Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

Abstract

The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat treatment for the eutectoidal phase transformation. Samples were cold rolled at seven different rolling reductions which was followed by heat treatment at five different temperatures. The second sample set was prepared to determine the activation energy of the eutectoidal decomposition process using the Arrhenius equation. Samples were cold rolled at seven different rolling reductions and were heat treated at the same temperature during eight different terms. A third sample set was made to study how another plastic-forming technology, beside the cold rolling, can influence the eutectoidal decomposition. Samples were elongated by single axis tensile stress and were heat treated at the same temperature. The results of the first and the third sample sets were compared. The rest δ-ferrite contents were calculated using the results of AC and DC magnetometer measurements. DC magnetometer was used as a feritscope device in this work. Light microscope and electron back scattering diffraction (EBSD) images demonstrated the process of the eutectoidal decomposition. The thermoelectric power and the hardness of the samples were measured. The results of the thermoelectric power measurement were compared with the results of the δ-ferrite content measurement. The accurate value of the coercive field was determined by a Foerster-type DC coercimeter device.

Investigation of Thermally Induced Deterioration Processes in Cold Worked SAF 2507 Type Duplex Stainless Steel by DTA

“…This is also confirmed by results of Mészáros et al [23], therefore it can be stated that cold working has negligible effect on the activation energies of both deleterious secondary phases. However, previous cold working has influence on the δ-ferrite decomposition process according to Mészáros et al [23], and thereby the α-ferrite decomposition process also can be affected by it.…”

“…The effect of cold working on the activation energies of σ-and α'-phases cannot be revealed by comparing the activation energies obtained in not cold worked SAF 2507 type duplex stainless steel [24]. This is also confirmed by results of Mészáros et al [23], therefore it can be stated that cold working has negligible effect on the activation energies of both deleterious secondary phases. However, previous cold working has influence on the δ-ferrite decomposition process according to Mészáros et al [23], and thereby the α-ferrite decomposition process also can be affected by it.…”

“…In duplex stainless steels activation energies of σand α'-phases have been determined in the last years. Mészáros et al calculated activation energy for σ-phase formation in SAF 2507 type duplex stainless steel with several cold-worked conditions through the KJMA model [23]. Results for activation energy of σ-phase formation were given between 296 and 302 kJ/mol (they decrease with increasing rate of cold working) and it was revealed that this activation energy hardly depends on the rate of cold working.…”

Microstructure Evolution during Hot Deformation of UNS S32750 Super-Duplex Stainless Steel Alloy

“…The observed behavior, in terms of GROD evolution, suggests that both the stress relieving phenomena and the dynamic recrystallization of new grains phenomena must be considered. The stress relieving phenomena, which occurs during heating, induces important changes within the deformed microstructure of the alloy, decreasing the imperfections density and lowering the residual stress fields and the elastic strains [ 30 , 31 , 32 , 33 ]. One must also consider the influence of the dynamic recrystallization of new grains, which can also decrease the elastic strains and residual stress fields [ 30 ].…”

Advances in Duplex Stainless Steels

“…Mészáros et al [ 6 ] investigated the eutectoidal phase transformation of 2507-type super-duplex stainless steel. The results demonstrate the decomposition of the δ-ferrite into the σ-phase and secondary austenite with the same tendency.…”