Rapid and continuous heat treatment of cold rolled steel sheet - with brief quenching and reheating to give good deep drawing behaviour

摘要

Cold rolled steel sheet is continuously heat treated by heating to above its recrystallisation temp. and then cooling rapidly by immersion in an aq. both kept at above 75 degrees C, pref. 85 degrees C, esp. using a bath with a uniform temp. Heating is pref. faster than 10 degrees C/second, esp. 30 degrees C/second in a non-oxidising, direct flame furnace. The bath may contain only water, or also materials in soln. or suspension to alter the heat transfer, e.g. CaCl2, borax, or surfactants such as palmitates or stearates; corrosion inhibitors may also be present, and the pref. bath temp. is 80-150 degrees C. Cooling in the bath is pref. at 25-180, esp. 35-150 degrees C/second to 200-400 degrees C., then at 90-500, esp. 150-450 degrees C. The steel may be high strength steel, or soft steel for deep drawing where the compsn. is 0.15, esp. 0.1% max C, 0.6, esp. 0.5% max. Mn,, 0.02% max. Si, opt. with 0,001-0.05%, B, esp. where the % B = 1 to 3 times the % N2. Steels can be made with an excellent combination of elastic limit and elongation, esp. for use in mfg. motor cars where good deep drawing properties are required. High tensile steels can also be made.