Thanks to sandy_r for pointing out this paper, originally published in the Proceedings of the Royal Society A. in April 1917.
The title of the article is “Spontaneous generation of heat in recently hardened steel” authors are
Charles F. Brush and Robert Abbott Hadfield.
The object of this paper is to show that various kinds of steel, including carbon tool steel, “high speed” tungsten-chromium steel, and other similar iron alloys, after being quenched at a high temperature and hardened, spontaneously generate heat for at least several weeks in appreciable and measurable quantity, the rate of generation of course steadily diminishing. The paper is divided into two sections. First the research work relating to this discovery which originated with one of us (Brush) and which in the second part has been further experimented upon and verified by one of us (Hadfield). As the paper contains important new facts of much interest, it seems desirable that the results should be brought before the Royal Society.
Link to the full article is here: https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1917.0013