People often buy pre-finished stainless steel, which adds to the complexity of the material that operators have to consider.
Like most materials, stainless steel has many advantages and disadvantages. A steel is considered “stainless steel” if the alloy contains at least 10.5% chromium, which forms an oxide layer making it acid and corrosion resistant. This corrosion resistance can be further improved by increasing the chromium content and adding additional alloying additions.
The “stainless steel” material properties, low maintenance, durability and various surface finishes make it suitable for industries such as construction, furniture, food and beverage, medical and many other applications requiring the strength and corrosion resistance of steel.
Stainless steel tends to be more expensive than other steels. However, it offers strength-to-weight benefits by allowing for thinner material than conventional grades, which can result in cost savings. Because of its overall cost, shops need to make sure they use the right tools to avoid costly waste and reworking of this material.
Stainless steel is generally considered difficult to weld because it dissipates heat quickly and requires great care during the finishing and polishing steps.
Working with stainless steel usually requires a more experienced welder or operator than working with carbon steel, which tends to be more stable. Its breadth can be reduced by introducing certain parameters, especially when welding. Due to the high cost of stainless steel, it makes more sense for more experienced operators to use it.
“People usually buy stainless steel because of its finishes,” said Jonathan Douville, senior product manager, R&D International, Walter Surface Technologies, Pointe-Claire, Que. “People usually buy stainless steel because of its finishes,” said Jonathan Douville, senior product manager, R&D International, Walter Surface Technologies, Pointe-Claire, Que. «Люди обычно покупают нержавеющую сталь из-за ее отделки», — сказал Джонатан Доувилль, старший менеджер по продуктам R&D International, Walter Surface Technologies, Pointe-Claire, Que. “People usually buy stainless steel for its finish,” said Jonathan Douville, Senior Product Manager, R&D International, Walter Surface Technologies, Pointe-Claire, Que. “People usually buy stainless steel for its finish,” says Jonathan Douville, senior manager of international research and development at Walter Surface Technologies in Pointe Claire, Quebec. “This adds to the constraints that operators must consider.”
Whether it is a size 4 linear texture coating or a size 8 mirror finish, the operator must ensure that the material is gentle on the material and that the coating is not damaged during handling and processing. It can also limit preparation and cleaning options, which are critical to quality part production.
“When working with this material, the first thing to do is make sure it is clean, clean and clean again,” said Rick Hathelt, PFERD Area Manager for Canada, Ontario, Mississauga, Ontario. “It is very important to make sure you have a clean (carbon-free) atmosphere when cleaning stainless steel to remove impurities that can later cause oxidation (rusting) and prevent the passivation layer from recovering by creating a protective layer to minimize oxidation. ”
When using stainless steel, the material and the environment must be cleaned. Removing oil and plastic residue from materials is a good start. Contaminants on stainless steel can cause oxidation, but they can also create problems during welding and cause defects. Therefore, it is important to clean the surface before soldering.
The workshop environment is not always the cleanest and cross-contamination can be a problem when working with stainless and carbon steel. Often the store runs many fans or uses air conditioners to cool workers, which can push contaminants onto the floor or cause dripping or condensation to build up on raw materials. This is especially difficult when carbon steel particles are blown onto stainless steel. Separating these materials and storing them in a clean environment is essential when it comes to efficient welding.
It is important to remove discoloration so that rust does not build up over time and weaken the overall structure. It is also good to remove bluing to even out the color of the surface.
In Canada, due to extreme cold and winter weather conditions, it is very important to choose the right grade of stainless steel. Douville explained that most stores initially chose the 304 because of its price. But if the shop were to use this material on the outside, they would recommend switching to 316 even though it costs twice as much. 304 is susceptible to corrosion when used or stored outdoors. Even if the surface is cleaned and a passivation layer is formed, external conditions can act on the surface, destroying the passivation layer and eventually causing rust again.
“Welding preparation is important for a number of fundamental reasons,” says Gabi Miholix, Application Development Specialist, Abrasive Systems Division, 3M Canada, London, Ontario. “Removal of rust, paint and bevels is essential for proper welding. The weld surface must be free of contaminants that could weaken the joint.”
Hatelt adds that area cleaning is necessary, but pre-weld preparation may also include chamfering the material to ensure proper adhesion and strength of the weld.
When welding stainless steel, it is important to select the correct filler metal for the grade being used. Stainless steel is particularly sensitive and requires welds to be certified for the same type of material. For example, base metal 316 requires filler metal 316. Welders cannot just use any type of filler metal, each grade of stainless steel requires a specific filler to weld properly.
“When welding stainless steel, the welder really has to keep an eye on the temperature,” said Michael Radaelli, product manager for Norton | Saint-Gobain Abrasives, Worcester, Massachusetts. “There are many different devices that can be used to measure the temperature of the weld and the part as the welder heats up, because if a crack appears in the stainless steel, the part is practically destroyed.”
Radaelli added that the welder must ensure that he does not stay in the same place for a long time. Multi-layer welding is a great way to keep the substrate from overheating. Prolonged welding of base stainless steel can cause it to overheat and crack.
