Phase analysis of Ca-containing inclusions in Ca-treated steels

The determination and phase control of Ca-containing inclusions are important for the successful production of Ca-treated steels such as hydrogen induced cracking resisted steels. In this work, the quantitative isolation of calcium aluminate (mCaO . nAl(2)O(3)), CaS and CaO in Ca-treated steels has been investigated. All operations of isolation procedure from matrix dissolution to filtration were carried out in a glovebox with an Ar atmosphere. The atmosphere was controlled to a relative humidity of 25% to prevent H2O from attacking the inclusions. Using this protection, 10% bromine-methanol method was capable of the quantitative isolation of mCaO . nAl(3)O(3), whose reactivity with H2O was found to be increased with increasing the ratio of m/n. Constant current electrolysis in 10% acetylacetone-1% tetramethylammonium chloride-methanol electrolyte (AA electrolysis method) was capable of the quantitative isolation of mCaO . nAl(2)O(3) and CaS. However, CaO was not isolated. On the basis of these results, the method for evaluating the amounts of the Ca-containing inclusions has been developed. The amount of mCaO . nAl(2)O(3) was evaluated by converting the analytical values of metal elements in the residue isolated by 10% bromine-methanol method into oxide forms. The amount of CaS was calculated from the difference between the amounts of Ca isolated by AA electrolysis method and 10% bromine-methanol method. The amount of CaO was calculated from the difference between the amounts of total oxygen and oxygen as mCaO . nAl(2)O(3).