Chromising carbon steels

Fig. 12.17 Illustration of grain patterns for chromised low-carbon steel and nickel, (a) Chromised steel, etched with nital (b) chromised steel etched with Marble s reagent (c) chromised nickel etched with nitric and acetic acids (d) chromised nickel etched with Marble s...

Fig. 12.21 Chromised low-carbon steel coating thickness as a function of temperature ...

Fig. 12.23 shows the variation of hardness with distance from surface for a chromised high-carbon steel (1% C). The full line represents the material as treated , the broken line corresponds to conditions after full-hardening and tempering. The apparent greater depth of the hard zone in the heat-treated material is due to the effect of small concentrations of chromium... 

Fig. 12.23 Hardness as a function of distance from surface-chromised high-carbon steel (1 % C)...

These features are well illustrated in the case of the chromising of ferrous materials. The weight increase of chromised low-carbon steel as a function of time at different temperatures is shown schematically in Fig. 12.24. At a temperature of 700° C, the weight increase in air is practically negligible, and... 

It must always be remembered that diffusion coatings are produced by a form of heat treatment and that, with the exception of low-temperature zinc diffusion (sherardising), the treated ferrous materials are usually in the annealed condition. Whenever the mechanical properties of the parts must be restored to their original level, a subsequent heat treatment is necessary . This does not as a rule present any difficulty with chromised or boronised steels. In order to prevent undue distortion and internal stresses during treatment and subsequent hardening, it is recommended that high-carbon and alloy steels should be processed in the normalised condition. 

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