No, because very little steel is actually used in absolute terms.
Total embodied carbon, even using GWRM style overhead wiring is about 313 tonnes of CO2 per mile. Note that a simple calculation based on the numbers given in the article, and the article text implies that that is per route mile of twin track railway.
So a low density, largely single track railway will be much lower than that.
Especially as you won't need enormous anchor portals.
So about 150 tonnes of CO2 per track mile.
The averaged lifespan of the equipment will be very long, since the biggest deal is the foundations and mast, which can be shown to have lifespans well over 50 years from historical examples (see Greater Anglia and Manchester 1500V electrification).
So about 3 tonnes of CO2 per mile per year.
That is about burning about 1 tonne of diesel per mile per year.
Or about ~3.3L of diesel per day, assuming 365 day running. Call it 3.5L to account for blockades etc etc.
A two car Class 170 (according to T618 '
Traction Energy Metrics') consumes about 0.94L per km, or 1.5L per mile.
So if a single track railway has traffic totalling more than about three two-car Turbostars over it a day, electrifying it (assuming zero carbon electricity is available) is worthwhile compared to diesel operation.
Note that that is trains travelling in one direction only, so somewhere between one and two round trips by two-car Turbostars is the carbon breakeven point.
I can think of very few railways (if any) in the Uk that do not meet that criterion.
(Biodiesel doesn't help here because we could potentially bury the biodiesel or carburise it and bury the carbon, so burning it is still a net emission relative to not burning it,)
Making things causes emissions of carbon, sure, but nothing emits carbon like burning carbon fuels.