Siemens had a scientific education and he applied his knowledge systematically. He was initially concerned with improving furnaces—any furnaces—and his first successful one was used for making glass. The novelty lay in the fact that the waste gases, which normally went up the chimney stack, were used to heat the air used to burn the fuel. By 1857, Siemens was able to claim that he could save 70–80 per cent of the fuel previously used in glassmaking. The Siemens furnace was first applied to making steel in France, by Emil and Pierre Martin in 1863. Siemens set up a small works in Birmingham in 1866 to demonstrate how steel could be made in his furnace, and by 1869 a company at Swansea was producing about 75 tonnes a week. By 1870 the Siemens process (often called the Siemens-Martin process for the obvious reason) was fully established.
Wrought iron now had some really serious competition. The Siemens and Bessemer processes were complementary, but both could use phosphoric or non-phosphoric iron. Bessemer was cheaper since it used no fuel, but it needed to be charged with molten iron. This was easy when the Bessemer plant was adjacent to blast furnaces. Molten iron could be used in the Siemens openhearth furnace, and it often was, but an advantage of this process was that it could melt scrap iron. With the spread of industry, scrap had become a useful raw material as machinery of all kinds wore out or was replaced by new and better types and it was cheaper than pig iron.
The Siemens process was slower than the Bessemer. A Bessemer charge of iron took about thirty minutes to convert to steel; in the Siemens furnace it took eight to twelve hours. This could be an advantage, for it enabled the furnace operator to make frequent checks on the steel and to adjust its composition as required. Various grades were now demanded, and the new steelmaking processes were able to provide them.
In the second half of the nineteenth century steel began, slowly but surely, to push the wrought iron trade out of existence; although it survived in a small way until recently, from about 1870 onwards steel was what really mattered. Cast iron continued to be made, partly for castings but increasingly as the raw material for steel and this is still the position today.
The Thomas Process
