1.
Segregation in steel chemical composition and the impurity distribution uneven phenomenon, known as segregation.
In general will be higher than the average composition, referred to as positive, below the average composition, called negative segregation.
There are macro segregation, such as regional segregation and micro segregation, such as dendritic segregation, intercrystalline segregation.
Segregation is closely related to the ingot segregation of large forgings, and ingot segregation degree and steel grade, mould, smelting and casting quality condition and so on.
Alloying elements, impurity content, the development of the gas are intensifying segregation in steel.
The greater the ingot, the higher the pouring temperature, the faster the casting speed, the more serious segregation degree.
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1)
Regional segregation it belongs to the macro segregation, a crystallization of molten steel in the process of solidification choosing, solubility and proportion of difference.
Such as steel gas drive the concentration of impurities in the process of floating in the liquid steel strip trajectory of rising form shall be Sunday afternoon form of segregation.
At the top of the first crystal crystal with high melting point impurities sink, like crystal rain falling axis formed by ∨ segregation.
Sediment on the bottom of the ingot form negative segregation sedimentary cone.
Finally the upper area of solidification, segregation element such as carbon, sulfur and phosphorus enrichment, defects become more positive.
(1) 'Sunday afternoon' type of segregation (2) '∨' type of segregation (3) the negative segregation countermeasures to prevent the regional segregation area is: 1)
Reduce the sulfur and phosphorus segregation in steel elements and gas content, such as by refining outside the furnace, vacuum carbon deoxidization (
VCD)
Processing and ingot bottom blowing argon process.
2)
Using multiple furnace pouring and riser casting, casting and heat insulating riser vibration, to enhance the measures, such as the feeding capacity.
3)
Strict control of temperature and injection speed, using short spindle type, improve the crystallization conditions.
On forgings transverse specimens at low, rendering and spindle type corresponding frame feature, which is also called frame segregation.
Picture 6 -
2 is shown on the 30 specimens crmnsinia steel die forgings low power spindle type of segregation.
Because of segregation in the ingot during deformation, extending along the parting surface, which appear as the frame.
Segregation band is composed of small pore and enrichment of elements, the uniformity of microstructures and properties of forgings has bad influence.
Electroslag remelting with its high purity, crystal structure reasonable, become an important method of large forging billet production, but if in the process of remelting current, voltage instability, will form a corrugated segregation.
When higher current, voltage, molten steel overheating, speed is slow, solute elements in liquid steel on the crystallization front zone of enrichment of partial poly formation;
When electricity, electricity, reduce hours together will decrease molten mass element, the cyclical change, formed corrugated segregation bands, 6 - such as images
3.
Regional segregation on the transverse specimens at low acid leaching of scattered with dark mottled, called dot segregation.
Picture 6 -
(4) for distribution in the transverse section of punctate segregation.
1:1 HCL aqueous solution heat corrosion (
2)
The micro segregation dendritic segregation it.
Dendritic crystals and intergranular non-uniformity of micro elements, may cause
