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Quality of Steel


The art of steel  making lies in the reproducibility of  uniform microstructure. The quality of steel  can always be determined by metallography  techniques which analyze microstructure to  determine phases, orientation of grains, uniformity,  inclusions and size of grains.

It is very common  for metallurgists to correlate microstructure  to hardness, tensile strength, elongation,  ductility, fatigue strength, creep rupture  strength, impact strength, and corrosion resistance.   So the quality of steel is well related  to the microstructure as well as physical  properties of steel.

Metallographical techniques,  physical properties, chemical analysis, and  non –destructive testing together determine  the quality of steel.  


Product  specifications:

ASTM, ASME, ISO, DIN,  BS, standard specifications are related to  products.  

The steel grades called  out with specific UNS number system’s  have unique properties these properties are  used to determine where the products can  be used. Mechanical properties, corrosion resistance,  creep resistance, fatigue resistance, ductility,  hardness, impact strength, high temperature  properties, are all considered in forming  the product specifications.  

One specific grade of  steel can be used in multiple product  specifications depending on the conditions  where the product will be used. Multiple  products specifications can call out for  the same grade of steel except that  they might be more stringent on few  specific properties.  
 
 

Cleanliness  of steel: Mr. Zhang in his publication “ Evaluation and control of steel cleanliness” described that steel cleanliness is achieved by lowering non-metallic oxide inclusions, residual impurity elements such as - sulphur, phosphorous, and trace elements such as As, Sn, Sb, Se, Cu, Pb, and Bi. Mr. Zang also tabulated the effect of impurities on the mechanical properties as below –  

Table_1.jpg

The most common impurities  are added to steel during tapping, ladle  treatment, and continuous casting operations.  Alloy additions, damaged refractory, and slag  also contribute to steel as impurities.