Calcium in Steels

Calcium in Steels Calcium (Ca) (atomic number 20 and atomic weight 40.08) has density of 1.54 gm/cc. Melting point of Ca is 842 deg C and boiling point is 1484 deg C. Ca additions are made during steel making for refining, deoxidation, desulphurization, and control of shape, size and distribution of oxide and sulphide inclusions . Ca is not used as alloying element since its solubility in steel is very low. Further it has a high vapour pressure since it boiling point is lower than the temperature of the liquid steel. It has a high reactivity and hence special techniques are necessary for its introduction and retention  of even a few parts per million in the liquid steel. Advantages directly attributable to Ca treatment include greater fluidity, simplified continuous casting and improved cleanliness (including reduction in nozzle blockage), machinability, ductility and impact strength in the final product. Available forms Ca is added to steel in the stabilized forms of calcium silicon (CaSi), calcium manganese silicon (CaMnSi), calcium silicon barium (CaSiBa) and calcium silicon barium aluminum (CaSiBaAl) alloys or as calcium carbide (CaC2). Elemental Ca is difficult and dangerous to add to liquid steel. CaSi in steel sheath (also called cored wire) is the most commonly used addition agent for Ca addition. The cored wire is injected into the liquid steel with help of wire injection system. It has higher recovery of Ca in steel than the virgin Ca / CaSi lumps addition into the ladle. The CaSi cored wire contains 4.5 % of iron (Fe) and 55 % to 65 % of Si. Ca content is usually in three ranges of 28 % to 31 %, 30 % to 33 %, and 32 % to 34 %. It contains around 1 % carbon (C)...

Clean Steels

Clean Steels There are various definitions of clean steel. The term clean steel is also vague. Clean steels are generally those steels that have low levels of the solute elements sulfur, phosphorus, nitrogen, oxygen and hydrogen; controlled levels of the residual elements copper, lead, zinc, nickel, chromium, bismuth, tin, antimony and magnesium; and, a low level of non metallic or oxide inclusions. The requirements vary with the steel grade and its end use. Clean steels used for one application may be often not acceptable for a different use. Steels with low levels of solutes are sometimes termed as ‘high purity steels’ while steels with low percentage of tramp elements are often called ‘low residual steels’. Sometimes steels with a low frequency of product defects that can be related to the presence of oxide inclusions are called clean steels. Hence the definition of ‘clean’ is not absolute. Instead it is based upon the product formed from the casting and the in-service use or life of the product. In addition, the definition ‘clean’ is comparative since the cleanliness standard desired by the customer is continuously changing as a function of time and technological improvements. The term ‘clean steel’ is therefore continually variable depending upon the application. Effect of solute elements on steels The individual or combined effect of solute elements such as carbon (C), phosphorus (P), sulphur (S), nitrogen (N), hydrogen (H) and total oxygen (T.O.) is known to have a remarkable influence on the steel’s properties, such as tensile strength, formability, toughness, weldability, cracking resistance, corrosion resistance, and fatigue resistance etc. The extent of control of the solute elements needed in the steels depends on the performance expected from the steel. The influence of the solute elements on the properties of steels is given in...