title = "Case Hardening: Carburizing and Case Depth Control"

content = """
Case hardening produces a hard, wear-resistant surface layer (case) on a component while maintaining a tough, ductile core. This combination—hard surface for wear resistance and soft core for impact resistance—is ideal for gears, camshafts, bearing races, bushings, and pins. Carburizing is the most widely used case hardening method at Ridgecrest Metalworks.

Carburizing introduces carbon into the surface layer of low-carbon steel (typically 0.10–0.25% C core steel such as 1018, 8620, or 9310) by exposing it to a carbon-rich atmosphere at high temperature (1650–1750°F / 900–955°C). At this temperature, carbon diffuses from the atmosphere into the austenitic steel surface, enriching the surface carbon content to 0.7–1.0%. After sufficient time at temperature, a carbon gradient exists from the enriched surface to the original core carbon level. The part is then quenched to harden the high-carbon case, while the low-carbon core remains soft and tough.

Gas carburizing uses an atmosphere of carbon-carrying gases (endothermic gas with enrichment gas—natural gas, propane, or methanol) in a sealed furnace. Carbon potential of the atmosphere is controlled by adjusting the enrichment gas flow rate, measured by an oxygen probe or dew point analyzer. This allows precise control of surface carbon content.

Pack carburizing (parts packed in carbonaceous compound in sealed boxes) and liquid carburizing (salt bath containing cyanide compounds) are older methods still used for special applications or small quantities. Vacuum carburizing (low-pressure carburizing with acetylene or propane at sub-atmospheric pressure) provides excellent uniformity, no oxidation, and ability to process complex geometries with through-holes.

Case depth is controlled by temperature and time: higher temperature and longer time produce deeper cases. Total case depth (the full carbon-enriched zone) and effective case depth (the depth to a specific hardness, typically 50 HRC) are measured on metallographic cross-sections. Required effective case depths are specified on drawings based on load and wear requirements: light-duty parts 0.010–0.030 inch; gear teeth and heavy-duty parts 0.030–0.090 inch.

After carburizing and quenching, parts are tempered at 300–400°F to relieve quench stresses while retaining maximum case hardness.
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version = "0.0.1"
