[ Duplex ]
Table 1 . Tensile values for each forging reduction and longitudinal / transverse testing direction , together with minimum mechanical property requirement according to the relevant standard .
Longitudinal testing direction Transverse testing direction
Reduction ratio ( RR ) |
Yield strength / MPa |
Tensile strength / MPa |
Elongation /% Yield strength / MPa |
Tensile strength / MPa |
Elongation /% |
Specified minimum |
550 |
750 |
25 |
550 |
750 |
25 |
1,5 |
546 ± 3 |
765 ± 3 |
45 ± 1 |
543 ± 4 |
765 ± 1 |
33 ± 4 |
2.0 |
551 ± 1 |
771 ± 1 |
43 ± 4 |
549 ± 1 |
768 ± 2 |
37 ± 1 |
2.5 |
554 ± 8 |
789 ± 4 |
45 ± 1 |
551 ± 5 |
786 ± 1 |
41 ± 1 |
3,0 |
557 ± 1 |
791 ± 3 |
43 ± 1 |
554 ± 8 |
799 ± 2 |
37 ± 2 |
3,5 |
558 ± 7 |
796 ± 3 |
45 ± 1 |
550 ± 8 |
799 ± 3 |
37 ± 1 |
4,0 |
559 ± 4 |
789 ± 1 |
45 ± 1 |
566 ± 1 |
798 ± 1 |
35 ± 1 |
5,0 |
559 ± 2 |
800 ± 3 |
43 ± 0 |
555 ± 3 |
790 ± 1 |
35 ± 1 |
6,0 |
566 ± 7 |
805 ± 1 |
44 ± 1 |
560 ± 1 |
796 ± 1 |
37 ± 1 |
Mechanical properties of as-quenched Elongation average values for both the longitudinal and transverse at each level of deformation ratio are given in Table 1 . The room temperature mechanical properties at the transverse section showed 0.7 to 0.8 % lower elongation ( ductility ) values compared to longitudinal specimens . The mean values for longitudinal and transverse strength at each level of deformation ratio are shown in Table 1 . The red colour indicates the transverse and longitudinal yield strength of specimens ( RR = 1.5:1 and 2.0:1 ) that did not satisfy the acceptance criteria requirement . Otherwise , no significant differences in yield and tensile strength were obtained for separate forging schedules at the same total reduction . The yield strength above 550 MPa and ultimate tensile strength above 750 MPa with lower scatter was obtained in between RR = 2.5 and RR = 6.0 after hot-forging followed by quench-annealing .
Charpy V-notch impact toughness test Notch impact values for both longitudinal and transverse specimens at each level of deformation ratio are provided in Figure 4 ( a-b ). Impact energy in the longitudinal direction as a function of the total forge reduction ratio for the specimens in the quenchannealed condition is shown in Figure 4a . The longitudinal single and average impact energy above 35 J and 45 J respectively with low scatter were obtained for all reduction ratios . The transverse single / average impact energy above 35 / 45J with high scatter was acquired between RR = 2.5 and RR = 6.0 after hot forging followed by annealing . A common design criterion for NORSOK standards is that the impact energy obtained in Charpy-V specimens should be higher than 35 J single and 45 J average at a temperature of -46 ° C ( -51 ° F ) in wrought bar products . The red triangle in Figure 4b indicates the transverse average impact energy level of specimens ( RR = 2.0:1 ) that did not meet the desired NORSOK requirement of 45 J average .
Hardness HRC test Transverse hardness tests with total reduction ratios at the mid-radius position were performed using the Rockwell scale C according to the EN ISO 15156-3:2019 standard . The transverse hardness value of a minimum of 18.5 HRC and a maximum of 23.5 HRC with low scatter was achieved for detached total reduction ratio after forging followed by quench annealing .
Pitting corrosion resistance A ferric chloride corrosion test in accordance with ASTM G 48 , Method A was performed . The test temperature and duration of the test were 50 ° C ( 122 ° F ) for 24 hours . The transverse test specimens were taken from the surface to center position . No more than 0.24 ± 0.05 g / m 2 of weight loss was detected for all single reductions in the solution annealed-condition . No pitting at 20 x magnification was observed .
Advancing together Virtually no influence on reduction ratios was found from 1.5:1 to 6.0:1 on the materials properties of the forged super duplex and the research cites the following highlights :
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No porosities were observed on the macro-etched continuous cast material and a higher total reduction of 2.0:1 has a major influence on structure breakdown .
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A higher forging reduction led to slightly higher yield strength after quench-annealing . However , no significant differences in the mechanical properties were detected .
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The highest as-quench annealed yield strength measured in the longitudinal and transverse directions was 566 MPa / 560 MPa , respectively . The highest ultimate tensile strength was 805 MPa / 795 MPa respectively , both of which occurred in the sample forged to the largest total reduction ratio . All samples showed good ductility ( above 35 %). Above 2.5:1 forge reduction subsequent annealed sample met relevant industry standards .
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For all total reduction ratios , the microstructure after solution annealing showed no harmful phases . The ferrite fraction percentage for all tested specimens was between 35 % and 55 %.
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No significant differences were found between the HRC hardness values of the reduction ratios . These values are between 18.5 HRC and 23.5 HRC and are lower than the material property requirements ( 28 HRC ). For all conditions , the studied samples exhibited a weight loss of less than 0.24 g / m 2 evaluated according to the ASTM A48-A standard .
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34 Stainless Steel World April 2023 www . stainless-steel-world . net