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A DIVISION OF J.T. ADAMS CO., INC.

4520 WILLOW PARKWAY CLEVELAND, OHIO 44125

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CERTIFIED TEST REPORT

of 24 This Report May Not Be Reproduced Except In Full This report represents Tensile Testing interpretation of the results obtained from the test and is not to be construed as a Guaranty or Warranty of the condition of the materials tested. Tensile Testing shall not be held liable for misinterpretation of conditions, loss, damage, injury or death arising from or attributable to delay preceding a test or subsequent to performance of a test.

Chandler Products Job No.: B1-110-742A 1491 Chardon Road Date: 5-20-11 Cleveland, OH 44117 Cust. PO#: 54883 Attn: Dan Hunnell

Summary Microstructure analysis shows the product heat treatment produced a uniform, through hardened bolt. Corrosion products were observed on the shank and flange of failed bolts and intact bolts that failed proof load and wedge tension testing. Corrosion products covered the fracture surface initiation regions but not the overload regions. An intergranular fracture mechanism is present within the fracture initiation region of the primary failure and in secondary cracks located at the shank-head fillet radius. The lack of microstructural decarburization and oxide within the secondary cracking and the lack of extensive crack branching indicates the intergranular fracture is most likely from delayed hydrogen cracking. The source of the hydrogen is most likely service derived from a crevice corrosion mechanism occurring under the bolt flange when installed.

1.0 Subject

Failure Analysis Flange Bolt, Part No. A23530768

2.0 Background

Flange bolts that were installed as head bolts in a diesel engine were received for analysis of in-service failure. A total of 31 bolts were received consisting of one head and shank failure (sample 1), one head failure (sample 2) and 29 intact samples. The part drawing, part# A23530768, specifies the flange bolt as ISO 898 class 12.9 bolt heat treated to 39-44 HRC. Chemistry certifications for a grade 8640 and a grade 4037 were received as possible raw material certs for the part. The client also provided heat treat process parameters performed by two suppliers and a phosphate, bake & oil process performed by one suppler.

3.0 Testing Methods

3.1 Visual Observation 3.2 Chemistry 3.3 Mechanical Testing 3.4 Macroscopy 3.5 Metallography 3.6 SEM w/ EDS

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Job No.: B1-110-742A

4.0 Testing Results

4.1 Visual Observation The first failed bolt, sample 1, is presented in Figure 1. The bolt was fractured at the fillet radius change from the major diameter to the pitch diameter located just below the head. No other visible damage was present on the bolt. Corrosion products appear on the shank and flange face as shown in Figure 2. The second failed bolt, sample 2, is presented in Figure 3. The bolt was fractured at the fillet radius change from the major diameter to the pitch diameter located just below the head. Corrosion products appear around the shank and the shank-head fillet radius as shown in Figure 4. No uneven wear marks are observed on the flange pressure face. The 29 intact bolts were examined and visually sorted into 25 that had no visible damage and 4 that showed some form of surface corrosion. Two bolts were selected from the first group, identified as samples A & B, and two bolts were selected from the second group, identified as samples C & D, for further analysis. The four intact bolts are presented in Figure 5. Surface conditions of the four bolts are shown in Figure 6. The shank and flange regions of intact bolts A and B show no corrosion on their surfaces. Intact bolts C and D show corrosion products along their shank and flange face.

4.2 Chemistry Chemical analysis was performed using optical emission spectroscopy on a sample removed from the shank portion of sample 1 after the fracture face was sectioned off the sample. The results are presented in Table I.

Table I. Product Analysis of Elements in % (OES per TTML C-01):

Req C Mn P S Si Cr Ni Mo Cb Al Cu V

Min Max

0.33 0.38

0.60 0.80

0.035

0.0400

0.15 0.35

0.80 1.05

shank 0.36 0.68 0.011 0.0098 0.23 0.91 0.05 0.05 <0.0010 0.029 0.09 0.002

The results of the chemical analysis were matched to AISI 5135 steel, the compositional limits presented in the table. The chemistry did not match the two certs provided by the client for either 8640 or 4037 grade material. The chemistry noted in ISO 898, the specification listed on the part drawing, is incomplete and associated notes indicate the chemical composition and tempering temperature for class 12.9 bolts is under investigation.

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Job No.: B1-110-742A

4.3 Mechanical Testing The four intact bolts A, B, C and D were submitted for determination of tensile properties. The bolts were first proof tested and then wedge tested following the guidance of ASTM F606. The results are presented in Table II. Table II. Product Analysis of Mechanical Properties (per ASTM F606-10A):

Sample Proof Load 6o Wedge Tensile M16 x 2.0 flange bolt MPA MPA

ISO 898 class 12.9 970 1220 A 975 1436 B 975 1420 C 470 -- D 975 1393

A photo of the four bolts after testing is presented in Figure 7. Samples A, B and D passed the proof load test requirement contained in ISO 898 for a class 12.9 bolt. Sample C fractured at the shank-head fillet radius during the proof load test. Samples A and B passed the wedge tensile test while sample D passed the load requirement for the wedge tensile test but failed due to the location of the fracture.

