Heat treating

• Author: International Labour Organization
• Pages: 62-62

62

MEISI05-R-2005-02-0159-1-En.doc

12. Heat treating

12.1. Hazard description

12.1.1. In heat treating, steel products are heated and cooled in a controlled way to

change their physical or mechanical properties without changing their shapes. Heat treating

is used to relieve stresses in the metal created during cold rolling, to improve its hardness

or strength, or to change its electromagnetic properties. Some heat treating is done by

quenching, in which heated steel is plunged into a cold bath of water or oil to rapidly cool

it. The most common heat-treating process is annealing, in which the steel is slowly

heated, maintained at temperature, then cooled. Often this takes place in a closed furnace,

using an inert gas to prevent oxidation, or a gas that conveys desired properties to the steel.

12.1.2. Hazards in heat treatment include burns and scalding, mechanical hazards

from steel handling, and hazards arising from the annealing gases, including nitrogen,

hydrogen and carbon monoxide. Furnace insulation wools can expose workers to

hazardous fibres.

12.2. Hazard control

12.2.1. The work area and the flow of material through it should be designed so as to

minimize the possibility of worker contact with hot steel, or to scalding in the case of

quenching operations.

12.2.2. Inert annealing gases should be handled in a way that prevents their build-up

in enclosed spaces other than the furnace itself, so as to prevent asphyxiation. Annealing

furnaces should be considered to be hazardous confined spaces.

12.2.3. The system for handling flammable annealing gases like hydrogen should

minimize the possibility of an explosive build-up.

12.2.4. Carbon monoxide should not be used for carburizing (a process for adding

carbon to the surface) where safer processes are practicable.

12.2.5. The safest practicable furnace insulation should be used. In general, this

means using insulation wools with a low content of respirable fibres, and which do not

convert to silica when heated. Compressed air should never be used to clear away residual

insulation wool gasketing used around box annealing furnaces.