PROPERTIESEffects of Carbon in 1020A and 1040A annealed samplesThe 1040A sample has a carbon content of 0.4 %, twice as much alloying material as the 1020A sample, which has a carbon content of 0.
2%. Comparing the Yield Strength and Ultimate Tensile strength for the two annealed steels, the results show that both the YS and UTS for the 1040A sample are approximately 40% higher than in the 1020A sample. The addition of more carbon in the 1040A steel has caused its crystal matrix to become more stressed. The atomic bonds are much harder to slip, resulting in a metal roughly 40% stronger than the lower carbon 1020A. Comparing the calculated values for % elongation, the 1020A sample underwent a 38.2% elongation while the 1040A sample only stretched 26.
7%, approximately 2/3 as much as the lower carbon steel. As mentioned previously, the higher carbon content in the 1040A sample makes it harder for atomic planes to slip, lowering the materials ductility. The result is that the 1040A can only stretch about 2/3 as much as the lower carbon 1020A can before failure. Similarly, the higher carbon 1040A sample experienced a 40.
8% reduction in area (% RIA), approximately 2/3 of the 61.2% RIA observed in the 1020A steel. This is again due to the decrease in ductility caused by higher carbon content. The lower carbon 1020A sample is more ductile and withstands a higher degree of deformation before failure. The necking of the material shortly before failure is more severe in the 1020A, and therefore results in a greater % RIA than in the higher carbon 1040A. (Faculty of Manufacturing and Automation , 2017)Rapid Quench vs slow cool (anneal)Comparing the Yield Strength and UTS values for 1040A and 1040Q samples, the results show that the UTS of the two alloys is very close, within 3%.
However, the Yield Strength of the 1040Q sample is approximately 50% higher than that of the 1040A. These alloys have the same carbon content, however the quenched 1040Q has smaller grains and a more stressed out matrix due to the rapid cooling process. As a result, the quenched steel is much more resistant to slip and took approximately 50% more force than the annealed steel before beginning to plastically deform. The quenching process also caused the 1040Q to become more brittle than the 1040A. The quenched sample’s YS and UTS values are equal, showing that the sample failed spontaneously upon reaching the Yield Load. This is further demonstrated by the quenched steel’s observed % Elongation (0%) and % RIA (0.257%). These values show that the 1040Q sample did not stretch or neck during the tensile test.
This is a characteristic of brittle metals, whose atomic bonds are stretched to maximum and cannot undergo any further deformation before failure. By comparison, the slow cooling process in the annealed steel allows the atoms in the crystal matrix to relax and diffuse, and the material is more ductile as a result. The Yield strength in the 1040A is lower, approximately 2/3 that of the 1040Q, however the annealed sample’s % Elongation (26.7%) and % RIA (40.8%) values show that the sample underwent significant deformation before reaching its UTS. (Faculty of Manufacturing and Automation , 2017)Comparison of FCC and BCC Crystal StructuresComparing the mechanical properties AL 6061-T6 (FCC) and 1040Q (BCC) in terms of their crystal structures, the most notable differences are in strength and ductility.
Front Center Cubic crystal structures as seen in the Aluminum sample are more ductile because they have many slip planes and can easily form new bonds when atomic bonds are broken. During testing, the 1040Q sample (BCC) was very brittle and failed before undergoing any work hardening. The AL6061-T6 sample (FCC) was more ductile than the BCC steel with 6.68% increase in strength due to work and a moderate % elongation and % RIA. The 1040Q sample did not experience any significant % elongation or % RIA. The 1040Q sample is an example of the increase in strength present in a Body Center Cubic crystal structure. The atoms in a BCC structure are harder to slip than in an FCC structure; increasing in strength but making it more brittle.
This is demonstrated by the values for Ys and UTS. The Ys for 1040Q is almost 2x higher than the AL6061-T6 and its UTS is approximately 80% higher due to its BCC structure. (Faculty of Manufacturing and Automation , 2017)