Temper Embrittlement

Temper Embrittlement Meaning?

The tempering of some steels may result in a reduction of toughness as measured by impact tests, which is known as ‘ Temper Embrittlement ‘. Temper embrittlement is applicable mainly for low alloy steel and carbon steel (where <0.5% Mn) is exempted.

The phenomenon occurs when the steel is tempered at a temperature above 525°C, followed by slow cooling to room temperature or when tempering is carried out between 375°C and 525°C.

Temper embrittlement does not affect other material properties apart from material toughness. The effect of temper embrittlement can be reversed by a suitable tempering temperature.

Temper Embrittlement in Steels

Temper Embrittlement in Steels means the reduction of Charpy V notch toughness when these steels experience heating-cooling within the temper embrittlement range of  750°F–  1110°F (approximately 400°C to 600°C).

Temper Embrittlement temperature range chart
Temper Embrittlement temperature range chart

Steel alloys that are susceptible to temper embrittlement have been found to contain significant concentrations of alloying elements like Mn, Ni, and Cr, and in addition one or more of Sb, P, Ar, and Sn as impurities in relatively low concentrations.

The presence of these alloying elements and impurities shifts the ductile-to-brittle transition temperature to significantly higher temperatures. Crack propagation in these embrittled materials is intergranular as in brittle materials.

How to check Temper Embrittlement in Steel?

Temper embrittlement is a phenomenon that can occur in some steels during heat treatment. It is important to know how to check for this condition, as it can adversely affect the properties of the steel.

There are three main ways to check for temper embrittlement in steel:

  • The first is to check the notch toughness of the material. A Chapry V-notch specimen is used to verify the reduction of the material toughness due to temper embrittlement.
  • The second is to perform a hardness test on the steel. If the steel is found to be significantly harder than usual, it may be indicative of temper embrittlement.
  • The third way to check for temper embrittlement is to perform a metallographic examination of the steel. This will allow you to look for any changes in the microstructure of the steel that could be indicative of this condition.

Formula to check Susceptibility to temper embrittlement for Cr-Mo steels

There is a simple formula to check the susceptibility of Cr-Mo steels to temper embrittlement.

The formula is:

  • J = (Mn + Si)(P + Sn) x104 (in weight %),
  • X =( 10P + 5Sb + 4Sn + As)/100 (in ppm)

Note: The chemical composition shall be considered for the weld metal and not the base metal when using this formula.

The ”J” value should be less than or equal to 180 and the ”X” value should be less than 20.

If either of these values is met, then the risk for temper embrittlement is low in Cr-Mo Steels ( E.g., P5, P9, P22).

How to avoid Temper Embrittlement in Steel?

Temper embrittlement can be avoided by the following processes:

  1. Control of the composition of the alloy.
  2. Tempering above 1067°F (575°C) or below 707°F (375°C) followed by quenching to room temperature.
  3. Use carbon steel having less than 0.5% Mn and these simple carbon steels are not prone to temper embrittlement.

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