Studying at Western University starts with a knife-forging competition

Chapter 115

Lin Yuan picked up the metal sheet and examined it. The surface had been acid-washed, and the pattern was faintly visible, but judging from the oxidation color at the edges and the blurring of the interlayer interfaces, it clearly hadn't achieved the desired effect. He placed the metal sheet on the microscope stage, adjusted the focus, and then stepped aside to move it out of the way.

Nielsen leaned closer to the eyepiece and frowned. In the image, the boundaries between the dark and light layers weren't clear straight lines, but rather blurred, diffused transition zones. In some areas, the interlayer boundaries were completely blurred together, making it impossible to distinguish one layer from another.

"This is it." Nelson straightened up, took off his glasses, wiped them with the hem of his shirt, and put them back on. "The pattern was still quite clear when it was folded six times, but it started to blur after another fold. By the eighth fold, it was completely ruined."

Jason also came over and glanced at the microscope, then stepped back and leaned against the materials rack, arms crossed. "We've been working on this for several nights, trying different temperature windows and incubation times, but nothing works. It's not like we haven't put in the effort."

Lin Yuan didn't answer immediately. He removed the metal sheet from the microscope, placed it on the workbench, and felt the texture of the acid-washed surface with his finger. It was rough, uneven, and the dark layer showed signs of localized peeling.

"What temperature are you using?" he asked.

"Around 1050 degrees Celsius," Nelson said. "The furnace temperature is controlled within that range during forging, just like when you're making regular Damascus steel."

Lin Yuan shook his head. He walked to the coke oven, opened the door, scooped two shovelfuls of fresh coal from the coke basket beside him, and then used an iron hook to stir the already burnt coals in the furnace to make the air circulation more even. The blower was turned on to the lowest setting, and flames emerged from the gaps between the coals, turning from red to orange.

"It's not a matter of temperature, it's about temperature difference control." Lin Yuan took out a 1085 steel plate and a 15N20 thin plate from the material rack, placed them on the worktable, and measured their thickness with calipers. "The carbon content of 1085 and 15N20 is quite different, and their coefficients of thermal expansion are different. When heated, the two materials heat up at different rates. You control the temperature at a fixed value, but during the heating process, the temperature difference between the high-carbon layer and the nickel steel layer has already begun to affect carbon migration."

Nelson and Jason exchanged a glance.

Lin Yuan picked up the steel plate and the thin plate, quickly sanded off the oxide layer on the surface with a belt sander, and then wiped them clean with acetone. He stacked the two materials alternately—1085, 15N20, 1085—a total of six layers, with the outermost layer being 1085. After stacking, he used a spot welder to fix them at each of the four corners.

"Six initial layers. Fewer layers than what you used, making it easier to control." Lin Yuan used tongs to clamp the rough billet and feed it into the furnace, closed the furnace door, and adjusted the damper to allow the temperature to rise steadily. "The goal of the first round of forging isn't bending and forging, but to clean the oxides at the interlayer interfaces. How did you apply the borax?"

"Sprinkle it on the seams before folding," Jason said.

"It's right to sprinkle it before folding. But after sprinkling, you need to leave it at the seam for a while to allow the borax to fully melt into a glassy state before hammering it." Lin Yuan stared at the color changes in the furnace, and when the billet reached the critical point of turning from cherry red to bright orange, he used tongs to take out the rough billet and walked quickly to the anvil.

Nelson and Jason followed and stood beside the anvil, keeping a distance that would not interfere with Lin Yuan's operation.

Lin Yuan sprinkled borax on the surface of the steel billet. The powder melted into a transparent, glassy protective layer the moment it came into contact with the hot steel surface.

He didn't strike immediately, but waited a few seconds to allow the borax to spread and cover the entire forging surface. Then, he gripped the hammer firmly with his right hand, stabilized the billet with pliers in his left, and brought the hammer down.

The first hammer blow landed precisely in the center of the billet. The point was accurate, the force even, and the billet stretched slightly on the anvil. He didn't rush to strike a second time, but instead used pliers to flip the billet over, sprinkled borax on the other side, waited a few seconds, and then struck again.

"Before each round of forging, borax needs to be sprinkled twice, once on the front and once on the back. If it's only sprinkled once, the oxide scale on the back won't be cleaned properly, and there will be impurities at the interlayer interface."

Nelson nodded without saying a word, his gaze fixed on the contact surface between Lin Yuan's hand and the steel billet.

After the first round of forging was completed, Lin Yuan sent the billet back into the furnace. This time, the heating time was shorter than the first round, and the temperature range was also slightly lower. He waited until the billet turned a uniform bright orange color, then took it out and placed it on the anvil to begin the bending forging process.

A notch is chiseled. The depth is less than half the thickness, positioned precisely in the center of the rough blank. The metal on either side of the notch is pressed inwards by the hammer, creating a tiny V-shaped groove at the seam of the folded surfaces. Borax is sprinkled into the V-groove, melting into a glassy state and filling the bottom. A spoonful of water is poured onto the anvil surface, and the hammer falls as steam bursts forth.

This hammer blow was more powerful than the previous one. It wasn't brute force, but a precisely calculated impact—the thrust of steam expansion combined with the hammer's kinetic energy—that blasted the oxides from the folded surfaces out of the seam, while simultaneously forging and welding the two pieces of molten metal together.

Nelson leaned forward slightly. His fingers clenched unconsciously, as if he were mentally simulating the force and angle of the hammer.

Lin Yuan flipped the folded steel billet over and repeated the process of sprinkling borax, water forging, and hammering. After two rounds, he put the billet back into the furnace and looked up at the two men.

"The carbon migration rate at the interlayer interface depends on the product of temperature and holding time. For every 10 degrees Celsius increase in temperature, the diffusion rate of carbon atoms increases by about 15%. You controlled the furnace temperature at 1050 degrees Celsius, and the carbon migrated from layer 1085 to layer 15N20 too quickly. By the time you folded it in the later rounds, the carbon had already diffused evenly throughout the entire cross-section, the compositional differences between layers disappeared, and the pattern naturally became blurred."

Jason frowned and thought for a moment. "So we need to lower the temperature?"

"Lower it, but not too much. If the temperature is too low, the forging and welding won't be strong." Lin Yuan pointed to the furnace with his tongs. "My approach is to control the forging temperature to be about thirty degrees lower than yours, while shortening the holding time for each round of heating. The amount of carbon migration only needs to be enough to create contrast; it doesn't need to, and shouldn't, diffuse fully."

He lifted the billet from the furnace and placed it on the anvil, letting Nelson and Jason get a closer look. Most of the oxide scale on the billet's surface had been peeled away during the previous rounds of forging, revealing the faint layered structure beneath. Dark and light stripes were already visible, but still blurry; they would only become fully apparent after pickling.

"You can try this temperature range when you get back. Different furnaces have different thermal efficiencies, so you'll have to figure out the exact values ​​yourself, but the direction is this." Lin Yuan immersed the rough blank in the pickling tank, took it out after a few dozen seconds, rinsed it with clean water, and then neutralized it with baking soda water.

The pattern appeared.

Although it doesn't have the flowing, swirling patterns of cloud-patterned steel, the boundaries between layers are clear, and the contrast between dark and light colors is sufficient. The initial six-layer structure is transformed into twelve layers through a round of forging, with parallel and regular patterns extending from one end of the rough blank to the other.