The Jominy End Quench Test - Lab Report Example

Student Name: Tutor: Title: Jominy Lab Report Date: Executive Summary As per the Jominy End Quench Test: - ASTM A 255, hardenability of steel is a measure of its ability to get hardened at its autenitizing temperature when quenched at a particular depth of a cooler under specific set of conditions (Dobrzański & Sitek, 1999). This however may not be used interchangeably with hardness as the latter is the steel’s resistance to deformations under the action of external forces. This test is of great importance as it helps in the selection of proper alloy combinations and treatments by heat to reduce distortions, thermal stress and inefficiencies during the manufacturing process of steel parts. In our experiment, the test was performed as per the methodology explained in the latter sections of this report. Three specimens of steel were used and their results examined individually but with comparison with each other as shown in table 1. Subsequently, the steel samples got heated inside muffle furnace as shown in figure 2 then dipped in water to quench them. Individual hardenability was measured and recorder in terms of the distance from quenched end so as to show the individual hardenability properties suing a Rockwell Machine as shown in figure 3 below. The results then got plotted in graphs that represent individual Jominy curves as shown in figures 4, 5 and 6. It is evident from these curves that the alloy steel has the greatest hardenability as it forms martensite to the greater depth compared to steel composed of pure carbon. The level of martensite developed is an indicator of hardenability of the sample (Jominy, 1939). Samples that develop the largest volume of martensite indicate high hardenability while low hardenability is indicated by the formation of Bainite microstructures. The Jominy curves for the samples tested are plotted as in figure 4, figure 5 and figure 6 respectively. In can be established that the distance from quenched end is inversely proportional to the volume of martensite formed. This can be attributed to the difference in cooling rates for the different test trials. The experimental data obtained from the test have been used to show the alloying effect of steel and its microstructure effects on the hardenability of individual samples. Boron, Carbon, Chromium, Molybdenum, Nickel and Silicon are the elements that affect hardenability of steel samples. Predominantly, carbon is the preferred hardening agent as it slows down the formation of ferrite and pearlite (a process that increases hardenability). The affect is however minimal and was not used in the case of this experiment. The hardenability of steel is increased by slowing down the rate of austenite to ferrite transformation. The aforementioned elements affect the hardenability in this way and chromium is the most commonly used. This report covers the experimental procedures followed in the Jominy Test and parents the results thereof in Jominy curves. Subsequent sections of this report answers the question on the importance of hardenability of steel. Conclusions from the experimental test were also drawn and presented in the final section of this report. 5. Why is hardenability of steels important? Cite at least one typical application for each of the steels tested? As indicated earlier, hardenability refers to the conversion of steel to martensite on quenching, for optimum strength development, thus increasing the toughness of steel without great loss in strength. The selection of appropriate combinations of allow elements that produce the best quality of steel. This also minimizes stresses that develop due to heat and temperature changes while at the same time eliminating distortions during the manufacturing processes. Information of hardenability tests can be used to gauge whether or not steel elements can be adequately hardened in different quench media. It is also important to note prior processing for instance the temperature of austenitizing and the chemical composition affect hardenability. The information on hardenability also helps understand the effects of alloying in steel components. It is important for large steel sections, such as shafts and rotors, which require to have adequate strength throughout the section, to support whatever load is placed on them. Hardenability of steel also helps in selecting a steel components that can be heat treated. This is because of the fact that both the microstructure and alloying conditions do affect the hardenability of steel. Therefore knowing these properties would help in selecting the appropriate steel and matching it with individual quenching rates. Initial steel processes also affect the micro structure of steel and this further affects hardenability. As mentioned before, the capacity of steel to harden in a depth of quenching media under given conditions. The experiment will show that hardenability and of steel is related to depth of martensite formed and higher depth forms under relatively slower cooling, for instance oil quench. Hardenability also help in choosing steel components based on strength requirements, in that, components such as screws, mining shafts, aircraft undercarriages etc. require high hardenability. Understanding hardenability features of components therefore assist in choosing the best types of steel to use in the manufacture of components. However, in making these choices, cooling rates i.e. quenching cooling rates are important since they determine whether there are distortions and thermal stresses. For this reason, steel with low hardenability may be used for smaller components e.g. chisel and shears. As mentioned before, the Jominy Test is a standard way of estimating the hardenability of steels Hardenability also has an impact in the welding properties of components. It has an negative proportionality to the weldability of a component. The higher the hardenability of a material, the less easily it can be welded. Based on the derived properties of the samples tested, their applications can be determined as follows; in the manufacture of specific components; Sample No. 1 – used for couplings, crankshafts and cold headed parts Sample No. 2 – can be used in transmission devices such as gears and shafts for power transmission and in aircraft landing gears Sample No. 3 – used for fastening pieces and machine elements Conclusion The experiment explored the importance of the Jominy End-quench Test in the study of metals. The hardenability of various steel samples was analyzed and represented in a form of Jominy Curves. It was established that there are relationships between the variations in hardenability and the micro structure of the sample. The Jominy Curves of the various samples were also studied, subsequently establishing that sample 1 had a lower hardenability while sample 3 had high hardenability and can be applied in making components that require high strength. This test therefore can be used to determine the level of hardenability of samples and whether for different section diameters quenching media can sufficiently harden the samples. From the results, a correlation between the positions on the Jominy curves and the cooling transforms. In conclusion, the experiment was a success since the objectives were met. References ASM Handbook, Vol. 4, (1991) Heat Treating - Heat Treating of Steel. American Society for Metals. ASTM A370, (1997) Standard Test Methods and Definitions for Mechanical Testing of Steel Products. American Society for Testing and Materials. ASTM E18, (2000) Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials. American Society for Testing and Materials. ASTM E92, (1982) Standard Test Methods for Vickers Hardness of Metallic Materials. American Society for Testing and Materials. Dobrzański, L. A., & Sitek, W. (1999). The modelling of hardenability using neural networks. Journal of Materials Processing Technology, 92, 8-14. Jominy, W. E. (1939). Hardenability of Alloy Steels. ASM, 66. Steels: Microstructure and Properties, R.W.K Honeycombe and H.K.D.H. Bhadeshia. Edward Arnold, (1995). Yazdi, A. Z., Sajjadi, S. A., Zebarjad, S. M., & Nezhad, S. M. (2008). Prediction of hardness at different points of Jominy specimen using quench factor analysis method. Journal of materials processing technology, 199(1), 124-129. Read More