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).
Analysis of test results on case-hardened steel, including hardness, fatigue, and fracture tests.
| Identifier | ExFiles\Box 154a\1\ scan0103 | |
| Date | 10th November 1928 guessed | |
| 3. Table V. {VIENNA} Test Bar No. No. of Cycles. Average Height of Diagram. Brinell Hardness of Core. FD {Frank Dodd - Bodies} 8 140 3.0 cms. 269 FD {Frank Dodd - Bodies} 9 165 2.8 cms. 269 FD {Frank Dodd - Bodies} 10 145 2.95cms. 269 FD {Frank Dodd - Bodies} 11 123 2.90cms. 269 You will note that no fatigue tests have been made on the steel in the "non-case-hardened" state, and only one tensile test was made under these conditions, owing to shortage of material. It would be interesting to carry out these tests, and Izod tests also when more material is available. When making the above tests we observed that the case hardened surface was very brittle. This was especially noticed at sharp edges where it was found that quite a light tap was sufficient to cause chipping and flaking. This is illustrated by the accompanying photograph No.A602. On the Rockwell machine we were unable to obtain on the case any hardness figures greater than C63 and some were as low as C58. The case, however, is scarcely deep enough for satisfactory Rockwell tests. Further, the case starts to crack directly the load is applied to the diamond, and the resultant chipping and flaking may adversely affect the test. In photograph A602, two Rockwell impressions are shown. It will be seen that instead of symmetrical conical depressions, these are broken and irregular in shape. It is interesting to note that we have had 0.0025" removed from the surface of the case on one bar without entirely eliminating its tendency to crack under the Rockwell diamond. The removal of 0.005" appears to eliminate the tendency to crack, but it should be noted that the cavities formed by the breaking down of the surface when tested before grinding extend to a depth greater than 0.005". We shall refer to this later in connection with photomicrograph No.A603. In respect to this breakdown of the surface it should be noted that the nitrogen process definitely differs from the carburising process. We have never known a case produced by the carburising process to crack or chip under the Rockwell test. Referring again to the hardness of the case, the figures C58/C63 Rockwell according to the table of equivalents correspond to a Scleroscope range of 77/85 and on the Scleroscope machine we obtained the figures 78/90 which seem to confirm the variation. The maximum hardness figure obtained on the special steel, namely C63 Rockwell, is exactly the same as that obtained on a carburised nickel steel test bar (Spec.2071A). Fracture tests show the core to be fine in grain, but the case looked rather brittle. The inner edge of the case was sharply defined in all of the fractures examined. The total depth of the case was found to be 0.022". Photomicrograph No.A603 shows the full transverse section of the case. It should observed that the outer edge of | ||