Operational Terms: Annex B - Process diagrams for part B ...
Characterization of Microstructure and Composition ... Poster.pdf · Process A -OK and, b) a sample...
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We would like to thank Dianna Clute, Andrew Cummins, Walter Isenberg, Chad Miller, Mark Sattgast, and David Brewer from Caterpillar, as well as the Caterpillar Lafayette Metallurgical Lab, and Jameson Root, Tim Vanmeter, and Dr. David Johnson from Purdue University for all their help. Characterization of Microstructure and Composition Controlling Fracture Split Behavior in Microalloy Forging Steels Brandon Battas, Minghao Guo, Michael Krane Faculty Advisors: David Johnson Industrial Sponsors: Dianna Clute, Andrew Cummins, Walter Isenberg, Chad Miller, Mark Sattgast Project Background Quantitative Microstructural Analysis Recommendations One possible future avenue of research could include Charpy impact testing at higher temperatures to facilitate higher resolution of impact energy and ductile fracture measurements. Another approach could be an alternative test, such as a high strain rate tensile test. Fractographic Characterization MSE 430 - 440: Materials Processi n g and Design This work is sponsored by Caterpillar, Lafayette, IN Caterpillar uses fracture splitting to manufacture the connecting rods in large engines- using a wedge to completely fracture the bearing starting from two laser cut notches so that it can be bolted together around the crankshaft. These large engine connecting rods require a yield strength significantly greater than other conventionally smaller fracture split connecting rods. To achieve this strength they are made from a High Strength Low Alloy (HSLA) steel, which uses certain microalloying elements such as vanadium to form carbides that increase strength by grain size refinement. Selected Charpy samples were cut, and the face parallel to the fracture surface was mounted, polished, analyzed by optical microscopy. y = 384.81x -0.807 R² = 0.8522 0 20 40 60 80 100 120 140 160 0.00 5.00 10.00 15.00 20.00 PAGS Diameter (um) Ferrite Volume Fraction (%) The main characteristics analyzed on were prior austenite grain size (PAGS), pearlite colony size, and the relative amounts of proeutectoid ferrite and pearlite microconstituents, and the relationships between these features and the fracture performance of each heat. Optical micrographs of: a) a sample from the good heat, Forging Process A-OK and, b) a sample from the problem heat, Forging Process B-Problems. 0 5 10 15 Max Cooling No Cooling Ferrite Volume Fraction (%) Cooling Rate Acknowledgements Left: Brian Crower Sportsman Connecting Rod Set - VQ35DE / VQ35HR. Retrieved from https://www.z1motorsports.com Right: Fracture-split Connecting Rods “No, That's Not a Broken Part.” (2014, October 20). Retrieved from https://mitchell1.com SEM images of the fracture surfaces of: a) a sample from Forging Process A-OK and, b) a sample from Forging Process B-Problems. The maximum shear lip lengths have been marked, along with the Charpy notch and some characteristic areas of ductile (microvoid coalescence) and brittle (cleavage) fracture. Caterpillar, some time after a change in forging heats, found that fracture splitting manufacturing yields differed with changes in heat. A study was performed to assess the discrepancy through analysis of the microstructure and the fracture behavior of fractured Charpy v-notch bars. It was found that larger prior austenite grains and less proeutectoid ferrite corresponded to the best fracture behavior. Also, parts that had problems fracturing tended to have larger shear lips than the parts that did not have problems. When the material used in large engine connecting rods experienced a change in heat, some of the connecting rods began to fracture incompletely during fracture splitting. The purpose of this project was to investigate the relationships between microstructural characteristics of the metal used in different heats and the corresponding fracture performance, with the goal of determining a method to predict how well a given heat will fracture. Problem a) b) Cleavage Cleavage Microvoid Coalescence Microvoid Coalescence Notch Notch Shear Lip Length Shear Lip Length Descriptions for the different sample designations and color codings to be used in this poster. Optical microscopy demonstrated that a higher austenitization temperature lead to a larger prior austenite grain, whereas a lower cooling rate resulted in a higher ferrite volume fraction. The samples with better fracture performance had a greater PAGS and a lower proeutectoid ferrite volume fraction. The SEM fractography, specifically the measurements of the shear lip length, largely correlated with the Charpy impact energy measurements previously taken by Caterpillar. There was variance in the different samples, but the length of the shear lip did tend to correlate