What is Carbon Steel?
The majority of the nearly 3, 500 different types of steel produced and available in the global market today is carbon steel. Carbon steel is formed when two elements, iron and carbon, is combined with carbon being used as the alloying element. The carbon is used as a hardening agent to prevent iron atoms in the crystal lattice from sliding around. The carbon steel structure also has ferrite, pearlite and cementite present in varying quantities, depending on the carbon quantity of the steel.
Carbon Steel Coding
The AISI and the SAE have designed a four digit code to assign to all carbon and alloy steels to show its standard wrought steel composition. In carbon steel grades the last two digits indicate the nominal carbon content. When the code 10 appears in the first two digits of the code (ex. 10xx) the steel is plain carbon steel. If the code is 11xx it is resulfurized, 12xx refers to resulfurized and rephosphorized while 15xx refers to nonresulfurized with a Mn content of over 1 percent.
The presence of the letter L between the second and third digits of the code indicates that it is a leaded steel. The letter B indicates a boron steel. Cast-carbon steels will usually be specified by grade, such as A, B, or C. The A grade (also LCA, WCA, AN, AQ, etc.) has a 0.25 percent carbon content and a maximum of 0.70 percent of Mn. B-grade steel has a 0.30 percent carbon content and a Mn content of 1.00 percent while C-grade steel has a 0.25 percent carbon content and 1.20 percent of Mn. The mixture of carbon and manganese in a steel is used to improve the steel’s strength, toughness, and weldability. Cast carbon steels are specified to ASTM A27, A216, A352, or A487.
Carbon steel pipe tubes are usually cylindrical in shape, but may have round, rectangular, or square cross-sections. Tubing is specified in terms of outside diameter (OD) and, depending upon the material of construction, either rigid or flexible. There are several basic types of products.
Metal tubes are made of aluminum, brass, bronze, copper, steel, stainless steel, or precious metals. Plastic tubes are made of ethyl vinyl acetate (EVA), polyamides, polyethylene (PE), polyolefin, polypropylene (PP), polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinyl chloride, or polyvinylidene fluoride (PVDF). Rubber tubes are made of natural compounds such as polyisoprene or synthetic materials such as silicone. Glass and quartz tubes are commonly available. Electrical tubing is designed to contain wires and minimize the risks posed by electrical hazards. Fiberglass tubing is impervious to many caustics and suitable for extreme temperatures. Mechanical tubing includes stronger cross-sections and is designed for structural applications. Medical tubing is usually sterilized and relatively small in diameter.
Selecting tubing requires an analysis of dimensions, performance specifications, opacity, finish and temper. Tubes are specified in English design units such as inches (in) or fractions of an inch, or metric design units such as millimeters (mm) or centimeters (cm). Inside diameter (ID) is a tube’s longest inside measurement. Outside diameter (OD) is a tube’s longest outside measurement. Wall thickness is another important factor to consider. Performance specifications for industrial tubes include pressure rating, maximum vacuum (if applicable), maximum bend radius, and temperature range. In terms of opacity, some tubes are clear or translucent. Others are solid or multi-colored. Polishing or pickling imparts a bright finish. Galvanized tubes are coated with zinc for improved corrosion resistance. Painting, coating, and plating are other common finishing techniques. Annealing improves machinability by removing mechanical stress and altering ductility. Half-hard tubes are manufactured to a Rockwell hardness range of 70 to 85 on the B scale for steel. Full-hard tubes are fabricated to a Rockwell hardness of 84 and higher on this same scale.
Carbon steel pipe tubing differs in terms of features, applications, and materials transported. Some tubes are coiled, conductive, corrugated, explosion-proof, finned, multi-element or multi-layered. Others are reinforced, spark resistant, sterilized, seamless, welded, or welded and drawn. General-purpose tubing is suitable for a variety of applications. Specialized products are used in aerospace, automotive, chemical, cryogenic, food processing, high purity, high temperature, high viscosity, medical, pharmaceutical and petrochemical applications. Depending on the application, industrial tube is used to transport coolants, hydraulic fluid, salt water, slurries, or water. Slurry tubing is rated to resist the abrasion associated with its transport.
Carbon steels can be further categorized into three groups depending on their carbon content:
- Low Carbon Steel (Mild Steel) – Typically contain 0.04% to 0.30% carbon content. This is one of the largest groups of Carbon Steel. It covers a great diversity of shapes; from Flat Sheet to Structural Beam. Depending on the desired properties needed, other elements are added or increased. For example: Drawing Quality (DQ) – The carbon level is kept low and Aluminum is added, and for Structural Steel the carbon level is higher and the manganese content is increased.
- Medium Carbon Steel – Typically has a carbon range of 0.31% to 0.60%, and a manganese content ranging from .060% to 1.65%. This product is stronger than low carbon steel, and it is more difficult to form, weld and cut. Medium carbon steels are quite often hardened and tempered using heat treatment.
- High Carbon Steel – Commonly known as “carbon tool steel” it typically has a carbon range between 0.61% and 1.50%. High carbon steel is very difficult to cut, bend and weld. Once heat treated it becomes extremely hard and brittle.
Carbon steel pipe density
Density is calculated by dividing the mass by the volume. The density of carbon steel is approximately 7.85 g/cm3 (0.284 lb/in3).
Steel is much denser than water but shaped appropriately, the density may be reduced (by adding air spaces), creating a steel ship that floats. Likewise a life jacket reduces the overall density of the person wearing it, enabling him to float much easier.
There is not one value for density that is the same for all types of steel. Different steels are different alloys, although I wouldn’t have thought the values would vary greatly since all are largely steel.