The Bessemer converter is often cited as the critical invention causing a breakout in the production of cheap steel and enabling the industrial revolution. However, I just put together this chart today from data in "The Chemistry of Iron & Steel Making" by Williams which suggests another cause:
So, if this chart is right we see the Bessemer converter being invented in the middle of the breakout, not at the beginning. In the 1851 data point we see a large increase in the production of steel, yet the Bessemer converter had not come into use yet.
Is there some key technology advance that preceded the Bessemer converter that could have enabled this increase in production?
Note that I am just guessing that there was some key advance that led to the increase in production. It is entirely possible that there was no technological advance, and that the number of factories and workers simply increased.
(Just as an aside, some may wonder why there was a decline in the 1870s. The reason for that is a scrap effect. Much of the iron produced in the boom of the 1850s rusted and turned into scrap by the 1870s. By recycling all this scrap, the need for new production declined. A secondary cause was an increase in American production at that time.)