Quantification of hardening contribution of G-Phase precipitation and spinodal decomposition in aged duplex stainless steel: APT analysis and micro-hardness measurements

Abstract

h i g h l i g h t s Link of microstructural characterization to microhardness of the ferrite for a wide variety of duplex steels. Quantification of G-phase and spinodal contributions to ferrite hardening. G-phase can be the main contributor to hardening.

Microstructural evolution during long time aging of 15–5PH stainless steel

“…In some research works the effect of G-phase on mechanical properties is reported as negligible compared to the one of Fe-Cr unmixing, considered as the main responsible for properties change [5,28,33] and in others, it is claimed that G-phase had an important role in the material hardening [34,35]. Although, a very recent work by Badyka et al seems to prove that in many cases G-phase may play an important role in the material hardening during aging [12]. But the respective part of each mechanism in the properties evolution depends on the material under study and the aging conditions.…”

“…This change in mechanical properties of the material is caused by evolutions of its complex initial microstructure, which we have presented in details in a former work [7]. The two main microstructural changes during such stainless steels' aging are the precipitation of a Ni, Mn and Si-rich phase and the Fe-Cr matrix unmixing, both at the nanometer scale [8][9][10][11][12].…”

“…The Fe-Cr unmixing has also been the focus of a large number of studies since the theories of Cahn et al [36][37][38] until very recent reports [11,12,15,20,34,[39][40][41][42][43][44][45][46][47][48][49][50] with both an experimental and/or a numerical approach. Cahn and Hilliard were the firsts to propose a model for the early stages of spinodal decomposition in solids [36].…”

A comparative study of Fe-Cr unmixing using differential scanning calorimetry and small-angle scattering

“…Due to its very large impact on the industrial use of stainless steels, this Fe-Cr decomposition has been extensively studied over the past decades. Experimental characterization of the degree of unmixing has been mainly carried out using Atom Probe Tomography (APT) [2,4,[6][7][8][9][10][11][12][13][14][15] and Small-Angle Scattering (using neutrons or X-rays, respectively SANS and SAXS) [16][17][18][19][20][21][22][23][24][25]. These experimental data have extensively served as a basis for establishing the validity of physically-based models, most often using Kinetic Monte Carlo modelling, and for establishing the link between the degree of unmixing and the evolution of mechanical properties [2,4,9,15,24,[26][27][28][29][30].…”

Microstructural Evolution and Mechanical Behavior of Thermally Aged Cast Duplex Stainless Steel

“…Cast duplex stainless steel (CDSS) is widely used in the primary coolant pipe of a pressurized water reactor (PWR) nuclear power plant because of its excellent comprehensive properties [ 1 , 2 , 3 , 4 , 5 ]. However, CDSS is prone to phase decomposition when it is in the range of 280–500 °C for a long time, resulting in thermal aging brittleness, which reduces the plasticity and toughness of the material and increases the hardness and brittleness, thereby increasing the possibility of a sudden failure of components and affecting the safe operation of nuclear power plants [ 6 , 7 , 8 , 9 , 10 ].…”