Iron and Carbon: The Hidden Truth of Steel

When I woke up, Dalia was still asleep in my arms. I guess I'll have to get used to the noise of the cities. With the first rays of sunlight slipping through the window, I tried to slide out of bed without waking her. I tiptoed across the room and gently closed the door behind me.

However, all that stealth went to waste—just as I turned toward the stairs, I ran into a wall of muscle and beard. It was Durman, freshly awake.

Without saying a word, he grabbed my shoulder and led me to the patio.

― Durman ― How did you sleep? ―

●― Fine ― I replied, swallowing hard. I got nervous immediately.

― Durman ― I guess there's nothing I can do now about you sleeping with Dalia ―

●― Nothing has happened between us yet ―

― Durman ― That doesn't make me feel any better ― he said, now completely unfazed.

While we were talking about how I felt after using up all my mana, Peter showed up carrying a pile of firewood with just one arm. Shortly after, Astrid came out from the dining hall to call us in for breakfast.

― Astrid ― So, Neo, any plans for today? ―

●― Not really, nothing in particular ―

― Astrid ― Then how about joining Durman at the guild? ―

During breakfast, Durman opened up to me about what he was going through.

He said he felt exhausted, like a spark inside him had burned out. He confessed that his passion for blacksmithing seemed to have faded, and he no longer knew how to move forward. He told me that watching me forge that dagger—one capable of nicking a holy sword—had made him think.

That simple Iron-Carbon diagram had rekindled something in him. A small light in the middle of the burnout.

After we finished eating, Durman explained that, as his apprentice for the past few days, I needed to be mindful of the image we projected. Yesterday, he had covered for me in front of the other blacksmiths, saying I had stayed at his place to study and train.

We were about to head out when Astrid called out to him. She gave him a hug and a loving kiss on the neck.

― Astrid ― Don't expect the same from Dalia—she usually gets up later ― she said, glancing upstairs.

The walk to the guild was quiet. Once the chimneys began to appear in the distance, Durman broke the silence with advice: how to behave, how to talk to others, how to work as a team.

― Durman ― If someone asks about your absence yesterday, say it was for personal reasons. If it's Ruki and he asks you privately, tell him you were training mana control with Astrid. ―

●― I nodded without saying anything.

I couldn't help thinking of my father. Back on Earth, we used to work together on the farm, and he would give me advice during the walk too. If it weren't for the ache of leaving my family behind, I'd say Durman is starting to take on that fatherly role in this world.

As we entered the guild, a strong smell of rusted iron and other metals hit me. The entrance hall was similar to other guilds, like the hunter's or merchant's. A large board was divided into two columns: personal requests and company commissions.

Durman asked me to wait by the door while he went upstairs—probably to his office. Meanwhile, a young man came in, browsed the postings, picked one, and handed it to the receptionist to get it stamped. Then he disappeared through a side door, but not before I caught a glimpse of a massive hall filled with dozens of furnaces, each shared by four workstations.

Minutes later, Durman came down wearing his analysis glasses, accompanied by a man—Ruki, the guild's administrator. Durman called me over with a nod.

― Durman ― Ruki, this is Neo. ― I gave him a firm handshake.

― Ruki ― So you're the one who made this. ― he said, pulling a poorly drawn Iron-Carbon diagram from his pocket. ― This drawing is yours, right?

● ― Not exactly. Someone taught it to me as well.

― Ruki ― But you were the one who showed it to Durman, correct?

● ― Yes, but I'm not the original creator.

― Ruki ― I don't know what plans you have with Durman today, but if you have a moment, I'd like you to explain this to me too.

With Durman's approval, Ruki gathered several of the guild's top blacksmiths in a meeting room adjacent to the workshop. Among them were Emordis, Thorn, Merric, Garran, Levos, Branik, Orlin, Derek, Vael, and Korim. All well-known names within the guild.

Among them, I recognized Emordis, the older man who had brought that strange sword which even my Dacian falx couldn't cut. His gaze was inquisitive, as if he were waiting for me to reveal some ancient secret.

For the next two hours, I focused on explaining the fundamentals of material engineering, with a particular emphasis on steels. I showed how the Iron-Carbon diagram works, and how the different proportions between the two elements affect the hardness, toughness, and ductility of the material. I talked about the eutectic point, where iron completely transforms into liquid at a specific carbon composition (~4.3%), and how the phases can change from pearlite to austenite depending on the temperature, explaining that pearlite is harder but brittle, while austenite is more ductile and tough. I also covered annealing, where the material transitions from a mixture of pearlite, ledeburite, and cementite to liquid austenite if heated enough, explaining what this change means structurally.

