Sunday, December 4, 2022

Welding stainless steel


In modern civilization, the role of stainless steel is immense. From home appliances to large constructions, stainless steel is used in almost every instance. The unique ability of this alloy to resist corrosion and rust makes it more suitable and long-lasting than other alloy steels or iron.

Welding techniques differ in the case of stainless steel as there are multiple aspects that you need to keep in mind. Here, you will get a detailed guide on welding stainless steel to become an expert welding professional.

What Is Stainless Steel?

Stainless steel is an alloy made of iron, carbon, a minimum of 11% chromium, and a small amount of Nickel. Adding Nickel and chromium makes stainless steel corrosion and rust-proof steel alloy that is lustrous and can be moulded into different shapes and sizes. On top of that, stainless steel has a high melting point of 2500 degrees F and is a great conductor of heat and current.

Best Way To Weld Stainless Steel

The best part about stainless steel is that it can be easily welded by any arc welding procedure. Since it can withstand hot and cold temperatures, it can be moulded and fused in almost every way.

Things Needed To Weld Stainless Steel?

For welding stainless steel, you can follow any welding method. The equipment list is as follows-

  • MIG, TIG, Flux-core, Stick welder, choose depending on the method you are using
  • Stick electrodes with the required filling material and refill for
  • Welding wire feeder
  • Gun liner and welding gun
  • Shielding gas (either inert or non-inert)
  • Welding table or workstation
  • Clamps
  • Safety gear, including helmets, sleeves, gloves, leather apron, safety goggles, and welding boots
  • MIG pillars
  • Ventilation for indoor workstations
  • Grinder pr wire brush or solvent to clean the metal slug after and during welding.

Preparing a Welder

You must prepare the welder properly to ensure the welding procedure is successful. That includes using and choosing proper filling electrodes, the proper work environment, and the right method.

Please remember that each welding technique has different preparation stages.

TIG Welder Preparation

TIG or Tungsten Inert Gas welding is often used for stainless steel work pieces. It is ideal if the joints are critical and you need precise and clean fused joints.

Amperage

The amperage is one of the crucial points to make TIG welding a success. The first state with the maximum amperes, and as the welding procedure progresses, decreases it slowly to complete the procedure.

Foot or Finger Amperage Control

For successful TIG welding, you need to minimize the excessive heat to prevent any distortion in the workpiece during welding. Mostly, welders use their foot pedals to control; the amperage and heat. But, if there are some hard-to-reach areas, you may also need to use finger controls. While welding, check the welding piece and then choose the welding control you need to use.

While some welding projects will require either foot or finger control, others will require both controls.

Electrode Details

As a welder, you need to choose the ideal electrode size. The thickness and diameter of the electrode depend on the thickness of the work piece you arousing. In general, electrodes of various depths, starting from 3/32 inch to ¼ inch are used.

There are different tungsten electrodes which are often colour coded for convenience. You will have to choose the electrode as per the work piece base material and thickness. In general, the red-coloured tungsten electrode is used. But other colours may be required for different stainless steel alloy work pieces.

The next thing you need to check is the tapered shape of the electrode tip. Experts recommend using a tape of (2.5 times) the electrode diameter for precise fusion. If the taper is larger than this size, it may not penetrate deeper and may not even weld the joints properly.

Polarity and Pulsing

Welding for stainless steel, you need to set the TIG welder polarity to Direct Current Electrode Negative or Straight Polarity Electrode positive can harm electrodes instantly. Hence, do not use that.

Next comes the pulsing or pulse rate. The pulsing is generally set to 100 pulses to 500 pulses per second, depending on the work piece you are using.

TIG Shielding Gas

The gas shield is extremely important as it protects the welder from occasional splatter and the work piece from reacting with airborne gases.

In general, for TIG welding argon gas shields are used. Sometimes, Helium or nitrogen or hydrogen is also added to make the gas shield more fluid and to strengthen its power of the gas shield.

Experts recommend going for a gas shield with a flow rate of 35-50 cubic per hour. But, the flow rate may change depending on the project.

MIG Welder Preparation

The best part about MIG welding is that it can be automated so that the wire feeder constantly works with a proper pulsed current supply. It is an ideal welding technique because the joints and the steel work piece are intricate.

But, MIG welding is ideal for longer welding projects. With automation, things become easier to handle. But, sometimes, the welding project cost can increase due to the expensive gas shields.

MIG Wire

The main and initial step before starting MIG welding is to choose the right wire with the core. Depending on the base steel work piece, you must decide on the filler material and the filler rod size. Most welders use ER309L filler. But you can also use the other available options.

