Carbon steel is one of the most commonly used materials in industry. Its popularity is due to its favorable mechanical properties, relatively low price, and wide range of applications. It is used in the construction of steel structures, pipelines, pressure vessels, bridges, as well as in technological installations used in the chemical, petrochemical, food, and energy industries.
The welding process of carbon steel plays a key role in ensuring the durability and reliability of these structures. Properly made welds guarantee high mechanical strength and resistance to environmental factors. However, the wrong choice of welding method, technological errors or insufficient parameter control can lead to serious defects, such as cracks, deformations or reduced weld quality.
Why do cracks and deformations occur?
In the welding process of carbon steel, it is crucial to control the many factors that can lead to weld defects. The most common problems include:
Cold cracks – resulting from high hydrogen content in the weld and welding stresses. Particularly dangerous in the case of high-carbon steel and thick structural steel.
Hot cracks – caused by inappropriate chemical composition of steel, excess sulfur and phosphorus, and too high welding temperature.
Welding deformations – resulting from thermal expansion of the material and improper sequence of welds. They can lead to deformation of the structure and weakening of its strength.
Incorrect weld quality – resulting from incorrect selection of welding parameters, poor post-weld heat treatment or use of inappropriate welding materials.
These problems can lead to costly failures, increased risk of cracks in service and the need for costly repairs. To prevent them, it is necessary to use proven welding methods, properly prepare the material and control the welding parameters at every stage of the process.
The most common causes of cracks and deformations in carbon steel welding
Welding carbon steel requires precise control over the process, because technological errors can lead to cracks and deformations. These defects not only weaken the structure, but also increase the risk of failure and repair costs. To effectively prevent them, it is worth understanding their main causes and mechanisms of formation.
Types of cracks in welds
1. Cold cracks
Cold cracks, also known as hydrogen cracks, occur at low temperatures after the welding process is complete. Their main cause is the presence of hydrogen in the weld and residual stresses resulting from uneven metal shrinkage during cooling.
Factors that increase the risk of cold cracking:
Too high hydrogen content in the welding material – may come from moisture in the electrodes, shielding gases or contamination on the steel surface.
High-strength steels – materials with increased hardness are more susceptible to cracking under stress.
Lack of heat treatment after welding – uncontrolled cooling promotes the formation of residual stresses in the weld.
How to prevent?
Use of low-hydrogen electrodes and dry welding consumables.
Control of hydrogen content in shielding gases.
Proper preparation of carbon steel surface – removal of moisture and contamination.
Preheating and controlled cooling after welding.
2. Hot cracks
Hot cracks occur during the solidification of the weld, when the metal is still in a liquid or semi-plastic state. They are most often caused by improper chemical composition of the material, especially excessive amounts of sulfur and phosphorus, which reduce the resistance of the metal to cracking.
Factors affecting hot cracking:
Too high welding temperature – leads to excessive grain growth in the heat affected zone (HAZ).
Inappropriate chemical composition of steel – high sulfur and phosphorus content promotes brittleness at high temperatures.
Incorrect welding methods – e.g. too high welding line energy leading to overheating of the metal.
How to prevent?
Selection of appropriate welding materials with low sulfur and phosphorus content.
Application of optimal welding parameters – avoidance of excessive metal overheating.
Control of interlayer temperature and appropriate cooling rate.
3. Welding deformations
Weld deformations result from thermal expansion and contraction of the metal as it cools. They are particularly problematic in thin sheet metal and large steel structures, where uncontrolled deformations can lead to loss of dimensionality and reduced strength.
Factors causing deformations:
Lack of control over welding sequence – welding in the wrong sequence can lead to uneven shrinkage and stresses in the structure.
Incorrect selection of welding method – e.g. single-sided welding in the case of thick sheets can cause significant deformations.
Inappropriate heating and cooling temperature – sudden temperature changes promote uncontrolled metal shrinkage.
How to prevent?
Use of symmetrical welding sequence – stress distribution in the structure.
Use of clamps and templates to control the shape of the welded part.
Use of welding methods with lower heat input, e.g. TIG welding for thin parts.
Preheating and controlled post-weld cooling.
Factors influencing the formation of defects
In addition to the welding process itself, technological and material factors play an important role and may increase the risk of cracks and deformations.
1. Hydrogen content in the material
Hydrogen is one of the main causes of cold cracking. It can enter the weld from wet electrodes, contaminated surfaces or shielding gases.
How to prevent this?
Use of low-hydrogen electrodes and store them in dry conditions.
