If you work with steel, you may be aware that there are four main types of steel:
- Carbon steel, which can be low-, medium- or high-carbon
- Alloy steel, which contains elements other than carbon along with the base iron
- Tool steel, which is hard and durable
- And stainless steel
Of these, stainless steel is often the one steel users prize the most. What exactly makes up stainless steel, and what makes it special? Can you plate on stainless steel and, if so, is there a benefit to doing so? Here's what you need to know about stainless steel plating.
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What Is Stainless Steel?
Stainless steel is steel that does not corrode. It is also known as inox (for "inoxidizable") steel or corrosion-resistant steel. It is an alloy steel that contains at least 10.5 percent chromium, which makes it highly resistant to oxidation. When typical steel is exposed to air or water, the iron quickly bonds with oxygen to form iron oxide, or rust, which in turn accelerates the oxidation. This causes the surface of the steel to flake off.
The chromium in stainless steel reacts with the oxygen to create a chromium oxide film, which has the opposite effect of the iron oxide, becoming a protective layer that blocks further oxygen penetration into the seal and its subsequent corrosion.
Can You Plate Onto Stainless Steel?
Yes, plating onto stainless choice is an excellent choice for various applications. SPC can electroplate your stainless steel products using the same techniques we use for electroplating any other parts. We can electroplate carbon steel and alloy steel as well. Before plating stainless steel, we prime it with a nickel strike to enable the plating to adhere to the steel. Then, we deposit the metal finish using standard electroplating methods.
Why plate stainless steel? Although it is already corrosion-resistant, the protective effects of chromium only work if it can form a chromium oxide film. This is not always easy in low-oxygen environments or environments with poor air circulation since the chromium forms its protective layer by binding with oxygen. Therefore, if your industry calls for you to use your components in these kinds of environments, your stainless steel may need an added layer of protection.
The other reasons to plate stainless steel are the same reasons you might plate any other component. For example, you may want to alter the appearance of the stainless steel using gold or silver plating. Many people like the appearance of stainless steel, but a precious metal overlay will add an aesthetic element.
You may also need to plate stainless steel to add certain qualities to your components that aren't present in stainless steel. For example, if your part requires higher surface conductivity or needs to be more solderable, as is the case for many computer components, you can plate the stainless steel part with nickel to enhance these attributes.
Types of Metal Used For Stainless Steel Plating
What types of metal can be used for stainless steel plating? Some of the leading options are copper, rhodium, zinc, nickel, gold and platinum.
Copper is used mainly for its excellent conductivity. Combining the conductivity of copper with the strength of stainless steel is valuable for a variety of applications. Copper is useful because it's soft and malleable, which makes it perfect for use with flexible metal materials and objects. It also won't separate from other metals even if it gets bent.
Copper electroplating is used in many applications that require high electrical conductivity and plating thickness. It's often used for semiconductors and printed circuits. It's also used as heat treat stop-off for masking, an undercoat to improve adhesion, a treatment to prepare surfaces for soldering and in several other applications. Many different industries, including the aerospace and electronics sectors, rely on copper electroplating.
Sometimes, to improve the adhesion of copper to stainless steel as well as other metals, you can strike a nickel layer before plating the copper. You can also use a cyanide solution with the copper solution, but it's important to note that cyanide is highly toxic. Certain surface preparation methods, such as abrasive blasting, may also help to improve adhesion.
Rhodium is a popular coating as it can enhance resistance to corrosion, wear and abrasion and increase a component's durability. It will not oxidize even if exposed to extreme heat, has an extremely high melting point and is resistant to most kinds of acids. It's also exceptionally dense, enabling you to create as thick a coating as you need.
Rhodium also has a unique aesthetic appeal and creates a brilliant, white, reflective finish. Additionally, it has low electrical resistance and low contact resistance and is chemically inert.
The manufacturing of catalytic converters is responsible for about 80 percent of the rhodium used in industry because the metal can decrease the level of nitrogen oxides in exhaust gases. It's also used to manufacture detectors used to measure the level of neutron flux in nuclear reactors.
Electroplating is a common method used to plate rhodium. When plating rhodium onto stainless steel, you may first plate a thin layer of gold, copper or nickel to help the rhodium adhere to the component. You might also add another layer of palladium or palladium mixed with another metal in between the first layer and the top layer of rhodium.
Zinc offers excellent corrosion protection and is relatively inexpensive, making it an excellent choice for certain plating applications. When in its natural state, this metal has a shiny, blue-white appearance, but commercial-grade zinc is usually grayer. Zinc is hard and brittle but becomes pliable if subjected to extreme heat.
This metal has valuable corrosion protection properties, and you can enhance its natural corrosion resistance by using passivation treatments or alloying it with nickel, cobalt, iron or other metals. Zinc produces a smooth, clean finish.
Zinc plating is frequently used for fasteners such as nuts, bolts and brackets and as an undercoating on surfaces before painting. The automotive sector often uses zinc and zinc alloys. It's also used for electrical transmission components and in the manufacturing of armored vehicles.
