I got this by Googling; it wasn't the horror I suspected (scientific inaccuracies everywhere. Called just "Dust", and I have determinedly forgotten the author.) but seems to fit your description .
'The year when stardust fell' Raymond F Jones (1958)
"Cometary dust contaminates the atmosphere and begins a catalytic
breakdown of the surface tension of various metals, welding everything
shut. This is a scientific mystery of finding out why machines are
suddenly seizing up in increasing numbers, and how to slow or prevent it.
As it becomes worse, we have a great return to the Dark Ages scenario, with
people resorting to clubs and spears (since modern weapons are becoming
non-functional). This reaches a crescendo in an attack on College
Hill--the home of a small country college whose physics department is
working feverishly to find a solution. The local town in its foresight has
(mostly) agreed to provide the scientists and students with the resources,
food and medical gear they need to keep alive in a world without plumbing,
and with rampant anthrax and plague. How does one do physics research with
equipment failing as fast as one can use it, a mob at the gates (with
torches no less) and with only medieval living conditions? "