Removal of moisture and contamination from steel surfaces before welding.
Control of hydrogen content in shielding gases.
2. Carbon Steel Thickness and Welding Strategy
The thicker the steel, the greater the risk of internal stresses and deformation. Special preventive strategies are necessary when welding thick elements.
How to prevent this?
Preheating to reduce the temperature gradient in the weld.
Creating multi-layer welds instead of a single thick layer.
Controlling the inter-layer temperature to avoid overheating.
3. Incorrect welding parameters
Incorrect settings for current, voltage, welding speed and interpass temperature can lead to weld defects.
How to prevent this?
Adjusting parameters to the type of carbon steel and its thickness.
Monitoring the welding process – automation and modern quality control systems can help eliminate errors.
Using proven welding technologies, e.g. TIG or MIG/MAG welding, depending on the specifics of the material.
Proven solutions for welding carbon steel
To avoid cracks and deformations in welding of carbon steel, it is necessary to use proven welding methods, appropriate materials and preventive measures. The right selection of technology depending on the material thickness, working conditions and required weld quality is crucial.
Proper selection of welding method
1. TIG welding – precision and high quality of the weld
TIG (Tungsten Inert Gas) welding is recommended where high quality and precision of the weld are key. This method uses a tungsten electrode and shielding gases, which allows for clean and aesthetic joints without spatter.
Application:
Thin elements made of low-carbon and medium-carbon steel.
Precision welding in technological installations.
Chemical, food and pharmaceutical industries.
Advantages:
Very high quality weld.
Minimization of heat input – lower risk of deformation.
No spatter, clean weld.
2. MIG/MAG welding – efficiency and speed
MIG/MAG welding is one of the most commonly used methods for welding carbon steel. It uses a welding wire as an electrode and shielding gases (e.g. argon, CO₂ or gas mixtures), which ensures arc stability and good mechanical properties of the weld.
Application:
Steel structures, pipelines, heavy industry.
Welding of medium and heavy steel.
Mass production of steel elements.
Advantages:
High welding efficiency and speed.
Possibility of welding in various positions.
Good weld quality at a relatively low cost.
3. Covered Electrode Welding (SMAW) – Ideal for Field Work
The SMAW (Shielded Metal Arc Welding) method, also known as covered electrode welding, is commonly used in field conditions where shielding gases cannot be used.
Application:
Pipeline installations, bridge structures.
Welding in field conditions, e.g. on construction sites.
Repairs and modernization of steel structures.
Advantages:
Can be used in all weather conditions.
Does not require access to a shielding gas cylinder.
Good weld quality even on dirty surfaces.
4. Arc welding – automation and robotics
In the case of large-scale production and complex industrial structures, robotic arc welding is increasingly used. Process automation allows for increased repeatability, reduced errors and cost optimization.
Application:
Mass production of steel elements.
Structures requiring high precision and repeatability.
Technological and industrial installations.
Advantages:
High repeatability and quality of welds.
Reduction of manual labor costs.
Optimization of production time.
Selecting the right welding materials and shielding gases
1. Low Hydrogen Electrodes – Minimizing the Risk of Cold Cracking
Low hydrogen electrodes are essential in welding high strength steels to reduce the risk of cold cracking. Their use reduces the amount of hydrogen diffusing into the weld, which increases its resistance to stress.
When to use?
In the case of high-strength steel.
In thick elements requiring minimal residual stress.
2. Shielding Gases – Arc Stability and Weld Quality
Selecting the appropriate shielding gas has a key impact on the arc stability and mechanical properties of the weld.
Argon (Ar) – used in TIG welding, provides arc stability and minimizes oxidation.
Carbon dioxide (CO₂) – often used in MAG welding, improves penetration depth and weld strength.
Ar+CO₂ mixtures – used in welding structural steel, combine the advantages of both gases.
3. Types of carbon steel and additional materials
The selection of appropriate welding consumables depends on the type of carbon steel.
Low carbon steel – easily welded, requires standard electrodes and welding wires.
Medium carbon steel – requires preheating and appropriate cooling parameters.
High carbon steel – more susceptible to cracking, requires low hydrogen electrodes and precise temperature control.
Preventive measures in the welding process
1. Carbon Steel Surface Preparation
To avoid welding defects, the surface must be thoroughly cleaned of grease, rust and moisture. Contamination can lead to weld porosity and weakening of the joint.
How to prepare the material?
Removal of grease and oils using solvents.
Removal of rust and oxides from surfaces by mechanical grinding or brushing.