To improve the adhesion of zinc onto stainless steel or other metals, you may want to use a nickel strike before applying the copper plating. It's also essential that you clean the surface of the substrate to remove contaminants that may prevent adhesion. You can clean the surface by using an alkaline detergent and then treating it with acid.
Nickel plating can enhance stainless steel's already impressive corrosion resistance, its wear resistance and its hardness. It also makes it easier to solder, improves its resistance to radiation and increases its electrical conductivity. Additionally, nickel plating produces a smooth, even coating, and you have flexibility in plating volume and thickness.
Nickel plating is used for many different applications across various sectors. Its electrical conductivity makes it useful for battery and generator applications, while its hardness and durability make it ideal for equipment used under harsh conditions such as valves, pumps mixer shafts and heat exchangers used in the oil and gas industry. The automotive sector also frequently uses nickel, and you'll find electroless nickel plating on gears, fuel system components, motor housing starter inserts, brake caliper pins, heat sinks and more. It's also used for manufacturing hydraulic components, firearms and other items.
You can plate nickel using both electroplating and electroless plating methods. We also use two different kinds of nickel electroplating — sulfamate and sulfate. In electroplating, you need an electric current to deposit the metals onto the substrate. In electroless plating, a specially made solution triggers chemical reactions that cause the metals to bind to the substrate. Whichever method you use, you typically will need to clean the substrate thoroughly before plating and then apply a nickel strike to improve adhesion.
Gold plating is often used for its aesthetic appeal, but it also increases resistance to corrosion, wear and tarnishing. Additionally, gold has high electrical conductivity and stable contact resistance. It can also act as a heat shield to protect the substrate from damage caused by extreme heat.
Because of its electrical conductivity and its durability, the main industry that uses gold plating is the electronics industry. Connectors, switches, contacts and other components are often plated with gold. Dentistry also uses gold for false teeth, crowns and caps.
Like with other plating metals, cleaning the substrate and applying a nickel strike can help with adhesion.
Platinum is another metal that you can plate onto stainless steel. It offers numerous benefits, including excellent protection against corrosion, wear and tarnishing. It also improves electrical conductivity and heat resistance and is aesthetically pleasing. Additionally, it can absorb excess hydrogen, which is why the automotive industry uses it in the manufacture of catalytic converters. The absorption of extra hydrogen improves the converter's performance.
The auto industry also uses platinum to manufacture spark plugs and other components. Other sectors that use platinum include agriculture, oil and gas and the medical sectors.
You can also plate various other metals onto stainless steel, and other options include silver and nickel-chrome plating. The right metal to use depends on the qualities you need your components to have, the processes you want to use, your budget and other factors. The experts at SPC can help you choose the right plating materials and processes for your needs.
What Are Some of the Uses of Stainless Steel?
The strength, corrosion resistance and low maintenance requirements of stainless steel make it useful for many different applications. It plays a key role in many industries and many parts of our daily lives. Some of the most common areas in which stainless steel is used include:
- Architecture and construction: Stainless steel is frequently used in the construction of buildings. It's used for the exterior cladding for large buildings as well as for the interior. Countertops, handrails, backsplashes and other elements are often made with stainless steel. In addition to its durability, strength and corrosion resistance, stainless steel is also recyclable and is often made of recycled materials, which complements the shift toward more sustainable buildings.
- The foodservice industry: Stainless steel is often used in food and catering businesses as it does not impact food flavor. Its corrosion resistance is also useful for storing and serving acidic foods and beverages. Various kinds of kitchen tools, appliances and accessories are made using stainless steel, including cutlery, cookware, grills and sinks. It also serves as a finish on countertops, refrigerators, freezers and dishwashers. More ductile types of steel are used for items that need to be molded such as sinks and saucepans, while less ductile steel is used to make knife blades.
- The medical field: Stainless steel is easily sterilized, making it ideal for use in the medical field. Its resistance to corrosion and durability are also useful for medical applications. Surgical and dental instruments are often made with stainless steel, as are operating tables, MRI scanners and cannulas. Surgical implants, replacement joints and stainless steel pins and plates used for broken bones are also often made with stainless steel.
- The automotive sector: The automotive sector uses a large amount of stainless steel for everything from structural components to accessories. Trims, grills, bumpers, exhaust systems, brake pedals, gears, battery casings, seat belt buckles and much more are made with stainless steel. It's also used for other forms of transportation equipment such as aircraft, ship containers, road tankers and more.
- The energy sector: Many of the components used in the energy sector need to be able to withstand harsh conditions that include high heat and corrosive environments. The energy sector uses high-grade stainless steel to construct valves, pipes, storage tanks and other vital components. Because crude oil is highly corrosive, steel is ideal for use in the construction of oil rigs. Stainless steel also helps offshore wind farms withstand the corrosive marine environment.
- The chemical industry: The chemical industry often works with toxic, corrosive substances, and its equipment must be able to withstand harsh environments. This makes stainless steel an ideal candidate for use in this sector. Because of its high strength, storage tanks and other equipment can also be thinner, reducing costs and equipment weight.
