Welding is a safe and reliable process tested and perfected over the years of human existence, but it comes with its fair share of risk when done wrong. During the process of welding, a plethora of things could go very wrong indeed, including but not quite limited to contamination and the degradation of the final material which could come as a result of atmospheric or contaminants in the metal fillers.
This has understandably dire consequences leading to financial, time and productivity loss on the part of the welding company. As technical experts in weld-cracking, we have put together a list of pros and cons as well as Dos and Don’ts to note and look out for when welding your metal to prevent such disastrous inconveniences as cracking.
These tricks and maneuvers will help you master weld, anticipate and correct weld-cracking as well as show and improve what you do when your welding activity goes awry. You will also learn ways to prevent occurrences like this. You don’t have to be scared of Weld-cracking and we will prove it.
Hot Cracking
As obvious in its name, hot cracking occurs at extremely high temperatures, usually above 538 degrees Celsius (1000 degrees Fahrenheit). Hot cracking basically occurs in a direction parallel to the length of the weld bead or, in other times, in a directly adjacent direction to it. Hot weld cracking can also manifest in intervals throughout the length of the weld. Hot weld cracking occurs mostly upon hardening of the weld but it is rather impossible to notice immediately.
There are two major types of hot cracking; Centerline hot cracking and crater hot weld cracking. Any pause or abrupt stop welding before the completion of a pass on a weld joint is the main cause of crater cracking as this causes a narrow and wide depression. It is common in areas with tack welding with great disparity in the tacks.
The centerline hot weld cracking is then subdivided into two; Bead shaped cracking and segregation hot weld cracking. Segregation hot weld cracking is mostly caused by the collection of elements with low melting points (e.g. excessive use of boron during the welding process) in the middle of the weld during hardening. Bead shaped weld cracking, on the other hand, is caused by poor joint design or poor part fit-up.
To adjust for this, welders make use of a welding process that involves a wide weld bead with a significantly narrow throat that places the centerline under immense pressure and ultimately leads to a crack when the centerline buckles under this pressure. The extent of the concavity of the weld bead also depends, in part, on how high the welding voltage is and what type of electrode or welding wire is used which are determinants that influence the throat thickness and the strength of the finished product.
Thankfully, hot welding can be prevented by using the best techniques during your welding processes as well as making use of the right joint design and perfect parts fit up. The selection of adequate base materials or filler metals is also a good prevention tip to take note of.
Cold Cracking
Cold welding makes the finished product susceptible to some kinds of cracking and cracks from these welds are noticeable only hours or days after the welding process, therefore great care has to be taken in the prevention of this kind of cracking. Cold welding typically occurs at temperatures below 600 Fahrenheit.
Often, in cold cracking, the cracking takes place in the filler metals or base materials and are then passed on to the weld so the careful inspection and selection of materials in cold welding is of utmost importance in preventing cold cracking.
As we know by now, pressure or stress residue in the microstructure of the weld is what leads to cracking. In cold cracking, this pressure is mostly caused by Martensite and diffusive hydrogen accumulation.
Cold cracking, also called hydrogen-induced and/or heat-affected zone (HAZ) cracking takes place in the HAZ as stated before as a result of intense pressure residue in the base material as well as the presence of diffusible Hydrogen. The presence of these restrict the final product and are common in materials with high density where they create high tension with strain parts that heat sinks that expedite the cooling process. The shortened cooling rate leads to the formation of a new crystalline microstructure called Martensite in the fine structure of the HAZ.
As a hard microstructure, Martensite has some features that make it rather unsuitable for sending processes e.g. it is coarse and has low ductility and malleability and these allow it to serve as the perfect host to diffusible hydrogen could accumulate to such great amount that causes intense pressure in the HAZ.
The vulnerability of welding materials to cold cracking increases with an increase in the level of carbon or alloy in them. Prevention of cold cracking? That’s easy, employ the backstepping technique, heat the base materials before welding commences or keep the weld at a constant temperature for a whole after welding e.g the induction heating to reduce the rate or cooling.
In your welding process, you should also try to look out for materials with low Hydrogen designator when purchasing materials for welding.
As stated, earlier, you do not have to fear cracking, armed with these defense and preventive measures, you can go about your welding process, exploring new frontiers with absolutely no fear of cracking.
