Abstract
The characteristic of electric resistance welding process for making pipe from steel strip was considered and the effect of chemical composition on the weldability especially by low frequency current was studied.There are many factors affecting the weldability of electric resistance welding steel pipe. The following four factors are most important from metallurgical view-point:a) Deformability from steel strip to round pipe, b) Upset-butt weldability by heavy current and short transmission time, c) Hardenability of welded part by rapid heating and cooling, d) Morphology of non-metallic inclusion in steel strip, The deformability of steel strip seems to be mainly dependent upon the level of yield strength of steel strip. The formula between the carbon equivalent and the yield strength of welding structural steel plate will be useful.On the upset-butt weldability the carbon content has the greatest influence. The carbon in steel strip most decreases the weldability. Silicon is the greatest element after carbon. Manganese and chromi-um have smaller effect on the weldability than carbon and silicon. Molybdenum and nickel have no effect up to about 1.0 weight percent respectively in steel. Phosphorus, sulphur, aluminum, nitrogen, titanium, vanadium, zirconium, niobium and cerium in steel have also no effect within the range of content in practical use respectively.As for the hardenability of welded part the formula between the carbon equivalent and the hardness in arc-welding heat-affected zone of heavy steel plate will be useful.The non-metallic inclusion has also great influence on the soundness of welded part. The sort of deoxidizing and desulphurizing agent, the usefulness of sulphide-fouming element, the size of steel ingot and the rolling ratio of steel strip on both directions longitudinal and transverse must be considered. The decrease of amount of non-metallic inclusion and the change of its morphology from ribbon to oval type will be effective.In selecting the sort of steel strip for electric resistance welding pipe from metallurgical view-point, these four factors must be considered synthetically.
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