In our last post, Steel Grades and Specifications Explained (Part 3), we discussed how different steel grades resulting in different tensile strength and yields can affect the quality of the finished product. In part four, we’re going to take a look at the different carbon steel finishes available.
Carbon steel mainly differs from stainless steel in having a much lower percentage of chromium. Stainless steel’s higher percentage of chromium gives it a better resistance to corrosion, but with a higher price tag. The high amount of carbon in carbon steel makes it more vulnerable to corrosion (rust). So, if you need a rust-free carbon steel product and want to avoid the high costs of stainless steel, then surface finishing treatments will be needed.
Here’s a look at the surface finishes available for carbon steel.
Carbon Steel Finishes
Powder Coated Carbon Steel
Powder coating is the most common finish for pallet rack. Powder coating is applied a free-flowing, dry powder. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a “skin”. It is a tough, durable finish.
Hot-Dip Galvanized Carbon Steel
With the hot dip galvanizing process, an already formed part is dipped in a bath of molten zinc. While the steel is in the bath, the iron in the steel metallurgically reacts with the molten zinc to form a tightly-bonded alloy coating that provides superior corrosion protection to steel. One advantage of hot dip galvanizing is that the entire part is covered including the edges, welds, etc. giving it an all-round corrosion protection. But a disadvantage of hot-dip zinc coating is that for bolts and nuts size US 3/8″ or smaller, the thick hot-dipped coating fills in too much of the threads, which reduces strength. Galvanized steel products can be used outdoors in all different weather conditions.
Pre-Galvanized Carbon Steel
Pre-galvanized steel refers to steel which was galvanized while in sheet format, prior to further manufacturing. The process is also called mill galvanized because it is produced by coating coils of sheet steel with zinc by continuously rolling the material through molten zinc at the mills. One of the advantages which pre-galvanized steel has over hot-dip galvanized steel is that it has a better appearance. Though anywhere the wire and coil steel are cut or welded, the zinc covering is compromised, it is still an acceptable finish for most applications.
Zinc Electroplated (also called electro-galvanized)
Zinc electroplating is a process where zinc is applied by using a current of electricity. It is a thinner coating than hot dip galvanizing making it unsuitable for outdoor applications (except in very dry environments). The advantages are brightness and uniform color, making it more aesthetically appealing. Also the thickness of the coating can be accurately controlled using this process.
Recap of “Steel Grades & Specifications Explained” Parts 1-4
While steel is comprised primarily of carbon iron, each grade is comprised of unique physical, chemical, and environmental properties. But it’s the amount of carbon, and additional alloys, as well as the level of impurities, that determine the properties of each steel grade.
The major standards organizations for steel are:
- American Iron & Steel Institute (AISI)
- Society of Automotive Engineers (SAE)
- American Society for Testing and Materials (ASTM)
- American Institute of Steel Construction (AISC)
Regarding materials specification for pallet rack, the ANSI MH16.1: 2012, Specification For The Design, Testing And Utilization Of Industrial Steel Storage Racks assumes the use of steel of structural quality as defined by the specifications of the ASTM that are listed in the AISI North American Specification for the Design of Cold-Formed Steel Structural Members, and the AISC Specification for Structural Steel Buildings.
While there are over over 3,500 different grades of steel, there are, according to the AISI, four basic groups based on chemical compositions:
- Carbon Steel
- Alloy Steel
- Stainless Steel
- Tool Steel
Steel can also be classified by several different factors, such as:
- Production method
- Finishing method used
- Form or shape
- De-oxidation process
- Physical strength
- Heat treatment
While all steel contains carbon and iron, the category of “carbon steel” is steel in which the main interstitial alloying constituent is carbon in the range of 0.12–2.0 percent.
Carbon steels are further categorized into these four groups, depending on their carbon content:
- Low Carbon Steels (or Mild Steels)
- Medium Carbon Steels
- High Carbon Steels
- Very High Carbon Steels
Tensile strength and yield strength are important measures of a material’s ability to perform in an application, and the measurement is widely used when describing the properties of metals and alloys.
Different grades of steel will have different tensile and yield strengths. It’s generally accepted and recommended by engineers that steel used for pallet rack have a minimum yield strength of 50,000 psi.
The mill certificate is mill-issued document that provides the end-user of the raw material verification that the material received matches the requirements of their order. maintain traceability of the material from its start to its inclusion in a finished part.
The high amount of carbon in carbon steel makes it more vulnerable to corrosion. If you need a rust-free carbon steel product and want to avoid the high costs of stainless steel, you’ll want a surface treatment on your product. Here are the options:
- Powder coating
- Hot-dip galvanized
- Zinc electroplating
Photo Credit: Trissi1234 – Own work, CC BY-SA 4.0; click on image to view source.