When it comes to the quality of your steel items, including alloy steel, you want the process that is going to result in the highest-quality product in the end. A high-quality product starts with high-quality steel, which are made from semi-finished casting items. As a rule, these semi-finished casting items are divided into four main types:
- Ingot: This is a very large casting product. It generally has a rectangular, square, and polygonal cross-section in various sizes as per end use. It has a hot top which helps in improved quality of the end product and is discarded after production as it has all the impurities but is a very important part for good ingot quality. Sound ingot with the solidification characteristics give a good quality of the material in alloy steel.
- Blooms: These have rectangular or square cross-sections that are greater than 36 square inches, or 230 square centimeters in length . Blooms can be used as rolling material when manufacturing products such as seamless pipes, rails, and many more.
- Billets: These are usually made with the help of a continuous casting machine, or CCM, have cross-sections that are the same throughout the length and start from 100mm onwards depending on the size of the billet caster.
- Slab: The cross-section of a slab is less thicker and much wider than that of a bloom.
When ingots, blooms, billets, and slabs are compared based on their weight, this is what we find:
- Ingots are heavier than blooms.
- Blooms are heavier than billets.
- Billets are heavier than slabs.
In short, both billets and ingots are semi-finished steel. When you take an ingot and apply uniform pressure to the surface, the process results in a much denser alloy, in part because it can remove tiny imperfections due to the nature of casting.
Is steel made through billet better than ingot?
Not really, although ingots are heavier than billets as a general rule, ingots are considered to be much more reliable in the end by most experts.
- Firstly, Due to the solidification pattern being better in ingot vs billet this leads to better internal soundness after the metal is processed by hot rolling or hot forging.
- Secondly, the discard of the bottom and the hot top of the ingot leads to much cleaner steel metallurgically compared to ingot.
- Thirdly, as solidification cannot be so accurately controlled in billet vs ingot , there is heavy porosity in the billet and hence a very high reduction ratio has to be given compared to ingot for the same internal soundness.
- Finally, the grain flow is well developed after steel is rolled from ingot and hence the end product grain flow is excellent, where as in as cast billet there is no grain flow and structure is as cast so even on heating and directly forging require a high reduction ratio for obtaining the suitable grain flow and still unidirectional property remains inferior with respect to ingot route materials.
Therefore, steel processed through ingot is considered as good if not superior to billet for alloy steel applications.
On the other hand, steel made through billet is much cheaper than the ingot due to no wastage of hot top and bottom, also lesser wastage when bars are required in fixed length which can be high compared to ingots and hence most preferred for the most widely used carbon steel applications