with the quality of the fracture splitting. However, extreme variance within the same forging heats such as High-High and Forging B-OK, indicated that there were likely factors other than a microstructural correlation, possibly factors such as elemental segregation, driving the differences in fracture. Conclusions Room temperature Charpy impact testing had already been conducted, the results of which did not have enough resolution for useful conclusions. These fractured Charpy bars were provided for analysis, of both the middle of the bar and the fracture surface. Location Caterpillar retrieved Charpy bars from in connecting rods 0 20 40 60 80 High T Low T PAGS (um) Austenitization Temperature Sample Type Name Description Forging Process A-OK Samples from the previous heat Forging Process B-OK Samples from the new heat prior to any problems Forging Process B-Problems Samples with the same forging procedure as Forging B-OK but that had significant fracture splitting issues High-High Forging trial with a high austenization temperature and high cooling rate High-Low Forging trial with a high austenization temperature and low cooling rate Based on the possible appearance of a shear lip, it was determined that further investigation of the fracture along the Charpy notch was necessary. The samples were cleaned with acetone and then placed in a scanning electron microscope (SEM) to take five secondary electron images per sample. Image of a fractured Charpy bar, with the red squares indicating the locations that the five SEM images were taken for each sample. Where there were regions of ductile fracture along the notch, the maximum length of the shear lip, perpendicular to the Charpy notch, was measured and then graphed. Maximum shear lip length for different heats. Maximum shear lip length plotted against the previously measured room temperature Charpy impact energies. The line is meant as a guide for the eye. Plot of the PAGS versus proeutectoid ferrite volume fraction The proeutectoid ferrite volume fraction decreased with increasing prior austenite grain size. Average PAGS based on austenitization temperature. High T is High-High and High-Low, while Low T is the other three heats. Proeutectoid ferrite volume fraction for the different cooling rates at high austenitization temperature. 0 50 100 150 200 250 2 4 6 8 10 12 Shear Lip Length (µm) Impact Energy (J) 0 50 100 150 200 250 Forging A- OK Forging B- OK Forging B- Problems High-High High-Low Shear Lip Length (µm) Heats
Transcript of Characterization of Microstructure and Composition ... Poster.pdf · Process A -OK and, b) a sample...
We would like to thank Dianna Clute, Andrew Cummins, Walter Isenberg, Chad Miller, Mark Sattgast, and David Brewer from Caterpillar, as well as the Caterpillar Lafayette Metallurgical Lab, and Jameson Root, Tim Vanmeter, and Dr. David Johnson from Purdue University for all their help.
Characterization of Microstructure and Composition Controlling Fracture Split Behavior in Microalloy Forging SteelsBrandon Battas, Minghao Guo, Michael KraneFaculty Advisors: David JohnsonIndustrial Sponsors: Dianna Clute, Andrew Cummins, Walter Isenberg, Chad Miller, Mark Sattgast
Project Background Quantitative Microstructural Analysis
RecommendationsOne possible future avenue of research could include Charpy impact testing at higher temperatures to facilitate higher resolution of impact energy and ductile fracture measurements. Another approach could be an alternative test, such as a high strain rate tensile test.
Fractographic Characterization
MSE 430-440: Materials Processing and Design
This work is sponsored by Caterpillar,Lafayette, IN
Caterpillar uses fracture splitting to manufacture theconnecting rods in large engines- using a wedge tocompletely fracture the bearing starting from twolaser cut notches so that it can be bolted togetheraround the crankshaft. These large engineconnecting rods require a yield strength significantlygreater than other conventionally smaller fracturesplit connecting rods. To achieve this strength theyare made from a High Strength Low Alloy (HSLA)steel, which uses certain microalloying elementssuch as vanadium to form carbides that increasestrength by grain size refinement.
Selected Charpy samples were cut, and the faceparallel to the fracture surface was mounted,polished, analyzed by optical microscopy.
y = 384.81x-0.807
R² = 0.8522
0
20
40
60
80
100
120
140
160
0.00 5.00 10.00 15.00 20.00
PAG
S D
iam
eter
(um
)
Ferrite Volume Fraction (%)
The main characteristics analyzed on were prioraustenite grain size (PAGS), pearlite colony size,and the relative amounts of proeutectoid ferrite andpearlite microconstituents, and the relationshipsbetween these features and the fractureperformance of each heat.
Optical micrographs of: a) a sample from the good heat, Forging Process A-OK and, b) a sample from the problem heat, Forging Process B-Problems.
