NEUTRAL HARDENING

neutral hardening is a heat treatment used to achieve high hardness/strength on steel. It consists of austenitising, quenching and tempering, in order to retain a tempered martensite or bainite structure.

PROCESS DETAILS

The hardening processes described here are typically neutral, which means that the chemical composition of the steel surface of the parts is not intended to be changed during the process.

Direct quench hardening is the most common practice for hardening of steel.

  • The first step is to heat up in stages to the hardening temperature which is, depending on steel type, between 800 and 1220°C. At a temperature between 730 and 900°C (depending on steel type) a transformation of the microstructure into austenite takes place.
  • The second step is to hold at this hardening, austenitising temperature to simultaneously fully equalise the temperature of the parts, and transform the microstructure into austenite. NB: this gives a reduction in the specific volume.
  • The third step is quenching the part direct from the austenitising temperature in a cold medium. This kind of quench medium is usually water, liquid salt, oil or high pressure nitrogen, depending on the steel type and part dimensions. The quenching speed must be high enough to prevent the material from transforming back into the original soft structure.
NEUTRAL HARDENING | modernmetalsindia

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