Innovative approach for steel design procedures tailored to component machining (Promach) : final report

The objectives of the Promach project were, on the one hand, determination of microstructural effects on machinability improvement technologies for engineering steels at the same strength level, and, on the other hand, definition of a steel design procedure to minimise running costs of mechanical components of strength above 900 MPa. Steels with improved machinability by means of the control metallic/non-metallic inclusions (low S, medium S, high S, Ca treatment and lead addition) and with different microstructures (pearlitic, bainitic and tempered martensitic steels) with Rm between 900 and 1 000 MPa have been studied. A complete mechanical and metallurgical characterisation was performed on the 15 manufactured grades. The machining tests included the following. • Basic machining operations: turning V15, drilling (3D, 5D and 20D). • Screening for chip controlled breakability. • Orthogonal cutting operations: force and temperature measurements, high-speed filming and quick-stop tests. • Semi-industrial machining: tapping and autolathe tests. In tool-wear-related tests, pearlitic steels (%S 0.040-0.090 %) tend to perform the best, and also good results are obtained with bainitic steels. For all the microstructures, leaded and high S grades had the higher machinability. In chip-quality-related tests, leaded grades are the best ranked, and also steels with temp. martensitic and bainitic microstructures. A steel design procedure was developed by means of a benefit or utility analysis, using the four targets of criterion chip form, cutting force, surface quality and tool life typically more critical for machinability. Cost savings taking as reference real crankshaft production data were also calculated for turning and drilling operations.