People often buy pre-machined stainless steel, which adds to the complexity of the material that operators must 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 that makes it acid and corrosion resistant.This corrosion resistance can be further improved by increasing the chromium content and adding additional alloying agents.
The material’s “stainless steel” 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 that require the strength and corrosion resistance of steel.
Stainless steel tends to be more expensive than other steels.However, it offers strength-to-weight ratio advantages, allowing the use of thinner material thicknesses compared to conventional grades, which can lead to cost savings.Because of its overall cost, stores need to ensure they are using the right tools to avoid costly waste and rework of this material.
Stainless steel is generally considered difficult to weld because it dissipates heat quickly and requires great care in the final finishing and polishing stages.
Working with stainless steel generally requires a more experienced welder or operator than working with carbon steel, which tends to be more resilient.Its latitude may be reduced when certain parameters are introduced, especially during welding.Due to the high cost of stainless steel, it makes sense for more experienced operators to use it.
“People usually buy stainless steel because of its finish,” says Jonathan Douville, senior product manager for international research and development at Walter Surface Technologies in Pointe-Claire, Quebec.”This adds to the constraints that operators have to consider.”
Whether it’s a size 4 linear texture finish or a size 8 mirror finish, the operator must ensure that the material is respected and the finish is not damaged during handling and processing.This can also limit options for preparation and cleaning, which are critical to ensuring good part production.
“When working with this material, the first thing to do is make sure it’s clean, clean, clean,” said Rick Hatelt, Canada Country Manager for PFERD Ontario, Mississauga, Ontario.”It’s very important to make sure you have a clean (carbon-free) atmosphere, cleaning the stainless steel to remove impurities that could cause oxidation (rusting) later and to disallow rebuilding of the passivation layer, creating a protective layer to minimize oxidation.”
When using stainless steel, the material and surrounding environment must be cleaned.Removing oil and plastic residue from materials is a good place to start.Contaminants on stainless steel can cause oxidation, but they can also be problematic during welding and can cause defects.Therefore, it is important to clean the surface before starting to solder.
Workshop environments are not always the cleanest, and cross-contamination can be an issue when working with stainless and carbon steel.Often a store runs many fans or uses air conditioners to cool workers, which can push contaminants onto the floor or cause condensation to drip or build up on raw materials.This is especially challenging when carbon steel particles are blown onto stainless steel.Separating these materials and keeping them in a clean environment makes a big difference when it comes to effective welding.
It is important to remove discoloration to ensure that rust does not build up over time and weaken the overall structure.It is also good to remove bluing to even out the surface color.
In Canada, due to the extreme cold and winter weather, choosing the right grade of stainless steel is important.Douville explained that most stores initially chose the 304 because of its price.But if a store were to use the material outside, he would recommend switching to 316, even though it costs twice as much.304 is susceptible to corrosion if used or stored outdoors.Even if the surface is cleaned and a passivation layer forms, outdoor conditions can affect the surface, eroding the passivation layer and eventually causing it to rust again.
“Weld preparation is important for a number of fundamental reasons,” says Gabi Miholics, application development specialist, Abrasive Systems Division, 3M Canada, London, Ontario.”Removal of rust, paint and chamfers is necessary for proper welding. There must be no contamination on the welding surface that could weaken the bond.”
Hatelt adds that cleaning the area is essential, but pre-weld preparation can also include chamfering the material to ensure proper weld adhesion and strength.
For stainless steel welding, it is important to select the correct filler metal for the grade used.Stainless steel is particularly sensitive and requires welding seams to be certified with the same type of material.For example, 316 base metal requires 316 filler metal.Welders cannot just use any type of filler metal, each stainless grade requires a specific filler for proper welding.
“When welding stainless steel, the welder really has to watch the temperature,” said Michael Radaelli, product manager at Norton | Saint-Gobain Abrasives, Worcester, MA.”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 there is a crack in the stainless steel, the part is basically ruined.”
Radaelli added that the welder needs to make sure he doesn’t stay in the same area for a long time.Multilayer welding is a great way to keep the substrate from overheating.Prolonged welding of the base stainless steel can cause it to overheat and crack.
“Welding with stainless steel can be more time-consuming, but it’s also an art that requires experienced hands,” Radaelli said.
