Abstract
AAR Grade E steel is extensively used in the rail industry for the manufacture of rail related components. Due to the environment in which these components operate, it is required that they exhibit good mechanical properties. The casting process is amongst the most economic methods of manufacturing. In the rail industry, rail components are predominantly manufactured by means of sand casting. Sand casting accounts for a significant majority of the total tonnage cast. Sand casting consists of pouring molten metal into a sand mould, allowing the metal to solidify, and then breaking up the mould to remove the casting. After the component is cast, it is usually followed by a heat treatment process. For some components a machining operation follows after the heat treatment process. Depending on the application of the component, the heat treatment required may have a significant effect on the mechanical properties and the machinability of the alloy. It is therefore important to schedule the machine appropriately and to use the most efficient and cost effective machining strategy. This may reduce costs as well as energy usage. It is also important to optimize the heat treatment process for the required mechanical properties along with an appropriate machining strategy for the alloy and family of parts concerned. A literature review has indicated that limited information exists to optimize the heat treatment of AAR Grade E steel as related to heat treatment and machining strategy. The objective of this research is to investigate the effect of heat treatment on the mechanical properties and machinability of AAR Grade E steel. A detailed literature review of the various topics that are covered in this research was conducted. These include the characterization of AAR Grade E steel, fundamentals of heat treatment, the applications of heat treatment on medium carbon steel alloys, the fundamentals of metal cutting and machinability of steels. An experimental program was developed to address the objectives that were established. This was executed by producing sample castings of a given diameter and thereafter subjecting them to various heat treatment cycles. These samples were then subjected to various heat treatment processes. Thereafter, various tests were conducted in order to determine its mechanical properties as well as machinability by using an instrumented lathe. The results obtained with regards to heat treatment showed that AAR Grade E steel responds positively to normalising, quenching and tempering when executed at the prescribed temperatures and soaking times. In addition to this, through a positive response to the various heat treatment processes, the respective samples exhibits mechanical properties that is typical to other steel grades having a similar chemical composition and that have undergone the same heat treatment process. In terms of the effect of heat treatment on the machinability of AAR grade E steel, it was found that depending on the machinability performance measure of interest, each material condition performs in a manner that is consistent with the fundamentals of machining as has been investigated in the literature review. A number of recommendations were made for consideration for future investigations of AAR grade E steel.
M.Eng. (Mechanical Engineering)