What are some defects in steel products?
- Roll marks
- Quench cracking
- Oxide scales
Steel manufacturers need to make sure that any defects in steel products are minimized or altogether avoided. After all, haphazardly-done steel cannot really be suitable for its intended purpose. Many applications and structures greatly rely on this material for stability, durability, hardiness, and ductility.
There are a few common defects that can be encountered on fabricated steel parts. These can range from roll marks, pinchers, ridges, overlaps, to quench cracking, oxide scales, and the like. Knowing how to identify these material deformations is an integral part of the Quality Assurance process for steel. Continue reading to learn more.
Oftentimes, the culprit for many steel defects can be traced back to the quality of the processing plant. Roll marks, for example, are one of these issues and are typically evident in steel sheets. While it may also be evident in thicker-walled products like billets, it’s more commonplace in sheet materials.
Roll marks are also sometimes referred to as bruises, roll bruises, or whip marks. One type of roll mark also has aesthetic implications on the steel material. These usually don’t have any effect on the product’s quality and are dismissed most of the time during the manufacturing process.
But the case is entirely different when the roll marks seem to slightly protrude and appear as bumpy to the touch. These issues aren’t really visible to the eye during primary processes like hot rolling, but they are far more discernible in succeeding techniques that are done to completely flatten the steel sheet.
Quenching is a process that’s used on most alloys and metals. It belongs to a sub-branch of heat treatment techniques that are used to elevate the internal pressure or internal stresses in the property of the alloy or metal, in order to harden it.
However, there are cases where the quenching process might experience issues. This is arguable because the material is constantly subject to extreme heat and temperature changes that can affect its inner workings. When a steel product, like a 4140 chrome steel billet, for example, is subject to a rapid application of low temperatures, cracks may begin to form on its surface.
Fortunately, quench cracking can be avoided by manufacturers through a series of changes. Since the process relies on a fast rate of cooling steel, it’s important that the steel specimen has an ideal hardenability rating. Manufacturers can also make modifications to the design of the product as a way of anticipating where potential cracking may take place.
Pinchers usually appear as uneven ridges or grooves that may surface on the metal. It’s more ubiquitous in steel products that have to be rolled, such as billets, pipes, or tubes.
Unless manufacturers are trying to design a reinforced steel bar, the presence of pinchers isn’t really ideal. But the problem can be diagnosed by inspecting the quality of the components used, especially the rollers.
Ideally, pinchers shouldn’t really be present at all, but they don’t really have any harrowing effects on the quality of the steel product. This is because they can only be spotted microscopically and have more of a design implication.
In cases wherein the pinchers are too prominent, however, then the steel fabricators can make several changes on the tension force of the strip or the speed of casting.
The severity of the oxide scales that can also be found across steel materials largely depends on the chemical composition.
To give an example, steel that has a higher silicon content can produce another iron oxide form on the surface. These layers of iron oxides — i.e. magnetite, hematite, ferrous oxide, and the like — form during the heating process in steel rolling techniques. They appear distinctively gray in color with a blue hue to them in some cases
While the scales can easily be removed through polishing and sanding, they generally don’t have any effects on the functionality of the steel product. But if there is a need to avoid them completely, then the rolling process should be done in a controlled environment with the presence of an inert gas. This ensures that no chemical reaction between the surrounding air composition and the fabricated steel material will occur.
Like many steel manufacturing techniques, the different types of welding also require precision. This is done to prevent issues that can decrease the workability of the material, especially when it’s intended for a structural purpose.
Keeping this in mind, overlaps are just some of the welding issues that can happen during welding. These may refer to instances wherein a molten filler material hangs down from the specimen, or when there is an “overlap” of excessive filler that does not create an even surface on the targeted material.
Likewise, there are many changes in the welding technique that can be done to reduce any cases of overlapping. For example, the alternating current should only be at an ample level that suits the requirements of the welding proper. On the side of the welder, they can improve their method of welding by ensuring that all variables are well-monitored — i.e. surface treatment, type of shield gas, and the like.
Some of the defects in steel products include quench cracks, roll marks, overlaps, oxide scales, and pinchers. As much as possible, these issues should be avoided altogether, especially when the defects/deformations have any bearing on the utility of the steel material.
Nevertheless, some of these defects only affect the appearance of the material. In this case, manufacturers may not really do anything drastic to modify it. Through good practices, basic equipment maintenance and cleaning, repair, and equipment inspection, however, it’s certainly possible to prevent these steel product issues from surfacing.