[ Duplex ]
2.5 V , 3-10 sec , at RT to reveal sigma phases . The procedures were listed in ASTM E 407 . Metallographically prepared longitudinal / transverse sections of broken tensile / notch impact specimens were etched in 40 % NaOH at 2.5 V , 3-10 sec , at RT to reveal the prior austenite / ferrite grains ’ boundaries . investigated sample position , surface , mid-radius , and center of a total deformation level are given in Figures 2 and 3 . The average ferrite fraction measured by electron diffraction backscattered analysis for the different deformation levels produced by the forging process is within 35-55 % in solution-annealed base material .
Test results The cast structure was nearly broken down in workpieces forged using total reductions : 1.5:1 and 2.0:1 . However , large columnar grains were still visible . This was not the case for total reductions above 2.0:1 where the cast structure was totally broken down . Very small differences in structural breakdown were seen in forge reductions above 2.0:1 . LOM images for a total reduction ratio of 1.5:1 and 5.0:1 on etched specimens showed free from intermetallic precipitates , sigma phase and discrete / stand-alone nitride precipitates , Cr2N . The shape of austenite in the longitudinal direction was smaller / thinner with more straight boundaries and elongated relative to the transverse specimens ( Figure 1 ). Round austenite grain structures were observed with all forging reductions . However , they were small , isolated lakes of equiaxed coarse grains dispersed through a ferrite-grained matrix . The ferrite area occupied by the coarse austenite grains appeared in irregular fractions for the forge reductions . For the reduction of 1.5:1 at the transverse direction , equiaxed austenite grains were observed , which mostly nucleated at the ferrite-ferrite grain boundaries . The forging of super duplex SAF™ 2507 formed a fine elongated grain structure of austenite and ferrite along the forging direction .
Ferrite content measurement The changes in the longitudinal / transverse ferrite content with
Figure 2 . Variation of the longitudinal ferrite fraction with sample position , surface , mid-radius , and centre , of a total deformation level .
Figure 3 . Variation of the transverse ferrite fraction with sample position , surface , mid-radius , and centre , of a total deformation level .
Figure 4 . Variation of the ( a ) longitudinal and ( b ) transverse Charpy V-notch impact energy with a total reduction ratio .
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