Steel Heat-Treat API

Steel heat-treatment maths as an API, computed locally and deterministically — the temperatures and hardness numbers a bladesmith, machinist or metallurgist works to. The critical-temp endpoint gives the critical and process temperatures from carbon content: the lower critical A1 is 727 °C and the upper critical A3 ≈ 910 − 203·√(%C), so a 0.4 %-carbon steel has an A3 around 782 °C and hardens about 817 °C (austenitize 30–50 °C above A3, then quench), while a hypereutectoid steel austenitizes just above A1. The tempering endpoint maps temper oxide colours to temperature both ways — light straw at about 204 °C for hard cutting edges, purple around 282, blue around 304 for springs — with the typical use at each, the colour you watch on bright steel as you draw the hardness back. The hardness endpoint converts between Rockwell C, Brinell and tensile strength (SAE J417 / ASTM E140): HRC 50 is roughly 481 Brinell and about 1,660 MPa tensile, since tensile ≈ 3.45 × Brinell. Everything is computed locally and deterministically, so it is instant and private. Ideal for bladesmithing and metalworking apps, machine-shop and heat-treat tools, materials-engineering calculators, and trade study aids. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 compute endpoints. Plain-carbon-steel estimates — alloy steels and a tested chart differ.