Method for manufacturing an Fe-Ni cold-rolled sheet excellent in cleanliness and etching pierceability

A method for manufacturing an Fe-Ni alloy cold-rolled sheet excellent in cleanliness and etching pierceability, which comprises the steps of:

• preparing an Fe-Ni molten alloy, containing nickel in an amount within a range of from 30 to 45 wt. %, and subjected to dephosphorization and decarburization;
• adding aluminum and flux to said Fe-Ni molten alloy thus prepared, in a ladle made of an MgO-CaO refractory containing CaO in an amount within a range of from 20 to 40 wt. %;
• strongly stirring said Fe-Ni molten alloy which contains said added aluminum and flux in said ladle to produce a CaO-Al.sub.2 O.sub.3 -MgO slag in said ladle, so as to react said Fe-Ni molten alloy with said CaO-Al.sub.2 O.sub.3 -MgO slag to deoxidize said Fe-Ni molten alloy while controlling a value of activity of SiO.sub.2 (a.sub.SiO2) within a range of from 0.001 to 0.005 and a value of activity of Al.sub.2 O.sub.3 (A.sub.al2O3) within a range of from 0.1 to 0.3 in said CaO-Al.sub.2 O.sub.3 -MgO slag, and said CaO-Al.sub.2 O.sub.3 -MgO slag having the following chemical composition so as to satisfy said values of activities of SiO.sub.2 (a.sub.SiO2) and Al.sub.2 O.sub.3 (a.sub.Al2O3):
• ______________________________________ CaO and Al.sub.2 O.sub.3 at least 57 wt. %, MgO up to 25 wt. %, SiO.sub.2 up to 15 wt. %, ______________________________________ wherein, the ratio of CaO/(CaO + Al.sub.2 O.sub.3) being at least 0.45,
• and oxides of metals having an oxygen affinity lower than that of silicon:
• up to 3 wt. % in total;
• casting said deoxidized Fe-Ni molten alloy into an ingot;
• and
• blooming, hot-rolling and cold-rolling said ingot to manufacture an Fe-Ni alloy cold-rolled sheet containing non-metallic inclusions comprising a composition in a region of a melting point of at least 1,600.degree. C., which region is defined by a liquidus curve of 1,600.degree. C. in a CaO-Al.sub.2 O.sub.3 -MgO ternary phase diagram and having a particle size up to 6 .mu.m in a total amount of up to 0.002 wt. % as converted into oxygen.