Cold and Cryogenic Treating of Steel

[Astronuc]

Cold treatment of steel consists of exposing the ferrous material to subzero temperatures to either impart or enhance specific conditions or properties of the material.

Unlike heat treating, which requires that temperature be precisely controlled to avoid reversal, successful transformation through cold treating depends only on the attainment of the minimum low temperature (-84°C, or -120°F) and is not affected by lower temperatures. Typical cryogenic treatment consists of a slow cool-down (~2.5°C/min, or 4.5°F/min) from ambient temperature to liquid nitrogen temperature. When the material reaches approximately 80K (-315°F), it is soaked for an appropriate time (generally 24 h). At the end of the soak period, the material is removed from the liquid nitrogen and allowed to warm to room temperature in ambient air. Temperature can be controlled accurately and thermal shock to the material is avoided by conducting the cool-down cycle in gaseous nitrogen.

http://asm.asminternational.org/ht-echarts/3046_OMM120707_figure.pdf

 

[Astronuc]

Effects of Cryogenically Treated Steel

The absence of a clear-cut understanding of the mechanism(s) by which cryogenic treatment improves performance has hindered its widespread acceptance in the industry.

Nevertheless, studies have been conducted to determine the effects of cryogenic treatment. Theories about the reasons for the effects of cryogenic treatment include a more nearly complete transformation of retained austenite into martensite; precipitation of submicroscopic carbides; and a reduction in internal stresses in martensite that occurs when the submicroscopic carbide precipitation occurs.

A reduction in microcracking tendencies resulting from reduced internal stresses is suggested as a reason for improved properties.

http://asm.asminternational.org/ht-echarts/3046_OMM121407_figure.pdf
ASM Handbook, Vol. 4, Heat Treating, ASM International, 1991, p 205


http://www.airproducts.com/NR/rdonlyres/3433A3DC-1899-4093-A094-9964342C38C0/0/33005019GLB.pdf PDF - use 'Save target as'

 

[Q_Goest]

Cool! er... so to speak.

This question keeps coming up over on the Cryogenics forum at Eng-Tips. I'll have to point all such questions over here for further consideration.

Edit - Link to additional information on cryogenic material processing:
http://www.cryogenicsociety.org/publications/cold_facts/current/cryogenic_processing_articles.php