title = "Tempering After Hardening: Temperatures and Properties"

content = """
Tempering is the heat treatment applied to hardened (quenched) steel to reduce brittleness, relieve quench stresses, and establish the required balance of hardness and toughness for the intended application. As-quenched martensite is very hard (60–67 HRC for medium and high-carbon steels) but also extremely brittle and under high residual stress; it would fracture catastrophically in service without tempering. At Ridgecrest Metalworks, tempering always follows hardening—typically within one hour of quenching.

Tempering is performed by reheating the hardened part to a specified temperature below the lower critical temperature (Ac1), holding for a specified time (typically 1–2 hours per inch of cross-section), and then cooling—usually in air or still furnace. The tempering temperature determines the resulting hardness and toughness through a predictable relationship.

Low-temperature tempering (300–450°F / 150–230°C) relieves quench stresses with minimal hardness loss. Hardness typically drops from 62–67 HRC (as-quenched) to 58–64 HRC. This range is used for cutting tools, wear-resistant parts, and surfaces where maximum hardness is the design requirement—hardness is preserved but toughness improvement is modest.

Medium-temperature tempering (450–750°F / 230–400°C) provides a better balance of hardness and toughness. Parts tempered in this range (50–58 HRC) are used for springs, dies, and components requiring resilience. Note that many alloy steels exhibit a phenomenon called tempered martensite embrittlement (also called 500°F embrittlement or one-step temper embrittlement) at 480–650°F—this range should be avoided for alloy steels requiring high toughness.

High-temperature tempering (900–1200°F / 480–650°C and above) produces the tempered sour (also called sorbite) structure—a fine dispersion of carbide particles in ferrite—with significantly lower hardness (32–45 HRC) but high toughness and ductility. This is the required temper for structural bolts, gear teeth, shafts, and components where toughness and fatigue strength are primary. The combination of high-temperature quench-and-temper is called QT treatment.

Multiple tempering (double or triple tempering) is required for high-alloy and high-speed tool steels where retained austenite is present after quenching—it transforms during each temper cycle, requiring re-tempering to fully convert and stress-relieve the additional martensite formed.
"""

version = "0.0.1"
