Low-carbon steel, also known as mild steel, has a comparatively low radio of carbon to iron compared to other steel types. Typically, its carbon content is within the range of 0.05% and 0.32% by weight. This gives low-carbon steel low strength while making it more malleable and ductile compared to high-carbon steel.
One of the major benefits of mild steel is its cost-effectiveness. As it requires less carbon and other alloying elements, it’s normally less expensive than other types of steel. Moreover, it’s more readily available and simpler to work with than higher-carbon steels, which makes it a popular choice for a wide range of applications.
Despite its low strength compared to other steel types, low-carbon steel is still strong enough for use in structural applications. It’s also used for machinery parts, as it helps to reduce machining costs. It’s easy to shape, which speeds up production times and reduces the cost of machining compared to other materials, such as aluminum.
There are different low-carbon steels with varying amounts of carbon. Below are examples of different types and their applications:
Type Industry Applications Low-carbon structural steel Construction Buildings, bridges Low-carbon sheet and strip steel Sheet metal work Automotive body panels, appliances and other uses that require thin, flat material Low-carbon tubing and piping steel Construction, automotive, heavy equipment, oil and gas Mechanical tubes, pipes for fluid transport, and structural tubing Low-carbon pressure vessel steel Heavy equipment, machinery manufacturing Boilers, pressure vessels and other uses where material must withstand high internal pressures Low-carbon galvanized steel Construction, HVAC, automotive Roofing, automotive body panels, ductwork High-strength low-alloy (HSLA) steel Construction Building frames, bridges, support structures
The three primary standards for all carbon steels in the U.S. are:
ASTM is the most widely used. For example, one standard is ASTM A307, which covers the specification for carbon steel bolts, studs, and threaded rod with 60,000psi tensile strength.
Under this standard fall two grades:
Standards provide a consistent framework to ensure that materials meet the necessary performance criteria for their intended applications. Grades, on the other hand, are specific classifications within those standards.
Each grade has unique properties and characteristics determined by factors such as chemical composition, heat treatment and mechanical properties. For example, in the table below, you’ll notice the same standard – SAE J403 – with three different grades. This is due to the carbon content in each grade.
Some commonly used grades of low-carbon steel include:
Standard Grade Application ASTM A36/A36M A36 Structural steel grade used in buildings, bridges, construction equipment ASTM A513/A513M 1010 Automotive parts, machinery components ASTM A53/A53M B Structural and pressure applications, such as water and gas transmission ASTM A516/A516M 70 Boilers and pressure vessels SAE J403 1006 Wire products and fasteners SAE J403 1008 Sheet metal work, automotive components, and wire products SAE J403 1010 Cold heading, automotive components, and sheet metal work ASTM A1011/A1011M 33 Sheet metal work, automotive components and construction materials
Each grade has slightly different properties, although the melting point of low-carbon steel is about the same. That said, we can still give a range of values to give you an idea of this material’s overall properties.
Property Value Density 0.103 – 0.292 lb/in³ Tensile Strength, Yield 20300 - 347000 psi Fracture Toughness 30.0 – 105 ksi-in½ Shear Modulus 10200 – 11600 ksi Melting Point 2600°F Thermal Conductivity 176 – 645 BTU-in/hr-ft²-°F
Medium-carbon steel has a carbon content typically ranging between 0.3% and 0.6%. This category of steel offers a balance between the ductility and formability of low-carbon steel and the strength and hardness of high-carbon steel.
Medium-carbon steels are stronger and harder than low-carbon steels. This is due to their increased carbon content, but it also means they’re less ductile and more difficult to form and weld. They often require heat treatment, such as quenching and tempering, to achieve desired mechanical properties. This is possible with its manganese content, which ranges between 0.30% to 0.60%.
Medium-carbon steels are commonly used in applications where higher strength and toughness are needed, as shown in the table below. It’s also used to make small components, such as concealed hinges.
Common types of medium-carbon steel and their applications include:
Type Industry Application Medium-carbon structural steel Construction, Manufacturing Buildings, bridges, heavy-duty equipment Medium-carbon sheet and strip steel Sheet metal work Machinery parts, Automotive parts Medium-carbon tubing and piping steel Construction, automotive, heavy equipment Mechanical tubes, pipes for fluid Medium-carbon pressure vessel steel Oil and gas, food and beverage, pharmaceutical Pressure vessels Medium-carbon alloy steel Automotive, Heavy machinery Gears, shafts, axles, connecting rods Medium-carbon quenched and tempered steel Automotive, Construction, Heavy machinery Gears, axles, transmissions, crane booms, excavation arms
Products made from medium-carbon steel adhere to specific standards. Within those standards are grades. Commonly used grades of medium-carbon steel – and the standard they fall under – include:
Each grade has its own properties that distinguishes it from other medium-carbon steel grades. The table below gives you a range of values for medium-carbon-steel properties.