“Welding stainless steel can take longer, but it is also an art that requires skilled hands,” Radaelli said.
Post-weld preparation really depends on the end product and its application. In some cases, Miholix explained, the weld is never visible, so only limited post-weld cleaning is required, and any noticeable spatter is quickly removed. Or the weld may need to be leveled or cleaned, but no special surface preparation is required. If a fine or mirror finish is required, more advanced polishing steps may be required. It just depends on the application.
“The problem is not the color,” Miholic said. “This discoloration of the surface indicates that the properties of the metal have changed and may now oxidize/rust.”
Selecting a variable speed finishing tool will save time and money and allow the operator to customize the finish.
It is important to remove discoloration so that rust does not build up over time and weaken the overall structure. It is also good to remove bluing to even out the color of the surface.
The cleaning process can damage surfaces, especially when using harsh chemicals. Incorrect cleaning can prevent the formation of a passivation layer. This is why many experts recommend manual cleaning of these welded parts.
“With manual cleaning, if you don’t allow oxygen to react with the surface for 24 or 48 hours, you don’t have time to create a passive surface,” Douville said. He explained that the surface needs oxygen to react with the chromium in the alloy to form a passivation layer. In some stores, it’s customary to clean, pack parts, and ship them right away, which slows down the process and increases the risk of corrosion.
Manufacturers and welders typically use multiple materials. However, as mentioned earlier, the use of stainless steel imposes some limitations. Taking the time to clean up the part is a good first step, but it’s only as good as the environment it’s in.
Hatelt said he continues to see contaminated jobs. The key is to eliminate the presence of carbon in the stainless steel working environment. It is not uncommon for shops using steel to switch to stainless steel without proper preparation of the working environment for this material. This is a mistake, especially if they cannot separate the two materials or buy their own set of tools.
“If you have a wire brush for grinding or preparing stainless steel and you use it on carbon steel, you can no longer use stainless steel,” Radaelli said. “The brushes are now contaminated with carbon and rust. If the brushes are cross-contaminated, they cannot be cleaned.”
Stores must use separate tools for material preparation, but they must also label tools “stainless steel only” to avoid unnecessary contamination, Hatelt said.
Shops should consider many factors when selecting stainless steel welding preparation tools, including heat dissipation options, mineral type, speed, and grain size.
“Choosing a heat dissipative coated abrasive is a good start,” Miholix said. “Stainless steel is very hard and generates more heat when grinding than mild steel. The heat has to go somewhere, so there is a coating that allows the heat to flow to the edge of the disc, rather than stay exactly where you are grinding. at that point it was perfect”.
The choice of abrasive also depends on what the overall finish should look like, she adds. It really is in the eye of the beholder. Alumina minerals in abrasives are by far the most common type used in the finishing steps. To make stainless steel look blue on the surface, the mineral silicon carbide should be used. It is sharper and leaves deeper cuts that reflect the light differently, making it blue. If the operator is looking for a specific or unique surface finish, it is best to speak with the supplier.
“RPM is a big problem,” Hatelt said. “Different tools require different RPMs and often run too fast. Using the correct RPM provides the best possible results, both in terms of how fast the job gets done and in terms of quality. Find out what finish you want and how to measure it.”
Douville added that investing in variable speed finishing tools is one way to solve speed problems. Many operators try a regular grinder for finishing, but it only has a high speed for cutting. Completion of the process requires slowing down. Selecting a variable speed finishing tool will save time and money and allow the operator to customize the finish.
Grit is also important when choosing an abrasive. The operator should start with the best grit for the application.
Starting with a 60 or 80 grit (medium), the operator can jump to 120 grit (fine) and 220 grit (very fine) almost immediately, giving stainless steel a 4th place finish.
“It could be as little as three steps,” Radaelli said. “However, if the operator is dealing with large welds, he cannot start with a 60 or 80 grit and may choose a 24 (very coarse) or 36 (coarse) grit. This adds an extra step and can be difficult. remove deep scratches in the material.”
Also, adding an anti-spatter spray or gel can be a welder’s best friend, but it’s often overlooked when welding stainless steel, Douville says. Spattered parts must be removed, which can scratch the surface, require additional sanding steps and take more time. This step can be easily eliminated with a splash guard system.
Lindsay Luminoso, associate editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. Lindsay Luminoso, associate editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. Линдси Луминосо, помощник редактора, вносит свой вклад как в Canadian Metalworking, так и в Canadian Fabricating & Welding. Lindsey Luminoso, Associate Editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. Lindsey Luminoso, Associate Editor, contributes to Metal Fabrication Canada and Fabrication and Welding Canada. She was Associate Editor/Web Editor at Metal Fabrication Canada from 2014 to 2016 and most recently Associate Editor in the Design Department.
Luminoso holds a Bachelor of Arts degree from Carleton University, a Bachelor of Education degree from the University of Ottawa, and a Graduate Certificate in Books, Magazines, and Digital Publishing from Centennial College.
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