Post-weld preparation really depends on the final product and its application.In some cases, Miholics explained, the weld is never actually seen, so only limited post-weld cleanup is required, and any noticeable spatter is quickly removed.Or the weld may need to be leveled or cleaned, but no specific surface preparation is required.If a fine or mirror finish is required, more elaborate polishing steps may be required.It just depends on the application.
“It’s not the color that’s the problem,” Miholics said.”This surface discoloration indicates that the metal properties have changed and can now oxidize/rust.”
Choosing a variable speed finishing tool will save time and money and allow the operator to match the finish.
It is important to remove discoloration to ensure that rust does not build up over time and weaken the overall structure.It is also good to remove bluing to even out the surface color.
The cleaning process can damage surfaces, especially when harsh chemicals are used.Improper cleaning can prevent the formation of a passivation layer.This is why many experts recommend manual cleaning of these welded parts.
“When you do manual cleaning, if you don’t allow oxygen to react with the surface for 24 or 48 hours, you don’t have time to build 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.Some stores tend to clean, package parts and ship them immediately, which slows down the process and increases the risk of corrosion.
It is common for manufacturers and welders to use multiple materials.However, as mentioned earlier, the use of stainless steel adds some limitations.Taking the time to clean the part is a good first step, but it’s only as good as the environment it’s in.
Hatelt said he keeps seeing contaminated work areas.Eliminating the presence of carbon in the stainless steel work environment is key.It is not uncommon for shops that use steel to switch to stainless steel without properly preparing the work environment for this material.This is a mistake, especially if they can’t separate the two materials or buy their own toolset.
“If you have a wire brush for grinding or prepping stainless steel, and you use it on carbon steel, you can’t use stainless steel anymore,” Radaelli said.”The brushes are now carbon-contaminated and rust. Once the brushes are cross-contaminated, they cannot be cleaned.”
Stores should use separate tools to prepare materials, but they should also label tools “stainless steel only” to avoid unnecessary contamination, Hatelt said.
Shops should consider many factors when selecting stainless steel weld prep tools, including heat dissipation options, mineral type, speed and grain size.
“Choosing an abrasive with a heat-dissipating coating is a good place to start,” Miholics said.”Stainless steel is very hard and will generate 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 instead of just staying where you are grinding At that point, it was ideal.”
Choosing an abrasive also depends on what the overall finish should look like, she adds.It’s really in the eye of the beholder.Alumina minerals in abrasives are by far the most common type used in finishing steps.To make stainless steel appear blue on the surface, the mineral silicon carbide should be used.It’s sharper and leaves deeper cuts that reflect light differently, making it blue.If the operator is looking for a specific or unique surface finish, it is best to talk to the supplier.
“RPM is a big problem,” Hatelt said.“Different tools require different RPMs, and they often run too fast. Using the right RPM ensures the best results, both in terms of how fast the job is done and how well done it is. Know what finish you want and how Measurement.”
Douville added that investing in variable-speed finishing tools is one way to overcome speed issues.Many operators try a normal grinder for finishing, but it only has a high speed for cutting.Completing the process requires slowing down.Choosing a variable speed finishing tool will save time and money and allow the operator to match the finish.
Also, grit is important when choosing an abrasive.The operator should start with the best grit for the application.
Starting with a 60 or 80 (medium) grit, the operator can almost immediately jump to a 120 (fine) grit and into a 220 (very fine) grit, which will give the stainless a No. 4 finish.
“It can be as simple as three steps,” Radaelli said.“However, if the operator is dealing with large welds, he can’t start with a 60 or 80 grit, and might choose a 24 (very coarse) or 36 (coarse) grit. This adds an extra step and can be difficult to remove in material There are deep scratches on it.”
Plus, adding an anti-spatter spray or gel can be a welder’s best friend, but it’s often overlooked when welding stainless steel, says Douville.Parts with spatter need to be removed, which can scratch the surface, require additional grinding steps and waste more time.This step can be easily eliminated with an anti-splash system.
Lindsay Luminoso, Associate Editor, contributes to Metal Fabrication Canada and Fabrication and Welding Canada.From 2014-2016, she was Associate Editor/Web Editor at Metal Fabrication Canada, most recently as Associate Editor for Design Engineering.
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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