890-940 C°

960 - 1100 C°

727-757 C°

800-840 C°

Increasing the price of the product by using additional heat treatment in the manufacturing of the part

Controlled heating and cooling of a solid material, so as to change the microstructure and obtain specific properties

Heating and cooling the metal at the desired speed

Heat the metal up to phase change limit and cool at a suitable speed

polymorphism (K12 and K8) 

high melting point of steel 

Internal stresses arising from the rapid cooling of the steel

Liquid phase resulting from heating the steel

To reduce toughness.

To make mechanical properties of the item suitable for specific needs.

To increase strength.

To increase hardness.

To pass the exam, no practical application

The properties of metallic materials strongly depend on heat treatment

To understand possible problems with delivery material or thermally treated part is necessary to understand material content and thermal treatment

The materials are sold in various heat treatment conditions, which understanding is possible if you know the heat treatment. 

Often technical drawings imply to mechanical properties obtainable only through some kind of thermal treatment. For heat treatment cost evaluation is necessary to know their types and in which country or firm they can be done. 

Most heat treatment operations can not be carried out in Estonia, so it is not essential to know about the heat treatment

Carburizing heat treatment may contain double hardening followed by low temperature tempering to ensure high hardness in surface layer

Carburizing followed by heat treatment results in surface hardness ~ 62 HRC in depth of 1-2 mm

Carburizing is performed in a carbon-enriched medium for about 5...10 hours at about 900 °C

The part is machined, then carburized and then heat treated

Hardening depth in surface hardening is determined by heating depth as hardness increases only in austenitized regions.

For surface hardening, induction or flame hardening is used to quickly austenitize the surface layer at the desired depth and then cool down.

In case of surface hardening, core properties or thermal treatment is not changed.

After surface austenitization and cooling, low temperature tempering is made, which does not affect core tempering as it was done in higher temperature. 

Tempering temperature is choosed based on required hardness given on the technical drawing

Optimal toughness, hardness and strength properties of the part are obtained by choosing the correct tempering temperature 

Higher tempering temperatures result in lower hardness but higher plasticity

Tempering temperature does not affect the mechanical properties of the steel

The component may be protected from oxidation by isolating it from direct contact with air (e.g. by Nickel foil)

Oxygen can be used as a protective environment

In air, decarburization occurs in the surface layer and iron oxidizes

In inert gas environment carbon decarburization is small or absent