Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process (2021) / Chapter Skim
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16 The experimental test program included tests of steel tension specimens in air (RT and ET and in different galvanizing baths) and steel WOL specimens tested in the loaded condition in the galvanizing bath.
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Experimental Test Program 17 Figure 4-1. Standard 505-type tension specimen.
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18 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process Figure 4-3. 505- and 252-type specimens.
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Mechanical properties from mill cert: Fy = 40.9 ksi Fu = 68.7 ksi Percent elongation over 8 in. = 27.2% C Mn P S Si Cu Ni Cr Mo Cb V Al Ti N B Ca Chemical composition from mill cert: 0.19 0.85 0.01 0.008 0.06 0.18 0.06 0.08 0.016 0.002 0.004 0.03 0.001 0.004 0.0002 0.0021 Chemical composition from laboratory testing: 0.18 0.81 0.006 0.008 0.05 0.15 0.07 0.07 0.01 -- -- -- -- -- -- -Table 4-2.
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20 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process these values were assumed to be zero, resulting in lower CEZ values than those computed based on the mill certificate. However, the data show a similar trend with A572-50 and A572-65 being more susceptible to LMAC than A36.
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Experimental Test Program 21 Hardness values obtained for the 6% and 8% cold-worked specimens are shown in Figure 4-7. Material hardness increased for the 6% cold-worked specimens over the base metal hardness, and the 8% cold-worked specimens exhibited a higher average hardness than the 6% coldworked specimens.
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22 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process were deformed by a 90° cold-bend; the process for fabricating these specimens is illustrated in Figure 4-8. First, a ¾-in.
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Experimental Test Program 23 specimens. These specimens were included in the test program to provide additional information beyond that obtained from specimens that were cold-worked through tensile loading.
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Experimental Test Program 25 had greater strength than the two ends, and initial tests performed on the 252-type specimens resulted in failures at the end of the reduced sections. To ensure failure at the mid-length point for the 252-type specimens, the specimens were modified by fabricating a notch that circumscribed the diameter of the tension specimen, presenting an SCF of 2.5.
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26 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process Tension Test Setup and Testing Protocols The tension specimens were loaded until failure under four different environments: while submerged in a galvanizing bath, while cooling after being submerged in a galvanizing bath, in air at ET, and in air at RT. Testing protocols for the different test environments are described as follows.
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Experimental Test Program 27 To MTS hydraulic pump Threaded coupler Steel tensile coupon Galvanizing bath, 450C/840F Enerpac hydraulic cylinder Load Cell Insulation and external support framing LVDT Remote Servovalve Digital signal to/from MTS Controller Plate Western Technologies Electric Crucible Furnace Figure 4-15. Schematic of setup for tension tests in molten zinc environment.
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Kettle Lid Load frame Enclosure Load frame Actuator Support frame for preparation Support frame for testing Kettle Load frame Actuator Tension specimen Figure 4-16. Test setup for tension tests in molten zinc environment.
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Experimental Test Program 29 load-deformation behavior recorded while loading a compliance specimen would reasonably indicate only deformations that were occurring in the grip region and in the frame, allowing those system compliance deformations to be "backed out" from actual tests on 505- and 252-type specimens. In this manner, adjusted load-deformation curves for the 252- and 505-type specimens that represent deformations occurring over their respective reduced lengths, similar to what would be obtained with an extensometer, could be developed.
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30 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process In-Air ET Tests Tension tests were also performed in air at an ET of 840°F. A test frame equipped with a temperature chamber was used to perform these tests (see Figure 4-19)
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Experimental Test Program 31 HPS-100W A36 A572-65 A572-65 Figure 4-20. Unadjusted load-displacement curves.
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32 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process Tension Test Results The strain value at failure (εf) for each specimen tested in liquid zinc is defined as the last data point captured on the stress-strain curve before the LVDT data became unstable due to specimen failure; this strain value is a direct indicator of susceptibility to cracking of the specimens tested while either in air or fully submerged in zinc.
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Experimental Test Program 33 reduced section. However, failure of the specimens tested while cooling in air always occurred at the zinc surface, which indicates that having direct contact with liquid zinc was more critical to failure.
