title = "Hardening and Quenching: Media and Procedures"

content = """
Hardening is the heat treatment process by which steel is heated to the austenitizing temperature, held until the carbon is dissolved in the austenite, and then rapidly cooled (quenched) to produce martensite—the hard, high-strength microstructure that makes steel valuable for cutting tools, bearings, dies, and structural components requiring high strength. At Ridgecrest Metalworks, hardening and quenching procedures are among the most critical and most closely controlled heat treatment operations.

Austenitizing temperature and time must be precisely controlled. Austenitizing temperatures range from approximately 1400°F (760°C) for high-carbon tool steels to 1550°F (843°C) for medium-carbon alloy steels such as 4140 and 4340. The part must be held at temperature long enough to dissolve all carbides and achieve a uniform carbon concentration in the austenite. Insufficient hold time leaves undissolved carbides and produces a soft martensite. Excessive temperature causes grain growth, reducing toughness.

Quench media are selected based on the steel's hardenability (its ability to harden in section size) and the required balance between hardening speed and distortion/cracking risk. Water quenching is the most severe—it cools rapidly and is effective for low-alloy steels with low hardenability, but it maximizes thermal shock, distortion, and cracking risk. Oil quenching (petroleum quench oils at 100–150°F) is less severe than water, used for medium-alloy steels. Polymer quenchants (polyalkylene glycol, PAG, in water solution) provide cooling rates adjustable by concentration and temperature between water and oil. Air cooling is used for air-hardening tool steels (A2, D2) that have high alloy content providing sufficient hardenability to harden fully without a liquid quench.

Transfer time—the time between opening the furnace and immersing the part in the quench—must be minimized (typically under 7–10 seconds for most applications) to prevent excessive pre-cooling before quench. Salt bath quenching (using molten nitrate/nitrite salt at 300–400°F) is used for marquenching (martempering) of complex shapes: the part is quenched into the hot salt, temperature equalized throughout the section, then removed and air cooled. This dramatically reduces thermal gradients and distortion compared to conventional cold quenching.

After quenching, steel must be tempered immediately—never left overnight in the as-quenched state—to avoid cracking from quench stresses and hydrogen embrittlement.
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version = "0.0.1"
