Why Do Welds Crack?

What are the major causes of cracked welds?

A weld will crack most often due to improper welding techniques before, during, and after the welding process. Common causes of cracking include inadequate preparation of the work piece, poor part fitment, inaccurate welder settings, and contaminated filler materials. There is good news, however. Many, if not all of these issues can be resolved by simply taking more care when welding. 

In this article, we’re going to discuss what causes the majority of welds to crack. Not only will we be naming for you each of the various types of individual cracks, but we’ll also provide answers as to how to avoid them in the future.

Welding, like many skills, is all about making mistakes and learning from them. We hope this article serves to teach you about what behaviors to avoid when welding and aids you in producing a better weld that will hold up for years to come. Because we all know that circumventing any headaches, additional costs, and extra work is key to succeeding in any welding career.     

Before we begin talking about the bad, let’s take a look at what model welding behavior looks like. Every welder is going to have their own style, techniques, and preferences, but we encourage you to follow these steps to ensure a weld that performs well and keeps you employed.

Welding 101: What Welders SHOULD Do

Photo by Sergio Zamudio on Unsplash

Popular Mechanics put together a short piece on the basics of welding. We realize most readers are probably already well-versed in the art of welding, but it never hurts to double-check your practices. How do you prepare yourself and your materials for welding?

Beyond equipping yourself with the proper tools and outerwear, you should always make sure your work piece is clean. You can’t successfully glue 2 pieces of wood together if there’s a layer of sawdust between them. The same goes for metal. Remove the excess debris stuck to the surface either by using a wire brush or a cleaning solvent, depending on what type of metal you are working with. This will combat any issues you might have with contamination and/or fitment.

Secondly, make sure your pieces do just that—fit together. It’s true that you’re going to be creating the joint between these pieces but do what you can to make that gap as easily bridgeable as possible. Welding a seam is much easier than filling a one-inch gap.

Finally, whether you’re TIG or MIG welding, make sure you’ve double-checked your settings and obtained the correct filler materials. Did you select the right amperage? Which type of current are you using? Do you have everything you need during the entire welding process? Having the right tools at hand will solve a number of problems from the get-go. Hot metal waits for no man, or woman.

There’s much more to welding than just these simple steps but setting yourself up for success is half the battle. Keep these tips in mind as we discuss how and why welds crack. Knowing what to do and what not to do will help you ensure a successful weld and time and effort well spent.

Welding Practices to Avoid

While it may go without saying, here are a few bad welding habits you should definitely break right now. Not only will they help prevent weld cracks, but your future self will also thank you.

  • Not knowing your metals. A degree in metallurgy isn’t required to weld, but a basic knowledge of metal properties is extremely useful. Do you know what types of welding are optimal for each type of metal? What about joining 2 different metals? Understanding your materials will help you become a better welder in the long run.
  • Winging it with your welder. There are certain skills that allow for a simple process of trial and error. Welding, however, is not so forgiving. Read up on your machine and make sure you know what settings to adjust for the types of welding you’ll be doing. Trust us, being informed and reading the owner’s manual is worth the time.
  • Using inferior gear and materials. Electricity flowing between the electrode to the work piece is blinding—literally. Invest in a proper welding helmet. Buy and maintain high-quality filler materials, gloves, and any other accessories you need during the welding process. Don’t come to the welding table ill-prepared.

These are just a few aspects you’ll want to think about as you prepare to weld. Learning how to weld can be a life-long journey for some and an afternoon’s study for others, but the most important thing to remember is safety. Make sure there’s a next time by taking care.

The Cracks of the Welding World

Now we’re going to get down and dirty with welding cracks. With each type of crack we introduce, look for the causes and solutions that will help you diagnose and prevent further cracking, if it were to occur. The best welders are not just those who can stack dimes atop one another; rather, they’re able to learn from their mistakes and apply their new knowledge at the next arcing.

Hot Cracking 

First on our list is what is known as “hot cracking.” These types of fissures occur at incredibly high temperatures, as you might have guessed. When the work piece achieves a temperature above 1000 degrees Fahrenheit or 538 degrees Celsius, hot cracking almost immediately appears along the weld itself, or parallel to it. Not all hot cracking is visible to the naked eye, however.

Welding experts categorize the types of hot cracking as either centerline or crater. Let’s take a closer look at each of these types to help you determine why the cracking occurred and how to prevent it in the future.

Centerline  

Centerline cracking nearly explains itself. Consider the seam, lying underneath the weld, to represent the path of the centerline crack. Running the length of the piece at any point near or on the weld, a centerline crack weakens the joined piece to its most extreme. While novice welders might think to simply weld the crack up as they did the joint, such a solution will only provide a band-aid fix.

Preventing centerline cracks requires consideration of the crack itself. A centerline crack can be classified as either a segregation or a bead crack. Segregation cracks are characterized by “elements with low melting points being rejected to the center of the weld upon solidification.” That is, those parts of the metal which melt faster than the surrounding components gather at the seam. Think of the cheese in your burger, dripping to the table while your patty stays in one piece.

