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).
Metallurgical analysis report on a fractured, case-hardened steel specimen, comparing its properties to nickel steel.
| Identifier | ExFiles\Box 154a\1\ scan0104 | |
| Date | 29th March 1927 guessed | |
| 4. the microspecimen is broken and chipped. Remnants of a white band on the edge are visible. It will be also observed that the fractures extend into the major part of the case below the white band. It was found very difficult to preserve the edges of the micro-specimens during grinding, against breakdown. Photomicrograph No.A604 is of higher power and shows the structure of the white band on the edge of the specimen. The total depth of this white layer is 0.003". The gray band just below the surface should be noted; its presence was confirmed by grinding the surface of the case on another specimen, when the gray colour was again exposed. It may be noted that the gray colour is more distinct when visually examined than in the photograph. At the inner edge the white band is composed of white wavy lines roughly parallel to the surface. These are also present in the case below the white layer, but are more widely dispersed. Photomicrograph No.A605 of considerably higher power, shows the character of these lines at a point about midway through the case. It is probable that this constituent is similar in properties to massive cementite in an over-carburised steel. When the white layer is fractured there is a tendency for the fracture to travel along these lines deeper into the case. It is of interest to note that we have re-produced a thin case by the nitrogen process, using the special steel and a period of eight hours at a temperature of 500/525°C. This case also cracked under the Rockwell test. Photomicrograph No.A606 illustrates the structure of the core. This appears satisfactory, confirming the fractures obtained. In conclusion, we consider the samples submitted to have a case which, in respect to its toughness and resistance to shock, appears to be definitely inferior to that produced on nickel steel (Spec.2071A) by carburising. We understand that more samples of the material will be available in the future. It has been suggested that we should case-harden some of these ourselves. If desired, the remains of the test bars used in the above tests can be submitted for examination. Copies of Photomicrographs A602 - A606 to By. {R.W. Bailey - Chief Engineer} " " " " " R. {Sir Henry Royce} " " " " " Rg. {Mr Rowledge} " " " " " Hs. {Lord Ernest Hives - Chair} Hl. HP | ||