Preferably, the first solution further comprises from 0.15 to 0.25 weight percent total trace elements, of which from 0.010 to 0.020% is boron, from 0.0065 to 0.0095% is copper, from 0.060 to 0.090% is iron, and from 0.030 to 0.080% is zinc, and the remainder comprises other trace elements such as manganese and molybdenum, and the second solution comprises twice the level of trace elements of the