What is the Difference Between Galvanized Steel and Stainless

Both galvanized and stainless steel are incredibly strong metals with high durability and corrosion resistance, but with so many similar benefits and uses, it can be difficult to tell them apart. In order to choose the security door that best suits your premises, however, it’s important to know the details of how they differ as well as how they are similar.

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Galvanized Steel

Galvanized steel has a zinc coating which halts the rusting process for the underlying steel by corroding first. Though a thorough preventative method, adding molten zinc does not halt the rusting process completely and it is possible for this layer to begin to corrode after a time, revealing the underlying metal. For this reason, galvanized steel is often utilized as a product material where aesthetics are less of a concern, such as automotive components, metal cabinetry, traffic signs, and steel high security doors.

How is Galvanised Steel Made?

The galvanization process begins with sheets, coils, or fabricated components of stainless steel. The metal surfaces are cleaned to get rid of any dirt, oil, and the outer oxide layer. Next, the steel is given heat treatment, typically via Hot-Dip Galvanizing, the most common method. Clean steel is dipped into a bath of molten zinc where a metallurgical reaction occurs. During this reaction, iron and zinc bond to create zinc-iron alloy layers topped with pure zinc. As a result, the heat treated steel is topped with a tough, corrosion resistant coating which is metallurgically bonded.

The Galvanised Steel Security Door

Unlike plain steel, galvanized steel security doors do not require regular painting or rust-proofing with a protective layer and can withstand years outdoors with minimal upkeep. This is ideal for those who have significant time constraints or who may lack the resources to continually perform maintenance work. Another key benefit of the galvanized steel security door is its lower price tag when compared with stainless steel. This makes it an economical choice for homeowners and businesses in search of robust security without the high cost.

Stainless Steel

What makes stainless steel different from its galvanized relative are the literal elements it is composed of. Stainless steel components include iron, nickel, carbon, and chromium. The latter reacts with oxygen in the surrounding air to form a thin, invisible film of chromium oxide on the surface. This extra layer forms the ‘stainless’ component of stainless steel as it prevents rusting and makes it highly corrosion resistant. Types of stainless steel include:

Austenitic Stainless Steel For Medical Use

As well as being corrosion-resistant, this is a non-magnetic type. Austenitic stainless steel components consist of high levels of chromium and nickel, and it is commonly used in kitchenware, medical tools, and marine equipment.

Economical Ferritic Stainless Steel

More affordable than austenitic stainless steel, ferritic stainless steel comes with more moderate levels of corrosion resistance and lower levels of nickel. It is useful for automotive trim and various appliances.

Impact Resistant Martensitic Stainless Steel

Martensitic’s strength and toughness means it can be used for knives and tools. It also has aerospace applications, being useful for turbine blade construction. With higher levels of carbon but lower chromium than austentic and ferritic stainless steel, martensitic is less corrosion resistant but remains durable.

Impact Resistant Duplex Stainless Steel

Composed of around 50% ferrite and 50% austenite, duplex stainless steel has very high levels of impact resistance. With extra strength from the ferrite and toughness from the austenite, this type is able to retain its toughness in aggressive environments such as at sub-zero temperatures. It is used in oil and gas as well as for chemical processing.

How Stainless Steel is Made

Stainless steel is produced by melting raw materials together in a furnace, where the mixture is heated at high temperatures to approximately 2,700–2,900 °F until fully melted. The molten steel is then refined to maintain the structural integrity of its chemical composition, removing impurities like carbon, sulfur, and phosphorus. Once refined, the steel is then cast into semi finished shapes such as slabs for sheets or strips or blooms for structural steel shapes. When every process has been completed, the stainless steel is finished depending on the end use. This can be via polishing, brushing, or coating for extra corrosion resistance.

The Stainless Steel Security Door

The properties of stainless steel make it an ideal choice for a security door. For one thing, the base metal is a better option for fire safety, being able to better maintain its strength at higher temperatures compared with galvanized steel, which offers a limited level of fire resistance. Its manufacturing processes enable stainless steel security door or fire doors to hold their own for decades with minimal maintenance. It is resistant to cracking, warping, and pitting corrosion. Its low maintenance needs also extends to its exterior; unlike galvanized steel or wood, stainless steel security doors do not require frequent repainting or recoating. A mere wipe down will be enough to maintain its clean and polished appearance.

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Many of our high security doors, including our Double Steel Security Door, come with stainless steel handles in addition to a full weather seal and multi-point locking system. We also supply brushed stainless steel lever handles whose aesthetic appeal can give security doors great versatility in terms of design.

Whether they are manufactured using galvanized or stainless steel, our security doors and accompanying hardware are invaluable purchases with their wide-ranging functionality. Whether you are most concerned with impact resistance, better corrosion resistance, or service life, we have the doors and accessories to suit your needs.