Furthermore, keep some replacement fillers handy as you will need these if the filler gets consumed in the middle of the project.

You can always buy a MIG welding machine with a gun and a sample welding wire. It can help you a little with finding the right filter material.

If you are using a welding gun, get a liner that allows you to switch between the wires faster.

Shielding Gas

After deciding on the wire filler, you must decide on the shielding gas. Since stainless steel is highly reactive to atmospheric gases, mainly inert gases with a mixture of carbon dioxide are used. The standard formula for this mixture is 90% helium, 2.5% carbon dioxide and 7.5% argon. This mixture is popular as it prevents the steel work piece’s carrion and offers better bead contouring.

In this case, pure inert gases are not used as these gases may prevent the MIG feeder arc from working properly.

Polarity

For MIG welding Direct Current Electrode Positive arrangement is recommended.

Wire Feed Speed

The wire feeder speed should be decided depending on the work piece and the thickness. In general, a higher wire feed speed is recommended with mild steel.

Amperage and Voltage Settings

You can use the manual or experience to set the amperage and voltage settings. Generally, a lower amperage setting is recommended due to its higher wire feeding speed. On top of that, higher voltage is used to keep the molten metal poodle wet to make the welded joints flatter and more precise.

Flux-cored Welder Preparation

Flux core welding is also a semi-automated or manual process that can be used with stainless steel. In this method, a flux-cored wire-fed electrode is used. The flux creates a shielding gas effect while the feeder is consumed as the filler material.

Wire Selection

The filler material inside the consumable electrode wire is essential for stainless steel. Since this wire is flux coated, it has a more complex structure than a MIG wire. Always choose the flux-coated wire depending on the stainless steel; alloy and its thickness.

If you are using the wire outdoors, always use a gasless wire that does not emit gas during consumption. But, such wires usually work only with horizontal and flat welding. Furthermore, procuring such wires is also difficult.

Polarity

The polarity for flux core welding depends on the core wire you use. Hence, always check the wire and then set the polarity accordingly.

Shielding Gas

In the case of flux-coated welding, dual shielding is used to protect the project. But, since you are using stainless steel, you may not always need it. Even though keeping a cylinder of the shielding gas handy is a great option.

For flux core welding, a gas shield of carbon dioxide or a mixture of 75% argon with 25% carbon dioxide is used.

Stick Welder Preparation

Stick welding is a good choice for stainless steel as this method offers high cracking resistance and good strength. On top of that, it can also re-join stainless steel workpieces that are already used.

In most industrial and construction projects, the appearance of the fused material does not matter. Due to this, welders prefer stick welding in those projects. Besides that, it is also commonly used as stick welding can be performed outdoors, even in windy environments.

Stick Electrode

The stick electrode or welding rod is the most crucial for this project. You can find stick electrodes in stainless steel, with or without flux coatings. So, you must consider the options before choosing the best one for your current project.

In case the project involves uneven joists or intricate patterns, it is also better to check out the composition of the flux coating. If you choose the wrong stick, the flux may get mixed with the electrode, resulting in poor-grade welding.

Amperage

You can generally find the amperage settings on the welder manual or the chart on the welder. In the case of this method, the amperage is kept as low as possible.

You will also notice that the stick will get hotter as you start welding, and the beading texture will also change. Before proceeding, you may lower the amperage and allow the stick to cool for a few minutes.

Anti-Spatter Product

The main concern with stick welding is the frequent splattering of the molten stick. Since you are working with stainless steel, spray some anti-spatter liquid or use anti-spatter gel on the work piece before you start welding.

Preparing Stainless Steel For Welding

The preparation of the workpiece is important for a successful welding project. Here are the steps you need to follow-

Cleanliness

Always clean the workstation surface and the work pieces properly before you start welding. Make sure to remove paint, rust, oil or dirt thoroughly. Stainless steel is more vulnerable to contamination, and a small particle of dust or dirt can also create issues, including poor welding joints.

Fit-Up

After cleaning, make sure to check the alignment of the work pieces. Ensure there are no gaps (for gapless welding). If you need to maintain gaps after welding, always ensure that the gap is even throughout the work piece.

Edge Prep

If you work with thicker stainless steel work pieces, you may need to prep the wedges to ensure the edges are fused correctly. Try to file the edges and make sure they fit together nicely.

