Cryogenic Treatment
Cryogenic treatment · Cryogenic
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability.
Cryogenic at a glance
Four scores, each 0–100 against every heat treatment in this catalog. Hardness is derived from the HRC target (20 HRC = 0, 70 HRC = 100) — treatments without a hardness target (anneals, stress relief, HIP, cryo) are not rated. Toughness, dimensional stability and cost are FabDigit's engineering assessment.
What is Cryogenic?
Cryogenic treatment cools a previously hardened alloy below room temperature to transform retained austenite and improve dimensional stability. It is a supplemental step, not a substitute for a qualified harden-and-temper cycle.
How it works
Some high-carbon and high-alloy steels finish a room-temperature quench with retained austenite because their martensite-finish temperature lies below ambient. Controlled cooling to subzero or liquid-nitrogen temperature drives additional martensitic transformation. A slow ramp limits thermal shock, and the part is normally tempered after warming because newly formed martensite is untempered and stressed. Deep cryogenic holds may also alter fine-carbide precipitation during the subsequent temper, but results depend on alloy and the complete prior cycle. Stable austenitic alloys do not transform usefully merely because they are cold.
Why specify it
- Reduces retained austenite in selected tool and bearing steels
- Improves dimensional stability of precision gauges and bearings
- Uses -80 to -196 °C processing followed by tempering
Where it falls short
- Benefits are alloy- and prior-cycle-dependent
- Can crack parts if cooling or warming is too rapid
- Does not harden low-carbon steel or replace austenitizing
The Cryogenic cycle
Typical furnace parameters from the governing specifications and shop practice; the heat treater sets the exact recipe from the alloy, section size and required result.
| Temperature | −196 to −80 °C (−321 to −112 °F) — Shallow subzero through liquid-nitrogen deep cryogenic treatment. |
|---|---|
| Soak | 8–24 h — Deep cryogenic commercial practice; qualified procedures vary. |
| Cooling | Liquid nitrogen |
| Atmosphere | Nitrogen |
| Door to door | 18–36 h — Slow ramps, hold, warm-up, and post-temper. |
Stages
- 1Ramp down under controlled nitrogen cooling
- 2Hold at the specified subzero temperature
- 3Warm slowly to ambient and temper promptly
What Cryogenic does to the part
| Hardness | No hardness target — the treatment is specified by condition, not by HRC. |
|---|---|
| Section affected | The whole section transforms. |
| Toughness | Transforming retained austenite can improve stability but creates fresh brittle martensite that requires tempering. |
| Distortion | Low risk. No liquid quench gradient is imposed, but transformation strain can move high-retained-austenite parts. |
| Surface after treatment | No scale forms in dry nitrogen; moisture condensation must be prevented during warm-up. |
| Machining sequence | Apply after hardening and before the final temper or stabilization grind; verify dimensions after the complete cycle. |
Specifications for Cryogenic
The documents a drawing cites to define this treatment. Each links to a page explaining the standard, its classes and the tests it invokes.
| Standard | Role | Classes used | Status |
|---|---|---|---|
Heat Treatment of Steel Parts, General Requirements | Governing | — | Active |
Automated Gaseous Nitriding Controlled by Nitriding Potential | Governing | — | Active |
Heat Treatment, Martensitic Corrosion-Resistant Steel Parts | Governing | — | Active |
Test and related methods: ASTM E18 (Standard Test Methods for Rockwell Hardness of Metallic Materials), ASTM E384 (Standard Test Method for Microindentation Hardness of Materials), AMS 2750 (Pyrometry).
