FAILURE ANALYSIS OF TORN HINGES

Transcription

1 Steel Image Inc. Failure Analysis and Metallography 7 Innovation Dr. Suite 155, Flamborough, ON, L9H 7H9 understand@steelimage.ca, (905) FAILURE ANALYSIS OF TORN HINGES EXAMPLE REPORT OVERVIEW & OUTCOME During manufacture of a hinge, numerous hinges began to tear during forming. Some of these defective hinges were also reported downstream at a customers site. Analysis was conducted to better understand the cause of the tear and to determine corrective actions. Tearing was due to a quality issue with the steel. The steel comprised of unwanted, entrained material caught in the steel during casting. This reduced the local ductility, causing it to tear during forming. The entire material lot would be at risk of having this entrained material and it was recommended the lot be deemed unfit for use. This work was completed in 24 hours. This short-report format is used when time is critical. Casey Julich-Trojan, B.Eng. Metallurgist Shane Turcott, M.A.Sc. Principal Metallurgist

2 FAILURE ANALYSIS OF TORN HINGES SUMMARY A manufacturer submitted three hinges, two of which exhibited large tears. The third hinge was taken from the same suspect run as one of the failed hinges. Figure 1 displays the three hinges with the tears indicated. The hinges comprised of an HSLA steel. The hinges were found to have torn due to poor material quality. Optical examination found foreign, entrained material within the steel adjacent the tears and at remote locations (Figures 3 and 4). The presence of the foreign, entrained material in the steel caused the material to tear during forming. Entrained material was also observed in the third, not-torn hinge. Energy dispersive spectroscopy (EDS) analysis determined the entrained material to comprise of embedded refractory and mould powder from the steelmaking process (Figure 5). Chemical analysis of the Painted Hinge found the material to conform to the compositional requirements of SAE J XF (Table 2). Rockwell hardness testing of the material obtained results expected for this material type (Table 3). CONCLUSIONS The hinges tore due to poor material quality. The hinges contained embedded refractory and mould powder, which resulted in tearing during the forming operation. Other hinges from the same material lots may also contain entrained material and thus may also be susceptible to tearing during forming. Table 1: Chemical Analysis Results Composition (wt%) C Mn Si S P Cr Al Ni Cu Mo Ti Nb Ca < < <0.005 Chemical analysis was performed in accordance to ASTM E , E (modified) and E1479(2011). The obtained chemistry conformed to the compositional requirements of SAE J XF. Table 2: Rockwell Hardness Test Results Sample Measurements Avg. Hardness (HRB) (HRB) Painted Hinge (Remote) 82.0, 81.5, Coated Hinge (Remote) 80.0, 79.5, As-Formed Hinge (Remote) 81.0, 81.5, Rockwell hardness testing was performed in accordance to ASTM E18. The hardness results were within the expected range for SAE J XF HSLA steel. Failure Analysis of Torn Hinges Page 1 of 7

3 Painted Hinge Coated Hinge As-Formed Hinge a) Overall Forming Tear Forming Tear b) Painted Hinge Forming Tear c) Coated Hinge d) As-Formed Hinge Figure 1: Photograph displaying the three hinges submitted for evaluation of tearing. Locations of tears are indicated. Failure Analysis of Torn Hinges Page 2 of 7

4 a) Painted Hinge, location of cross-section Tear (Figure 3a-c) Entrained Material (Figure 3d) Figure 2: b) Painted Hinge, locations of images Photographs displaying (a) the location of cross-section and (b) the metallographic specimen of the Painted Hinge. Locations of micrographs shown in Figure 3 are indicated. Failure Analysis of Torn Hinges Page 3 of 7

5 Tear Initiation (Occurred during first stages of forming) a) Tearing, 20x This Section Necked and Fractured during First Stages of the Forming Operation Entrained Material b) Initiation Region, 100x Entrained Material (Remote from tearing) Figure 3: c) Tear, ~66x d) Entrained Material, 100x Macrograph and micrographs displaying the tearing observed on the Painted Hinge. Entrained material at the initiation region caused a portion of the material to neck and fracture during the first stages of the forming operation. The tear propagated during the remainder of the forming operation. Entrained material was also observed remote from tearing. Failure Analysis of Torn Hinges Page 4 of 7

6 a) Tearing, 30x b) Initiation Region, 100x Localized Necking due to Entrained Material c) Entrained Material, 200x d) Entrained Material, 400x Figure 4: Macrograph and micrographs displaying the tearing observed on the Coated Hinge. Entrained material at the initiation region caused a portion of the material to neck and fracture during forming. Failure Analysis of Torn Hinges Page 5 of 7

7 a) Entrained Material, Painted Hinge, 600x b) Entrained Material, Coated Hinge, 75x Entrained Refractory (Al, O, Mg, C, Si) Entrained Mould Powder (Si, Ca, Al, C, Na, Mg) Figure 5: EDS analysis found the entrained material to be embedded refractory and mould powder in the Painted and Coated Hinges. Failure Analysis of Torn Hinges Page 6 of 7

8 Fracture Surface Lab Fracture a) Opened Tear, Painted Hinge, 10x Fracture Surface Lab Fracture b) Opened Tear, Coated Hinge, 10x Figure 6: Macrographs displaying the opened tears of (a) the Painted Hinge and (b) the Coated Hinge. These surfaces were covered by coating/paint. Due to the coating/paint, fractography could not be performed on the torn surfaces. Failure Analysis of Torn Hinges Page 7 of 7