Steel is found in all kinds of products, from aerospace to kitchenware. Such diverse applications require a versatile material—and steel fits the bill.
‘Steel’ actually describes an entire family of metal alloys, with hundreds of application-specific grades, however most people understand steel in two broad categories: carbon steel and stainless steel.
Carbon steel and stainless steel have the same basic ingredients of iron and carbon. Their main difference is alloy content—carbon steel has under 10.5 percent alloy content, while stainless steel must contain 10.5 percent chromium or more. That essential difference is what gives carbon steel and stainless steel their distinct physical characteristics.
The essential elements of steel are iron and carbon. In general, steels with a higher carbon content are hard and brittle, while steels with a lower carbon content are ductile and tough.
Of course, it’s rarely that simple. Alloying elements like chromium, molybdenum, nickel, manganese, or silicon can be added to increase corrosion resistance or attain a better balance between strength and toughness.
Carbon steel is composed of iron and 0.12 - 2.00 percent carbon. The broader definition includes alloy steels, which can also contain up to 10.5 percent alloy content. Even within the confines of under two percentage points of carbon, there is huge variance in physical characteristics—especially hardness.
When people talk about carbon steel, they are usually referring to the high carbon steel used in knives and tools. High carbon steels are very hard, which makes them good at resisting abrasion and retaining shape. They can withstand significant force before deforming. Unfortunately, hard metals are also brittle: when placed under extreme tensile stress, high carbon steels are more likely to crack than bend.
Low carbon steels are more common than high carbon because of (1) lower production costs, (2) greater ductility, and (3) ease of use in manufacturing. Low carbon steels tend to deform under stress instead of breaking, and that ductility makes low carbon steels easy to machine and weld. They are frequently used in automobile body panels, bolts, fixtures, seamless tubes, and steel plate.
Stainless steel contains iron, carbon, and at least 10.5% chromium content. The chromium is key—it reacts with oxygen to create a passive layer that protects the steel from corrosion. That protection allows stainless steels to function in wet environments without rusting. The higher the chromium content, the better the corrosion resistance.
It’s important to pay attention to the stainless steel grade when purchasing appliances and other big ticket items. Not all steels are created equal. A stainless steel with the minimum 10.5% chromium content is much cheaper and less durable than one with 16%, and the difference will show in maintenance costs and service life.
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Carbon steel and stainless steel are different, but one is not necessarily superior to the other. It’s all about context. Each material has advantages and disadvantages—the key is matching the steel to the job requirements.
High Carbon Steel
- Vulnerable to rust
- Resistant to rust
- Less brittle
- Less wear-resistant
This list is a good primer reference, but there is a lot more to learn about steel metallurgy. Some grades of steel can be made more or less ductile by heat treatment, while surface treatments can increase corrosion resistance. You can learn more about steel composition and grading here.