Drawing call-out
SUBZERO TREAT AISI D2 AT -185 °C OR COLDER FOR 8 h MINIMUM AFTER QUENCH; TEMPER TWICE; VERIFY 58–60 HRC PER ASTM E18 ON FACE SHOWNWhich alloys take Cryogenic?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: A2, D2, M2, 440C, 52100, AISI 4340.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | High-carbon, tool, bearing, and selected high-strength steels can retain transformable austenite after hardening.
| |
| With care | Sintered hardenable steel may be treated only after density and heat-treatment response are qualified. | |
| With care | Printed hardenable steels may receive cryogenic treatment only after a qualified conventional hardening cycle. | |
| With care | Martensitic stainless may use subzero treatment; austenitic stainless generally does not transform usefully.
| |
| Limited | Cryogenic stabilization is a specialized dimensional-control practice and is not a standard strengthening treatment for aluminum. | |
| Limited | Cryogenic processing is not a standard strengthening route for cobalt-chrome parts. | |
| Limited | Stable nickel alloys generally do not gain the retained-austenite benefit seen in hardened steel. | |
| Limited | Cryogenic exposure is not a standard production strengthening cycle for titanium alloys. | |
| No | Brass requires lower-temperature stress relief or recrystallization annealing. | |
| No | Bronze requires composition-specific annealing or precipitation treatment. | |
| No | Copper alloys require alloy-specific annealing or precipitation-hardening cycles. | |
| No | Magnesium requires tightly controlled alloy-specific cycles. | |
| No | Precious metals require alloy-specific annealing or age-hardening practice. | |
| No | Refractory metals require material-specific vacuum annealing practice. | |
| No | Tungsten heavy alloys require supplier-specific sintering and stress-relief practice. | |
| No | Zinc alloys melt or lose properties at temperatures used by this process. |
Design rules for Cryogenic
What to decide on the drawing before the part goes to the heat treater.
- Identify the alloy designation and incoming condition on the purchase order.A temperature that is correct for one grade can overtemper, sensitize, or fail to transform another grade.
- Place hardness test locations at least 3 mm from an edge where geometry permits.Edge decarburization, local cooling, and indentation spacing can bias the reported result.
- Leave 0.2–0.5 mm finish stock on critical ground surfaces when a quench or scale-producing atmosphere is used.Final grinding removes oxide, decarburization, and dimensional movement after the thermal cycle.
- Allow 3–6 working days beyond machining.Furnace scheduling, controlled cooling, hardness testing, and certification extend beyond the soak time.
- Temper promptly after returning to ambient temperature.Subzero transformation creates fresh untempered martensite that carries high internal stress.
Cryogenic versus the alternatives
Treatments engineers weigh against Cryogenic, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Cryogenic this page | — | 40 | 90 | $$ | — |
| 38 | 55 | 45 | $$ | when the selected steel reaches its required stability without a subzero step | |
| — | 75 | 95 | $ | when machining or welding stress rather than retained austenite is the stability concern |
Cost, lead time and applications
Relative cost
Cryogenic Treatment is a standard-cost treatment ($$) relative to the other heat treatments in this catalog.
Heat treatment is priced per lot with a furnace minimum. The exact figure appears on the instant quote once the part is uploaded.
Lead time
| Added lead time | 3–6 working days |
|---|---|
| Furnace time | 18–36 h |
What Cryogenic is used for
- Precision gauges
- Bearing races
- Tool-steel punches and dies
- Metrology fixtures
Cryogenic — frequently asked
What temperature is used for Cryogenic?
The representative process window is -196–-80 °C, but the exact setpoint follows the alloy and governing specification. The listed soak is 8–24 h after the load reaches temperature.
What hardness does Cryogenic produce?
The catalog result is not a specified hardness target. Hardness must be verified on the part or a qualified witness coupon using the test method called out on the drawing.
How long does Cryogenic take?
The thermal cycle is typically 18–36 h door to door. Commercial lead time is normally 3–6 additional working days because loading, certification, and inspection are separate from furnace time.
Will Cryogenic distort the part?
The catalog rates distortion risk as low. Reserve machining stock and verify critical datums after treatment when tolerances are tighter than 0.05 mm.
How should Cryogenic be specified on a drawing?
State the governing process specification, alloy condition, required result, and inspection location. Report hardness to ASTM E18 or ASTM E10 as applicable, and do not substitute a furnace recipe for an acceptance requirement.