1. CRYOGENIC HARDENING
Prepared by
MILBIN KOSHY
SIT
MANGALORE

2. CONTENTS
• Introduction
• Process of cryo treatment
• Austenitising
• Quenching
• Cryo treatment
• Tempering
• Metallurgical aspects
• Benefits of the cryogenics
• Applications

3. INTRODUCTION

The word, “Cryogenics” is taken from two Greek
words “kryos” which means ‘frost’ or freezing, and
“genic” meaning to ‘produce’ or generated.

Cryogenic hardening is a Cryogenic heat treating
process. Heat treatment is a combination of heating
and cooling applied to a metal or alloy.

Where the material is cooled to approximately -185
c.

Whenever material is subjected to any
manufacturing operation, it is subjected to stresses.

4. Process of Cryo-Heat-Treatment
.

5. Austenitising

Austenitization means to heat the iron,
iron-based metal, or steel to a
temperature at which it changes crystal
structure from ferrite to austenite.

During austenitising, the final alloying
element partitioning occurs between the
austenite matrix (that transforms to
martensite on cooling) and the retained
carbides.

6. Quenching

After Austenitising temperature,the steel is
cooled to ambient temperature rapidly in a
suitable quenching media like water,oil,air.

Once the austenite is cooled below its critical
temperature,it becomes unstable and it starts to
transform in to martensite

After CHT there would always be some
retained austenite in the steel.Which is up to
20-30%.

7. Cryotreatment

Cryogenic Treatment (CT) of tool materials
consists of three stages
1) cooling of tool material fromroom
temperature, at an extremely slow rate ranging
from0.5 to 1 C/min,̊
2)Shallow Cryogenic Treatment (SCT) for the
period of -84 C̊
3) Deep Cryo-genic Treatment (DCT) for the
period of -196 C̊

9. Tempering

Tempering is the process of reheating the steel
at predetermined temperatures which is lower
than the transformational temperature

Martensite precipitates fine carbides, which are
named as transition carbides. Nucleation of
these carbides relieves micro-stresses inthe
brittle primary martensite and prevents micro
cracking on surface of the steel

10. Metallurgical Aspects

Transformation of Retained Austenite to
Martensite
- After CHT there would always be some
retained austenite in the steel.Which is up to
20-30%.
- The retained austenite as a soft phase in
steels could reduce the product life, it can be
transformed into martensite

11. 
Precipitation of Fine η- Carbides
Deep cryogenics is due to an enhancement of the
precipitation of fine eta-carbides during the
subsequent temper.
-The strain energy in the martensite lattice increases
at a lower temperature. As a consequence Carbon
atoms migrate and form a clusters.
- During the subsequent heating back to the room
temperature or even a tempering, these clusters
act as nuclei for the formation of the ultra fine eta-
carbides.

12. Cryogenic agent

A "cryogenic agent" is an agent (solid, liquid or
gas) that can be used to cool an object to
cryogenic temperatures, namely temperatures
below below –150 °C (–238 °F).

13. Benefits of Cryogenics
• Promotes a more uniform micro-structure
• Reduces abrasive and adhesive wear
• Permanently changes the structure of the metal resulting in
improved machining properties
• Improved surface finishing
• Reduce the cost of tool remanufacture

14. Applications
• Gun barrels: increases the wear life of the barrel and
makes cleaning easier and faster.
• Grinding: allows a better cut, less, a better finish, and
less tensile residual induced into the work piece.
• Machining: lathes, drill bits, cutting and milling tools
• Dental and Surgical Instruments
• Engine parts:

15. Conclusion
Cryogenic hardening is a permanent, non-
destructive, non-damaging process, which reduces
abrasive wear , relieves internal stress, minimizes the
micro cracking due to shock forces, lengthens part
life, and increases performance.

16. References

www.sciencedirect.com/

en.wikipedia.org/wiki/ScienceDirect

Material science and metallurgy- Kestoor
praveen

17. THANK YOU