Folding, hammering, and refining into steel.

This is true for most weapon forges, and longswords are no exception. By rapidly cooling the molten iron and repeatedly folding and hammering, it can remove excess harmful chemical components that affect the quality of iron, increase the carbon content, and thus improve the hardness and toughness of steel.

The method of casting a sword is to put molten iron into a mold made in advance to form a rough shape, and then repeatedly forge and hammer it to produce a shaped sword.

It's just that this time it's different from usual, this time instead of using pig iron to forge it, it's using a sword that has already been forged to form a new sword again, and to be honest, it's much more difficult than recasting a sword.

Qin Shi Huang collected the world's soldiers and cast twelve gold men, but he just re-turned those weapons into molten iron and then cast them into a bronze man, which did not require much technical content, which was different from what Li Zimu did this time.

He had already carefully examined the three swords earlier, and there was one obvious problem, that is, the three swords were undoubtedly made of a piece.

He has seen the Tai'a sword, so he naturally knows what it looks like, these three swords, one part of each one is different from the other parts of the whole sword, and the pattern is also completely different, which is different from the part in other places, which is the part that originally belonged to the Tai'a sword.

Take the Sun-Chasing Sword as an example, the material of the hilt and the sword body is completely different, the sword body is only fine iron when it reaches the sky, and the material of the sword handle is unrecognizable, but from the completely different patterns and textures on both sides, he can know that the hilt of the Sun-Chasing Sword is the hilt of the original Tai'a Sword.

Ouyegong is a swordsmith in the world, and he can combine these two materials without interfering with each other, this Li Zimu has no doubt, because he is confident that he can do it.

It's just that there is a problem in the middle, it's easy to separate and difficult to synthesize, if the Tai'a Sword is mixed with another little impurity, then is it still called the Tai'a Sword?

After thinking for a while, Li Zimu found a solution, only to see him turn around and set fire to the other second fine iron furnace. Most of the materials in these three swords are only two, one is fine iron, the main body of the three swords, and the other should be extraterrestrial meteoric iron, which is the main body of the Tai'a sword.

The melting point between the two is very different, the refined iron can be dissolved in the second refined iron furnace, but the extraterrestrial meteorite will not, because it has not yet reached its melting point, so it is only necessary to put these three swords in the second furnace first to dissolve the part that belongs to the refined iron. Thinking of this, Li Zimu couldn't help but breathe a sigh of relief in his heart.

"Jingyang, can you help me pull the bellows?" Li Zimu turned his head to look at Zhang Jingyang, who was sitting on the stone platform and observing him, and said, these two furnaces have two bellows, and he can't be busy alone.

"Okay" Zhang Jingyang nodded and said, if the coal in the furnace wants to burn continuously, it needs to be filled with oxygen, which even a layman like him knows, so naturally he is not ambiguous, sitting next to the bellows and began to pull it up, the bellows here are not the kind of hydraulic outside, nor the kind of electricity in the factory, it is the most traditional human bellows, which need people to keep pulling.

Judging the temperature of the flame by the color of the flame, this is a technical job, and the general sword-casting master can accurately grasp it, Li Zimu still has some experience to talk about this, the russet flame is generally about 600 degrees, the orange flame is 900 degrees, and the white-yellow flame is 1,200 degrees, and the temperature at that time can melt the fine iron.

The two worked together, about half an hour later, the flame that came out of the fine iron furnace had already turned white and yellow, and there was a special device in the iron furnace that could raise the temperature of the flame, and the more complicated the furnace could rise, the higher the temperature, and the highest temperature that the fine iron furnace could produce in front of him was only about 1,300 degrees, which was just enough to dissolve the fine iron.

Opening the lid of the furnace, Li Zimu threw the three swords directly into it without hesitation, if he expected it to be good, it should be the result he thought before.

"I'll come, you can rest for a while" Li Zimu covered the furnace lid and said to Zhang Jingyang, who was still pulling the box, and sure enough, it was much more convenient to have one more helper to do things.

It takes about an hour for a fist-sized piece of refined iron to completely dissolve into molten iron, so Li Zimu doesn't have to keep staring at the furnace, he only needs to open the lid and check it when the time is about the same, so this time is for Zhang Jingyang to take a break.

The two of them were doing their own thing in this underground palace, what was happening outside was irrelevant to them, only the sound of the flames burning in the furnace could be heard around, and the rest was quiet, neither of them spoke, just waited quietly.

After about an hour and a half, Li Zimu stood up and asked Zhang Jingyang to take over his work, turned around and walked to the furnace and opened the lid.

The temperature of the entire Sword Casting Pavilion rose, and the fire shone on Li Zimu's face, making Zhang Jingyang feel as if he was doing some ritual.

Looking at the scene in the furnace, the corners of Li Zimu's mouth raised a slight arc, and sure enough, as he expected, in the furnace at this time, in addition to a pool of golden refined iron liquid, there were also three solid objects of different shapes, and if these three solid substances were spliced together in order, it was the Tai'a Sword that had been separated for thousands of years!

Absolutely, there is not even a pattern on it that has been melted, he can naturally recognize it, but he is a little strange that this is a little different from what the legend says.

According to the legend, Tai'a Sword is indeed divided into three swords chasing stars, running to the moon and chasing the sun, yes, he has now confirmed it, but where is the map leading to the Jieshi Underground Palace? He doesn't know, in the legend, these three swords have a parchment scroll inside, recording the passage of the Stone Underground Palace and the situation inside, but Li Zimu has already checked it when he got the star-chasing sword, and the weight of the sword body is definitely not hollow, and there will definitely be no such thing as a parchment scroll in it, so where is this map?

After thinking about it and finding no answer, Li Zimu was not in a hurry, so he restored the Tai'a Sword first, and waited for a while to make sure that all the fine iron in it was dissolved into molten iron, and then Li Zimu used a tool to take out the three solid items belonging to the Tai'a Sword.

Immediately after, he threw the three extraterrestrial iron pieces into the third, smaller furnace that had been prepared, quickly closed the lid and sat back to pull the bellows.

These three pieces of meteorite iron also have to be melted, otherwise the interface cannot be perfectly connected, and they must all be turned into molten iron and then recast into the Tai'a Sword.