From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Micro-examination report on the fractures and material composition of a side steering tube spring.
Identifier | ExFiles\Box 68\1\ scan0229 | |
Date | 31th December 1927 | |
X8450 20H OF L5/50 Micro-Examination Report. M573. Hs.{Lord Ernest Hives - Chair} Hl2/EA31.12.27. Laboratory. c to By Re Side Steering Tube Spring F54759. ( Your Ref. Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}3/LG28.12.27.). Examination of the fractures in the above spring showed that each was associated with a flaw in the wire, which was visible on the surface after removal of the enamel and oxide. The flaws were longitudinal and, to the eye, did not appear as continuous seams, but were broken here and there, giving the impression that they were due to impurities rather than to mechanical marking. Part of the spring containing about three coils broke in two parts when gently compressed, revealing a fracture containing an obvious crack of half-moon shape. This crack had started at one of the longitudinal flaws mentioned. A transverse micro-section through the wire, at a point adjacent to this crack, showed five flaws starting from the surface and varying in depth from 0.005" to 0.030". One or two of these had the appearance of oxide-filled seams extended by cracking, and others to be purely cracks. A longitudinal section, taken from another part of the spring, showed similar flaws, some of which contained slag. Freshly made fractures showed a somewhat coarse grain. This was confirmed by examination of the micro-structure. The analysis of the material was as follows :- Carbon -------- 0.85 % Manganese ------ 0.68 % Chromium ------- Negligible. Phosphorus ----- 0.032 % The manganese content is high, and this would tend to make the material more sensitive to rapid cooling in oil or water, thus making it liable to cracking, particularly in the presence of surface flaws. The Brinell hardness figure, as determined with a 1/16" dia. ball and 100 Kg. load, was 440. Hl. He | ||