Tips For Welding Stainless Steel Successfully

1. Keep the Heat Down

Stainless steel is vulnerable to heat. It may even start to get wrapped when the heat is extremely high. This can create porous and easily breakable joints or even distortion after welding. So, it is better to keep the heat on the lower side. For this, always keep the amperage to a lower level. You can also be investing in a temperature-tracking device that will help you to monitor the heat.

2. Use a filler core with a smaller diameter

You may be tempted to go with a large-diameter filler rod for completing the welding project faster. But that may result in more problems. Thicker filler materials need higher heat, which can result in warping in the work piece.

So, always choose a smaller filler diameter to get precise and cleaner welded joints.

3. Fine Tune The Fit-Up

Fine-tuning the whole range of equipment is necessary. It will allow you to choose the right filler material to complete the project. On top of that, this prevents heat-related damage as well. So, take your time to fine-tune everything, as there is no going back once you start!

4. Use an Electrode Designed or Filler Material for the SS Alloy

You will find filler electrodes made of different stainless steel compositions, but for the best results, you need to use a filler rod with the same composition. If you use a different filler steel, the welding bead may start to get damaged from rust, but if you use the filler stick with the same steel alloy, such issues do not happen. On top of that, using a filler material or stick with the same composition as the base material also prevents contamination during the welding.

5. Choose the (Stick and Flux-Cored) Right Torch Angle

In any consumable welding method, be it flux cored or stick welding, slugs form. The slug can create a hindrance and may not allow the filler material to properly reach the joints to fuse work pieces. In this case, the angle and movement of the torch are crucial. You must give the torch in such a way that it keeps the slugs away and allow the filler material to reach the joist without any contamination directly.

While a 10-degree torch drag angle is recommended for flux core welding, you may need to go for steeper angles for stick welding. Always make sure to hold the torch at a 90-degree angle.

If there are intricate joints like lap joints or t-joints, use a drag angle of 45-70 degrees.

6. Have the Right Wire Stick Out

In the case of flux core or MIG welding, you must ensure the wire stick is out. On top of that, the nozzle and the workpiece should be at the right distance to ensure the filler material reaches the joints properly.

Another issue with FCAW is the flux coating. With heat, often the core metals, while the flux coating, does not melt at the same rate. So, you will have to trim the top of the electrode to make it smoother and to bring out the filler material a little more. Similarly, trimming the consumable electrode wire also helps in the case of MIG welding as it offers a smoother and cleaner tip.

7. TIG Weld Puddle

In the case of TIG welding, you need to melt the extra filler material to ensure that it matches the base material thickness. If the molten metal pool is thinner, it will create a poor fused joint. On the contrary, thicker poodles often create larger and more distorted beads.

Suppose there is more molten metal. Reduce the heat with the pedals and stop adding the filler material. Wait till the molten metal hardens, and then proceed with the next welding.

8. Deposition Rate

As each welding process is different, the metal decomposition also differs. The thumbs rule says that if you need a higher decomposition rate; go for a flux-coated welder with dual shields.

9. Travel Speed

The speed of the torch and your hard work should not be too slow. If you move too slowly, excessive heat will start to wrap the heated position of the work piece.

If you move slowly, the beads will have a higher crown, while the slag will not cover the welded area properly. This will result in a greyish colour of the head and the fused area. On top of that, such issues often create highly porous welds, which may break or develop rust easily.

So, always keep your pace up. But do not move too fast, as this will create narrower beads with ropey welds.

10. Rust Prevention

Although stainless steel does not develop rust, the welds can develop rust. There are a few hacks to prevent rust on the welded area-

  • Ensure the gas shield is effective and doesn’t get blown away.
  • Always keep the amperage lower to keep the heat low to prevent heat-related damages.
  • Always use the ideal shielding gas or gas mixture, depending on your welding method.
  • Always clean the welded areas properly with pickling paste or wire brushes. If there is some discolouration, you can also use grinders or abrasives. Alternatively, you can also use electrochemical cleaners. But, if you are using a brush, do not use a steel wire brush, as it can increase the chances of rust.

To prevent warping, try clamping a piece of copper or brass below the welding seam. It will offer some cooling effect and will not cause burning of the oral piece.

In case you are using MIG welding, go for the push method. It will offer you to produce less beading with a cleaner welded joint. Use the pull technique only when you need to penetrate deeper through the material.

Conclusion

Since stainless steel is more vulnerable to high heat, you need to find a welding technique to weld the steel work pieces. You need the right equipment and guide alongside a good workstation to complete the welding project. You can use this article as a guide to initiate the welding project.



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