Heat Treatment Guide

Get heat treatment parameters for common steel grades — annealing, normalizing, quenching, and tempering temperatures.

Analysis

How to Use

  1. 1
    Select the Alloy and Desired Condition

    Choose the alloy from the database and specify the required final condition: annealed (soft), normalized, quenched and tempered (Q&T), solution treated, or aged.

  2. 2
    Confirm Section Thickness and Furnace Type

    Enter the maximum section thickness of the part, which determines soaking time requirements; select the furnace atmosphere (air, inert gas, vacuum) to identify any surface protection measures needed.

  3. 3
    Review the Complete Heat Treatment Procedure

    The recommended heat treatment cycle is displayed: austenitizing or solution temperature, soaking time formula, quench medium, tempering temperature range, aging parameters, and expected hardness and mechanical property ranges.

About

Heat treatment is the principal means by which the mechanical properties of alloys are adjusted after forming, enabling a single alloy chemistry to achieve a wide spectrum of property combinations by controlling microstructure through thermally-activated phase transformations. A quenched and tempered 4340 steel can range from 35 HRC with good toughness (for structural applications) to 55 HRC with high strength (for tooling), purely through variation of the tempering temperature.

The AlloyFYI Heat Treatment Guide provides complete heat treatment cycles for over 800 alloy grades, including all major carbon and alloy steels, tool steels, stainless steels, aluminum alloys, titanium alloys, and nickel superalloys. Parameters are sourced from ASM Handbook Volume 4 (Heat Treating), AMS specifications, and ASTM standards, with notes on critical process variables such as atmosphere control, furnace accuracy class, and quench media selection. The guide supports both procedure development and incoming material inspection — verifying that a supplied material will respond correctly to the specified heat treatment before committing it to production.

FAQ

What is the difference between annealing, normalizing, and stress relieving?
Annealing (full annealing) heats steel above the critical temperature (A₃) and cools slowly in the furnace, producing the softest possible microstructure (coarse pearlite or ferrite+pearlite) with minimum strength and maximum ductility. Normalizing heats above A₃ and air cools, producing finer pearlite than annealing and slightly higher strength due to faster cooling. Stress relieving heats below A₁ (typically 550–700°C for carbon steels), where no phase transformation occurs, to reduce residual stresses from machining, welding, or forming without changing the bulk microstructure or hardness significantly.
What factors determine the choice of quench medium?
Quench severity must be sufficient to suppress diffusional transformation (pearlite and bainite formation) and produce the desired martensite fraction across the entire section of the part. Water quenching is the most severe commonly used medium and is used for low-alloy and medium-alloy steels that cannot achieve full hardening with slower quenches; its high severity risks quench cracking of complex shapes. Oil quenching is less severe and preferred for high-alloy steels, carburized case-hardened parts, and complex geometries. Polymer quenching (PAG solutions) allows the quench rate to be adjusted between oil and water by varying concentration, providing process flexibility. Vacuum furnace gas quenching (nitrogen or helium at elevated pressure) is used for tool steels and high-speed steels to minimize distortion.
What is precipitation hardening and which alloys use it?
Precipitation hardening (age hardening) achieves high strength through the formation of fine precipitate particles within the matrix during controlled aging heat treatments. The alloy is first solution treated at high temperature to dissolve all alloying elements, then rapidly cooled (quenched) to preserve the supersaturated solid solution, and finally aged at an intermediate temperature where precipitate nucleation and growth occur. Key systems include: aluminum alloys (Mg₂Si, CuAl₂, MgZn₂ precipitates in 6000, 2000, 7000 series); precipitation-hardening stainless steels (Cu or NiAl precipitates in 17-4 PH, 15-5 PH); nickel superalloys (γ' Ni₃Al precipitates in IN718, Waspaloy); and maraging steels (Ni₃Mo, Fe₂Mo precipitates).
How is soaking time determined for heat treatment?
Soaking time must be sufficient to achieve temperature homogeneity throughout the entire cross-section of the part and complete any required diffusion or transformation reactions. Rules of thumb for steel vary by furnace loading: approximately 1 hour per 25 mm of section thickness for open furnaces with good circulation, increasing to 2 hours per 25 mm for densely loaded furnace charges. For thick sections and alloy steels requiring complete carbide dissolution during austenitizing, carbon diffusion kinetics must also be satisfied. Temperature homogeneity measurement (thermocouple surveys) is required for qualification of heat treatment furnaces per AMS 2750 and ASTM A991.
What is the risk of decarburization during heat treatment?
Decarburization is the loss of carbon from the surface of steel during heating in oxidizing atmospheres (air furnaces), forming a surface layer with lower carbon content and therefore lower hardness and fatigue strength after quenching. Surface hardness may be 10–20 HRC below specified values on decarburized parts. Mitigation approaches include controlled protective atmospheres (endogas, nitrogen-methanol, nitrogen-hydrogen mixtures), pack hardening in spent case-hardening compound, vacuum furnace processing, or post-treatment grinding removal of the decarburized layer. All aerospace heat treatment specifications (AMS 2759) limit the allowable decarburization depth and require metallographic verification.
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