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Surface reactions in the interstage annealing of phosphated mild steel.

Kirby, P. C. (1968) Surface reactions in the interstage annealing of phosphated mild steel. Doctoral thesis, University of Surrey (United Kingdom)..

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An introductory section describes the cold extrusion process. A works investigation into a cracking problem is then described which indicated that the cracking is associated with the formation of an abnormal coating during the re-phosphating cycle after interstage annealing. When the steel was normalised in a reducing atmosphere, if the initial layer of phosphate and lubricant was incorrectly removed, part of the coating reacted to produce a diffused metal layer containing a dispersed non-metallic phase. Tests showed that zinc was largely volatilised and played no significant part in the reaction. Phosphorus in the form of an iron phosphate coating and of phosphorus pentoxide, was found to produce the layer under investigation. Sodium salts as an additive to phosphate coatings promoted the reaction by retaining larger quantities of phosphoric oxide as a stable slag. Carbon as an additive produced no significant effect. Moisture in the hydrogen atmosphere increased the concentration of inclusions in the surface layer. These contained a high concentration of manganese and there Was an impoverishment of manganese in the surrounding areas. Pickling experiments showed that the phosphorus rich layer destroyed the immunity to acid attack conferred by the inhibitor used. The layer was found to produce a reduction in surface ductility with fine cross-cracking similar to that seen in extruded cups. Annealing in a vacuum reduced severity of the attack, but did not eliminate it completely. By using a cyanide solution for cleaning before annealing, the phosphate-soap coating could be removed much more effectively than with the normal caustic soda solution, and the resulting reaction suppressed. It. was concluded that the best method of control is by an improved preliminary cleaning cycle using a cyanide solution.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Kirby, P. C.
Date : 1968
Contributors :
Additional Information : Thesis (M.Sc.)--University of Surrey (United Kingdom), 1968.
Depositing User : EPrints Services
Date Deposited : 22 Jun 2018 14:27
Last Modified : 06 Nov 2018 16:54

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