This is just a small selection of the industries that use stainless steel. You can find it in a wide range of equipment, structures and components across many different sectors.
The Process of Plating Onto Stainless Steel
There are various methods you can use to plate on stainless steel. The two main techniques are electroplating and electroless plating, but there are many variations within those two overarching methods.
Electroplating is the most common method of metal plating. It involves using an electric current to cause a thin layer of metal to deposit onto the surface of a substrate. In electroplating, you attach the plating metal to the anode, which is the positively charged electrode, of an electrical circuit. You also connect the substrate to the cathode, the negatively charged electrode. You then submerge both the plating metal and substrate in a specially developed electrolytic solution called a plating bath.
Once the parts are immersed in the plating bath, you supply an electric current to the anode. This current oxidizes the metal atoms of the plating metal and dissolves them into the electrolytic solution. The dissolved metal ions get reduced at the cathode and are deposited onto the substrate. You can adjust the outcome of the process by adjusting factors such as the chemical composition of the bath, the temperature of the bath, the voltage level of the current, the length of time during which you apply the current and the distance between the anode and cathode.
SPC performs various types of electroplating, including rack and barrel electroplating. Rack plating involves attaching substrates to a rack using metal hooks or bands before submerging them in the plating bath. We use specially built racks, which enables us to provide coatings that meet our customers' needs.
Barrel plating is ideal for plating a high number of small parts all at once. To perform barrel plating, you place the items to be plated in a barrel-shaped cage made of a nonconductive material. You then submerge the cage into the plating solution and use a slow tumbling action to begin the plating. The individual pieces establish a bipolar contact with each other, which improves the efficiency of the plating. This method is not recommended for engineering or ornamental finishes because of the contact between the pieces.
At SPC, we can electroplate stainless steel substrates using the same kinds of techniques we use for plating onto other materials. When plating onto stainless steel, we typically clean the substrate and then apply a nickel strike to help the metal coating adhere to the component.
2. Electroless Plating
Electroless plating is a popular alternative to electroplating. This method of plating, also called autocatalytic plating or conversion coating, does not require an electric current. Instead, a chemical reaction causes a nickel coating to deposit onto the substrate.
To cause this chemical reaction, you place substrate into a bath that contains a nickel salt, hypophosphite and various other chemicals that control the pH levels and keep the process stable. Once you place the base material in the bath, it acts as a catalyst and causes the nickel to deposit onto it. This process is purely chemical and does not require any electrical power or extra machines.
When you use the electroless plating method, the resulting coating is typically exceptionally hard and less porous than coatings deposited using electroplating. This makes the coating more corrosion-resistant and makes electroless plating popular for products that need high resistance to corrosion and wear. Electroless plating also produces very uniform deposits even on complex shapes.
Some options for electroless plating include using a nickel-phosphorous alloy, which is ideal for corrosion resistance. A nickel-boron alloy, meanwhile, provides excellent wear resistance. We can also infuse ceramics into the coating to increase durability.
Before we begin the electroless plating process, we clean the substrate using chemical cleaners. We then dip it into the solution and add anti-oxidation chemicals. Electroless plating is a simpler process than electroplating and gives you more control over the process.
Can You Plate Components With Stainless Steel?
Stainless steel plating has numerous benefits that vary depending on which type of metal you decide to plate with. However, since stainless steel is a metal itself, can you also use it as a metal finish for plating?
While it is possible to use stainless steel as your metal finishing substance, there is little benefit to doing so. The corrosion-fighting benefits of stainless steel will not transfer to your component to any greater degree than traditional metal finishes will, so you are better off finishing your plated components with a substance like nickel, silver or gold that will confer other useful properties to your parts while still providing durability and corrosion resistance.
Choose SPC for Stainless Steel Plating Services and All Your Electroplating Needs
Whether you're interested in plating stainless steel or some other type of material, whether you're seeking gold plating, silver plating, copper plating or another type of metal finish, SPC is the company you can rely on. With over 80 years of experience in the plating industry, you can be confident SPC can meet all your plating needs, regardless of your industry.
If you've never considered electroplating for your components before, you should be aware that it confers many advantages beyond merely protecting against corrosion and other atmospheric conditions, although these are valuable benefits. Electroplating can also enhance the appearance of your components, reduce friction, absorb excess hydrogen, absorb light, shield from radiation, increase your product's electrical conductivity and more, depending upon the type of plating you choose. Electroplating can be extremely cost-effective and dramatically improve the efficiency of your operation.
Our full-service electroplating facility has managed requests from a range of industries including the electronics, telecommunications and automotive sectors as well as others. Our loyal and growing customer base knows we bring value and quality to every electroplating project we take on. We'd love to show you how we can put our techniques to work for you.
To learn more about how electroplating your components can benefit your business or for a free quote on our plating services, contact SPC today.
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"I would like to thank you for the help you have provided us in developing an electroless nickel plating technique on an unusual substrate. The sample platings you provided show that we should be able to reach our goals. I especially appreciate your willingness to take on an unusual job, with the uncertainties that that entails...We are looking forward to working with you in the future on our plating needs."
– Robert K.