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Santa Rosa Junior College ENGR 45 Fall 2011 December 14, 2011.

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Presentation on theme: "Santa Rosa Junior College ENGR 45 Fall 2011 December 14, 2011."— Presentation transcript:

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2 Santa Rosa Junior College ENGR 45 Fall 2011 December 14, 2011

3 Purpose Cold Working Recovery Recrystallization Grain Growth Procedure Results Conclusion Errors

4 To document the recovery, recrystallization, and grain growth phases of cold-worked carbon steel.

5 Increasing strength through plastic deformation and increasing dislocations Cold working because deformation temperature drastically less than melting Higher dislocation density, more hindered dislocation movement, increase hardness Elongates grains

6 Applied heat increases dislocation motion Metal decreases in hardness as dislocations leave faster Additionally, original electrical and physical properties are restored

7 Continuation of recovery Continued decreasing dislocation density New grains form between larger grains Start small, eventually engulf parent grain boundaries Recrystallization temperature for carbon steel is about 1000˚F Possible to increase rate of recrystallization by increasing %CW

8 Recrystallization completes, continued applied heat Grain growth due to migration of grain boundaries outward Large range of grain sizes

9 Cold work a 40 cm long carbon steel wire to approximately 55% CW Cut wire into 12 equally sized pieces and assort into two groups of 6 Heat one group at 500˚F and the other at 800˚F Take one metal out of each after 1, 5, 10, 30, 60 minutes, and 24 hours Make two molds of each group taking note of how to distinguish between the samples Sand, polish and etch the samples Use the microscope to photograph each sample

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12 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 1 minute Magnification: Magnification: 300x Description: Description: Recovery and minor recrystallization. Visible grain stretching.

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14 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 5 minutes Magnification: Magnification: 300x Description: Stretching not visible. New grains forming. Description: Stretching not visible. New grains forming.

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16 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 10 minutes Magnification: Magnification: 300x Description: Description: New grains continuing to form. Increasing grain boundaries. Dislocation density begins to decrease due to the increased motion of the dislocations.

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18 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 30 minutes Magnification: Magnification: 300x Description: Grain size of larger grains increasing. Smaller grain boundaries are forced smaller. Dislocation density continues to decrease. Description: Grain size of larger grains increasing. Smaller grain boundaries are forced smaller. Dislocation density continues to decrease.

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20 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 60 minutes Magnification: Magnification: 300x Description: Description: Large grain boundaries continuing to increase, forcing other grains smaller.

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22 Annealing Temperature: Annealing Temperature: 500˚F Time: Time: 24 hours Magnification: Magnification: 300x Description: Very large and very small grain sizes visible. Grain growth is apparent. Number of dislocations is much less than at the beginning of recovery. Description: Very large and very small grain sizes visible. Grain growth is apparent. Number of dislocations is much less than at the beginning of recovery.

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25 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 1 minute Magnification: Magnification: 300x Description: More visible grain stretching than in 500 F. Recovery phase. Description: More visible grain stretching than in 500 F. Recovery phase.

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27 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 5 minutes Magnification: Magnification: 300x Description: New grains forming, much larger than those formed in 500 F at same annealing time. Description: New grains forming, much larger than those formed in 500 F at same annealing time.

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29 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 10 minutes Magnification: Magnification: 300x Description: Large grains increasing size, pushing adjacent grains smaller. Description: Large grains increasing size, pushing adjacent grains smaller.

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31 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 30 minutes Magnification: Magnification: 300x Description: Description: Large grains continue to grow, forcing others smaller. Dislocation density is decreasing.

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33 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 60 minutes Magnification: Magnification: 300x Description: Large grains are very apparent. Notice the wide variety of grain sizes. Description: Large grains are very apparent. Notice the wide variety of grain sizes.

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35 Annealing Temperature: Annealing Temperature: 800˚F Time: Time: 24 hours Magnification: Magnification: 300x Description: Grain growth is very apparent in larger grains. Smaller grains are much smaller than in previous slides. Dislocation density is at its minimum. Description: Grain growth is very apparent in larger grains. Smaller grains are much smaller than in previous slides. Dislocation density is at its minimum.

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37 Although some of the pictures of the recrystallization of carbon steel did not match perfectly with the theoretical outcomes we expected, we think that our experiment was still successful because the overall stages still followed the recrystallization model very closely.

38 Pictures did not come out as clearly as we had liked; over-etching and excessive scratching made the patterns in the grains less noticeable or difficult to see. Lack of a control sample makes it difficult to compare the other metals without a base frame of reference. Although the first metal was only heated for 1 minute, the fact that the steel was so thin may have caused drastic changes in the grain patterns.

39 The extreme thinness of the carbon steel may have caused the recrystallization process to end much faster, resulting in the grain growth phase occurring much sooner. The relatively small surface area of each metal may have caused the patterns in the grains to be distorted. Near the edges of each metal there was stretching of grains and other deformations. The inside of the metal were so close to the edges of the metal that the deformations may have extended to some of the grains in the middle.

40 warren.org/ALevelRevision/engineering/i mg2/coldrolling.gif ed.org/EducationResources/CommunityC ollege/Materials/Graphics/Recovery.gif /met205/annealingstages.html

41 Younes


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