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0 25 50 75 100 125 0 0.05 0.1 0.15 0.2 0.25 St re ss (k si ) Strain (in./in.)
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Experimental Test Program 35 65% (A36)
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36 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process 0 0.05 0.1 0.15 0.2 0.25 St ra in a t F ai lu re (i n.
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Experimental Test Program 37 Stress Concentration Figure 4-31 shows the strain-at-failure data for un-notched and notched A36 steel specimens tested in two in-zinc environments: SHG and SHG + 0.1% Bi + 1% Pb. Two SCFs were considered: 1.5 and 2.5.
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0 0.05 0.1 0.15 0.2 0.25 St ra in a t F ai lu re (i n.
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Experimental Test Program 39 and another reduction of 67.1% due to exposure to SHG zinc. For SCF = 2.5, a reduction of 68.5% was introduced in air because of the notch and another 79.1% due to exposure to SHG.
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40 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process 2. The notched specimens experienced a higher strain reduction than un-notched specimens in SHG zinc (86.1% for notched specimens with SCF = 1.5; 82.5% for notched specimens with SCF = 2.5; and 70% for un-notched specimens)
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Experimental Test Program 41 4. A36 specimens tested in SHG + 0.1% Bi + 1% Pb exhibited lower strains than those tested in SHG, indicating some effects of HAZ, notching, and bath chemistry on this grade of steel.
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42 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process Cold-Working Figure 4-37 shows the strain values at failure for non-cold-worked and cold-worked A36 steel specimens tested in SHG and SHG + 0.1% Bi + 1% Pb. Results for the two cold-work levels applied in uniaxial tension (6% and 8%, or CW6 and CW8)
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Experimental Test Program 43 0 0.05 0.1 0.15 0.2 0.25 St ra in a t F ai lu re (i n.
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44 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process 2. Despite the loss in total strain after cold-working, strains at failure in zinc were at a level similar to those for non-cold-worked specimens, indicating no effect of cold-working on A572-50 steel in SHG zinc.
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Experimental Test Program 45 Relative Effect of Factors Figure 4-40 shows average strain-at-failure data for specimens tested both in air and in SHG zinc. The total height of each bar shows the average strain at failure in air, and the height of the solid portion indicates the average strain at failure in SHG zinc.
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46 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process occurrence of LMAC in steel structures during galvanizing)
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Experimental Test Program 47 0.0000 0.0500 0.1000 0.1500 0.2000 0.2500 SCR MCR FCR SC 1.5 SC 2.5 HPS100W CW 8 CW 6 A50 A65 A36 Av er ag e St ra in a t F ai lu re (i n.
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48 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process 0.0000 0.0500 0.1000 0.1500 0.2000 0.2500 SCR MCR FCR SC 1.5 SC 2.5 CW 8 HPS100W CW 6 A50 A65 A36 Av er ag e St ra in a t F ai lu re (i n.
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Experimental Test Program 49 tip of some WOL specimens before they were submerged in zinc to investigate the potential of cracking due to hydrogen embrittlement caused by the pickling process. After testing in zinc, the specimens were retrieved and inspected to determine propagation of the initial fatigue crack.
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50 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process The other specimens were subsequently tested; Figure 4-46 shows photos of the specimens after testing and polishing for inspection. The inspection indicated no crack propagation resulted from immersion in zinc.
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Experimental Test Program 51 Specimen #1: A36 Specimen #3: A572-65 Specimen #2: A572-50 Specimen #4: HPS100W Specimen #5: A36 Specimen #6: A572-50 Specimen #7: A572-65 Specimen #8: A36 Figure 4-46. WOL specimens after being tested in zinc and then polished.
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52 Mitigation of Weldment Cracking in Steel Highway Structures Due to the Galvanizing Process of 6.0 × 10−6 in./in./F and a specific heat of 0.11 British thermal unit per pound per degree Fahrenheit [Btu/lb/°F]
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Experimental Test Program 53 Figure 4-48. FE model of the WOL (left)
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