Globulization annealing of structural steels
N.B.: The information contained in this sheet comes from reliable sources. Nevertheless, it is provided without any guarantee, express or implied, of its accuracy.
Principle:
This annealing consists, after heating to a temperature slightly lower than Ac1, to maintain the steel at this temperature for a more or less long time, then to cool it slowly, so that it is in a state as soft as possible and free of stresses.
Treatment temperature : Ac1 - 20°C or oscillating cycle around Ac1
Treatment time: 1 to 2h / 25 mm thickness
The maximum softening is given by a structure formed by globular compounds (cementite or carbides) of spherical shape in a ferritic matrix.
Example of treatment on a C110 U steel
APPLICATIONS
On structural steels intended to be processed by cold forming (forging, extrusion, drawing, etc.). After this processing by deformation, it may be necessary to do a normalization annealing to raise the hardness level and make the machinability suitable.
On high carbon steels such as 100Cr6 (bearing steel) to ensure its machinability.
Implementation
Most of the time, these anneals will be performed under a neutral protective atmosphere such as nitrogen in a bell furnace or a metal muffle pot. A hydrogen atmosphere is also used for the annealing of wire rods in coils to guarantee a very clean surface and a good "penetration" of the atmosphere between the turns of the coil.
Main equipment (furnace, reactor, line, machine...)
Additional equipment (washing, degreasing, pickling, finishing, handling)
Ancillary equipment (pumps, turbines, resistances, burners, quenching tanks, filters, exchangers, refractories...)
Process control and monitoring ( pyrometry, atmosphere analyzers and probes, automatons, regulators, recorders...)
Energy and fluids (gases, chemicals, quenching liquids, salts...)
Tools and handling (assemblies, baskets, trays...)
Control of the result (hardness test, mechanical test, metallography, NDT, thickness measurement...)
Application materials (steels, cast iron, titanium alloys, aluminum alloys...)
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