If one was to comment as an historian, starting with blast furnaces (where ore is converted to a metal), one would conceivably have to choose some period, not just a few hundred years back, but perhaps two or more thousand years back to a period when cattle driven bellows provided the necessary “blast” for the furnace which, (as in some ways is now) produced iron. However, it did not then produce iron for the steel process, but only iron for the foundries.
One may skip a few of those stages of development and save oneself the research of the recorded history (or other evidence from those periods). Thus, if not relying on the historical evidence, one may assume one can comment from one’s own experiences and/or memories. That will take us considerably closer to present day than the earliest evidences of iron production.
Integrated steel plants generally refer to plants that convert ore to iron, then to steel, and further on to other semi-finished or finished products. This would be in comparison to those plants that start with scrap metal and convert it to semi-finished or finished product (usually rolled and not cast, as in a foundry).
In the mid 1960’s, many blast furnaces were producing around 2,000 tons of iron per day. The iron was still, in many cases, directed to Open Hearth furnaces – even though the around 100T Basic Oxygen Furnaces were also receiving the iron. Perhaps most of the steel was poured into ingots, while most continuous casters, which also existed, were mostly casting blooms. The ingots, after soaking pits, were rolled through break down mills from where they were then further rolled into various semi-finished, or finished, shapes and sizes. The processes (excluding blast furnace to steel making) were often interrupted, and the products ended up cooling down to ambient temperatures only to be reheated completely to rolling temperatures, as opposed to being supplied with enough heat to somewhat elevate and equalize the temperatures of the to-be rolled product. If this process between iron making and steel making was interrupted, some plants had pig casters to cast the iron into manageable uniform sizes, while failing that, the iron ended up being “beached” (poured over a layer of sand from where, after cooling, it was broken into pieces and usually used in steel making as “scrap”).
As the years went on, the blast furnaces and BOF vessels became bigger and the continuous casters started to cast more and more different shapes, progressively reducing the pouring of ingots and the use of breakdown mills. Similarly, the open-heart furnaces became a thing of the past. There were still many situations where the process ended up being interrupted and thus involved moving, storing and “complete” reheating before the next stage in operation.
Presently 10,000T per day or bigger blast furnaces, 250T or bigger BOF’s, various sizes and shapes of continuous casters – along with continuously moving product through “tunnel furnaces” (as opposed to reheat furnaces) – keep the metal moving without it hardly ever seeing “ambient” temperatures until the final hot rolled shape.
These developments have resulted in huge economic benefits, along with environmental impact improvements. Manpower needs have also been reduced.
There may be some businesses which relied on some special metallurgical compositions (in some smaller quantities) which now are more difficult to get. In the older methods, one could request/purchase part of a “special” 100T heat, have the steel plant store the remaining part until a need arose for that for that composition elsewhere. This could then be reheated it and rolled as requested – this would continue until the remainder was either used or sold.
Interestingly enough, many foundries can, and do still provide specialized metallurgical compositions, in smaller quantities, while also being cost effective by the very nature of not looking or needing to mix hundreds of tons in one batch.