As Rafael Herrera noted above, chemistry had not developed sufficiently until about mid to late 1800's for makers to know what was in the steel they were making. The big problem was sulfur which made steel "hot-short" meaning that it was not malleable when red-hot. The iron ore from Sweden was low in sulfur.
When Bessemer was developing his process, he used low sulfur ore and had good results. Then, he licensed the process to others and they used higher sulfur ore and had serious problems. It took Bessemer a while to understand the problem but he eventually did and the process really took off. If chemistry had not developed to the point where it did, Bessemer may not have been successful with his process.
There's also a problem known as "cold-short" and it's often caused by excessive phosphorus in the ore.
In the early days of industrial production of steel, sulfur was a serious problem - not from sulfur in the ore, but from sulfur in the coal that they were using to heat the ore.
Mike
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