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Heat affected zone (HAZ) after thermal cutting of QT-steels

Thermal cutting inevitably leads to the formation of a Heat Affected Zone (HAZ) independent of the steel grade. In the case of quenchable steels, the HAZ can be divided into two distinct zones: a re-quenched zone and a tempered zone (see graph below).

Critical cutting temperatures

The resistance of the steel to softening depends on its chemistry, microstructure and how it was processed. If the temperature of the steel becomes too high, the hardness of the steel will be reduced.

Small size increase risk of softening

The smaller the piece that is thermally cut, the greater the risk of the whole component being softened. When small parts are cut, the heat supplied by the cutting torch and by preheating will accumulate in the workpiece. Consequently, the smaller the size of the cut part, the higher the risk of softening.

How to reduce the risk of softening

The best way of eliminating the risk of softening is to use cold cutting methods, such as abrasive water jet cutting. If thermal cutting must be performed, laser or plasma cutting is preferable to oxy-fuel cutting, as oxy-fuel cutting subjects the workpiece to higher levels of heat compared to plasma or laser cutting.