When you consider the quality of the steel that you’re working with, whether alloy steel or any other type, the cleanliness of that steel is an important factor. In fact, when it comes to the cleanliness of all types of steel, this one factor alone can affect the metal’s formability, toughness, tensile strength, weldability, and resistance to cracking, fatigue, and corrosion. Because the consumers of steel products have insisted on purchasing products that have better mechanical properties, steel manufacturers have put a lot of emphasis on improving the cleanliness of the product.
What Is “Cleaning” Steel?
Because of the emphasis on cleanliness, new steels have been developed that can tolerate applications such as transmission parts for the automotive industry and many more. When you hear the term “clean” steels, it refers to steels that have no inclusions, which are non-metallic particles that are embedded in the steel matrix. Cleaning steels means not only lowering these inclusions but lowering other impurities as well, which can include sulphur, nitrogen, total oxygen (O2), and phosphorus as well as selenium, lead, copper, and others.
In addition to reducing the amounts of these chemicals in the steels, attempts are made to avoid inclusions that are large enough to be harmful to the product. The actual cleanliness of the steel is controlled by certain operating practices that are utilized throughout the steelmaking processes. This includes aspects such as the location and time of both deoxidant and alloy additions, transfer and stirring operations, the shrouding systems, the sequence and extent of secondary metallurgy treatments, and the casting practices themselves, among others.
Operation Practices for Clean Steel
The cleanliness of alloy steel and other steels is affected by steel refining and continuous casting operations and some of the practices used include:
- Ladle operations
- Mold and caster operations
- Transfer operations
- Tundish operations
Of course, you have to determine which methods are used to evaluate the cleanliness of steel, which include both direct (including image analysis, sulphur print, cold crucible (CC) melting, and cold sample scanning, among others) and indirect methods (measuring total oxygen, measuring slag composition, and measuring dissolved aluminum loss, to name a few). Once the results are reviewed together, you get a more accurate evaluation so you can know what to do next. Indeed, there is no single method that works best when it comes to measuring steel cleanliness, which is why using more than one of them is always recommended.
There is no inclusion free steel, it is always the acceptable limit and a mutual understanding between the buyer and the seller
At Kisco, we generally make steels with less than 1.5 in thin and 0.5 in thick for ABD and almost NIL in C. We also have a best in class microscope from Carl Zeiss Germany to auto test the inclusion reducing the human error and giving accurate and actual results to our customers. This is also one reason steels at Kisco have been able to consistently win end customers for superior mechanical properties when subject to required heat treatment.