Jominy Hardenability test - Lab Report Example

Jominy Hardenability Test Abstract. Hardenability is a property that involves determining the distribution, as well as hardness depth often introduced through the process referred to as quenching with the use of a condition called austenization. In quenching, the hardness dependence can be understood from the transformation of the time and temperature steel characteristics. This experiment setting up of this experiment was driven by the urge to investigate the Jominy hardenability test. This way, A part was hardened through quenching by water and oil. Following this, the part surfaces were cooled at a somewhat faster rate leading to high hardness. Through this, the inside of the part cooled at a somewhat slow rate and, therefore, did not get hardened up. Moreover, due to the T-T-T diagram, variation in hardness was not linear considering the outward part to the central part (Bain 6). It was evidenced that the hardenability of steel was dependent on the steel composition, the grain size austenitic, and the steel structure before quenching. The hardenability of steel increased with the content of carbon, as well as the content of the alloy. This indicates that the Maximum hardness was influenced by the metal mass being quenched. Considering a small portion, the heat was extracted rapidly, thereby, surpassing the specific steel critical rate of cooling. This implied that the part was fully martensitic. Critical rate of cooling is the cooling rate that must be exceeded to inhibit the formation of martensite products. Whenever the section size increased, it was hard to have the heat extracted fast to surpass the critical rate of cooling and avoid the establishment of the non-martensitic components. The steel hardenability was found to correlate directly with the critical rates of cooling. This experiment has various objective, key among them include heating different steels above the temperature of austenization, quenching the given specimen from one end in order to introduce a gradient of cooling, measuring hardness using the Rockwell scale along the cooled bar length, and comparing the curves of experimental hardenability with the curves of the published hardenability. Introduction. Hardenability entails the extent to which, a substance or material is hardened following a complete process of heat treatment. As widely cited, Hardenability is measured using the measurements of length. It serves the purpose of indicating how deep inside a material of given hardness can be obtained. This is one such vital property in welding and it is inversely proportional to the weldability of a material. This property can be demonstrated in a case where whenever a workpiece that is made of steel is quenched; the contact area having water is suddenly cooled and it is often evened out of the given medium. On the contrary, the internal depth of the medium fails to cool in a rapid in a rapid way and the workpieces inside, cool at a slow rate allowing the austenite to change into a structure besides martensite. The main effect is that the resulting component would be a workpiece with different crystal structures, having a hard shell and a core considered being soft and hard for the entire structure. In this case, the softer core is a combination of cementite and ferrite such as the pearlite. In ferrous alloys such as steel, hardenability is a component of the carbon content and other different elements of the alloy. The other alloying elements have relatively important including the calculation using the equivalent material’s carbon content. In quenching, the fluid used facilitates the rate of cooling for the materials as a result of the changing thermal conductivity and specific heat. Components such as water and brine that have the ability to cool faster than oil and air (Callister 9). Apart from this, whenever a fluids are agitated, their rate of cooling is fast. In other cases, the part geometry influences the rate of cooling rate for two samples having different volumes. This means that the material having a high surface area will have the tendency of cooling fast. Jominy test is used in measuring the hardenability in the ferrous alloy (Bain 5). Around a metal bar having a size that is standard is transformed to a one hundred percent austenite through a treatment of heat. It is then quenched at one end using water at room temperature. The rate of cooling will increase at the end that would be quenched, and reduce whenever the end distance increases. After this, a surface that is flat is ground using the test piece and the hardenability established through measuring the bar's hardness. As the quenched hardness end extends further, the increase in the hardenability. Procedure. The specimen was assumed to be normalized keeping it at the austenitizing temperature for about an hour. In this case, the specimen was kept inside the furnace at nine hundred degrees Celsius for about one hour. The operation of the Jominy apparatus was checked before quenching of the specimen. In this case, the jet’s height was two inches on top of the orifice without the specimen in place. The scale at the bottom of Jominy Fixture was cleared. The specimen was removed from the furnace, placed in the fixture, and quenched for a period of five seconds. The time of quenching was recorded. After this, the longitudinal flat was ground along the specimen. The fixture was used in measuring the Rockwell hardness against the distance to the quenched end. The Rockwell hardness was measured every 1/16" for the initial inch and in every 1/8" increments for the following inches of steel. Results. The collected data was recorded in table 1. Table 1. Hardness HRB Average HRB number distance from the end 1043 4340 2691.5 1 0.0625 89.6 112.5 101.05 2 0.125 94.6 112.4 103.5 3 0.1875 94.6 112.1 103.35 4 0.25 91.7 111.1 101.4 5 0.3125 92.3 110.3 101.3 6 0.375 92.4 110.6 101.5 7 0.4375 91.7 110.7 101.2 8 0.5 90.7 109.7 100.2 9 0.5625 90.5 109.2 99.85 10 0.625 89.7 107.9 98.8 11 0.6875 90 107.9 98.95 12 0.75 90.3 107.4 98.85 13 0.8125 90.3 106.9 98.6 14 0.875 89.5 106.9 98.2 15 0.9375 89.7 106.1 97.9 16 1 88.6 106.3 97.45 18 1.125 86.7 103.5 95.1 20 1.25 85.1 103.2 94.15 22 1.375 84.9 102.2 93.55 24 1.5 81.9 101.2 91.55 26 1.625 82.8 100 91.4 28 1.75 70.4 99.1 84.75 30 1.875 79.7 98.8 89.25 32 2 78.4 78.4 Data analysis. Graph 1: Experimental hardenability curves. Graph 2: published hardenability curves. Discussion. The test data for the Jominy test indicate that the effect of microstructure and alloying towards the steel hardenability. Some