MENG_3331-Group_report-ASME-HeatTreatment

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MENG 3331 Materials Science Department of Mechanical Engineering Oct. 18, 2023, Statesboro, Georgia, USA Technical Report 6 HEAT TREATMENT OF STEEL BY ANNEALING AND NORMALIZATION Lawrence Almeter Georgia Southern University Dearing, GA, USA Dylan Butler Georgia Southern University Albany, GA, United States Scott Rhodes Georgia Southern University Warner Robins, GA, United States Bryce Cone Georgia Southern University Sparks, GA, United States A BSTRACT The heat treatment experiment consists of two 1045 Steel samples heat treated in two different ways, those being normalizing and full annealing. Heat treatment alters the microstructure and adjusts the hardness of the samples. After the treatment, the samples went through a hardness test and underwent a metallography examination. Doing this shows how the hardness and the microstructure reacts to the hardness test. The two cooling processes used on the metals were normalized and annealed. Annealing allows the material to become more ductile but it will lose its hardness. Normalized will allow the metal to form an ultra fine grain structure and this will decrease its softness. Typically the material would become harder and lose ductility but as the experiment shows the hardness decreased from the original material pre normalization. As seen in the metallography experiment, the 1045 normalized material had a much more fine crystalline structure while the 1045 annealed structure had a larger grain structure that was less aligned. N OMENCLATURE HRB Rockwell Hardness B Scale INTRODUCTION The process of heat treating has a long history that has almost become synonymous with the human race, as it dates back to 6000 B.C.E when humans began smelting stones in fires or blast furnaces to recover the metallic ores that the stones contained [1]. The earliest heat treated artifacts consisted mostly of copper. A great advancement came in 1863 when an English geologist examined the microstructure of different steels and noted that the treatment of these metals determined and shifted the crystalline structures of steel [1]. The discovery of the effects of heat treating led to many great advancements in the late 19th century and early 20th century allowing for stronger steel alloys to be created and utilized for the growing industrial needs. 1 Copyright © 2023 by ASME

The process of heat treatment involves heating or cooling a metal to often extreme temperatures to allow for microstructures such as ferrite or pearlite to form and achieve desired properties of the material [3].The different processes include Quenching, Normalizing, Annealing, Tempering, Curborization, and Hardening, all which give different qualities to the sample being treated [3]. Quenching is performed by cooling metal very rapidly in water or most times oil, which keeps the metal from developing the soft phases thus creating a very hard material [4]. Normalizing is performed by heating metal in a furnace and allowing it to air cool thus cooling the sample somewhat quickly causing for a more fine grain structure to appear, which is very similar to Annealing which is when metal is heated in a furnace and allowed to cool inside the furnace which gives the metal plenty of time to develop its soft phases making for a more ductile material with a less fine grain structure [4]. Tempering is performed by heating metal to a temperature below the critical point for a certain amount of time then allowing it to cool in still air which makes the material tougher by reducing some of the interior stresses [4]. Hardening is performed by heating the metal to a certain temperature then Quenching it to create a very hard material but often brittle [4]. Curborization is the process of adding carbon to a low carbon steel by heating it in a carbon rich environment [4]. EXPERIMENTAL METHODS The heat treatment experiment is performed by placing metal samples into a furnace. To start, begin by cutting out two ¾’’ long 1045 steel samples. Once each sample is filed down, it will be time to place them into the furnace. The furnace is set to 900° celsius, the samples will be placed into a basket then inserted into the furnace. One 1045 steel sample will be left in the furnace for 45 minutes, making it a normalized sample once removed and cool. The other 1045 steel is left to heat all night and then cool in the furnace leaving the sample fully annealed. Once the samples are cooled, grind the face down on each to have a nice surface. Now perform the rockwell hardness test on each sample once they have been heat treated. Now sandpaper and polish the face of the metal samples using the metallography procedures. Once polished the surface will be acid etched in Nital (Ethanol and nitric acid mixture) and then observed under the microscope. DATA AND R ESULTS Table 1 shows each steel sample, the heat treatment process used on each sample, and also the hardness (HRB) values of each sample. The 1045 steel did not behave as expected. The 1045 steel before heat treatment had an average hardness of 98.7 HRB while the experimental 1045 steel after normalizing was softer at an average hardness of 80.0 HRB. This is surprising because the normalization process causes the grain size of the steel to become smaller thus making the steel harder. However, the data in this experiment showed the opposite case where the normalized steel was softer than the untreated steel. The normalized 1045 steel should have had a value closer to 90.0 HRB rather than 80.0 HRB as shown by the Standard Normalized data in Table 1. Figure 1 shows the smaller grain size of the normalized 1045 steel as compared to Figure 2 which shows the larger grain size of the untreated 1045 steel. Figure 3 shows the grain size of the full annealed 1045 steel. In all three figures, the white ferrite and more colorful pearlite regions are clearly visible. Table 1. Heat Treatment Process and Hardness of Samples Steel Heat Treat Process Hardness (HRB) Avg Std Dev 1045 As-Received 98.0 99.0 99.0 98.7 0.577 1045 Normalized Experimental 78.0 80.0 82.0 80.0 2.000 1045 Normalized Standard 90.0 91.0 88.0 89.7 1.528 1045 Full Annealed 79.5 80.0 81.0 80.2 0.764 Figure 1. Microstructure of Normalized 1045 Steel 2 Copyright © 2023 by ASME

