made to do. That’ll tell you everything else you’d ever care to know.