Bead cracking makes itself well known. Pieces of material not fitted together properly will exhibit bead cracking when the welded bead is not able to bridge the gap. While both segregation and bead cracking weaken the weld significantly, their respective solutions relate back to our best practices. Simply join work pieces more closely to avoid bead cracking. With segregation cracking, however, the cause might well be “an improper width-to-depth ratio, low melting point of tramp elements in the base material, and a concave weld surface,” or any combination of the 3. Check the underside of your newly-welded piece for penetration and decrease your amperage or travel speed accordingly. Ensure your work space is level and square, including the pieces you’re welding together.

There’s one more type of hot cracking we want to address. Akin to bead cracking, it requires more material to be placed in the open space. 

Crater

Consider a welding pass. As the operator moves from one end of the piece to the other, the weld should join the touching sides of the separate pieces. If, however, a welder was to stop early and not complete the pass to its full extent, crater cracking is likely. Crater cracking occurs when the weld pool cools more rapidly than the surrounding material, pulling it in to cause stretching, or stress. Put simply, crater cracks form “due to lack of fill at the end of the weld.”

One of the best ways to prevent crater cracking is to ensure the weld completely melts each side of the separate pieces together. Just as you add a bit more filler metal to the beginning of your weld path, in order to get the pool or puddle started, you should also take a bit more time at the end to insure full penetration and a complete weld. Otherwise, you’ll have to go back and fill the imperfection.

A common method used to prevent and/or remedy crater cracking is called back stepping. To back step, simply weld as normal for a short distance. Then, begin your next weld about an inch or so away from the start of the weld you just completed. Stop welding when you’ve reached the beginning of your first weld. It may seem a bit backwards, but back stepping a weld is great insurance against hot cracking.

Now that you know a little bit more about hot cracking, let’s take a closer look at how cold cracks can occur. These types of cracks are a bit harder to diagnose, especially since they tend to appear well after the initial welding has occurred.

Cold Cracking

As you might have guessed, cold cracks occur at temperatures below 600 degrees Fahrenheit. It only takes one weld pass to realize that proper welding penetration requires a potent mix of heat, amperage, and speed with both the filler material and the arc. If you don’t have enough heat, your welds won’t be very strong.

The majority of cold cracks begin in the base metal and extend into the welded metal. You might have gotten the welded metal hot enough to melt into the base piece, but if cracks are happening, you didn’t get both up to the right temperature to induce proper joining. For this reason, cold cracking can often occur in thicker metals.

Before we get too involved in helping you prevent cold cracking, let’s consider the most common type: heat-affected zone cracks.

Heat-Affected Zone (HAZ)

According to WeldingAnswers.com, the “most common causes for this type of crack are: excess hydrogen, high residual stress levels on the weld, and high carbon content on the base material.” Stress levels on the weld can cause a number of different cracks, depending on the circumstances, but we’re going to focus on heat-affected zone, or HAZ cracks here. These types of cracks have a lot to do with the element hydrogen.

First let’s clarify something about hydrogen when it comes to welding. As the welded metal cools, hydrogen diffuses outward, much like heat transferring from the source out to the metal’s extremities. However, hydrogen creates more stress than the heat transfer. As it moves through the metal, it may distribute unevenly, creating weak pockets among the metal’s structure. And in any case that metal is being used, you can be sure failure is not an option.

To prevent the hydrogen from created HAZ cracks, pay attention to your use of it during the welding process. For example, your filler material should be low in hydrogen. Either choose one with an H4 or H8 designation or ones that are rich in hydrogen scavengers like fluoride, sodium, and calcium. You should also keep your filler material in a dry, room-temperature area.

Another method for taking care of any hydrogen issues that might occur is to pre-heat your metals. Think of it as preheating your oven to bake your favorite sugar snack. You want to bring your materials up to temperature before welding, so that stress levels on the metals are low. Mechanics know that a car performs best when it reaches operating temperature, and the same goes for your welding materials. As you are heating your metals, be sure to wear proper safety equipment such as gloves and safety glasses.

Diagnosing and Preventing Future Cracks

As TheFabricator.com puts it, the “major cause of a crack is when internal stresses exceed the strength of the weld metal, the base metal, or both.” Understanding why welds crack will help you diagnose and treat any future problems you may encounter while welding. Become familiar with the types of cracks above. If—and when—they occur in your workspace, consider the causes and identify a solution. The best education you can give yourself is to know what to do when things go wrong, because inevitably they will. If you can tackle the worst problems, you’ll be a better welder for it.

We hope you’ve enjoyed this article on why welds crack. Which cracks have you dealt with? What methods do you prefer? Do you have any unique solutions to share? Let us know in the comments below!

Leave a Comment