Centre De Recherches Metallurgiques-centrum Voor Research in De

Vincent M Leroy

Marcel Lamberigts

Joseph H Richelmi

A steel product having a coating based on a hypereutectic zinc-aluminium alloy made by passing it through a zinc bath containing aluminium and silicon wherein the aluminium content is approximately 55% by weight, the silicon content is 1% to 2% by weight, and the bath further includes strontium in a quantity in the range 0.0001% to 0.2% by weight and at least one other element selected from among vanadium in a quantity in the range of 0.02% to 0.2% by weight and chromium in a quantity in the range of 0.005% to 0.2% by weight. The addition of strontium and chromium and/or vanadium stabilizes the structure of the coating and reduces the formation of acicular precipitates of silicon. The coating has an improved adherence and ductility which permits it to be formed without cracking, while retaining an excellent resistance to corrosion. The resulting crystallization pattern of the coating is also finer and more regular and is independent of the substrate.

Steel product having a coating based on a hypereutectic zinc-aluminum

A process for continuous dip coating of a steel strip by passing it through a zinc bath containing aluminum and silicon wherein the aluminum content is approximately 55% by weight, the silicon content is 1% to 2% by weight, and the bath further includes strontium in a quantity in the range of 0.0001% to 0.2% by weight and at least one other element selected from among vanadium in a quantity in the range of 0.02% to 0.2% by weight and chromium in the range of 0.005% to 0.2% by weight. The addition of strontium and chromium and/or vanadium stabilizes the structure of the coating and reduces the formation of acicular precipitates of silicon. The coating has an improved adherence and ductility which permits it to be formed without cracking, while retaining an excellent resistance to corrosion. The resulting crystallization pattern of the coating is also finer and more regular and is independent of the substrate.

Process for the continuous dip coating of a steel strip

Before or during the coiling of cold-rolled sheet steel for stamping, the sheet steel is covered with a substance comprising an agent capable of reacting with amorphous carbon present on the sheet as a contaminant so as to form a volatile compound, such as carbon monoxide or carbon disulphide, during subsequent annealing of the coil. Suitable substances for forming carbon monoxide are (1) certain gels (e.g., gels deposited in the form of a very thin layer from a solution of a soluble silicate such as sodium, potassium, or lithium orthosilicate) which liberate water of adsorption on heating, as during annealing, which water of adsorption reacts with the carbon contaminant to form carbon monoxide; and (2) certain salts [e.g., Ba(OH).sub.2. 8H.sub.2 O, Ca(OH).sub.2, and Zr(OH).sub.4 ] which liberate water of crystallization or water of constitution on heating, as during annealing, which waters of crystallization and constitution react with the carbon contaminant to form carbon monoxide. Suitable substances for forming carbon disulphide are thiourea, diethyl thiourea, and sulphonates.

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Vincent M Leroy