0
5
10
15
Max Cooling No CoolingFerr
ite V
olum
e Fr
actio
n (%
)
Cooling Rate
Acknowledgements
Left: Brian Crower Sportsman Connecting Rod Set - VQ35DE / VQ35HR. Retrieved from https://www.z1motorsports.com
Right: Fracture-split Connecting Rods “No, That's Not a Broken Part.” (2014, October 20). Retrieved from https://mitchell1.com
SEM images of the fracture surfaces of: a) a sample from Forging Process A-OK and, b) a sample from Forging Process B-Problems. The maximum shear lip lengths have been marked, along with the Charpy notch and some characteristic areas of ductile (microvoid coalescence) and brittle (cleavage) fracture.
Caterpillar, some time after a change in forging heats, found that fracture splittingmanufacturing yields differed with changes in heat. A study was performed to assess thediscrepancy through analysis of the microstructure and the fracture behavior of fracturedCharpy v-notch bars. It was found that larger prior austenite grains and less proeutectoidferrite corresponded to the best fracture behavior. Also, parts that had problemsfracturing tended to have larger shear lips than the parts that did not have problems.
When the material used in large engine connecting rods experienced a change in heat, some of the connecting rods began to fracture incompletely during fracture splitting. The purpose of this project was to investigate the relationships between microstructural characteristics of the metal used in different heats and the corresponding fracture performance, with the goal of determining a method to predict how well a given heat will fracture.
Problem
a) b)
Cleavage
Cleavage
Microvoid Coalescence
Microvoid CoalescenceNotch Notch
Shear Lip Length
Shear Lip Length
Descriptions for the different sample designations and color codings to be used in this poster.
Optical microscopy demonstrated that a higher austenitization temperature lead to a larger prior austenite grain,whereas a lower cooling rate resulted in a higher ferrite volume fraction. The samples with better fractureperformance had a greater PAGS and a lower proeutectoid ferrite volume fraction. The SEM fractography,specifically the measurements of the shear lip length, largely correlated with the Charpy impact energymeasurements previously taken by Caterpillar. There was variance in the different samples, but the length ofthe shear lip did tend to correlate with the quality of the fracture splitting. However, extreme variance within thesame forging heats such as High-High and Forging B-OK, indicated that there were likely factors other than amicrostructural correlation, possibly factors such as elemental segregation, driving the differences in fracture.
Conclusions
Room temperature Charpy impact testing had alreadybeen conducted, the results of which did not haveenough resolution for useful conclusions. Thesefractured Charpy bars were provided for analysis, ofboth the middle of the bar and the fracture surface.
Location Caterpillar retrieved Charpy bars from in connecting rods
0
20
40
60
80
High T Low T
PAG
S (u
m)
Austenitization Temperature
Sample Type Name DescriptionForging Process A-OK Samples from the previous heatForging Process B-OK Samples from the new heat prior to any problemsForging Process B-Problems
Samples with the same forging procedure as ForgingB-OK but that had significant fracture splitting issues
High-High Forging trial with a high austenization temperature and high cooling rate
High-Low Forging trial with a high austenization temperature and low cooling rate
Based on the possible appearance of a shear lip, itwas determined that further investigation of thefracture along the Charpy notch was necessary. Thesamples were cleaned with acetone and then placedin a scanning electron microscope (SEM) to take fivesecondary electron images per sample.
Image of a fractured Charpy bar, with the red squares indicating the locations that the five SEM images were taken for each sample.
Where there were regions ofductile fracture along thenotch, the maximum length ofthe shear lip, perpendicular tothe Charpy notch, wasmeasured and then graphed.
Maximum shear lip
length for different
heats.
Maximum shear lip length plotted against the previously measured room temperature Charpy impact energies. The line is meant as a guide for the eye.
Plot of the PAGS versus proeutectoid ferrite volume fraction
The proeutectoid ferrite volume fraction decreasedwith increasing prior austenite grain size.
Average PAGS based on austenitization temperature. High T is High-High and High-Low, while Low T is the other three heats.
Proeutectoid ferrite volume fraction for the different cooling rates at high austenitization temperature.
0
50
100
150
200
250
2 4 6 8 10 12
She
ar L
ip L
engt
h (µ
m)
Impact Energy (J)
0
50
100
150
200
250
Forging A-OK
Forging B-OK
Forging B-Problems
High-High High-Low
She
ar L
ip L
engt
h (µ
m)
Heats
