stainless steel welding method

Stainless Steel Welding Method

Stainless steel can be welded using different welding methods. The activity requires certain parameters to be set keeping in mind the properties of the metal. Gas Tungsten Arc Welding, Shielded Metal Arc Welding, Gas Metal Arc Welding, Plasma Arc Welding, Submerged Arc Welding, Flux Cored Arc Welding, Electric Resistance Welding, and Laser Welding are some of the stainless steel welding methods.

But most common stainless steel welding methods are MIG, TIG, and Resistance Welding.


Post Highlights:

  • Stainless Steel Welding Meaning
  • Welding Process Selection for Stainless Steel
  • Welding Processes Used for Stainless Steel
  • Best Welding Method for Stainless Steel
  • Welding Machines for Stainless Steel
  • Weldability of Stainless Steels
  • Shielding Gases Selection for Stainless Steel Welding
  • How to Finish Treatments for Welds?
  • Safe Practices for Welding Stainless Steel

Stainless Steel Welding Methods, Weldability, and Safe Practices

Welders can use different welding types for stainless steel. Find various aspects of welding stainless steel with illustrations.

Stainless Steel Welding Mean

Stainless Steel Welding is a process and it is not much different from that required in welding standard carbon steel. Exceptions are everywhere. Welders need to exercise more control and care of heating and cooling stainless steel. It is noteworthy to properly match filler metals with the material being welded.

Welding Process Selection for Stainless Steel

The selection of the welding process for stainless steel mainly depends on the thickness of the materials. In the United States, welders mostly follow three methods for welding stainless steel i.e. MIG welding, TIG welding, and Resistance Welding types.

I. Stainless Steel MIG Welding

MIG (metal inert gas) welding is a semi-automatic welding type. It uses a continuous consumable solid wire electrode and an argon rich shielding gas for welds. It employs two modes i.e. short-circuit metal transfer mode for welding thin material, and spray arc transfer mode with thicker material. It also uses a gas mixture for improving stability.

Carbon Steel and Stainless-Steel Differences

Both stainless steel and carbon steel have physical and chemical differences. And It is an important factor that affects variables. Take a look at the following:

  • The coefficient of thermal expansion for austenitic types is about 50%. It is greater than carbon steel and could result in more distortion.
  • Stainless Steel has a lower thermal conductivity. This means the heat energy does not move away from the weld zone quickly.
  • Stainless Steel also has higher electrical resistance or lower electrical conductivity. It means the wire feed speeds at the same rate as used with carbon steel and will produce lower current levels with stainless steel.

II. Stainless Steel TIG Welding

It is an ideal choice for thin materials and stainless steel because of its aesthetic appearance, versatility, high quality, and longevity. GTAW is an arc welding process that employs a non-consumable tungsten electrode to produce the weld. TIG welding’s abilities like welding at low current, low heat input, adding filler wire at requirement make it suitable and stable for thin materials. Both pure argon and mixtures with helium or nitrogen, hydrogen are employed.

Welding Stainless steel may be tricky because due to retaining heat and it can lead to deforms like warping, embrittlement, and rust. Even five amperes can make the difference between the perfect weld and a blued or burnt-through part.

Tips for TIG Welding on Stainless Steel

Welders can master or make successful TIG welding on stainless steel by keeping in mind the following tips.

1. Selection of Filler Metal Appropriately – Before starting the welding process, make sure the diameter of the filler metal should be thinner than the base metal. This is because thicker the rod or wire it requires more heat to melt it. So, make sure the filler metal and base material should be compatible chemically. They should possess a similar mechanical property as well.

2. Taper Not more than 2.5 times the Electrode Diameter – The electrode geometry should be in balance. It means a taper should not be more than 2.5 times the electrode diameter. Further, it provides a focused arc capable of producing deep, thin beads and a narrow heat-affected zone. Contrary to it, if an electrode is with a taper of more than 2.5 times its diameter, then the arc may fan out. As a result, there is less penetration and a wider heat-affected zone.

3. Should be A Proper Fit up – This makes sure the use of only the required amount of filler metal. Without adding heat, it cannot be added filler metal.

4. The Puddle Size – Weld puddle should be the thickness of the base metal. In case, the puddle grows too large, welders should use foot pedals or fingertips to control/reduce heat input. Also, they can eliminate craters by easing down the current at the end of the weld or by adding a filler metal before puddle solidifies.

5. Apply Suitable Size of an Electrode – There are many sizes available. But the common size of tungsten electrodes ranges from 3/32 to 1-1/4 of an inch. Always select the right size and it depends on variables like amperage, joint size, polarity, and thickness of base metal.

6. Balance of Travel Speed and Gas Flow – Welders should not move the torch too fast. Rather than keep flowing the gas at the puddle until the orange color fades.

7. Use Fingertip and Foot Control Properly – By doing so, both foot and hand are free to control of torch and amperage. There are different designs, so make sure you select the one that works best for you.

8. Using Pulsed Gas and Polarity – Welders should use pulsed gas tungsten arc welding (GTAW-P) with a direct current electrode negative current. The current alternates between a low background amperage and a high peak amperage in pulsing. The peak current imparts a good penetration and fusion. And the background current maintains the arc and it allows the weld area to prevent cool, warping, and carbide precipitation.

III. TIG Spot/Resistance Welding

It is a welding process that uses electric currents for heating the edges of frayed metal and join them together. The TIG process is always an ideal way of welding for thin materials and metals with low melting points.

