Recrystallization of Cold-Worked Steel Wire

Santa Rosa Junior CollegeENGR 45Fall 2011December 14, 2011Recrystallization of Cold-Worked Steel Wire Edward AlicdanJared CarrPurposeCold WorkingRecoveryRecrystallizationGrain GrowthProcedureResultsConclusionErrors

Recrystallization of Cold-Worked Steel WireTo document the recovery, recrystallization, and grain growth phases of cold-worked carbon steel.Purpose

Increasing strength through plastic deformation and increasing dislocationsCold working because deformation temperature drastically less than meltingHigher dislocation density, more hindered dislocation movement, increase hardnessElongates grainsCold Workinghttp://www.the-warren.org/ALevelRevision/engineering/img2/coldrolling.gifhttp://adsabs.harvard.edu/abs/1985MTA....16..703CRecovery

Applied heat increases dislocation motionMetal decreases in hardness as dislocations leave fasterAdditionally, original electrical and physical properties are restored

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/Recovery.gif

Continuation of recoveryContinued decreasing dislocation densityNew grains form between larger grainsStart small, eventually engulf parent grain boundariesRecrystallization temperature for carbon steel is about 1000FPossible to increase rate of recrystallization by increasing %CW

Recrystallization

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/Recovery.gifhttp://info.lu.farmingdale.edu/depts/met/met205/annealingstages.html

Recrystallization completes, continued applied heatGrain growth due to migration of grain boundaries outwardLarge range of grain sizesGrain Growth

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/Recovery.gif

Cold work a 40 cm long carbon steel wire to approximately 55% CWCut wire into 12 equally sized pieces and assort into two groups of 6Heat one group at 500F and the other at 800FTake one metal out of each after 1, 5, 10, 30, 60 minutes, and 24 hoursMake two molds of each group taking note of how to distinguish between the samplesSand, polish and etch the samplesUse the microscope to photograph each sampleProcedure

500F 800F

Results500F10

ResultsAnnealing Temperature: 500FTime: 1 minuteMagnification: 300xDescription: Recovery and minor recrystallization. Visible grain stretching.

Annealing Temperature: 500FTime: 1 minuteMagnification: 600xDescription: Recovery and minor recrystallization. Visible grain stretching.Results

ResultsAnnealing Temperature: 500FTime: 5 minutesMagnification: 300xDescription: Stretching not visible. New grains forming.

Annealing Temperature: 500FTime: 5 minutesMagnification: 600xDescription: Stretching not visible. New grains forming.Results

ResultsAnnealing Temperature: 500FTime: 10 minutesMagnification: 300xDescription: New grains continuing to form. Increasing grain boundaries. Dislocation density begins to decrease due to the increased motion of the dislocations.

Annealing Temperature: 500FTime: 10 minutesMagnification: 600xDescription: New grains continuing to form. Increasing grain boundaries. Dislocation density begins to decrease due to the increased motion of the dislocations.Results

ResultsAnnealing Temperature: 500FTime: 30 minutesMagnification: 300xDescription: Grain size of larger grains increasing. Smaller grain boundaries are forced smaller. Dislocation density continues to decrease.

Annealing Temperature: 500FTime: 30 minutesMagnification: 600xDescription: Grain size of larger grains increasing. Smaller grain boundaries are forced smaller. Dislocation density continues to decrease.Results

ResultsAnnealing Temperature: 500FTime: 60 minutesMagnification: 300xDescription: Large grain boundaries continuing to increase, forcing other grains smaller.

Annealing Temperature: 500FTime: 60 minutesMagnification: 600xDescription: Large grain boundaries continuing to increase, forcing other grains smaller.Results

ResultsAnnealing Temperature: 500FTime: 24 hoursMagnification: 300xDescription: Very large and very small grain sizes visible. Grain growth is apparent. Number of dislocations is much less than at the beginning of recovery.

Annealing Temperature: 500FTime: 24 hoursMagnification: 600xDescription: Very large and very small grain sizes visible. Grain growth is apparent. Number of dislocations is much less than at the beginning of recovery.ResultsResults800F

23

ResultsAnnealing Temperature: 800FTime: 1 minuteMagnification: 300xDescription: More visible grain stretching than in 500 F. Recovery phase.

Annealing Temperature: 800FTime: 1 minuteMagnification: 600xDescription: More visible grain stretching than in 500 F. Recovery phase.Results

ResultsAnnealing Temperature: 800FTime: 5 minutesMagnification: 300xDescription: New grains forming, much larger than those formed in 500 F at same annealing time.

Annealing Temperature: 800FTime: 5 minutesMagnification: 600xDescription: New grains forming, much larger than those formed in 500 F at same annealing time.Results

ResultsAnnealing Temperature: 800FTime: 10 minutesMagnification: 300xDescription: Large grains increasing size, pushing adjacent grains smaller.

Annealing Temperature: 800FTime: 10 minutesMagnification: 600xDescription: Large grains increasing size, pushing adjacent grains smaller.Results

ResultsAnnealing Temperature: 800FTime: 30 minutesMagnification: 300xDescription: Large grains continue to grow, forcing others smaller. Dislocation density is decreasing.

Annealing Temperature: 800FTime: 30 minutesMagnification: 600xDescription: Large grains continue to grow, forcing others smaller. Dislocation density is decreasing.Results

ResultsAnnealing Temperature: 800FTime: 60 minutesMagnification: 300xDescription: Large grains are very apparent. Notice the wide variety of grain sizes.

Annealing Temperature: 800FTime: 60 minutesMagnification: 600xDescription: Recrystallization is nearly complete. Large grains are very apparent. Notice the wide variety of grain sizes.Results

ResultsAnnealing Temperature: 800FTime: 24 hoursMagnification: 300xDescription: Grain growth is very apparent in larger grains. Smaller grains are much smaller than in previous slides. Dislocation density is at its minimum.

Annealing Temperature: 800FTime: 24 hoursMagnification: 600xDescription: Grain growth is very apparent in larger grains. Smaller grains are much smaller than in previous slides. Dislocation density is at its minimum.ResultsConclusionsAlthough 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.

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.ErrorsLack 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.

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.ErrorsReferenceshttp://www.the-warren.org/ALevelRevision/engineering/img2/coldrolling.gifhttp://adsabs.harvard.edu/abs/1985MTA....16..703Chttp://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/Recovery.gifhttp://info.lu.farmingdale.edu/depts/met/met205/annealingstages.htmlSpecial ThanksYounes