STEEL PRODUCTS HAVING SUPERIOR WEATHERING, METHOD OF PRODUCING THE STEEL PRODUCTS, AND METHOD OF FORMING WEATHERING PROTECTIVE RUST ON STEEL PRODUCT SURFACES

摘要

The invention provides a steel product having superior weathering which iscoatedwith a rust layer containing 50 or more weight % of non-crystalline rust, amethod ofproducing the steel product, and a method of forming weathering protectiverust on amaterial surface of the steel product. A material of a steel product is placedin anatmosphere in which the dew point is kept constant and the temperature of thesteelproduct material is repeatedly varied between a temperature range of5°C or more higherthan the dew point and a temperature range of 5°C or more lower thanthe dew point.Weathering protective rust is thereby formed on the material surface of thesteel productand a steel product having superior weathering is obtained. Preferably, theatmospherecontains 15 to 50 volume % of oxygen gas, and the temperature of the steelproduct isvaried at a rising rate of 0.1 to 2°C/minute and a lowering rate of0.01 to 2°C/minute.Alternatively, a desired steel product can also be obtained by placing amaterial of thesteel product in an atmosphere containing 15 to 50 volume % of oxygen gas,keepingconstant the dew point in the atmosphere, and keeping the temperature of thesteelproduct material in the atmosphere at a certain value in a temperature rangebetween atemperature 5°C lower than the dew point and a temperature 20°Clower than the dewpoint; or by placing a material of the steel product in an atmospherecontaining 15 to 50volume % of oxygen gas, and forming and keeping a water film with a thicknessnot morethan 500 µm but not less than 50 µm on a material surface of the steelproduct.