Welding Stainless Steel – How To Weld Different Alloys Of Stainless Steel [Guide and Tables] 2021

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Stainless steel is one of the most popular materials when it comes to welding. It is both durable and possesses high resistance to corrosion, making it attractive for usage in various projects. However, the material does come with its ups and downs and a welder needs to have enough knowledge about it in order to manipulate stainless steel the proper way.

Today we will tell you all about the basics of welding stainless steel so you will know what to do when a project involving comes up.

Understanding Stainless Steel

Stainless still is an iron-based alloy that contains chromium. This substance is what gives stainless steel its most important property – corrosion resistance. The amount of chromium usually floats somewhere between 11% and 30%. Each individual metal actually has different chemical attributes and combined with the amount of chromium present comes with different needs.

The usage of stainless steel is expanding thanks to its somewhat unique properties. It is a strong type of material that is resistant to various gases, liquids, and chemical corrosion and is for that reason used in many fabrication shops. It is very durable and it does take a lot to actually tarnish it which is the reason why it has so many different applications.

Unfortunately, mainly due to its favorable properties, stainless steel is also expensive. It costs five times more than mild steel.

Welding of stainless steel pipe by electric arc welding in argon shielding gas. TIG welding.


Types of Stainless Steel

You may be surprised to learn that there is more than one type of stainless steel. Actually, there are five types that are characterized as stainless steel but most welders usually encounter three of them in their welding career. Each of them comes with its own characteristics and ways to weld stainless steel.

Austenitic Stainless Steel

Austenitic stainless steel is the most common type used today. It has non-magnetic properties and high weldability. Its main usage comes within the standard fabrication and is used for more than 70% of production that we have today.

It is labeled under the 300 series with the 304 being the most commonly used grade by far.

Range of composition: (C ≤ 0.10% – 16%) ≤ (Cr ≤ 28% – 3.5%) ≤ (Ni ≤ 32% – (Mo ≤ 7%)).

Austenitic Filler Metal Selection

Coils of stell stripes in store
AISI Steel Recommended Filler Material Alternate Filler Material
201, 202, 205 240 308, 347, 309
301, 302, 302B 308 347, 309
304, 304L 308L 347, 309
304H 308H 347, 309
303, 303SE 312 309MO
316, 309S 309 309CB, 310
310, 310S, 314 310 310CB, 310MO
316, 316L 316, 316L 309MO, 317
316H 316H 309MO, 317
317 317 317L, 309MO, 318
321 347 309CB, 310CB, 321
347, 348, 347H 347 309CB, 310CB
320 320LR 320
330 330
904L 385

Martensitic Stainless Steel

Martensitic stainless steel is known for being the first type of stainless steel developed for commercial use. It has magnetic properties and can be hardened through tempering and quenching. The most popular usage of martensitic stainless still is in the production of cutlery.

It possesses chromium levels between 12% and 18% and a relatively high carbon content of 0.1% to 1.2%. Due to this, the 410 grade is used as a standard filler material choice for overlays on carbon steel.

Most of the martensitic stainless steel out there is welded with TIG Welding machines 

Range of composition: (C ≤ 1.2% – 11.5%) ≤ (Cr ≤17%) – (Mo ≤1.8% – ≤ Ni ≤ 6% – V ≤ 0.2%)).

Martensitic Filler Metal Selection

AISI Steel Recommended Filler Material Alternate Filler Material
403 410 308, 347, 309
410, 410S 410 308, 347, 309
414 410 410NM, 309
420 420 309
431 410 309, 310
440A 312 309

Ferritic Stainless Steel

Ferritic stainless steel is known for being the cheapest type of the main three ones. Because of this, it is often used for making consumer products, auto parts, and sheet metal. It possesses magnetic properties and is very formable and highly ductile. Unfortunately, its greatest weakness is high temperature.

The automotive industry is the biggest consumer of ferritic stainless steel with grades 409 and 439 being used the most.

Range of composition: (C ≤ 0.08% – 10.5%) ≤ (Cr ≤ 30% – (Mo ≤ 4.5%)).

Ferritic Filler Metal Selection

AISI Steel Recommended Filler Material Alternate Filler Material
405 410 308L, 309, 410NM
409 409CB 430, 309LSi
430 430 308L, 309L
442 308L 309L
446 308L 309L


Preparing to Weld

Mechanized cleaning of the root surface of the weld control sample of thick-walled stainless steel pipeWhen welding stainless steel, preparation is the most important part. A welder needs to clean the material and their work areas thoroughly so there are no amounts of carbon steel present on the stainless steel material being worked on.

