Bar 20 °CGlow noneAt fireHits 0HRC 0Quality 0FPS 0

Safety reminder: real forging needs eye protection, gloves, ventilation and a trained supervisor. This is a physics model, not a how-to. Sparks flicker: use "Reduce flicker" if you are sensitive.

Forge and Anvil: From Heat Colour to Horseshoe

Heat a bar, read its glow, hammer it into a farm or household part, then quench and temper it and watch the Fe-C phase map and the hardness-toughness trade-off. Educational model; no weapons.

Where is the bar?

Fire, steel and time

Hammer

Keys: 1-6 stations, Space = strike, P = pause. Hit while the bar glows orange; below dark red it can crack.

Live readouts

Temperature along the bar

Fe-C phase map (simplified)

Hardness vs toughness

Bar temperature history

Experiment: quench medium vs hardness

Heats a fresh bar of the chosen carbon content to 900 C and quenches it in water, oil and air; reports cooling rate, martensite and hardness.

Independent numerical checks

Controls

Drag / one finger: orbit; wheel / pinch: zoom; keys 1-4: camera.
Stations: Fire heats toward the flame temperature (set by bellows air); Anvil allows hammering; Air cools slowly; Water and Oil quench; Temper plate holds the bar at the chosen temper temperature.
Strike position slides the bar in the tongs; draw blows flatten and lengthen, bend blows add turning at the horn side.
Orders show a template in the plan-view box (dashed); the Quality chip combines shape, hardness and crack damage.

The science

Heat flow. The bar is 40 nodes. Each node follows rho c dT/dt = d/dx(k dT/dx) + (P/A) q with rho = 7850 kg/m3, c = 490 J/kg/K, k = 45 W/m/K (typical plain-steel values). In the fire q = h (T_gas - T) with h = 450 W/m2/K, T_gas = 800 + 600 x air C; in air convection plus radiation (epsilon 0.8); water h = 5000, oil h = 1500 (illustrative).

Glow. Wien's law lambda_max = 2898 um K / T puts the peak of a 1000 C bar at 2.28 um, in the infrared; only its visible tail glows, so colour tracks temperature: dark red 550 to 650 C, cherry 750, orange 950, yellow 1100, white above 1250 C (rough table, depends on room light).

Hammering. Flow stress falls with temperature, sigma_y = 500 MPa exp(-(T-20)/420). A blow of energy E = 1/2 m v2 reduces thickness by dt = E / (sigma_y w a) over a contact length a = 20 mm; volume is conserved exactly (t w dx = const; 30 % of the spread goes into width, 70 % into length). A bend blow turns the bar by E / M_p, M_p = sigma_y w t2 / 4 (scaled). Hitting below about 650 C accumulates crack damage.

Carbon and phases. Iron below 0.02 % C, steel to 2.1 %, cast iron above. The austenite line A3 falls from 912 C to 727 C at 0.77 % C (A3 = 912 - 211 sqrt(C)). Above it the steel can harden. Quench. The cooling rate between 800 and 500 C decides the martensite fraction f = 1 - exp(-ln2 (rate/V_c)^2), V_c = 500/(1+7C) K/s (model value); HRC_max = min(66, 20 + 60 sqrt(C)). Temper. Reheating relaxes martensite: HRC = HRC_q (1 - 0.27 (T_t - 200)/250) after about 240 s hold (62 to 45 HRC from 200 to 450 C). Toughness is a model index that falls as hardness rises.

Honest simplifications. 1D conduction, no scale layer, no transformation kinetics (TTT curves), constant material properties, no tongs or anvil heat sink beyond a lumped term. Values marked as model values are not for practice. Not a how-to for working with fire and metal. Models built with Blender (anvil, forge, tools, smith, workshop, village backdrop) and rendered with Three.js.