Welding High Carbon Steel
High Carbon steel are comparable to mild steel except the carbon amount which is usually more than 0.45%. The definition of high carbon steel varies from 0.45% to 0.55%.
However, a carbon content more than 0.4% in carbon steels start giving rise to weldability issues. Higher the carbon content, lower the weldability with more issues such as cracking, brittleness, high stresses, high hardness, etc.
In this article, I have explained in depth, how you can weld a high carbon steel with minimal weldability issues and what should you do and don’t.
What is High Carbon Steel?
High carbon steel is a type of alloy steel that is composed mainly of iron and has a carbon content ranging from 0.45% to 1.7%.
It contains other elements, such as manganese, silicon, nickel, chromium and molybdenum which give it superior mechanical properties compared to other types of steel.
High carbon steel is commonly used in the manufacture of tools and machinery due to its ability to withstand wear and tear more effectively than other steel alloys.
Due to high carbon content, high carbon steel properties (such as hardness, toughness, tensile strength) can be easily altered by heat treatment.
The properties of High Carbon Steel make it more difficult to work with than low carbon steel due to its increased brittleness when heat treated compared to other types of steels.
Why it is difficult to weld high carbon steel?
Welding high carbon steel can be a difficult and strenuous process. The material is very strong, hard and brittle, which makes it challenging to work with.
High carbon steel is composed of iron and carbon alloyed together in varying amounts depending on the desired strength.
The main weldability issues faced during high carbon steel welding are:
- Weld cracking due to high hardness,
- Low ductility causing more distortion,
- High hardness,
- Formation of cracking due to high stresses,
- Formation of martensite,
- Bigger Heat affected zone (HAZ),
- Higher risk of welding porosity,
- Dissimilar weld metal properties.
Welding Preheat for High Carbon Steel
High Carbon steel requires higher welding preheat compared to low & medium carbon steel.
Generally, a high carbon steel requires welding preheat temperature of 450°F to 850°F (230°C to 450°C). Higher the carbon content in the steel, higher the welding preheat temperature.
In addition, it also needs post heating after weld completion to have low hardness and release of residual stresses.
You can easily calculate welding preheat temperature for high carbon steel using below free online welding preheat calculator.
Welding High Carbon Steel
Welding of High carbon steel requires:
- Ductile & low strength filler welding rod,
- High preheat and post heating,
- Control of welding penetration to give minimal weld dilution,
- Say No to cold weld,
- Anneal before welding in case of Quenched & tempered steel.
- Weld thicker passes.
High carbon steel requires special welding techniques due to the high hardness of the material and its propensity to form hard martensitic microstructures.
In addition, pre-and post-weld heat treatments are often required in order to reduce residual stresses caused by thermal expansion and contraction cycles during cooling.
Welding Electrode for High Carbon Steel
Low hydrogen electrodes are the most popular choice for welding high carbon steel, as they can withstand higher stresses without compromising ductility.
Nickel base rods are also an excellent choice when welding with high carbon steels, providing welds that retain their strength and ductility under extreme conditions.
Nickel base rods suitable for high carbon steel welding are ENiFeCr-3 or E309L-15. Some companies’ manufacturers special welding electrodes for high carbon steel although they are costly.
Low hydrogen electrodes produce less hydrogen-induced cracking in joints due to their ability to reduce the amount of hydrogen in the weld metal during the welding.
Low hydrogen electrodes produce superior results when working with higher grades of carbon steel such as AISI 1045 or AISI 1060.
Welding Procedure for High Carbon Steel
Follow this welding procedure when welding high carbon steel:
- Prepare the surface of the metal by grinding off any rust or paint. Make sure surface is free from moisture otherwise it can be a source of hydrogen in weld.
- Next, preheat the surface of high carbon steel (minimum 2 inches on each side from weld center) before beginning the welding process. This is important because it reduces stress on the material, making it easier to work with during welding.
- Use low hydrogen electrodes only. Make sure the rods are properly baked.
- Maintain welding preheat until the weld is completed. In case of weld interruption, cover the welding area under cawool. Preheat again before start of welding.
- After weld completion, apply a post heating of around 850°F (450°C) for 15-30 minutes. This will work as a hydrogen debaking as well as reduce the residual stresses and eliminate cold cracking.
- Carry out the final stress relieving.
Finally, set up your welding machine according to manufacturer instructions and begin welding at low heat settings with short welds until you have finished joining both pieces together securely
Welding High Carbon Steel to Low Carbon Steel
High carbon steel contains more carbon than low carbon steel which makes it much harder and stronger but also more brittle. Low carbon steel has less than 0.25% carbon.
No special precautions required for low carbon steel side, but on high carbon steel side, welding preheat must be applied.
Use E7018 low hydrogen electrodes for stick welding or ER70S-2 when welding High Carbon Steel to Low Carbon Steel with TIG or MIG welding process.
Weld using weaving beads as this will result in slow weld cooling and thus prevent weld cracking or high hardness in HAZ and weld zone.
Welding High Carbon Steel to Mild Steel
High-carbon steels are harder and more brittle than mild steels, so special attention must be paid to the right welding rod use.
You can use E7018 low hydrogen rod for welding High Carbon Steel to Mild Steel.
Apply weld preheating only for high carbon steel. No preheat is needed for mild steel.
Welding Quenched & Tempered (Q & T) High Carbon Steel
Welding Quenched & Tempered (Q & T) High Carbon Steel shall be carried out in annealed state.
As we know Q & T steels welding is also difficult and annealing them before welding will improve their weldability.