Best Welding Method for Stainless Steel

The best welding processes for stainless steel are as follows:

  • TIG welding (gas tungsten arc welding) might be ideal for thin materials
  • Spot welding might be a good option if you are seeking a more affordable weld type

Briefly, welders can weld stainless steel with many welding types. But the success rate depends on the selection of the welding process according to the thickness of the metal and finish of the material.

Welding Machines for Stainless Steel

Many companies manufacture machines for welding stainless steel. They carry different features depending on the brands. Some of the generally used machines are as follows:

  1. ESAB Rebel EMP 215ic Multi-Process MIG/TIG/Stick
  2. Hobart IronMan 230 MIG Welder
  3. Miller Dynasty 350 Water Cooled Welder

Weldability of Stainless Steels

There are normally four types of stainless steel and the composition structures are as follows.

1. Austenitic Stainless Steels

A. Structures containing a few percents of ferrite (usual case)

  • Excellent toughness and ductility
  • Embrittlement can occur after long exposures between 550 and 900°C due to decomposition of the ferrite to form sigma phase
  • Good resistance to intergranular corrosion for low carbon and stabilized grades
  • Insensitive to hot cracking

B. Fully Austenitic Structures (exceptional)

  • Excellent ductility and toughness
  • Good resistance to intergranular corrosion for low carbon and stabilized grades
  • It is sensitive to hot cracking during solidification

2. Ferritic Stainless Steels

A. Semi Ferritic Grades (0.04% C – 17% Cr)

  • Poor ductility and toughness
  • Post-weld heat treatment at about 800°C restores the mechanical properties and intergranular corrosion resistance
  • Sensitive to embrittlement by grain coarsening above 1150°C
  • Sensitive to intergranular corrosion

B. Ferritic Grades (0.02% C – 17-30% Cr)

  • Generally insensitive to intergranular corrosion
  • Satisfactory ductility and improved toughness compared to semi-ferritic grades
  • Sensitive to embrittlement by grain coarsening above 1150°C

3. Austenitic – Ferritic Duplex Stainless Steels

  • Excellent toughness and good ductility in the range from –40% C to 275°C
  • Insensitive to hot cracking
  • Sensitive to embrittlement by sigma phase when exposed between 500 and 900°C

4. Martensitic Stainless Steels

  • High tensile strength and hardness good toughness, particularly for low carbon grades
  • Sensitive to cold cracking, depending on the carbon and hydrogen contents and residual stress levels, below about 400°C

Shielding Gas Criteria for Stainless Steels Welding

Select shielding gases for welding of stainless steel is one of the most influential parts while welding with PAW, GTAW, FCAW, GMAW, and LBW. Before selecting, keep in mind the following things.

  • Arc Stability and Ignition
  • Corrosion Resistance – Loss of alloying elements, pickup of atmospheric gases, surface oxidation
  • Environment – Emission of fumes and gases
  • Metal Transfer (if any)
  • Metallurgy, Mechanical Properties – Loss of alloying elements, pickup of atmospheric gases
  • Shielding Efficiency – Controlled shielding gas atmosphere
  • Surface Appearance – Oxidation and spatters
  • Weld Geometry – Bead and penetration profiles

How to Finish Treatments for Welds?

Generally, arc welds require surface finishing. After completing an arc welding operation, the weld area and surroundings may contaminate sometimes. It happens due to various factors like weld spatter and oxide films, joint type, welding technique employed, and material thickness.

Finishing treatment may be any of the following ones employed, either singly or in combination, depending upon the welding technique.

  • Chemical Treatments – passivation and pickling
  • Grinding – to prevent overheating and associated heat discoloration
  • Polishing – removing the grinding marks using a 180 –320 mesh abrasive.
  • Removal of Slag, Splatter, and Oxide

Safe Practices for Welding Stainless Steel

All welders should follow general safety measures along with special guidelines and instructions attached by the manufacturer with the equipment. The following three measures are more important along with others.

1. Safety from an Electric Shock

It is the most dangerous shock. Normally, the arc voltage runs in the range from 10 volts to 40 volts. But in some cases, the voltage required to strike the arc may be higher, and the power sources have an open-circuit voltage up to 80 volts.

  • Do not let live-parts of the circuits and bare skin or wet clothing touch each other.
  • Insulate yourself from the workpiece and ground using dry insulation.
  • Do not dip the electrode holder in water.

2. Ventilation for Fumes and Gases

Welding produces gases and fumes in this way or that way. Some are hazardous to health, and others less harmful. Normally, these gases contaminate the atmosphere near the welding area. Therefore, the fumes and gases must be controlled and eliminated in the following ways:

  • Do not weld in areas near chlorinated hydrocarbon vapors.
  • Use a local ventilation or exhaust system at the arc to keep gases away from the breathing zone.
  • Use respiratory equipment only if all other measures have been eliminated.

3. Safety from Arc Radiation

Arc radiation is very harmful to the eyes and can burn the skin. Sometimes, it can blind the welders permanently. Welders should use the following measures to ensure safety from arc burns.

  • Employ a shield with a filter and glass screen to protect eyes from sparks and arc radiation
  • Protect other nearby people with suitable screening and warn them not to watch the arc.
  • Wear proper clothing to protect the skin from the radiation of an arc.

Conclusion

Thus, there are many welding processes for stainless steel. But for increasing the success rate, the most important factor is to select proper parameters for matching metal properties with other metals. Second, use proper equipment and welding guidelines for better welding results. Welders must go through the users-guide by manufacturers before starting welding stainless steel.

Related: Other Welding Types

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