Out of question, it, of course, is
Simply there's no steel element on earth, so the name is a telltale to us it is an alloy
There're matter elements such Fe, C, Ni, Cr, Co, Ti, V etc, but no e.g. St to mean 'steel' element
Use parallell Zener diode and a series source Resistor
Its voltage (refers to the reverse breakdown voltage) ranges of 2.4 V to about 200 V (some special one can be up to 1 kV). Most the surface-mounted device (SMD) has maximum about 47 V
Simply that value is guarding/supplying the intended...
