TPT January 2014

Article

Steel Plant Specialities

to quench cracking. Quench cracks appear when stresses generated during quenching are higher than tensile strength of thin sections of forgings and due to differential quench severity at different areas. Chrome-moly grades of steel are most susceptible to quench cracks, which usually occur in the gear-end portion of the crankshaft. By coating the gear-end with an anti- scale coating, the cracking is prevented. (Image 1). By coating the gear-end with anti-scale coating, cracking could be effectively prevented. Reputed forgers of largest crank shafts in India use this technique. (Endorsement 1).

Image 1 : Crank shaft gear-end section prone to quench cracking

treatment (Endorsement 1). Aesthetic appeal of components is automatically enhanced without much effort as scaling is either prevented or reduced by using anti-scale coating. 3. Salvaging fully machined components by protecting during re-heat treatment Often, fully machined forgings need to be re-heat treated for metallurgical reasons. However, there is no material allowance left for further scaling to take place and for subsequent machining or shot blasting. In such cases, even a small amount of scaling can render components to be scrapped. Use of anti-scale compound ensures prevention of scaling during re-heat treatment. Hence, huge losses can be prevented by salvaging fully machined components. Aesthetic appeal of components is retained (Image 2). The coating itself can be removed after heat treatment by cleaning the forging with diesel, emery paper brushing or light wire brushing (Endorsement 2).

2. Reduction in shot blasting time after heat treatment Operations like shot blasting, grinding, acid pickling etc. do not add value, but are expensive and time consuming procedures. These operations are necessary to remove adherent scaling from components and to enhance aesthetic appeal of forgings. Time required for these operations can be substantially reduced if a coating is applied on components before heat

Figure 2 : Benefits of using coating in processing of stainless steel pipe fittings

Image 2 : Fully machined spindle re-heat treated by applying anti- scale compound. Zero scaling observed. Aesthetic appeal is intact

PICKLING

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January 2014