Then I talked about what happens if the carbon content exceeds 6.67%, where iron can no longer absorb more carbon and becomes an almost unusable compound for tools, known as pure iron carbide. I discussed white steel, which is harder and more brittle, ideal for fine and precise cuts, and grey steel, which is softer but stronger, used in lathe beds, milling machines, and/or heavy structures. When I mentioned "the lathe," several of the blacksmiths looked at me confused, as if they didn't recognize the word. Some even whispered, asking what it was.

I then proceeded to explain the Law of the Lever for calculating proportions within the diagram. I used numbers like 123, 56, and 78, and someone raised their hand. Thorn, with a light laugh, commented:

― Thorn ― I like the idea of giving things names. "Toughness," "ductility"... it makes the work feel more precise, more ours. ―

― Branik ― As my brother says, if you can name it, you can understand it... That word "ductility" seems perfect. I never would have thought to call it that, but it's exactly what I've always felt when steel stretches without breaking. ―

The others nodded with murmurs and new comments. The atmosphere felt livelier, more curious. For the first time, I saw in them not just blacksmiths, but potential scholars of steel.

― Durman ― Come on, Neo! It's time to take a break and have something to eat. Come with me, we need to talk about a few things. ―

The others nodded with murmurs and new comments. The atmosphere felt livelier, more curious. For the first time, I saw in them not just blacksmiths, but potential scholars of steel.

― Levos ― And how do you calculate those proportions? ―

● ― With the Law of the Lever, you can calculate how much of each phase exists between two points on the diagram... but don't worry, you'll practice that. ―

I continued explaining how impurities like vanadium, molybdenum, tungsten, or chromium deeply alter the properties of steel, improving its wear resistance, hardness, or its ability to withstand high temperatures. I talked about how stainless steel is created by adding chromium in proportions higher than 10.5%, forming a passive layer that protects it from corrosion. I also covered the properties of copper, its excellent thermal and electrical conductivity, and how it can be used to create locks resistant to high temperatures. I got excited talking about the creation of thermometers and the principle of thermal expansion of metals, but just as I was about to explain how these devices work, Ruki interrupted me, raising an eyebrow with a mischievous smile.

― Ruki ― All of that is great, kid... but you haven't said anything about how to imbue or induce mana into steel. Don't you think that could make swords even better? ―

― Durman ― Ruki, Neo possesses exceptional knowledge, but for reasons I still don't understand, in his land, mana wasn't applied in the forging of powerful swords. That's a part he still needs to learn, and it's my responsibility to teach him. Likewise, he has a lot to teach us about the iron-carbon diagram and how it can revolutionize our forging techniques. ―

― Emordis ― It's clear you've chosen wisely. Neo is a good disciple ― He whispered to Durman in the background with a wide smile.

I calmly looked at Ruki and responded with a small smile:

● ― I'm not sure about that yet, Mr. Ruki. But if you allow me to research it, I promise I'll explain it to you in the best way I can ―

Durman, seeing my response, nodded with a slight smile, and after dispersing the assembly, he told me to accompany him to his workspace. We walked down an endless hallway until we reached a spacious area with high ceilings and a large number of tools of all kinds. This workspace was very different from the others I had seen before: well-equipped, with all the necessary tools within reach, and even a barrel of water in perfect condition. Nothing was missing. As I observed Durman's work station, I was surprised by the organization and the amount of materials he had at his disposal. It was a place where forging was carried out with true mastery.

― Durman ― This is where you'll learn. First, do you have all your mana available? ―

● ― Yes, I'm ready for whatever comes ― I replied, trying to stay calm, even though inside I was anxious.

― Durman ― Perfect. Now, feed the furnace fire with your mana, constantly, so the temperature rises above 1000 degrees. ―

I obeyed, and as I sent mana into the furnace, I saw Durman placing the sword into the fire. The flame began to burn with a blinding intensity. Then, Durman ordered me that, while I maintained the flow of mana, I should also send mana around the sword. Meanwhile, Durman, with impressive skill, hammered the sword, shaping it. The heat in the environment was unbearable, and trying to coordinate both actions, I realized how difficult it was.

(Damn, this is much harder than it seemed.)

● ― Durman, can you do all this by yourself? ―

― Durman ― Yes, I could do it more easily before. It's a minimum requirement to be a master blacksmith. You have to be able to handle all of this at once, with precision. ―

A few minutes passed while the sword took shape. At that moment, Ruki appeared at the work station, holding a Magiston crystal in his hands. He carefully placed it into the sword's hilt, right at the base. Durman changed his hammer to one specially made for shaping the steel that held the Magiston crystal.

― Durman ― Now, Neo, feed the crystal with your mana. ―

●― I have to use level 2 mana. I don't have any level 1 mana left ― I said, feeling a slight pressure.

