Understanding the Jominy and Quench Test - Report Example

Abstract This paper contains two reports: the first is a laboratory experiment on the Jominy end-quench test performed to explore the relationship between hardenability and composition of different steels. Three samples were tested and their results were compared to each other and used to the above relationship. The second is on CNC machining and the comparison of their performance with conventional machining. A CNC milling process was observed, recorded and its differences noted in comparison to the conventional machining process. The advantages of CNC machining was therefore noted and discussed. Abbreviations and terminology Quench – cooling (with water in this paper) HRC – Rockwell C scale obtained by exerting an indentation pressure of 150kgf using a 120⁰ diamond cone indenter CNC – Computer Numerical Control Introduction The hardenability of metals or their alloys is defined as the depth up to which the sample being tested is hardened after going through a standardized process of heat treatment. This can be tested using a variety of methods such as the Rockwell, Leeb, Vickers, Meyer, and Brinell. This experiment will employ the Rockwell hardness testing to test 3 sample of steel for their hardenability (Kalpakjian, 1989). Hardenability in this test will be measured as the depth to which the sample being tested can be indented using the Jominy end-quench test. It measures how deep into the sample it is possible to achieve a certain hardeness. Hardness units for this test will be in in HRC which is a Rockwell scale obtained by exerting an indentation pressure of 150kgf using a 120⁰ diamond cone indenter(Kalpakjian, 1989). The three test sample hardenability results will be compared against each other . Hardenability A work piece’s hardenability is its capacity to, under specified conditions, harden in depth. When quenched, the surface in contact with the water (quenched end) cools and becomes even in terms of crystalline structure. The rest of the sample that is not in contact with water does not cool as fast as the quenched end, and the hardenability therefore varies along the length of the work piece (Kalpakjian, 1989). This hardenability is a function of the ferrous alloy’s carbon content. When heated to a certain temperature, the steel sample is changes into austenite which on cooling transforms into a small amount of martensite at a specified depth below the surface. The cooling process is referred to as quenching and is done using a jet of room temperature water splashed on one end of the steel cylinder. After quenching a flat surface is ground on the test sample and hardness measured starting from the quenched end on a specified interval. The readings are plotted on the hardenability graph. The farther away from the quenched end the hardness extends, the higher the hardenability of the sample being tested (Kalpakjian, 1989). The quench and temper treatment of steal uses these principles to harden steel in order to give its martensite microstructure the optimum mix of strength and toughness. Without tempering, martensite is brittle, even though it is hard. If the cooling rate is not fast enough, materials other than martensite may form such as pearlite, ferrite, or bainite. The higher the proportion of martensite formed on cooling a steel sample, the higher its hardenability. The higher the hardenability of a material, the better it is suited for use in big high strength components like pistons for rock breakers and aircraft undercarriages among others. The lower its hardenability, the higher its suitability for smaller components like shears or chisels (Gliner & Vybornov, 2013). The Jominy End-Quench Test The Jominy end-quench test was named for Walter E. Jominy (1893-1976) who invented the test in conjunction with A.L. Boegehold. It is a standard measure of the hardenability of steel (test, n.d). A laboratory experiment was conducted to explore the relationship between hardenability and composition of different steels. For this experiment, three samples were tested each measuring 1” in diameter and 4” in length. The samples were austenitized by heating up to a temperature above 850 but not exceeding 900⁰C for at least 20 minutes. The samples were then quenched using water at 24⁰C for 10 minutes then cooled completely in a cooling tank. A flat surface was ground along the length of each test sample at a depth of 0.015” for the purposes of removing decarburised material. Rockwell C Hardness was then measured from the quenched end at an interval of 1.6mm (or 1/16”) up to a length of 2”. Readings below 20HRC were discarded. The same procedure was followed for each sample. The results were then tabulated and a Jominy curve plotted for each sample. Results Three Jominy curves were plotted for the three samples as shown in the three graphs below. The three samples were numbered as 661, 992, and 893. Figure 1: Jominy curves for the three test samples plotted against distance (mm) from the quenched end Table 1: sample 661 SAMPLE 661 Distance (mm) from quenched end HRC Microstructure justification 0 52 martensite cooling rate 10-20 ⁰C/s, HRC >50 25.5 22.2 Ferrite & pearlite cooling rate 10-20 ⁰C/s, HRC >15 but 15 but 27 25.5 37.3 pearlite cooling rate 10-20 ⁰C/s, HRC >27 44.7 32.2 pearlite cooling rate 10-20 ⁰C/s, HRC >27 SAMPLE 893 Distance (mm) from quenched end HRC Microstructure justification 0 53.8 martensite cooling rate 10-20 ⁰C/s, HRC >50 25.5 50.2 martensite cooling rate 10-20 ⁰C/s, HRC >50 50.8 48.6 Martensite & pearlite cooling rate 10-20 ⁰C/s, HRC >40 but Read More

The higher the proportion of martensite formed on cooling a steel sample, the higher its hardenability. The higher the hardenability of a material, the better it is suited for use in big high strength components like pistons for rock breakers and aircraft undercarriages among others. The lower its hardenability, the higher its suitability for smaller components like shears or chisels (Gliner & Vybornov, 2013). The Jominy End-Quench Test The Jominy end-quench test was named for Walter E. Jominy (1893-1976) who invented the test in conjunction with A.L. Boegehold.

It is a standard measure of the hardenability of steel (test, n.d). A laboratory experiment was conducted to explore the relationship between hardenability and composition of different steels. For this experiment, three samples were tested each measuring 1” in diameter and 4” in length. The samples were austenitized by heating up to a temperature above 850 but not exceeding 900⁰C for at least 20 minutes. The samples were then quenched using water at 24⁰C for 10 minutes then cooled completely in a cooling tank.

A flat surface was ground along the length of each test sample at a depth of 0.015” for the purposes of removing decarburised material. Rockwell C Hardness was then measured from the quenched end at an interval of 1.6mm (or 1/16”) up to a length of 2”. Readings below 20HRC were discarded. The same procedure was followed for each sample. The results were then tabulated and a Jominy curve plotted for each sample. Results Three Jominy curves were plotted for the three samples as shown in the three graphs below.

The three samples were numbered as 661, 992, and 893. Figure 1: Jominy curves for the three test samples plotted against distance (mm) from the quenched end Table 1: sample 661 SAMPLE 661 Distance (mm) from quenched end HRC Microstructure justification 0 52 martensite cooling rate 10-20 ⁰C/s, HRC >50 25.5 22.2 Ferrite & pearlite cooling rate 10-20 ⁰C/s, HRC >15 but 15 but 27 25.5 37.3 pearlite cooling rate 10-20 ⁰C/s, HRC >27 44.7 32.2 pearlite cooling rate 10-20 ⁰C/s, HRC >27 SAMPLE 893 Distance (mm) from quenched end HRC Microstructure justification 0 53.

8 martensite cooling rate 10-20 ⁰C/s, HRC >50 25.5 50.2 martensite cooling rate 10-20 ⁰C/s, HRC >50 50.8 48.6 Martensite & pearlite cooling rate 10-20 ⁰C/s, HRC >40 but

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