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Microstructure Defect of steel Tube billet
- Jan 14, 2018 -

Generally speaking, the standard of the Tube billet does not stipulate, but the microstructure of the alloy steel pipe and the high alloy steel tube billet with special requirements has corresponding requirements. These requirements are embodied in the composition of the tube billet, the composition and microstructure uniformity of the Tube billet, and the content and distribution of non-metallic inclusions.

When the tube billet contains As,Pb, Sn, bi and other harmful elements, because these elements are almost completely insoluble in the crystalline region of the crystal boundaries in the crystal boundary, the tube billet heated to a certain temperature, these than the steel melting point of much lower elements began to melt, thereby weakening the relationship between the grains, When the tube billet is hot deformed, metal rupture is easily produced, which produces a lot of quality defects. When the composition and microstructure of the billet are uneven and a serious segregation occurs, the steel tube will appear in a severe banded structure, which seriously affects the mechanical properties and corrosion resistance of the steel tube. The content of the inclusions is too many, especially the cluster-like distribution and the formation of large inclusions, not only seriously affect the performance of steel tubes, but also may cause cracks in the production process.

The harmful elements in steel, often because of smelting technology or cost reasons make it difficult to remove in molten steel. When the electric furnace steel making, the harmful elements of scrap steel tend to be higher. Steel smelting generally adopt the principle of concentrate.

The composition and segregation of the billet are often due to insufficient smelting time of molten steel (often more prominent when using a complete electric furnace steelmaking) or because of the poor mixing effect of molten steel. When smelting alloy steel, especially in the smelting of high alloy steel, the ferroalloy can be first melted in the power-frequency furnace, and then added to the refining furnace instead of directly to add Ferroalloy to the refining furnace. The smelting time of molten steel in refining furnace can be shortened, and the composition uniformity of molten steel is favorable.

The non-metallic inclusions of tube billet are unavoidable. It is a compound of iron and oxygen, sulfur and nitrogen in steel, and it is possible that steelmaking and pouring are mixed with pieces of refractory material. Oxides of Si, Al, Fe, Cr, Ca, MG, etc. The presence of metal inclusions leads to metal plasticity, making the steel deformed or cracking in the process. Non-metallic inclusions in steel include endogenous non-metallic inclusions and exotic inclusions.