What is Difference Between Carbon Steel Vs Stainless Steel?

Steel forms an integral part of our lives. It is one of the most widely used commodities. It is extensively used in Infrastructure, Transport, Energy, Packaging and consumer durable industries. Steels are classified as Plain carbon steels (containing maximum 1.5% carbon in commercial steels), Low-alloy steels (alloying elements <8%), High-alloy steel (alloying elements >8%)

In this article the focus will be on the differences between Plain carbon steel and Stainless steel.

Carbon vs Stainless Steels Content & Classification

Plain carbon steel comprises of mainly iron and carbon as the principle alloying elements. Classification of plain carbon steels is based on the composition of carbon present in metal.

 

 

Stainless steel is a high alloy steel containing minimum of 10.5 % Chromium along with other alloying elements. Stainless steels are classified based on the micro-structure present at room temperature.

 

classification-steel

Carbon vs Stainless Steels Nomenclature (ASTM)

Plain carbon steels are labelled using a 4 digit number. The latter 2-digits signify carbon percentage present in metal. For example- AISI/SAE 1040 signifies medium carbon steel with 0.40% carbon. Similarly AISI 1010 is a low carbon steel with 0.10% carbon.

 

AISI designation Type of Plain Carbon  Steel
10XX Manganese 1.00% max.
15XX Manganese 1.00 – 1.60%
13XX Manganese 1.60-1.90%
11XX Resulfurized
12XX Resulfurized and Rephosphorized

 

Stainless steels are divided into 2 series namely- 300 series (Austenitic grades) & 400 series (Martensitic and Ferritic grades), Duplex and Precipitation hardened grades have different nomenclature all-together. Below is a list of few of the most popular stainless steel grades-

Type Popular Grades
Austenitic Stainless Steel 304, 304L, 316, 316L, 316Ti, 303, 321
Ferritic Stainless Steel 409, 409Ti, 441, 446
Martensitic Stainless Steel 410, 416, 420, 420B, 420C, 430F, 431
Duplex Stainless Steel F51, F53, F60
Precipitation Hardened Stainless Steel 17/4 PH

 

Suffix “L” stands for low carbon variant; “Ti” denotes addition of titanium to improve intergranular corrosion; “B” & “C” indicate varying percentage of Carbon in martensitic grades.

Carbon & Stainless Steel Phase diagrams

Plain carbon steel structure can be studied using the Iron-Carbide diagram. The Fe-C diagram has carbon percentage on X-axis and temperature scale on Y-axis. Phase transformations are combined effect of Carbon composition and heat treatment process.

Phase diagram of Stainless steel is obtained by plotting percentage of chromium content on X-axis and temperature scale on Y-axis. The phase transformations are limited to just the martensitic and precipitation hardened grades of stainless steel as  they contain higher percentage of carbon. Austenitic, Ferritic and Duplex grades can only be strain hardened since no phase transformation takes place during and after heat treatment.

Properties Of Carbon & Stainless Steel

Plain carbon steels are soft and can be easily formed. With increase in carbon content, higher hardness can be achieved with reduced ductility. High carbon steels also exhibit poor weldability and temperature resistance.

Stainless steels are inherently resistant to corrosion. Chromium forms a thin self-reparable layer around the metal, thus protecting the underlying metal from exposure to corrosive environments. Stainless steels impart better aesthetic appearance due to its superior surface finish. They are formable into complex shapes. Composition of Stainless steels can be altered to suit specific applications.

Alloying Elements

Various alloying elements are used for imparting desired properties in stainless steels. Sulfur and phosphorous are added to improve machinability, Titanium and Niobium enhance weldability by reducing inter-granular corrosion. Aluminum, Copper is added in Precipitation Hardened grades to improve strength. Molybdenum is added to improve pitting and crevice corrosion resistance.

In plain carbon steels, alloying elements other than Carbon are in small traces and do not influence properties of steel to a large extent. Small traces of sulfur, manganese, phosphorous, silicon can be found in Plain carbon steels.

Carbon & Stainless Steel Applications

Choice of Steel is dependent on the application. If steel is going to be hidden as a structural component and exposure to corrosion is low, carbon steel can be preferred. Stainless steel with its higher corrosion resistance offers better up-time in corrosive environments. In situations where aesthetics of component is important, stainless steel is better suited as it offers superior surface finish. Choice can also be based on budget. Stainless steels contain expensive alloying elements and are also expensive to handle in comparison to plain carbon steel.

It is a matter of weighing in all the parameters for a particular application before choosing between the two types of steels.

About Ambica Steels Limited

Ambica Steels Limited (ASL) has over 5 decades of experience in Stainless steel manufacturing. ASL caters to diverse requirements of Stainless steel encompassing 150+ grades in various profiles including round, square, hexagonal, flat bars. The company also offers superior forging quality ingots and billets. For any further information, visit us at www.ambicasteels.com or write to us at info@ambicasteels.com

About Author

Aniruddha Bauskar is responsible for New Business Development and Sales at Ambica Steels Limited. He likes reading and writing articles on various industries including Steel, Automobile and FMCG. You can find him on LinkedIn.

diffrence between carbon and stainless steel

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