In "Artemis" Andrew Weir says that the hot flakes produced by striking flint and steel together do not ignite acetylene in vacuum. He says that the reason steel flakes get white-hot on Earth is that they have very high surface to volume ratio and oxidize in air so fast that they basically burn. No air -> no oxidation -> no white-hot flakes. In air, the process is as follows:
1) Flint striking steel scrapes off a flake, exposing fresh iron at a certain temperature $X$ before oxidation.
2) The iron oxidizes. This is an exothermic chemical reaction, which raises the temperature of the flake from $X$ to well above 1000 °C. This high temperature is what causes the flake to glow white-hot.
3) Acetylene's autoignition temperature is 300 °C, so the white-hot flake is more than enough to ignite/oxidize the acetylene.
What is the initial temperature $X$ of flakes just after the strike, assuming no oxidation (e.g. we are striking in vacuum)?