In order to make qualified spring steel, Chen Xian first had to fold and forge a piece of high-quality wrought iron repeatedly to remove impurities in wrought iron, and the final test showed that the number of folding and forging must exceed 40 forgings to meet the requirements.

Wrought iron of more than 40 forgings is hammered into a 5 mm iron plate with a uniform thickness by cold forging, and then the red-hot iron plate is cut into iron slats 80 cm long and 5 cm wide with a chisel.

These iron slats are mixed with toner and limestone powder and sealed into a ceramic casing, and placed in a furnace for a long time to smolder for carburizing.

The furnace temperature and calcination time of carburizing should also be controlled, and the carburizing is too high, and the carbon content of the steel plate is too high.

After carburizing, it is quenched with oil and water, and after quenching, it is put into the furnace for tempering.

After many tests, Chen Xian finally determined the control process of tempering.

The most difficult part of the tempering process is to control the temperature, if the heating temperature exceeds 570°, the tempering will become annealing.

Because there is no thermometer, Chen Xian can only roughly guess the temperature in the furnace through trial and error, and use a strict process to control the temperature in the furnace.

To this end, he built a special tempering furnace, stipulating the weight of carbon added during tempering, the intensity, frequency and time of the blast after ignition, the proportion of the furnace vent closed after the blast is completed, how long the furnace door lasts after it is closed before starting to put in the workpiece, and the heating time after putting in the workpiece......

Through this series of measures, Chen Xian struggled to achieve the tempering process without a thermometer.

Fortunately, he is in the case of already knowing the principle, to work backwards these empirical means, in order to succeed, if a person does not know the principle of heat treatment, even if he tries for a lifetime, it is estimated that he will not be able to touch this set of control methods.

After this set of treatment, the elasticity of the obtained steel plate is quite good, which is close to the elastic deformation performance of modern ordinary carbon spring steel.

After a certain amount of cold forging and shaping of such spring steel sheets, they can be mounted on the crossbow frame to act as a bow arm for heavy crossbows.

After more than a dozen failures and improvements, the final imitation of the Great Black Hawk was extremely bulky compared to the original, and the final total weight of the heavy crossbow using a large number of steel parts was as high as more than seven catties (Song catty, equivalent to about 4 kilograms).

In order to ensure the power of the crossbow, Chen Xian had to try his best to increase the bow opening pull of the crossbow, and after many improvements, the opening force of this imitation of the big black eagle was limited to more than 100 catties, that is, about sixty-five kilograms.

In order to ensure this opening power, Chen Xian used the design of two spring steel plates on the bow arm.

In fact, this tension is not very large for a crossbow that relies on the strength of the waist and abdomen, but because the imitation Black Hawk adopts a pulley set design, the pulling distance is twice as large as that of the ordinary crossbow, which makes the power of the imitation Black Hawk much greater than that of a crossbow with the same opening force.

In order to offset the low energy efficiency caused by the steel crossbow arm, Chen Xian equipped the imitation Black Hawk with heavy crossbow arrows.

In order to increase the weight of the crossbow arrows, and also to balance the weight of the front and back, Chen Xian even stuffed a lead bar into the wooden arrow shaft at the rear end of the crossbow arrow, so that the weight of this short crossbow arrow reached nearly two taels.

The heavy arrows fired by this heavy crossbow are terrifyingly powerful at a distance of fifty paces (eighty meters), and can easily penetrate a two-millimeter-thick steel plate, but after more than fifty steps, the power decreases.

When Chen Xian began to mass-produce this kind of heavy-duty steel-armed crossbow, he realized another benefit of the steel crossbow, that is, the output and production cycle.

Because of the use of steel instead of composite bow arms, the production cycle of this crossbow was suddenly shortened from years to days, and the output was naturally easy to increase.

In order to use this heavy crossbow, Chen Xian selected more than a dozen apprentices with relatively large stature and strength to conduct crossbow shooting training.

Chen Xian introduced apprentices through apprentices and opened up the recruitment of apprentices, rumors had begun to circulate that he and Yang Yuan were at odds outside, so his recruitment did not exchange for servants, but after all, he could eat enough and eat meat, and in this era, it was still very attractive to poor children.

In the end, Chen Xian recruited more than 30 apprentices, increasing the number of apprentices under his command to more than 100 at once.

After the number of people increased significantly, Chen Xian's courtyard blacksmith shop became very crowded, and Chen Xian had to arrange some of his apprentices to live in the attic.

Chen Xian sent two teams to the construction site every day, on the one hand, to monitor, so as not to be left behind by the Yang family in the new Zhuangzi or something, on the other hand, he also hoped that his apprentices could learn something in such a big project, so he assigned tasks to each apprentice who went to the new Zhuangzi construction site, asking them to ask, observe the operation of the construction site, and figure out the work and role of each worker.

……

After waiting for more than half a month, Yang Bai and his family simply dismissed the hunters who were waiting for the ambush, because he could see that this Chen Er would not go out if he didn't wait for the completion of Zhuangzi......

Of course, Chen Xian didn't know that someone had been waiting for him for almost two months, because he was too busy.

While Chen Xian was busy experimenting with replicating the Great Black Eagle, he was also busy with another matter.

As early as two months ago, Chen Xian quietly persuaded the children of several bricklayers in Zhuangzi through his apprentices, and let a few children secretly run to his shop to be his apprentices.

After a period of brainwashing, Chen Xian got the tile-making technology from these teenagers, and tried to make tile embryos and fire them himself.

After the trial production was successful, Chen Xian began to let the apprentices secretly make various tools needed for tile making and store them.

……

In this kind of hustle and bustle, the people of Dongzhuangzi ushered in the wax moon, and most of the earthen walls of the new Zhuangzi have been basically completed.

After the completion of the earthen wall, the follow-up is left to erect beams, erect rafters, pave attic slabs, and finally the grass roof.

The four defense towers at the four corners of Zhuangzi are also soil culture structures, but in the thick soil culture wall, Chen Xian's design is embedded with wooden beams as bones, and the strength is much higher than that of pure soil culture walls.

The height of the tower is nearly twice as high as the outer wall of Zhuangzi, and four floors are built with timber planks inside the tower, and each floor of the tower has many large and small shooting holes on the outer wall of the tower, which can provide strong fire support for the city walls on both sides.

There is only one gate in the whole Zhuangzi, the gate opens to the south, and the top of the Zhuangzi gate is a structure similar to a defensive tower, and the lower level is an adobe base and a door opening, which is like a low and deep earthen kiln.

The west side of Zhuangzi was the slowest to progress, as the waterwheels needed to be installed at the same time as the exterior walls were repaired.

The outer wall on the west side has only been repaired a little and a half, and the base of the waterwheel is basically safe, because the north ditch is frozen, and the waterwheel has not yet been installed, but while it is frozen, the simple herringbone dam has been piled up, and the water flow of the north ditch is not too large to be gathered under the west wall of the new Zhuangzi.

In order to prevent the west wall of Zhuangzi from being eroded by the current, the foundation on this side was padded with stones more than three feet high.

The New Year is approaching, people have to prepare for the New Year, the new Zhuangzi construction site can only be suspended, Chen Xian also called all the apprentices back to step up training.