4.4 Macroscopy The shank side fracture face on sample 1, presented in Figure 8, was left intact in the as-received condition. Multiple initiation points are noted around the periphery of the failure. A lenticular-shaped region extends in from the right side. The failure is from tensile loads where the crack progressed from initiation around periphery through inward propagation to center overload region (light gray). The initiation region is covered with corrosion products while the lighter-gray overload region in the center of the bolt appears un-corroded. The overload region is non-circular, where the typical tensile overload region is circular or oval in shape. The bolt head fracture piece from sample 1 was cleaned in a buffered HCl solution to remove the surface material for better examination of the surfaces and fracture face characteristics. After cleaning multiple cracks were observed within the shank-head fillet radius as shown in Figure 9. The cracking was present around the entire bolt. The bolt head was sectioned longitudinally down the center of the bolt to further examine these cracks.

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Job No.: B1-110-742A The bolt head fracture face on sample 2 is presented in Figure 10. Multiple initiation points are noted at the periphery in the lower right hand corner. Three lenticular-shaped regions are noted at the initiation points. The failure is from tension loads where the crack progressed from initiation across the instantaneous zone (light gray). The initiation region is covered with corrosion products while the lighter-gray instantaneous zone across the bolt appears un-corroded. The bolt head fracture face on sample C is presented in Figure 11. A change in fracture orientation is observed. The first has a single initiation point at the periphery on the bottom edge. A lenticular-shaped region is noted at the initiation point. The crack in this region extends midway through the bolt cross-section and is covered with corrosion products. The second has an initiation starting at the left edge of the corrosion region. Fast radial lines extend through the instantaneous zone (light gray) at an upward angle through the remaining bolt cross-section. The lighter-gray instantaneous zone across the bolt appears un-corroded. The failure is from two different load applications, the first which occurred with the corroded surface and the second during proof loading of the cracked bolt which resulted in a bending moment being applied to the bolt during testing. The failure observed on sample C is similar to the testing failure on sample D as shown in the images of Figure 12. The pre-existing crack in sample C was angled upward into the bolt head. When sample C cracked during testing, the fracture surface lay inside the bolt head resulting in a vertical shear lip where the instantaneous zone exited back to the shank-head fillet radius on the opposite side of the bolt. Sample D formed a shear failure at the shank-head fillet radius as the flange pulled up onto the 12-point flange head. The failure mode indicates un-seen cracks were present around the shank-fillet radius of sample D prior to testing.

4.5 Metallography The shank of sample 1 just below the sample removed for chemistry was sectioned to produce a transverse section and a longitudinal cross-section at the mid-plane of the bolt. Photo-micrographs of the bolt microstructure are presented in Figure 13 at edge and center locations in the transverse and longitudinal planes. The microstructure at all four locations is quenched and tempered martensite. The microstructure is consistent with the requirements stated in ISO 898 for a class 12.9 bolt. The heat treat process from the two suppliers follow similar steps, summarized as: austenitize at 1550oF for 45-60 min, oil quench, temper at 820oF for 60-75 min. The tempering temperature is below the known temper embrittlement temperature for steel, eliminating heat treatment as a cause for the failures.

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Job No.: B1-110-742A The results of hardness measurements taken on the shank surface and corrected for curvature are presented in Table III. The hardness values are at the lower end of the specified 39-44 HRC listed on the part drawing.

Table III. Product Analysis of Hardness (per ASTM E18-08B):

Bolt Shaft OD Surface Location HRC

0 39.7 +90o 37.7

+180o 38.4 +270o 38.2 Ave 38.5

Photo-micrographs of the cracking observed around shaft-head fillet radius of bolt head fracture from sample 1 are presented in Figures 14 and 15 after cross-sectioning the bolt head, mounting and polishing. The cracks are seen to emanate from the bolt surface starting within the shaft-head fillet radius and angle upward into the bolt head. Multiple cracks appear on the right side of the selected cross-section (Figure 15). Close examination of the cracks show they propagate in an intergranular manner, following the prior-austenitic grain boundaries in the quench and tempered microstructure. No oxide is observed within the cracks. No de-carburization is observed in the microstructure adjacent to the cracks. The characteristics observed for the cracking, wider at the surface and intergranular, are classic features of quench cracking in alloy steels. However, the microstructure next to the crack showed no evidence of decarburization which has been shown to occur on re-hardening. Further, there is no oxidation present in the cracks. It can therefore be concluded that these are not quench cracks occurring from the heading operation or the hardening operation.

