Know Your Metals: Carbon Steel vs Stainless Steel
Machining steel can be an intimidating material to work with due to its high strength and durability. This article will better familiarize you with steel and its working relationship with our favorite trade: machining. Success with machining steel comes after understanding its composition.
What is steel made of? Steel is primarily a mixture of iron and carbon. Steels come in different grades with varying components that make them useful for different objectives. Elements like tungsten, chromium, manganese, and nickel are added to develop certain mechanical properties. Those different mixes of metal are what create the different grades of steel. Each grade has qualities like hardness, ductility, and tensile strength, and all of these fluctuate depending on the amount of each chemical element mixed in.
Before you decide between the individual grades of steel, you have to first decide between carbon steel and stainless steel.
Carbon Steel vs Stainless Steel
Outlining the differences between the mechanical properties of stainless and carbon steels is not an easy task, and that’s mainly due to the different grades that are available.
The difference in elemental makeup of these two types of steel mainly results from very different corrosion resistance and mechanical properties. Which makes sense since they are intentionally built differently.
Additionally, both the appearance and the cost of these two steels is quite different.
Carbon Steel
Not only is carbon steel missing chromium to protect it from oxidation, but its high levels of iron also make it even more susceptible to corrosion. The main characteristic of carbon steels is their unparalleled strength and incredible hardness. Very high amounts of carbon are required to achieve that level of tensile strength.
It is possible to make carbon steel look pretty – with the right finishing processes – however, it will be difficult to beat that one-of-a-kind stainless-steel shine.
Because the elemental makeup of carbon steel is so much more straightforward than its counterpart, it is the more economical option. And if no one is going to see the part, why splurge on its appearance? One thing to keep in mind though is that if that part is stored in an environment that will subject it to corrosion, stainless is still the better option.
Stainless Steel
Iron is a primary element in steel and does not resist corrosion well. Chromium is added to the iron and carbon mix, protecting the metal from oxidation. For steel to be considered stainless, it must contain 11% of chromium. However, most stainless steels contain more than that.
Stainless steels have higher levels of nickel in them than carbon steel. Generally speaking, this allows stainless steel to win in the ductility competition against carbon steel. However, there are exceptions, like with martensitic grade steel, which is extremely brittle.
What makes the appearance of stainless steel even more impressive than it already is, is that a scratch to the finish will retain shine, whereas a scratch on carbon steel becomes dull and even more subject to corrosion than before.
Recommended Books
Machining of Stainless Steels and Super Alloys: Traditional and Nontraditional Techniques
Machining of Stainless Steels and Super Alloys
This book includes a 10-level machinability chart to rank important grades of steel. You will also find information on non-traditional machining processes along with hybrid processes that have successfully been applied to machining stainless steels and super alloys.
Steel Metallurgy for the Non-Metallurgist
Steel Metallurgy for the Non-Metallurgist
This book is great for machinists (or any non-metallurgists). It starts with the basics and builds to more complex concepts, like heat treatment of steel. This book is THE practical primer on steel metallurgy for those who heat, forge, or machine steel.
Heat Treatment of Steel
Heat-Treatment of Steel
This book presents a comprehensive dissertation on the hardening, tempering, annealing, and case hardening of various kinds of steel. Specifically, high-speed, high-carbon, alloy and low carbon steels. Although a vintage text, it remains relevant to the modern machinist.
Metallurgy for the Non-Metallurgist, Second Edition
Metallurgy for the Non-Metallurgist
Cutting Data for Turning of Steel
Cutting Data for Turning of Steel
This book walks you through detailed descriptions of the mechanical properties of steel and machining recommendations to ensure success with the metal. Expect a heavy focus on hardness conversion, specifically of carbon, alloy, stainless, tool and maraging steels.
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4 Comments
nothing better then hardened tool steel , holds an edge a lot better than stainless, you can read all you want , but you need to get in there and make some chips to learn the difference.
“Carbon is a primary element in steel and does not resist corrosion well.” I think you meant Iron, not Carbon
This article is ripe with errors. As Samir pointed out, it’s the iron in carbon steel that corrodes, not carbon. Also per ASTM specifications, most stainless steel sheet metal has at least 16% Cr, with 409 and 410 coming in at 10.5% and 11.5% respectively.
Who is this article written for? The receptionist in the lobby? Or maybe the janitor. I mean, even the book keeper needs better info than this.