CRYOGENIC HEAT TREATMENT - PowerPoint Presentation

Slide1

CRYOGENIC HEAT TREATMENTSlide2

What is cryogenic heat treatment?

Cryogenic heat treatment is the ultra low temperature processing of materials to enhance their desired metallurgical and structural properties

The temperature is about -196°C or 77°K

Ultra cold temperatures are achieved using computer controls, a well-insulated treatment chamber and liquid nitrogen (LN

2

)

They are completely environmentally friendly and actually help reduce wasteSlide3

The process is capable of treating a wide variety of materials, such as ferrous and non-ferrous metals, metallic alloys, carbides, plastics (including nylon and Teflon) and ceramics

The entire process takes between 36 to 74 hours, depending on the weight and type of material being treated

Strict computer control and proper processing profiles assure that optimum results will be achieved with no dimensional changes or chance of thermal shock

The process is not a surface treatment; it affects the entire mass of the tool or component being treated, making it stronger throughoutSlide4

The hardness of the material treated is unaffected, while its strength is increased

Other benefits include reduced maintenance, repairs and replacement of tools and components, reduced vibrations, rapid and more uniform heat dissipation, and improved conductivity

A tight control of the temperature curve is required

Each process requires a different curve, some remain at -195C for a number of hours and are slowly brought back to room temperature

Some materials require reheating to temper the material after cryogenic hardeningSlide5

Slowly cooling a tool steel to deep cryogenic temperatures and soaking it at this low temperature for a number of hours changes the material's microstructure

In ferrite steels, it is the transformation of austenite, a large soft crystal, into

martensite

, a smaller, harder, more compact crystal

The amount of

Martensite

formed at quenching is a function of the lowest temperature encountered

As the temperature reduces to -185C

ɳ

-carbides start to grow throughout the structure

The net result is that the crystal structure is transformed with the boundary adhesion between the various crystal elementsSlide6

Almost all of the austenite retained in the steel after heat-treating is transformed into a harder form,

martensite

, by the deep cryogenic process

An additional result of a deep cryogenic "soak" is the formation of fine carbide particles, called binders, to complement the larger carbide particles present before cryogenic treatment

Untransformed austenite is very brittle and can cause loss of strength or hardness, dimensional instability, or cracking

Most medium carbon steels and low alloy steels undergo transformation to 100 %

Martensite

at room temperature. High carbon and high alloy steels have retained Austenite at room temperatureSlide7

The

martensite

and fine carbide formed by deep cryogenic treatment work together to reduce abrasive wear

The fine carbide particles support the

martensite

matrix, making abrasions and scuffing of the cutting tool less

Cryogenic processing also relieves residual stresses in metals and some forms of plastics

All metals including copper and aluminum, benefit from the residual stress relief that cryogenic treatment promotes

Care should be taken to well control the cooling of the metal to lower temperature to avoid thermal shocksSlide8

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 thermal properties

Better electrical properties including less electrical resistance

Reduced coefficient of friction

Less creep & walk, and improved flatness for critical tolerance parts

Easier machining, polishing and grinding for better edges and finishesSlide9

Reduce the frequency and cost of tool remanufacture

Substantially reduce machine downtime caused by tool replacement

Improved surface finishing on material being manufactured with treated tooling. Treated tooling stays sharper and in tolerance longer that untreated

Reduces catastrophic tool failures due to stress fracture

Stress relieves to reduce inherit/residual stress caused by manufacture

Increases the overall durability of the treated productSlide10

Cryogenics should not be considered to replace the heat treatment, it is a complimentary treatment that enhances what took place during the heat process

Cryogenic Processing is

not a substitute for heat-treating

if the product is poorly treated cryogenic treatment, overheated during remanufacture or overstressed during use

This will result in destroying the temper of the steel which is developed during the heat treatment process rendering the cryogenic process useless

Cryogenic treatment is an additional treatment to heat-treatingSlide11

After cryogenic treatment the metals are taken out of the cryogenic equipment and tempered in a proper tempering oven to stabilize the newly formed

martensite

The process will not work on all metals to improve wear characteristics

If the carbon content is too low, or the proper heat treatment is not done correctly, the results may not show any value at all, or may even show the contrary characteristics

But controlled cryogenics processing can act as a stress relief in any circumstances Slide12

Applications of cryogenic treatment of steels

Cutting tools for different machining operations: sawing, milling, drilling, broaching, turning, slitting, shearing

Metal forming tools: dies, molds, punches

High precision parts: gauges, guides, shafts

Parts of high performance (sport) car engines and transmissions: crankshafts, connecting rods, piston rings, engine blocks, gear parts, camshaftsSlide13

Comparative microphotographs (1000x) of steel samples show the change in microstructure produced by the controlled deep cryogenic process. Uniform, more completely transformed microstructure and less retained austenite at right, is related to improvements in strength, stability and resistance to wear

Before processing

After processing