The same thing goes for your tools and welding machine, you have to clean them so no residue of carbon steel is found on them.

If particles of carbon steel end up in stainless steel, it can cause your final product to rust, ultimately defeating the purpose of using this material in the first place. Even trace amounts of carbon steel dust particles pose a threat.

Another thing to take into account when welding stainless steel is filler metals. The choice of filler material will depend on the type of base metal that you are working on. The best way to go about this is to use a filler metal with the same number as the base metal grade.

Common Stainless Steel Welding Methods

Choosing the right type of welding process for welding stainless steel depends on the finish, the thickness of the material, the base materials, and the use of the end product. Even though there are a variety of methods used the most common welding processes are TIG welding, MIG welding, and resistance welding.

TIG Welding or Gas Tungsten Arc Welding

TIG welding (Gas Tungsten Arc Welding) is the most commonly used type of welding process for welding stainless steel as it offers high-quality, longevity, and versatility. TIG uses low heat input, perfect for this type of material.

Preventing oxidation and increasing corrosion resistance can be done with a single-sided welding process. That way, inert backing gas protection is created between the interior and the exterior welds.

A full article about TIG welding can be found here

Resistance or Spot Welding

Resistance welding is great for stainless steel welding as it is the most economical welding process. The equipment used for resistance welding is versatile and can be used in various types of projects.

When spot welding, electrical current is used to heat up metal edges and join them together. This process is best used for materials with a low melting point as it can help in preventing distortion.

MIG Welding or Gas Metal Arc Welding

MIG welding is a semi-automatic process that results in a strong joint when it comes to stainless steel. MIG welding requires an argon shielding gas and a good welding wire electrode or steel wire. This process uses a pulsed current supply which allows the welder to get to some of the tougher spots of the base material.

Choice of Shielding Gas for Stainless Steel Welding

Choosing the correct shielding gas comes with several factors.

  • Shielding efficiency.
  • Resistance to corrosion.
  • Metallurgy and mechanical properties
  • Surface appearance.
  • Weld geometry.
  • Metal transfer.

Shielding Gas Choice

Shielding Gas, Plasma Gas Backing Gas
 

 

GTAW

Ar

Ar + H2 (tot 20%);

Ar + He (tot 70%);

Ar + He + H2;

Ar + N2

Ar;

N2;

N2+ 10% H2

PAW Same as GTAW Same as GTAW
 

 

 

GMAW

98% Ar + 2% O2

97% Ar + 3% CO2

95% Ar + 3% CO2 + 2% H2

83% Ar + 15% He + 2% CO2

69% Ar + 30% He + 1% O2

90% He + 7.5% Ar + 2.5% CO2

 

 

 

Same as GTAW

 

FCAW

No

97% Ar + 3% CO2;

80% Ar + 20% CO2

No

Same as GTAW

LBW He

Ar

Same as GTAW

Ar – Argon, H2 – Hydrogen, He – Helium, N2 – Nitrogen, CO2 – Carbon Dioxide, O2 – Oxygen;                                                                                                Table by: worldofstainless.org



Checking the Temperature of Weld Metal and Base Metal

While welding stainless steel, you have to mind the temperature of both the base metals and the filler metal. If you don’t monitor the surface temperature, you are more than likely going to end up with problems.

Monitoring the heat input to the base and filler metal can be done with the help of temperature-indicating sticks, electronic infrared thermometers, and electronic surface temperature probes.

Is Welding Stainless Steel Difficult?

Details of construction of the modern bridge

Welding stainless steel is not so easy, especially for a beginner. This material is highly unforgiving when it comes to mistakes and high heat.

First of all, every scratch or blemish will remain visible. Mistakes are aesthetically visible and you might end up with an unattractive end product if you are not careful enough.

Secondly, stainless steel retains heat, making it susceptible to distortion and warping due to applied high heat while working on it. It can even warp because of the interpass temperature and during the cooling process if the heat is too great.

Working on stainless steel is thus left to more experienced welders that know how to handle it.

Conclusion

Stainless steel is a material used all over the world for various reasons. It is one of the most important materials used today and its usage is not going to diminish any time soon. But you do need to be careful when working on it. If you treat it right, you will get the desired results.

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