The Economic Utilisation of Steels in Engineering Industry

Abstract

Literature records considerable evidence of the irrelevance to product performance of materials data, traditionally used in the design of engineering components. That such data forms the basis of steel specification schedules against which selection in design is made, would suggest that the selection process satisfies apparent rather than real engineering requirements, a factor of economic concern when steel costs, by way of steel composition, are considered as an essential part of selection procedure. The utilisation of heat-treatable steels in a major mass producing industry has been observed by way of field studies. They have shown that while the above situation is widely recognised among materials and engineering design staff, the revision of "traditional" attitudes is slow to occur. While confused ideas relating responsibility to the customer with product cost support the retention of such an unrealistic approach to steel selection in design, the primary reason for the continuance of such practice is the difficulty of re-phrasing steel design data in more realistic terms more closely paralleling the design situation. Failure of existing standards to reflect technological advances in precision heat-treatment techniques, on mass-production scale, further increases the discrepancy often existing between planned product performance and that actually attainable by these means. Difficulty in effecting meaningful communication on all aspects of steel selection, purchasing, and processing, between the disciplines most concerned, contribute to the continued dependence on "traditional" materials and methods of manufacture. The revision of engineering specifications is explored tentatively, using heat-treatment response as summarised for a given grade by a Jominy hardenability band. The flexibility of the method in meeting design requirements realistically is shown, although continuing to specify in terms of established strength criteria. For cost effectiveness in selection full exploitation of hardenability response in production heat-treatment systems is desirable and, to achieve this, the methods of calibrating quench severity are analysed, particularly for sealed-quench conditions. Limited experimental tests from one such procedure show the performance scatter among similar operational units. Analysis of heat-treatment data from the literature proved of limited use in the determination of expressions to describe heat treatment response in a given steel by means of compositional and microstructural factors. The results presented broadly support established qualitative principles, but the complexity of the equations obtained preclude their use at the present time, as a basis for the design of economic compositions.