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Property Value Density 0.280 – 0.285 lb/in³ Tensile Strength, Yield 35500 – 252000 psi Fracture Toughness 73.7 – 130 ksi-in½ Shear Modulus 10400 – 11900 ksi Melting Point 2597– 2800°F Thermal Conductivity 152 – 361 BTU-in/hr-ft²-°F
High-carbon steel contains a carbon content ranging between 0.60% – 1.5%. It’s the most corrosion resistant of the steels due to its high amount of carbon. This increased carbon significantly enhances the steel's hardness, tensile strength, and wear resistance. In turn, that makes it suitable for applications that demand high strength and wear resistance.
However, the higher carbon content also makes these steels more brittle and less ductile, which makes it more susceptible to cracking under certain conditions. High-carbon steel is also more challenging to weld than lower-carbon-content steels, due to the risk of cracking and brittleness in the heat-affected zone.
High-carbon-steel uses include anything needing wear resistance and durability, as shown in the table below. High-carbon steel is often used to manufacture springs. A note about plain high-carbon steel, which is often used to mean high-carbon steel. They are different. Plain high-carbon steel consists mostly of carbon and iron, without any significant amounts of alloying elements.
High-carbon steel types, and their applications, include:
Type Industry Application Plain high-carbon steel Manufacturing, automotive, construction Springs, knives, cutting tools, brake components High-carbon tool steel Manufacturing, metalworking, woodworking Cutting tools, punches, dies, injection molding tools, extrusion dies, router bits High-carbon bearing steel Industrial machinery, automotive, aerospace Ball and roller bearings for engines; also, transmissions, wheels, heavy machinery, gearboxes, pumps High-carbon spring steel Electronics, automotive, manufacturing Leaf springs, coil springs, machinery, springs for electronic devices
Grades of all carbon steels are subsets of specific standards. Some of the most commonly used grades of high-carbon steel include the following:
Standard Grade Application ASTM A29/A29M AISI/SAE 1060 Springs, gears, axles, heavy-duty machinery components ASTM A29/A29M AISI/SAE 1065 Springs, cutting tools, industrial knives and blades ASTM A29/A29M AISI/SAE 1070 Springs, automotive suspension components, agricultural machinery parts ASTM A29/A29M AISI/SAE 1080 Heavy-duty springs, automotive components, heavy machinery parts ASTM A295 AISI/SAE 52100 Bearing steel used in the manufacture of ball and roller bearings ASTM A600 AISI/SAE M2 High-speed tool steel used for cutting tools, drills, and taps ASTM A686 AISI/SAE W2 Water-hardening tool steel used for cutting tools, dies, punches, and woodworking tools
Because standards and grades vary between each other, there is no one value for the properties of high-carbon steel. Below is a broad range of what you can expect.
Property Value Density 0.0163 – 0.298 lb/in³ Tensile Strength, Yield 39900 – 484000 psi Fracture Toughness 12.0 – 150 ksi-in½ Shear Modulus 11300 – 12000 ksi Melting Point 2,800-2,900°F Thermal Conductivity 1132 – 361 BTU-in/hr-ft²-°F
The essential difference is in the steels’ carbon content, which gives each different characteristics.
Low-carbon steel Medium-carbon steel High-carbon steel Carbon Content 0.05% to 0.32% 0.30% to 0.60% 0.60% to 1.5% Characteristics Ductile
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Sorry but yours is one of those "it depends" questions " As was mentioned, leaded steels intended for free machining don't weld well but many weld it with some success.
There are two problems with welding free machining steels: one is as-welded strength where the free machining goodies affect the integrity of the weld deposit and the heat affected zone lowering strength,ductility, fatigue resistance and ultimately weld confidence. The other in the case of welding leaded steels is lead (or selenium) vapors evolve which are toxic to breathe.
So welding leaded steels into lightly loaded structures may be OK if you do so outdoor up-wind of your work. Do not weld free machining steels in high strength applications such as trailer axle stubs, high pressure fluid power,
or certified structure such as air frames, hoisting equipment - or anything you don't want to rust, bust, or turn to dust,
Be mindful that a pretty weld may not be strong and reliable. Joint design, filler metal, pre and post heat (where applicable), welder settings, shield gas (where applicable), weld cleanliness, arc manipulation, etc all play a part in a good welded joint. Which is to say, I'd rather have a strong, ductile, rough looking weld than a pretty low penetration scab holding poorly fitted dirty metal together - overstating it probably but you get the picture.
Free machining steels are great, they do deliver on good finishes and long tool life. The down side is they rust like crazy. Don't apply them to unprotected situations like saltwater or weather without a GOOD paint system protecting them.
Good finishes in low carbon steels are very possible provided feeds, speeds, coolant, and tool selection are up to snuff. Steels are supposed to meet specs but within these specs their constituents elements are allowed a range of percent points to be acceptable. Some steels are marginal and bars rolled from one particular lot may machine differently than another. 1018 and A36 steels machine just fine, generally, but good finishes may be problematic depending on the metallurgy. If all else fails run a HSS tool with a keen cutting edge and a nose radius 6 X the feed rate. I like the "magic 7" tool geometry where side and end
and the top rake are all 7 degrees.
Manage your stock removal so you leave 0.020 on a side for semi-finish and finish cuts of 0.010 DOC each. The semi-finish cut proves the tool, machining parameters, and coolant and the finish cut goes right to size.
I didn't mention weld distortion of finish machined parts. Should I have?
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