Making sure your weld does not have cracks is not just important for aesthetic reasons; it is also important for public safety. It is incredibly frustrating for a welder to see cracks in his final product. If you do not have much knowledge about cracks, you may wonder what causes a weld to crack.
Cracks in your weld mainly occur because of rapid cooling and contamination problems. In most cases, the internal stress becomes stronger than the base metal, which breaks the weld. There are two types of cracks: hot cracking and cold cracking.
In this article, I will tell you why welds crack. You will learn about different types of cracks and how to prevent these cracks from happening.
Cracks are the most potentially dangerous of all the defects that happen in a weld. A crack in a welding unit is a fracture of the metal resulting from a stress imbalance. Cracks are typically found in three locations:
- In the weld
- At the fusion line between weld and base metal
- In the heat-affected zone of the base metal
A crack can happen in a weld because of improper welding techniques during and after the welding process. It can happen even before the welding process begins because of not preparing the metals. Here are some of the most common reasons welding cracks can happen:
- Inadequate preparation of workplace
- Rapid cooling of weld metals
- Contamination in the base metal
- Using contaminated filler materials
- Not preheating the metals before the actual welding process
- Imbalance in internal stress between weld design and base metal
- Because of poor joint design
- Not fitting the parts properly
- High welding speed but low current
- Welding ferrous metals with hydrogen
- Presence of a high amount of sulfur and carbon in the metal.
Different Types Of Cracks
You will learn about distinct cracks in the weld. All of them are dangerous. Using cracked weld products to build objects, buildings, or infrastructures increases the chance of accidents and can be a threat to public life. Hence, it is considered one of the biggest failures for welders.
There are mainly two kinds of cracks when it comes to poor weld quality- hot cracking and cold cracking. Another common type of cracking is crater crack. Let us learn how and when these cracks can happen.
Hot cracking happens due to the formation of shrinkage during the solidification of weld metals. Thus, it is also known as solidification cracking. During the process, metals get too hot and remain hot in the solidifying state. When the stress is too high in the solidifying stage, hot cracks form in the fusion area.
Hot cracking is a common problem in all most all-metal welding. These cracks form immediately after the weld is complete or during the formation. Expert welders categorize hot cracking into two types: centerline cracks and crater cracks.
Here are the main reasons for hot cracking formation:
- When the liquid weld metal is insufficient to fill the spaces between solidifying weld metal, it causes cracks.
- The liquid metal solidifies and shrinks. The strain on the weld pool becomes too high. Thus, the cracks appear.
- When the temperature gets more than 1200 degrees Celsius or 2192 degrees F.
- Contamination is another cause of hot cracking. Paint, rust, dust, zinc, carbon, sulfur, phosphorus, or any impurities might get into the weld pool. These make the weld weak, and it cracks.
Another common reason for hot cracking is when the weld bead is too wide and has a thin throat. As a result, the beading does not have sufficient strength to maintain the stress, and it shrinks, forming hot cracks.
How to Prevent Hot Cracks:
- Choose the materials carefully.
- Clean the impurities from the metals before welding.
- Reduce heat input. It will reduce the time for segregation formation.
- To lessen the possibility of hot cracks, modify the design to maintain a depth-to-width ratio. The ratio should not be too small or too great.
- The weld bead should have more throat thickness so that it can maintain stress.
Cold cracking can happen instantly. It can appear in minutes or even hours after the welding process completes. Thus, this type of cracking is unpredictable and dangerous. These cracks happen at temperatures below 350 degrees Celsius or 600 degrees F. Cold cracking occurs on the base metal and not on the weld.
The heat-affected zone (HAZ) cracking or hydrogen-assisted cracking is a type of cold cracking. These cracks form because of the high hydrogen concentration present in the metal.
So, here are the main reasons for cold cracking:
- High residual stress level on the weld
- Excess amount of hydrogen
- It occurs under low temperature
- A high amount of carbon on the base metal
How to Prevent Cold Cracking:
- Preheat the base material at a high temperature. Learn the correct temperature for welding different materials.
- Maintain a high heat input when welding.
- Use low hydrogen electrodes.
- Make sure that the time delay between weld runs is reduced.
- Choose low hydrogen filler metals.
- The slower the cooling rate, the better chance of reducing cold cracking.
Other Cracks You Should Know About
Hot cracking and cold cracking are the main types of cracks during welding. You can also divide metal cracks into other types. Some common types are:
- Longitudinal Cracks: These cracks run along the length of a weld bead. These cracks are also known as centerline cracks.
- Transverse Cracks: These cracks are perpendicular to the direction of the weld. Transverse cracks are more common in welds that happen for a high degree of shrinkage stress.
- Crater Cracks: The cracks take place when the welding is suddenly terminated. Due to abrupt termination, the crater is left unfilled with weld metal. Crater cracks are “X” shaped or star-shaped. These cracks extend to the edge of the crater.
How to Prevent and Fix Cracks
When you learn to use new techniques for welding and use new materials (base metals and filler materials), cracks may happen. Yes, it is frustrating, but it is also a process of learning welding.
Through regular practice and learning new skills, you will eventually learn how to prevent cracks from happening in your work materials. Here are a few steps you can take to prevent cracks:
- The first thing you need to make sure of is choosing the right base and filler materials. They should not be contaminated while you store or handle them. Keep the materials clean to maintain their quality.
- The area where you are going to weld should be clean.
- Do not rush the welding process. The welds crack when they do not have much time to fill in the nooks and corners.
- Maintain the thickness of the weld beads. Do not weld them too thin.
- Regulate the correct temperature and pressure for different materials.
- Use the correct setting of the welder machine to weld. Be careful or over-welding and under-welding.
Sometimes, no matter how much you try, you cannot prevent cracks in the weld. So, you may wonder if it is possible to fix cracks. Yes, you can fix cracks. Unfortunately, some cracks are irreparable. Therefore, prevention is always better than fixing.
To fix the cracks, you have to scrape off the cracked area, and then grind the spot to prepare the surface to freshly weld over it again. You may have to gouge out the welded area completely. This time, use the correct filler material, heat, and equipment.
By now, you must have learned what causes a weld to crack. If you are a beginner welder,you must learn about different kinds of cracks and how they form on the metal. Cracks are common problems. But by following preventive measures, you can avoid cracks in the weld products.