elements in common use in alloying might adversely influence the hardenability of steel. Such elements include boron, carbon, chromium, molybdenum, manganese, nickel, and silicon. Of these, carbon works as a steel-hardening agent, though, it is known to characteristically cause an increase in the steel hardenability. It does this by reducing the formation of ferrite and pearlite (Bain 9). However, one thing to contend with is that its effect is quite minimal and, therefore, makes it unsuitable for use as a hardenability control factor. Steel, on the other hand, is an alloy that is commonly obtained from the combination of iron along with other elements such as carbon. This clearly implies that carbon alongside other elements can serve the purpose of hardening the component. Through this, they can help in preventing the crystal lattice of the iron atom and prevent them from dislocating, as well as sliding past another. The extent of the hardness of steel under the control and it is achieved by varying the quantities of the alloying elements and their present from inside the steel. Research indicates that Steel that has a high amount of carbon content is somewhat harder as compared to iron, though it might be associated with less ductility than iron. Boron, on the other hand, might be a suitable alloy for the improvement of steel hardenability approximated at a value below 0005% (Bain 12). This is the most useful alloy in steels and has a carbon content of approximately 0,25% or less. Boron mixes readily with both oxygen and nitrogen and affects the hardenability of steel. This implies that boron should always remain in a solution in order for it to remain efficient. Titanium and aluminum are mostly included as agents of gettering in order for them to react with nitrogen and oxygen in preference to boron (Callister 8). Whenever the austenite phase transformation is slowed to pearlite and ferrite the steel hardenability increases. Molybdenum, chromium, vanadium, manganese, nickel, and silicon all have some effects to the steel's hardenability. In many cases, molybdenum, manganese, and chromium are used in the hardening process. Whenever a specimen is quenched inside water or any other fluid, the heat is conducted out into the surface. This results in the temperature gradient at/dx in between the surface and central part of the specimen being heated. This makes the gradient of the temperature to vary with time. There is a less steep gradient of the temperature between the edge and the center at later times. In this respect, the center temperature behind the surface temperature. If edge and center time profile were to be plotted, the center time of reaching the required temperature would be longer than that at the edge (Callister 10). This implies that the rate of cooling will always vary the depth function. The increase in the depth the reduction in the rate of cooling. This is clearly shown in graph 1. This situation in respect to the rate of cooling could result in a change in hardness at the edge and at the center (Callister 9). The center transforms into a bainite or pearlite whereas the edge changes into a martensite. When one chooses a steel, he should observe its potential to cool at the center which always depends on the part thickness (Bain 9). When the thickness of the part has increased the rate of cooling would be slowed at the center. This means that for a certain thickness one should pick a steel which could be hardened at the center whenever that is required. The rate of cooling should, therefore, be kept constant. From the data, it is evidenced that the center section of the steel could be hardened through changing the time-temperature by use of the alloys. It is also evidenced that a slow rate of cooling could be utilized in reaching the state of martensitic (Callister 5). During testing, water was sprayed on one side of the steel bar when still hot so as to enhance a one-dimensional transfer of heat during cooling. Moving away from the end that was quenched made the temperature rate of change to be altered. The rate of cooling is observed being low as the temperature increases. When the hardness of the surface is measured as a distance function from the end, a profile of hardness was obtained. This profile can be applied to any specimen that is made from steel (Callister 4). Hardenability is, therefore different from hardness as hardness refers to a measure of the extent of resistance for a solid matter towards different types of permanent shapes whenever some amount of force is applied to the solid matter. The macroscopic hardness is hardness with intermolecular bonds that are strong. It occurs whenever the character of the solid matter under force appears to be complex. In this respect, there are a variety hardness measurements. These include indentation hardness, scratch hardness, and rebound hardness (Bain 3). Comparing the experimental and published hardenability values, it is evidenced that the two pairs of curves are similar to each other. The curves have a similar gradient with just a few differences. These differences were brought about due to experimental errors. Some of the experimental errors came about due to air resistance, parallax, the heterogeneous trait of the calibration plate, faultiness of the Rockwell scale, and wrong calculation. The experimental errors due to parallax could be minimised by conducting the experiment at least three times. The other errors could be reduced by conducting the experiment in a room that has vacuum conditions, and ensuring that the testing scale is accurate before beginning the experiment. Conclusion. From the experiment, it is evidenced that the treatment of heat is composed of cooling and timed heating operations that were applied to steel in a solid state in a manner to give out a specific microstructure or properties that are desired. This implies that normalizing, annealing, quench hardening, austempering, and tempering are five extremely vital treatments of heats that could be utilized in modifying the properties and the microstructure of steel (Callister 4). The given out microstructure could be identified using time temperature transformation, or the continuous cooling transformation diagrams for the particular steel that would be treated. In this experiment, all the objectives of the experiment were achieved. Work Cited. Bain, Paxton. Alloying Elements in Steel. New York: Metals Park press.2006. Print. Callister, Dan. Fundamentals of Materials Science and Engineering. New York: Wiley & Sons Publishers. 2005. Print. APPENDIX. Read More