Flame hardening is a localized surface hardening process in which selected areas of a steel part are rapidly heated above the austenitizing temperature with an oxy-fuel flame and then immediately quenched. The heated surface transforms to martensite while the core remains comparatively unaffected.
The process is most effective on medium-carbon and certain alloy steels that already contain enough carbon to develop martensitic hardness.
Unlike carburizing or nitriding, flame hardening does not rely on diffusion of new elements into the surface; it hardens the existing steel chemistry in place.
At Braddock, flame hardening would be used when only specific wear surfaces require hardness, and the component should retain a tougher, lower-hardness core.
Flame hardening is commonly used on large or selectively hardened steel components.
The surface is heated with a controlled flame until the target area reaches the austenitizing range. Quenching follows immediately, often by integrated water spray or an external quench, so the austenitized surface converts to martensite. Effective depth depends on steel chemistry, heat input, and quench severity.
Key variables include torch design, oxygen-to-fuel ratio, distance from the flame to the part, travel speed, heating pattern, part mass, and quench timing.
Because heating is localized, section geometry and heat sink effects strongly influence case depth and hardness uniformity.
Braddock would control flame settings, scanning pattern, surface temperature, and quench practice to achieve the required hardened depth while limiting cracking or distortion.