― Durman ― Go ahead, use whatever you need. ― he replied calmly.

Suddenly, an area of mana formed around me. It was as if the air around me had become dense. I began releasing my level 2 mana, and within seconds, the crystal started absorbing it. Of the 40 liters of mana I had released, the crystal absorbed 15 liters, leaving a considerable amount that I could still use in case of emergency.

― Durman ― Very good, Neo. Now, help the other blacksmiths. Don't let the mana you have left go to waste. ―

Three more hours passed as I helped other blacksmiths, feeding furnaces and adjusting temperatures with my mana. During that time, the blacksmiths began approaching me, asking questions and commenting on what I had shared about the iron-carbon diagram.

One of the younger ones came up with a look of amazement and said to me:

― Merric ― It's amazing what you do with that diagram! How do you make the steel have such specific properties? I'm used to forging without thinking about those details... Is it something anyone can learn, or do you need special knowledge?

I replied calmly:

● ― The basis is understanding how materials interact. It's not just about forging, but about how to control the phases of steel through heat and carbon. If you understand that, you can work with any kind of material, and yes, any blacksmith can learn it, but it requires patience and practice.

Another blacksmith, older with a face full of scars, leaned in and observed the diagram in my hands.

― Orlin ― I've worked with steel all my life, but this stuff about pearlite, cementite, and austenite sounds like something from another world. Is that something all blacksmiths should know, or just the more advanced ones? How do you know when you're hitting those phases with precision?

● ― Each phase is reached at specific temperatures, but you have to be careful when heating the steel. Pearlite forms when it cools slowly, while austenite appears at higher temperatures, between 727°C and 1,000°C. It's a matter of knowing how to measure the temperature, which is why we use precise thermometers. In my world, we use a thermometer in degrees Celsius to measure accurately. At that temperature, if the steel is kept steady, you reach austenite.

At that moment, Durman, who had been watching from a corner, interrupted me with a smile on his face.

― Durman ― Enough with the diagrams and temperatures, Neo! It's time to eat, you've earned it. Come on, follow me! ― He said, heading to the workshop door.

As Durman called me, a third blacksmith, with a thick beard and strong hands, looked at me curiously and asked:

― Vael ― That thing with the numbers has me intrigued too, those symbols you use... Are they just a way to write down quantities, or do they have another purpose? How do those numbers help you create steel with better properties? Ours, on the other hand, are more based on experience, not numbers... but those symbols seem much more organized, more precise.

● ― The numbers aren't just for writing quantities, they're the key to controlling the proportion of carbon in steel. In my world, each number has a specific purpose to perform precise calculations, and that helps predict how the material will behave. Blacksmiths here could use it too if they learn how to apply it. It's just a different way of organizing the information.

A fourth blacksmith, younger and more jovial in appearance, joined the conversation:

― Korim ― You say that pearlite is harder but fragile, and austenite is tougher. If I want to make a sword that's strong and durable, what proportions of carbon should I use? And, since you mention cementite... could it be used in something like mold casting, or is it just for swords?

● ― For a strong and durable sword, it's recommended to use a carbon content close to 0.8%. That will result in a mix of pearlite and cementite, offering good hardness and toughness. Cementite is harder, but also more brittle, so it should be used carefully. And yes, it can be used in mold casting, but what you get is more abrasion-resistant, not so much impact-resistant.

Seeing that everyone was interested, another young blacksmith, with a restless look, interrupted me:

― Branik ― And those numbers you mention... how did you learn them? We've never used that kind of math here. Who taught you? I've heard of some people teaching that way in other cities. Is it something related to magic, or more to the physical study of materials?

● ― I learned those numbers in my village; they're a way of representing information in a structured manner. It has nothing to do with magic, though it might sound strange. They're just a way to organize data to better understand what happens with materials. The physical knowledge of materials is universal, though the methods for applying it vary.

For a moment, everything stopped. I felt the pressure from the number of questions, but I was excited about the opportunity to share what I had learned.

― Emordis ― Hey, kid, your diagram has me quite intrigued. How do you apply it when you're forging? Because I've always worked with iron without thinking too much about the theory, but I see that you're more focused on knowledge than on pure technique. How do you apply it in your own forging work?

● ― For me, pure technique is important, but the diagram helps me understand how variables like temperature and carbon affect the material. When forging, the steel must be heated to the right temperature, and then I use the diagram to determine how I should cool it or what proportions of carbon I should maintain to achieve the correct phase. Without that knowledge, the result is uncertain for me.

― Durman ― NEO! ― He shouted from the other end of the workshop.

● ― I'm sorry, but if you'll excuse me, I have to go.