Figure 2. Microstructure of Untreated 1045 Steel Figure 3. Microstructure of Full Annealed 1045 Steel DISCUSSION Upon conducting the heat treatment experiment, it is discovered that the annealed material lost hardness and toughness and gained ductility. This is due to the annealing process. Annealing a material is the process of reducing the temperature of a material slowly after being heated to a high temperature. The grain structure of annealed material becomes much more chunky and a lot less fine such as shown in Figure 3, while the normalized sample shown in Figure 1 has a much more fine grain structure allowing for the material to be harder. The untreated 1045 values were 98.0 HRB, 99.0 HRB, 99.0 HRB with an average of 98.7 HRB. Figure 2 represents untreated 1045 steel. In this figure you can see the grain structure is not nearly as fine as the normalized steel but slightly more fine then the annealed structure. This means that the untreated steel is typically harder than annealed steel but softer than the normalized steel. The normalized material should have a much higher toughness than the pre-normalized material but, in the case of the following experiment, a lower hardness number was produced. The values of the normalized 1045 steel were 78.0 HRB, 80.0 HRB, 82.0 HRB with an average of 80.0 HRB. This could be due to some of the scaling on the material giving away allowing inaccurate results to be produced. Another reason for the inaccurate results could be a confusion in material being used or the temperament process is not used on the material tested. The normalized process happens when a material is heated to a high temperature then cooled gradually allowing the fine crystal structures to be formed such as being shown in Figure 1. The process of temperament is often the last phase of a heat treatment process after normalizing which ensures the hardness and toughness of a material is increased. The values for the fully annealed steel given to us are 79.5 HRB, 80.0 HRB, 81.0 HRB, and an average of 80.2 HRB. These values are much lower than the untreated 1045 steel. This makes the sample more ductile and less hard. In the microstructure as shown in Figure 3 you can tell the crystal structure is much larger and less fine. This is due to the rapid cooling process. CONCLUSION The heat treatment is an experiment consisting of heating up metal samples and then performing tests to analyze how the properties changed. It was observed in the hardness test that both the normalized and annealed 1045 steel had a lower hardness than the as-received 1045 steel. Under the microscope it was also seen that the normalized 1045 steel had small very uniform grain sizes of pearlite and ferrite. R EFERENCES [1] “The History of Heat Treatment.” Vacu Braze , 18 Jan. 2022, www.vacubraze.net/press/the-history-of-heat- treatment/#:~:text=If%20we%E2%80%99re%20going %20all%20the%20way%20back%20to,began %20treating%20metals%20through%20the %20process%20of%20smelting. [2] “Heat Treatment History: The Early Days of Industrial Heating.” Industrial Heating RSS , Industrial Heating, 4 Dec. 2017, www.industrialheating.com/articles/93910-heat- treatment-history-the-early-days-of-industrial-heating. [3] “Heat Treating.” Wikipedia , Wikimedia Foundation, 12 Oct. 2023, en.wikipedia.org/wiki/Heat_treating. [4] 15, November. “Heat Treatment: Types of Heat Treatment Process (PDF).” RiansClub , 15 Nov. 2022, www.riansclub.com/heat-treatment/. [5] “Tempering.” Materials UK , www.thyssenkrupp- materials.co.uk/technical-knowledge-hub/tempering. Accessed 18 Oct. 2023. QUESTIONS 1. Faster cooling rates increase the hardness for both 1045 and 4140 steels. 2. Two factors that can affect the actual cooling rate of an air-cooled sample is, initial temperature and air circulation. 3. The alloying additions of normalized steel changes the grain sizes of the microstructure and it also increases the strength and toughness. 4. The alloying addition of annealed steel increases grain size of the microstructure and decreases the hardness while increasing the ductility. 3 Copyright © 2023 by ASME

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