The sword exists for eleven months as a line of text before anyone melts it. The woman who wrote the alloy ran forty thousand candidates through the foundry’s cluster and kept the one whose simulated plates came out thinnest. Iron, with eight-tenths of a percent carbon. Silicon to keep that carbon from settling into carbide. Manganese and chromium to drag the transformation down to temperatures where nothing moves quickly, cobalt and aluminum to keep the wait there to ten days, and a trace of niobium to pin the grains.
Most days the floor in Seki presses tantalum liners for shaped charges and sinters tungsten into penetrator rods. The sword is budgeted as a capability demonstrator.
The charge melts under vacuum, stirred by an induction coil that never touches it, until its hydrogen and nitrogen are counted in parts per million. It pours into the atomizing tower, where argon jets moving faster than sound tear the stream into mist.
In the liquid nothing keeps a neighbor for long. An atom is pressed by a dozen others, then a dozen different ones, trillions of times a second, without an address. Then the droplet’s skin goes cold and order sweeps inward faster than the atoms can sort themselves by kind, so each carbon stays where the melt left it and each chromium freezes beside whatever it was beside. Milliseconds into the fall, every grain of gray powder carries the whole recipe at a smaller scale.
Sealed in an evacuated steel can, the powder is pressed for four hours from every side by argon at a thousand atmospheres, hot enough to glow orange. The spheres touch at points that widen into necks, and atoms cross the necks one vacancy at a time until the pores close and the particles become grains.
The old smith arrives on the second morning in the white of a shrine forge, carrying the kozuchi his teacher gave him, a small hammer whose face has worn into a shallow dish. Where his own shop has strikers, the foundry has a two-thousand-ton servo press, and its operator brings the ram down wherever the old man taps.
The billet comes out yellow. Under the ram its grains flatten into pancakes, then give way to new ones nucleating along the crushed boundaries, small and unstrained, held that way by niobium carbonitrides set along them like pins in a map.
Halfway through the drawing-out he asks to fold it. The woman who wrote the alloy shows him the fatigue curves.
“Folding was for slag,” she says. “There is no slag.”
He taps the anvil once.
They raise an argon tent over the press. The bar is notched, bent back on itself, and welded at heat, its two faces meeting without the film of oxide that every fold in a thousand years of Japanese swords has trapped. Atoms on one clean face settle into the hollows of the other. Within a minute there is no surface left to say which side was which, and no instrument the foundry owns will ever find the fold.
Ground to shape and heated until every grain is austenite again, the blade goes into molten nitrate salt at two hundred degrees Celsius for ten days.
At that temperature the austenite would rather be ferrite, and ferrite has little room for carbon. The iron changes shape a plate at a time, each plate twenty to forty nanometers thick, shoving its carbon sideways into the austenite it has yet to take. Silicon forbids that carbon to settle into carbide, and it piles up in the films between plates until those films are rich enough to lose the urge to change. A carbon atom there jumps perhaps once every ten seconds. Between jumps, the iron around it shivers a hundred trillion times.
The films that survive are metastable. Strained hard enough, they shear into martensite all at once and swell, pinching shut whatever crack arrives.
Before the final grind the smith draws the hamon with a stylus, his teacher’s line. A fiber laser walks it along the edge, lifting a band a millimeter deep past nine hundred degrees, and the cold blade behind it pulls the heat out faster than quench oil could. Carbon has no time to move. The lattice shears whole, a plate tipping into its new shape in about the time light takes to cross the room, catching the carbon where it stood and wedging each cube into a stretched box. The new structure takes more room than the old; the edge swells against the steel around it and is held in compression, and the curve the smith began at the press deepens.
A night in liquid nitrogen converts the edge’s last austenite, and a low temper eases it; the carbon-rich films in the body sit through the cold unchanged. At J-PARC in Tokai, a neutron diffractometer called TAKUMI, Japanese for master craftsman, maps the blade’s stresses through its full thickness and finds compression along the edge and nowhere a stress she had not planned.
The polisher kneels over his stones for nineteen days, and when he lifts the last finger-stone the smith’s line lies white along the edge.
The woman who wrote the alloy brings the finished blade to the smith herself.
“Would you listen to it?”
He taps the flat below the tang with the kozuchi. The wave runs to the tip at nearly six kilometers a second and back through itself, and the blade rings a long time. He listens until it stops, then hands the blade back and puts the hammer in his sleeve.
The reception room has a fireplace no one lights, installed by a president who admired Sheffield. Two brass brackets go up above the mantel. The blade goes on them bare, edge up, the ceiling lights running along the hamon, and the next procurement delegation waits beneath it. Inside, in films a few dozen atoms thick, the austenite holds its carbon at room temperature, ready to shear at the first real strain.