Regardless - steel's melting point is about 3,000 degrees Fahrenheit (it goes up or down, depending on the exact compositon of steel).
Now, given that this is a plasma weapon, you have to keep in mind that in order to have what would be considered plasma, it would be many times higher than steel's average melting point - we're talking hundreds of thousands of degrees at the very least.
So if this weapon merely disfigures steel, that means its heat level would be nowhere near the level of plasma. And given that you describe the plasma as 'superheated' then I would suggest one of two things -
1. Not calling this a plasma pistol, because it obviously isn't shooting superheated plasma if it only disfigures steel instead of outright vaporizing it.
2. Name a stronger metal - notably something like Andrium, which is the most common light armoring material. Because if this weapon can only deal cosmetic damage to STEEL, it's all but useless against any of the space-age alloys in use in this RP.
Also - this weapon is going to need not only a battery, but some reactionary matter (a gas of some sort, hydrogen or something you've come up with) in order to create the plasma.