The 8620 is a grade of steel that gives you a nice combination of wear resistance and toughness, and it’s meant mainly for industrial uses. It’s known to have good internal strength, but the strength on the outside is even greater. The 8620 steel is usually used for carburizing to develop a case-hardened part. This case-hardening process is generally responsible for its good wear resistance.
It’s regarded as a mild steel—it does have carbon, but it’s not all that much. It’s also regarded as a low alloy steel, because only a small percentage of its content is made up of alloying elements. It contains molybdenum, chromium, and nickel as well.
Some also call the 8620 steel as a case hardening steel. That is, it can easily undergo a processing method that hardens only the outer surface of the metal.
The 8620 steel is often sold in the form of round bars. But you can also get the 8620 steel in square bars, steel plates, and even in tube form.
The 8620 steel can be a bit strong, which is why it’s often used for certain situations where the parts need to have medium-level strength. These parts include:
This is very mild steel, and its resulting hardness doesn’t even qualify for the HRC scale. But it does offer good strength, especially when compared to non-carbon steels.
Manganese, 0.7% to 0.9%: Like carbon it also helps with the strength of the steel. That’s why some experts rate manganese as the most important alloying element next to carbon. The manganese here also improves the surface quality of the 8620 steel.
Nickel, 0.4% to 0.7%: The nickel also helps with corrosion resistance, but in this case it’s here to give the 8620 steel its characteristic good toughness and ductility. That means it’s not as likely to chip off, unlike harder (and more brittle) steel.
Chromium, 0.4% to 0.6: Obviously, this isn’t enough chromium to qualify the 8620 steel as stainless steel. You’d need at least 10% or even 12% chromium for that. But for 8620 steel, this amount of chromium (working with the molybdenum) helps with the hardness penetration and the wear resistance. That should help the 8620 steel last longer while bearing stress loads.
Molybdenum, 0.15% to 0.25%: The molybdenum here works with the chromium to improve hardenability and wear-resistance. It also helps with the steel’s creep strength and strength in higher temperatures.
Silicon, 0.15% to 0.35%: This is one of the main deoxidizers in steel. That means it takes out the oxygen bubbles in the molten steel that can weaken the steel as a result. It also dissolves in the iron to make it stronger. But you can’t have too much silicon, as that can reduce ductility.
Sulfur, 0.04%: You really don’t want sulfur in steel, because it reduces the impact properties of the steel. Too much of it also reduces the notched impact toughness. But in tiny amounts (like in this case), it increases the machinability of the steel.
Phosphorus, 0.035%: This is another unwanted impurity that you try to limit in any steel. Even a small bit can make a steel brittle. But in tinier amounts, it boosts the tensile strength of the steel and also improves the machinability.
The 8620 steel isn’t really all that hard, if you’re thinking about using it for a knife. It doesn’t even have an HRC rating—the hardness level is that low. It won’t really cut worth a damn, and it surely won’t hold a sharp edge.
Still, for industrial uses (like camshafts and bushings), it offers a noticeably greater strength compared to what you can get from non -carbon steels and steels with lower carbon content.
What this means is that the 8620 steel won’t just crack under the weight or load. It may bend or elongate first before it cracks, and cracking can be a greater disaster in some applications.
This is mainly due to the low carbon content. A general rule in steels is that the hardness of the steel is inversely proportional to its toughness (its propensity to crack, or the opposite of brittleness). It’s for this reason that it’s widely used in so many industrial components across a lot of industries.
Case hardening is a process that boosts the hardness of the metal. You end up with a rather thin layer of much harder metal on the outside. Meanwhile, the inside is still tough so the whole steel isn’t too brittle at all.
That means it’s easier to use to make the various components you want.
The polishing can have several goals. For industrial components, it removes oxidation and helps to prevent corrosion.
You won’t run out of the material when you’re manufacturing high-volume products.
You won’t bust your budget either when you’re using 8620 steel.
One way to better illustrate the properties of 8620 steel is to compare it directly with other steels that are somewhat similar. If you’re in the field of manufacturing industrial components, then these comparisons can help you decide which steel alloy is actually right for the parts you’re trying to make.
At first glance, it makes sense to compare these 2 steels. They’re both low alloy steels with nickel and chromium.
But the 9310 steel is much more reliably stronger, and with greater toughness as well. It offers greater tensile strength and yield strength. It’s why it’s used for components that require greater strength for safety. These include high-performance helicopter transmission gears, crucial aircraft engine gears, automotive parts, and structural parts.
But the 8620 can suffice in many other situations, and it’s much more affordable to use.
The 4140 contains significantly more carbon. It also has more chromium, though it doesn’t have nickel like the 8620 steel. The greater carbon content makes the 4140 steel stronger than the 8620, but the 8620 is more versatile.
These are almost the same steel alloy, with everything the same except that the 8630 steel has a little bit more carbon. Practically speaking, that makes the strength almost the same. But the 8620 depends more on the heat treatment to give you the strength you need.
The 5120 steel contains less carbon but more chromium. The 8620 steel is generally harder, with greater elongation at break, greater fatigue strength, greater shear strength, and greater yield strength. But the 5120 steel is more affordable, while it matches many of the other 8620 steel properties.
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