4.6 SEM w/ EDS The fracture surfaces from sample 1 and sample 2 were examined in the SEM for additional information on the failure mechanism.

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Job No.: B1-110-742A Examination of the lenticular-shaped initiation region on the bolt-head fracture surface of sample 1 shows an intergranular fracture mechanism, as seen in Figure 16A and 16B. Other locations around the periphery of sample 1 showed the same fracture mechanism. Examination of the overload region on the shank fracture surface of sample 1 shows a ductile dimple rupture mechanism, as seen in Figure 16C. This is the expected failure mechanism for a quench and tempered steel of this chemistry at the measured hardness level. Examination of the lenticular-shaped initiation region on the bolt-head fracture surface of sample 2 shows an intergranular fracture mechanism, as seen in Figure 17A and 17B. The surface corrosion products were removed from sample 2 with a buffered HCl solution to permit imaging of the actual fracture surface in the initiation region. Other two lenticular-shaped initiation regions on sample 2 showed the same fracture mechanism. Examination of the instantaneous zone on sample 2 shows tear ridges and a quasi-cleavage mechanism, as seen in Figure 17C. The smaller size of the initiation region and the fast fracture features on sample 2 indicates this bolt failed after the sample 1 bolt. The fracture surface shows no evidence of torsional stresses and damage, indicating the fracture did not occur during torque installation of the bolts. All three bolt failures (sample 1, sample 2 and intact bolt C) display tensile loading failures within their initiation and propagation regions. The presence of intergranular fracture within the initiation region on the primary fracture surfaces and along the secondary cracks in the shank-head fillet radius of sample 1 indicates an environmental attack was also present. Quench cracks have been ruled out as the source of the intergranular cracking. Intergranular fracture is also associated with stress corrosion cracking (SCC) and hydrogen embrittlement. SCC is usually observed to occur with extensive crack branching which is not observed in the cross-section of sample 1 bolt head (Figure 15), and so can be ruled out. Hydrogen embrittlement requires three components to be present to occur: a source of hydrogen, a susceptible material and application of tensile stresses. The source of hydrogen can be introduced from manufacturing process variables or from environmental exposure. The process history shows the flange bolts are acid cleaned and zinc phosphate coated. However, this process reportedly includes a baking step to remove hydrogen. Additionally, the phosphate process results in a porous surface compared to a plating process, and hence less of a barrier to hydrogen migration.

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Job No.: B1-110-742A The presence of corrosion products on the upper shank and flange face indicates the bolts that failed, including intact bolts C and D, were in contact with an aqueous environment while in service. If the observed corrosion would have occurred after failure then the overload regions on samples 1 and 2 would have been corroded similarly to the initiation regions. Crevice corrosion conditions are possible under a bolt flange face when installed. In the occluded zones of crevices, acidic conditions are more likely to occur with the chemical reactions within the crevice depleting species and forming a hydrogen cell, ultimately leading to hydrogen absorption and delayed hydrogen embrittlement of the stressed fastener. The sources of the aqueous environment are unknown but could have been a leaking gasket to the engine cooling system, or have been introduced during an engine overhaul.

5.0 Conclusion of Analysis 5.1 Microstructure analysis shows the product heat treatment produced a uniform, through hardened

bolt. 5.2 Corrosion products were observed on the shank and flange of failed bolts and intact bolts that

failed proof load and wedge tension testing. 5.3 Secondary cracking was located within the shank-head fillet radius of a failed bolt. 5.4 An intergranular fracture mode was present in the initiation region of the bolt primary failures

and along the observed secondary cracks. 5.5 Corrosion products covered the fracture surface initiation regions but not the overload regions. 5.6 The lack of de-carburization in microstructure adjacent to the secondary cracks and the lack of

oxide within the secondary cracks indicate these cracks did not occur from the heading operation or hardening operation, but at a later time.

5.7 The observed features on the primary fracture surface and the secondary cracks indicate that delayed hydrogen cracking is the most likely cause of failure.

5.8 The source of the hydrogen is most likely service derived from crevice corrosion mechanism occurring under the bolt flange when installed.

_________________________________________ Gary Coubrough, PhD, PE Metallurgist

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Job No.: B1-110-742A

Figure No.: 1

Condition: As-Received

Flange bolt sample 1 received for analysis.

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Job No.: B1-110-742A

Figure No.: 2


Side view of fractured bolt head sample 1. Failure transverse through bolt at reducing radius on bolt shank. Large feature appearing off-center on fracture surface indicated. Surface deposits and corrosion noted on shank and along shaft-head fillet radius.