2. Interlayer Treatment – Temperature Control and Stress Avoidance
Multi-layer welding requires control of the inter-layer temperature to prevent overheating and internal stresses.
Recommendations:
Maintaining a constant temperature in the process.
Avoiding too rapid cooling, which can lead to stress and cracks.
3. Hydrogen Content Control – The Importance of Heat Treatment
Hydrogen is one of the main factors causing cold cracking, so it is important to reduce it before and after welding.
How to reduce hydrogen content?
Use of low-hydrogen electrodes.
Preheating to evaporate moisture from the material.
Post-weld stress relief annealing to reduce internal stresses.
Heat treatment and quality control as key elements of defect prevention
To ensure the durability and reliability of a weld, welding alone is not enough – post-weld heat treatment and weld quality control also play a key role. Heat treatment reduces internal stresses and improves the mechanical properties of the joint, while advanced testing techniques allow potential defects to be detected before they lead to structural damage.
Post-weld heat treatment – reducing stress and improving metal structure
During welding, carbon steel generates thermal stresses that can lead to deformation or cold cracking. To prevent this, various post-weld heat treatment methods (PWHT – Post Weld Heat Treatment) are used.
Types of post-weld heat treatment:
Stress relief annealing
Used to reduce residual stresses that occur during welding.
It involves heating the structure to a temperature of 550–650°C and then gradually cooling it.
Recommended for welded elements of great thickness and high-carbon steels susceptible to cold cracking.
Normalization
A process that involves heating the weld to a temperature of approximately 850–950°C and cooling it in air.
Improves the metal structure and eliminates undesirable microstructures, such as weld brittleness.
Recommended for medium carbon steels and structures requiring high strength.
Hardening and tempering
Used when increased hardness and abrasion resistance are required, e.g. for machine parts.
After heating to 850–1000°C, rapid cooling is performed, followed by tempering in the range of 150–700°C to reduce brittleness.
Preheating
Reduces temperature differences between the weld and the base material, which reduces the risk of cracking.
Particularly important when welding high-carbon steels and thick elements.
Application of modern quality control technologies
Modern technologies enable precise assessment of weld quality without the need to damage them. Non-Destructive Testing (NDT) allows for detection of discontinuities, cracks and inconsistencies in the weld structure.
The most commonly used NDT methods in carbon steel welding:
Ultrasonic Testing (UT)
It uses ultrasonic waves to detect internal weld defects.
It allows for the identification of cracks, lack of fusion and discontinuities.
Used in the shipbuilding, aviation and energy industries.
Radiographic Testing (RT)
Uses X-ray or gamma radiation to scan a weld.
Detects internal cracks, gas pores, and non-metallic inclusions.
Popular method for testing pipelines and pressure vessels.
Penetrant Testing (PT)
Used to detect surface cracks and other discontinuities.
The method is based on the application of a dye that penetrates microcracks, making them visible.
Mainly used to control the quality of welds in thin elements and TIG welds.
Magnetic Particle Testing (MT)
Uses a magnetic field to detect cracks and discontinuities on and below the weld surface.
Effective for ferromagnetic steels, used e.g. in the railway and power industry.
Welding defects and methods of detecting them
Welding defects can significantly reduce the quality of the joint and affect the durability of the structure. Early detection is key to avoiding costly repairs and the risk of failure.
The most common welding defects and methods for detecting them:
| Type of defect | Cause | Detection method |
|---|---|---|
| Cold cracks | Excess hydrogen, internal stress | UT, RT, MT research |
| Hot cracks | Excess sulfur, poor welding parameters | RT, UT research |
| Porosity | Moisture in the material, bad shielding gas parameters | RT, PT tests |
| No melting | Welding energy too low | RT, UT research |
| Flooding | Welding energy too high | UT, PT research |
| Non-metallic inclusions | Contaminants in the material | RT, UT research |
Carbon Steel Fault Detection with Deffor
Carbon steel welding requires precise selection of the method, materials and quality control to avoid cracks and deformations. Proper surface preparation, interlayer temperature control, use of low-hydrogen electrodes and post-weld heat treatment are key.
Don’t skimp on materials – high-quality steel, wires and shielding gases translate into durability and safety of the structure. Modern technologies such as automation and robotics increase welding precision and efficiency, eliminating human errors.
If you care about the highest quality welds, durable structures and a professional approach, use the services of Deffor – experts in the field of carbon steel welding and technological installations. Contact us and find out how we can help with your project!