Steel doors and frames are popular products that LaForce provides. Galvanized and galvannealed steel are two of the most common forms of carbon steel used in manufacturing these doors and frames. Although they may sound similar, it is important to know the difference between the two coating types so you can choose the right one for your building. Manufacturing process differences will ultimately determine the steel’s capabilities; however, we have outlined the basic similarities and differences between galvanized and galvannealed steel to help you make the best choice.

Similarities Between Galvanized and Galvannealed Coatings

Due to its high iron content, steel is prone to corrosion. Both galvannealed and galvanized coatings are types of zinc coatings designed to prevent the rust and corrosion of the steel. Both are manufactured per ASTM A 653/A 653M. They start the same way by going through the hot-dip process; the steel is dipped into a hot zinc bath, bonding the zinc to the surface of the metal. The process that occurs after the initial dip determines the type of coating and the corresponding properties. It is important to note that zinc-coatings cannot be applied after fabrication due to the thermal distortion of the product.

Whether the coating is galvanized or galvannealed, the coating weight represents the amount of zinc on the steel’s surface. Heavy coating weights provide the most corrosion protection because they contain higher amounts of zinc. Zinc coatings are recommended for exterior applications or interior applications where rust/corrosion might be an issue. It is difficult to compare the corrosion performance of galvannealed and galvanized coatings because galvannealed metal is usually painted, and paint systems have a significant influence on corrosion performance. Whether you choose galvanized or galvannealed metal will depend on the location, application, and desired appearance.

Galvanized Metal

Once carbon steel goes through the hot-dip process, it is considered galvanized metal. The mostly pure zinc coating causes the galvanized coating to have a bright, shiny spangled (marbled) pattern of light and dark gray spots. The pattern of the coating can be controlled by the choice of zinc alloy, hot-dip temperature, and cooling rate, but no two pieces look the same. The unique, shiny surface gives galvanized metal a great industrial appearance. This type of coating is designated with a “G”.

Not only does galvanized steel look different than galvannealed steel, but it also performs differently. Galvanized metal is softer and is easily scratched. Its softness makes it more malleable; it can be formed and shaped without worrying as much about destroying the zinc coating. The thicker the galvanized coating, the better performance against corrosion and the longer the product life. However, a thicker coating also means it is harder to work with. Galvanized steel is also cheaper than galvannealed steel, but it does not react as well to painting or welding. It will also react with muriatic acid if it is not primed or painted. For these reasons, galvanized coatings are not usually recommended for doors and frames unless otherwise specified.

Galvannealed Metal

After going through the hot-dip process, the carbon steel goes through a secondary process to create a galvannealed coating. The zinc-coated steel is heated to a higher temperature, pulling the iron from the steel and causing it to mix with the zinc coating and create a zinc-iron alloy coating. The added iron is what makes the galvannealed metal have different properties than galvanized metal. It also contributes to a different appearance; galvannealed metal has a more consistent, matte finish made of 90% zinc and 10% iron. However, the presence of iron in the coating can cause it to have a red tint, but it does not mean that the steel is rusting. Galvannealed coatings are designated with an “A”.

Galvannealed steel is harder and stronger than galvanized steel – it is not easily scratched. This type of coating is also more easily painted without the need for a primer, although a pretreatment or primer will enhance the performance. Galvannealed coatings are usually painted because it increases their durability and hides the red tint that people associate with rust. Galvannealed metal can also be welded more easily; its high electrical resistance, melting point, and hardness allow for easy welding at lower currents. For these reasons, galvannealed steel is the most recommended for architectural applications, including steel door and frame construction.

Choosing the Correct Zinc-Coated Steel

Zinc-coated steel doors and frames are a great choice when you are worried about rust and corrosion inside or outside your building. To help you decide which one to choose, you should consider the location, appearance, and application of the steel. High-traffic locations are best suited for durable galvannealed metal. Painted or matte appearances are best achieved with galvannealed coatings and unique, industrial looks are best achieved with galvanized coatings. When it comes to shaping the metal, you will need to consider the coating thickness of both metals, but in general galvanized metal is more malleable. If the application of the metal requires welding, galvannealed is recommended. The risk of corrosion will also determine the coating thickness. Although galvanized coatings are sometimes specified, galvannealed coatings are the recommended choice for steel doors and frames.

There are three types of zinc-coated steel typically used for manufacturing doors and frames.

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• A40 is a galvannealed coating of 0.4 ounces per square foot and provides minimal protection.
• A60 is a galvannealed coating of 0.6 ounces per square foot and is 50% more protective than A40. The A60 coating is the most common choice for all exterior doors and interior doors exposed to excessive moisture; it is an average thickness that provides good protection but is still easy to work with while maintaining a good appearance.
• G90 is a very heavy galvanized coating that tends to look rough even after it is painted. The added protection of G90 coatings makes them a great choice for extremely corrosive environments (pool areas, salty environments, etc.).