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Job No.: B1-110-742A

Figure No.: 3


Flange bolt sample 2 (fractured head only) received for analysis.

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Job No.: B1-110-742A

B) Position + 90o A) Position 0

C) Position + 180o

D) Position + 270o

Figure No.: 4

Condition: As-received

Flange bolt sample 2 showing corrosion products around shank and pressure side of flange face.

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Job No.: B1-110-742A

Figure No.: 5


Intact flange bolt samples A, B, C and D received for analysis.

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Job No.: B1-110-742A

B) Sample B A) Sample A

C) Sample C

D) Sample D

Figure No.: 6


Intact flange bolt samples showing corrosion products around shank and pressure side of flange on samples C and D that is not present on samples A and B.

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Job No.: B1-110-742A

Figure No.: 7

Condition: As-Tested

Intact flange bolt samples A, B, C and D after Proof Load and Wedge Tensile Testing.

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Job No.: B1-110-742A

Figure No.: 8


Shank side fracture face on Flange bolt sample 1. Multiple initiation points are noted around the periphery of the failure. A lenticular-shaped region extends in from the right side. The failure is from tension loads where cracking progressed from initiation around periphery through inward propagation to center overload region (light gray).

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Job No.: B1-110-742A

B) Position + 90o A) Position 0

C) Position + 180o

D) Position + 270o

Figure No.: 9

Condition: As-Cleaned

Bolt head side on Flange bolt sample 1 after cleaning away surface deposits. Secondary cracking observed within shaft-head fillet radius. The cracking is present around the entire bolt shaft.

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Job No.: B1-110-742A

Figure No.: 10


Fracture face on Flange bolt sample 2. Multiple initiation points are noted at the periphery in the lower right hand corner. Three lenticular-shaped regions are noted at the initiation points. The failure is from tension loads where the crack progressed from initiation across the instantaneous zone (light gray).

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Job No.: B1-110-742A

Figure No.: 11


Fracture face on Flange bolt sample C. Two independent fracture processes noted, the first from service the second from testing. The first has a single initiation point at the periphery on the bottom edge. A lenticular-shaped region is noted at the initiation point. The second has an initiation starting at the left edge of the corrosion region. Fast radial lines extend through the instantaneous zone (light gray) at an upward angle through the remaining bolt cross-section.

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Job No.: B1-110-742A

A) Sample C

B) Sample C after testing

C) Sample D

D) Sample D after testing

Figure No.: 12


Intact flange bolt samples C and D showing bolt head failure after Proof Load testing for sample C and wedge tension testing for sample D. In both cases failure initiated at shank-head fillet radius.

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Job No.: B1-110-742A

A) Transverse section, center

B) Transverse section, edge

C) Longitudinal section, center

D) Longitudinal section, edge

Figure No.: 13

Magnification: 1000X Nital Etch

Photo-micrographs of microstructure observed in Transverse and Longitudinal sections at center and edge locations. Microstructure is quenched and tempered martensite at all locations.

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Job No.: B1-110-742A

A) Cross-section of cracking, left 25X

B) Cross-section of cracking, left 200X

C) Cross-section of cracking, left tip 200X

D) Cross-section of cracking, left 1000X

Figure No.: 14

Nital Etch

Photo-micrographs of cracking observed around shaft-head fillet radius after cross-sectioning bolt head sample 1. Cracking initiates at surface and is intergranular. No de-carburization observed within microstructure located adjacent to crack. No oxide noted within crack.

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Job No.: B1-110-742A

A) Cross-section of cracking, right 25X

B) Cross-section of cracking, right 200X

Figure No.: 15

C) Cross-section of cracking, right 200X

D) Cross-section of cracking, right tip 200X

Nital Etch

Photo-micrographs of multiple cracks observed around shaft-head fillet radius after cross-sectioning bolt head sample 1. Cracking initiates at surface and is intergranular. No de-carburization observed within microstructure located adjacent to crack. No oxide noted within crack.

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Job No.: B1-110-742A

B) Initiation Region 2000X A) Initiation Region 500X

C) Overload region 1000X

Figure No.: 16

SEM-fractographs of failure surface on bolt sample 1. Intergranular failure observed within initiation regions along edge of fracture. Ductile dimple rupture observed in overload region.

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Job No.: B1-110-742A

B) Initiation Region 2000X A) Initiation Region 500X


C) Instantaneous Zone 1000X

Figure No.: 17

SEM-fractographs of failure surface on bolt sample 2. Intergranular failure observed within lenticular-shaped initiation region. Tear ridges and quasi-cleavage observed in fast fracture region.

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