Abstract
This investigation indicates that the factors which influences the machinability of steel can be divided into two main categories. (a) Metallurgical Factors. (b) Engineering Factors. and for clarity they will be dealt with separately. (a) Metallurgical Factors. Due to the fundamental reactions involved all machining operations generate heat. It has been proved that the most heat resistant tools can only withstand a temperature of approximately 900 C prior to softening, consequently this inherent factor does influence and curtail machining operations. Thus, it can be stated that anything which can be controlled in the steel to lower the heat generated when it is machined had a beneficial effect on the machinability and vice versa. This investigation indicates that the following items and their judicious control do have a beneficial effect on machinability. 1. The addition of Sulphur to the Steel. 2. The addition of Nitrogen to the Steel. 3. The steel-making conditions to keep non-metallic inclusions to a minimum and ensure freedom from segregation of the elements. 4. The temperature of hot rolling to avoid a banding phenomena. 5. Cold reduction of the material. It will of course be realised that items 3 and 4 do control the inherent structure of the steel and these do have a profound effect on machining characteristics. (b) Engineering Factors. In this category such item as the rigidity of the tool its shape, the speeds, feeds and depth of cut, the amount of overhang on the tool and the general rigidity of the machine are all factors which influence to a degree the machining characteristics. Emanating from this study it was also found that at present:- 1. It is impossible to specify and guarantee machining characteristics in terms of a Chemical or Mechanical specification or a combination of both. 2. No laboratory technique is know which is capable of assessing the machining characteristics if any steel and applying these results with any degree of accuracy to production conditions.