Chapter 140: Steelmaking

The circular furnace hearth was already loaded with charge. Tailored to the iron quality of the Ming Dynasty, this electric furnace's lining was basic in nature; the bottom was spread with a layer of calcium oxide, above that a layer of iron oxide scale and charcoal powder, and on top of that were some iron ingots and a small amount of wrought iron accumulated at the base over recent days — the ship from Hangzhou was still en route, and this was the only two and a half tons of pig iron available.

Unlike open-hearth furnaces and blast furnaces, which once started must keep running day and night without stopping, the electric furnace's advantage lay right here: start and stop at will; with material you could smelt continuously, without material... clock out, go home, and fool around with the wife.

This was currently the steelmaking method best suited to the Kiln District's raw material conditions. Its only drawback was high energy consumption — yet that was precisely what the Transmigrators cared about least.

At Chen Jingtai's command, Zou Guoqing, moonlighting as operator in the control room, pressed the switch with a face full of smiles. At that moment, a black graphite electrode column above the furnace slowly descended; once the electrode inserted into the hearth, it immediately produced a violent electric arc reaction with the bottom electrode — smelting began.

First came a rhythmic, bright light bursting from the gaps in the furnace lid; then as the electrode column sank deeper, the arc intensified, the temperature soared violently, and the light grew fierce. The workshop, already dim, now flickered light and dark like a disco bar. Soon, the pig iron began melting into liquid, and through the gaps, in time with the arc's pulsing, fiery red slag sprayed outward, while billowing thick smoke and hot wind also belched from within the furnace.

Rumble, flash, thick smoke, fire rain... at this moment, it was as if some third-rate ghost film crew was at work inside the furnace — the sound and light effects were absolutely blasting.

Seeing the overhead smoke collection system begin operating normally, Chen Jingtai let out a breath. Up to now, the melting period had been safely navigated, and all systems were running smoothly. He glanced back at the honored guests standing beyond the safety line and noticed that a few brothers who'd never done industrial work still looked a bit pale. Chen Jingtai's mouth twitched slightly — this kind of DC electric furnace fitted with a rectifier was already quite advanced in its noise level; back when he was an apprentice, those old AC furnaces were truly ferocious.

Once the solids inside the hearth had fully transformed into liquid, Chen Jingtai directed the control room to adjust the insertion depth of the electrode column. When the molten steel inside was rolling steadily, the calcium oxide from the initial charge had fully reacted with the pig iron, and he now gave the order to tap slag.

Slag tapping would expel a portion of the sulfur and phosphorus. The overhead crane now began moving slowly; a bright yellow boom carrying a steel claw slid above the electric furnace — the slag skimmer. Amid the violent smoke and splashing molten steel, the steel claw effortlessly scooped away the waste residue floating on the liquid steel. The entire process required no manual operation.

The slag skimmer, a plug-in that one could easily do without, was something Chen Jingtai had strongly advocated importing: having utterly inexperienced Transmigrators and Ming furnace workers repeatedly approach the furnace to tap slag in an environment of high-temperature smoke and spraying steel slag... such extremely dangerous work was wholly unsuited to the current situation. Every single Transmigrator and Ming furnace worker was immensely precious. Not importing a slag skimmer now — once enough people had died, they'd have to import one anyway.

After slag tapping was complete, the environment inside the furnace moved from the melting period into the next stage: the oxidation period. The purpose of this stage was mainly dephosphorization and decarburization.

In theory, this was the moment to blow oxygen into the furnace — not only would it decarburize, but it would also accelerate the reactions inside; the violent upwelling of carbon-oxygen bubbles would bring waste residue to the surface, achieving multiple goals at once. However, the Transmigrators had no pure oxygen at present. After adding a little more calcium oxide to the furnace, Chen Jingtai simply waited for the furnace to react on its own... this amounted to using electricity consumption to bypass certain process steps.

Forty minutes after starting the furnace, he received the on-site testing results and found that the phosphorus content of the molten steel had already met requirements. He therefore ordered a second slag tap, then had all outlets closed; the furnace entered the next stage: the reduction period.

The reduction period was also unique to the electric furnace, setting it apart from traditional steelmaking furnaces like blast furnaces and converters. The purpose of this stage was deoxidation and desulfurization.

At present, the Kiln Area Base lacked various minerals and metals and could not yet produce qualified deoxidizers like silicon-aluminum powder, so this first heat of steel still used imported composite deoxidizer, which could deoxidize and desulfurize quite effectively. During the final reduction period inside the furnace, Chen Jingtai added 3 kilograms of deoxidizer and some calcium oxide, then continued waiting for the reaction to proceed.

By this point, the job was basically as good as done — one hour and fifteen minutes after the electrodes started, the Transmigrators' first heat of molten steel was formally ready for tapping.

This speed was actually quite slow: in later generations, large quantum electric arc furnaces could produce a heat of molten steel in just 25 minutes. But since the Transmigrators lacked so many necessary conditions here, they could only extend the time and increase electricity consumption to guarantee product quality; dragging it out to one hour was simply unavoidable.

After reading the second test report, Chen Jingtai formally ordered steel tapping: the most critical phosphorus and sulfur content in the molten steel was already within limits; other trace elements were slightly over, and the carbon content of the entire heat fell between low-carbon and medium-carbon steel... but this was unimportant, mere imperfections. As long as the twin scourges of phosphorus and sulfur were controlled in place, the rest could be resolved later by adjusting the process.

The graphite electrode column, now glowing red-hot, slowly rose. Then the control room began maneuvering the ladle forward on the slide rails beneath. In the next moment, the ladle, lined with refractory brick, was in position, and the molten steel was officially tapped. If this were continuous smelting, a portion of molten steel would be left in the furnace; however, today was a test run, and the penny-pinchers had no surplus iron ingots anyway, so today was just this one heat.

When the electric furnace was tilted 15 degrees by the hydraulic system, the eccentric bottom tapping hole began pouring molten steel into the ladle — right here, a branch of the technology tree could be lit up: the high-end secondary refining.

So-called secondary refining, simply put, is injecting oxygen or inert gas into the ladle, then selectively repeating the various impurity-removal processes described above, in order to purify the molten steel and adjust element content... basically, any steel grade that's fairly badass has to pass this hurdle.

The Transmigrators, of course, had no need to do this.

As long as the process was properly adjusted, the molten steel emerging from this electric arc furnace before their eyes could fully meet the carbon steel standards of later generations. Low-carbon steel for making steel bars and steel plates, high-carbon steel for making tools and gun barrels — at most adding stainless steel in the future — this was already enough to serve the Transmigrators until they died. There was no necessity to light up any surplus branches of the technology tree.

After the ladle was filled to three-quarters with boiling molten steel, it continued forward along the slide rails: a row of sand molds had long been prepared, just waiting for this moment. The nervous Ming furnace workers now stepped forward and, following the operating procedures from their training, slowly turned the handwheel beside the ladle. The ladle tilted slightly, and in the next instant, the molten steel flowed down the runner channel into this batch of molds.