The influence of nanocrystalline structure and processing route on corrosion of stainless steel: A review

Duplex austenite–ferrite stainless steels are susceptible to a variety of decomposition processes when aged within the intermediate range of temperatures (250–500 °C). One of these phenomena is the precipitation of the intermetallic G-phase. In the present investigation, the crystal structure and the chemical composition of the G-phase, precipitated in the ferritic phase of an AISI329 duplex stainless steel, is studied by electron microdiffraction and energy dispersive X-ray spectroscopy. It is determined that the space group of the G-phase is F 3 with a lattice parameter four times that of the ferritic matrix. The precipitation mechanism of the G-phase showed a synergetic relation with the ferrite decomposition in Cr-rich and Fe-rich domains. Based on the obtained results, the structural proximity of ferrite matrix and G-phase has been studied. Further analysis allows to suggest that the spinodal decomposition leads to an interdomain of a ferritic structure which is thermodynamically unstable and serves as a precursory site to the development of the G-phase by atomic position readjustments inferior to the atomic distances.

Characterization of the intermetallic G-phase in an AISI 329 duplex stainless steel

Hot deformation of duplex stainless steels

The hot deformation behavior of a cost-saving duplex stainless steel (DSS) of 22Cr–1Ni–0.7Mo with N content of 0.36 ms% was studied over the range of temperatures from 1000 to 1200 °C and strain rates from 0.01 to 10 s−1 by hot compression tests. The processing map was established to integrate the relationship between hot workability and microstructural evolution. Both domains for temperatures from 1000 to 1050 °C and strain rate of 0.01 s−1 and temperatures from 1150 to 1200 °C and strain rate of 0.01 s−1 were found to be the optimum hot working regimes, in which the microstructure exhibited dynamic recrystallization (DRX). The unstable hot working domains were clearly indicated by the processing map. Wedge cracking, macro-cracking and dynamic strain ageing (DSA) had occurred during hot deformation under these hot working conditions, in good agreement with the predictions by the processing map.

Hot deformation behavior of a new austenite―ferrite duplex stainless steel containing high content of nitrogen

The tensile flow properties of austenitic (S316-L) and martensitic (S410-L) stainless steel wall structures deposited by powder-fed laser additive manufacturing (LAM) process are evaluated. The properties obtained by the LAM process are compared to commercial rolled sheets of these metals. Strain-rate sensitivity, work hardening, and fracture behavior are assessed by conducting uniaxial tensile testing at different strain rates (0.001, 0.01, 0.1, and 1.0 sec−1). Moreover, a correlation between the final microstructure and mechanical properties is established for the LAM products through detailed analyses of grain structures and hardness indentation measurements. The results indicate a strong dependency for the strain rate in martensitic alloys compared to austenitic alloys produced by the LAM process. Interestingly, the tensile strength of commercial rolled martensitic stainless steel sheet doubles (∼100% increase) by increasing the strain rate, while preserving its elongation to failure. Comparing the two manufacturing methods, a lower strain-rate sensitivity factor is recorded for the additive manufacturing material (m of ∼0.0336) compared to the commercial sheet (m of ∼0.0775). This lower sensitivity is attributed to coarser grain structure and greater microstructural heterogeneity of the LAM product, which stems from directional solidification and cooling phenomenon during the layer-upon-layer deposition process. In contrast, the work hardening exponent (n value) varies little (0.1834–0.2854) for the different materials and manufacturing methods. Fractographic studies reveal that the fracture mode varies from ductile rupture towards ductile-brittle with the formation of greater martensitic phases, which is in combination with the failure component changing from shear to tensile at high strain rates.

Microstructure, strain-rate sensitivity, work hardening, and fracture behavior of laser additive manufactured austenitic and martensitic stainless steel structures

Duplex stainless steels are defined and the advantages of second-generation, nitrogen-alloyed grades are explained Information is provided on duplex stainless steel metallurgy, pitting and crevice corrosion resistance, stress corrosion cracking resistance, specifications, mechanical properties, fabrication procedures and applications See also abstract number 90051131

Practical guide to using duplex stainless steels

A guide to using duplex stainless steels

A review of worldwide developments in stainless steels

Guide pratique d'informations sur la composition chimique, la resistance a la corrosion caverneuse et sous tension, la conception et l'elaboration de plusieurs aciers inoxydables a 6% de molybdene

Practical guide to using 6 Mo austenitic stainless steels

Test methods and special requirements applied to second generation duplex stainless steels have been evaluated with the goal of simplifying specifications and assuring optimum quality material. The tests evaluated included tensile, bend, hardness, impact toughness, phase balance, metallographic, magnetic, and corrosion tests. Emphasis was placed on tests most appropriate for detection of detrimental intermetallic phases in mill products and welds, not on fitness-for-service tests.This evaluation has led to the following conclusions: - Narrow, standard specification composition ranges for chromium, molybdenum and nitrogen are especially beneficial. - Metallographic evaluation should be required for the qualification of mill products and welding procedures, but it requires superior metallographic technique. Because it may be open to subjective interpretation, metallography should be used for acceptance but not rejection. It should be used in addition to either impact testing or corrosion testing to qualify duplex stainless steel mill products. - Impact testing is useful if the test temperature and acceptance criteria are meaningfully related to the grade and condition being evaluated. - Corrosion testing, in accordance with ASTM A 923 Method C, is one of the most cost-effective methods of testing provided that the test temperature is meaningful for the detection of detrimental conditions, and the absence of edge corrosion is included in the acceptance criteria. Corrosion testing has low sensitivity to sample selection and preparation.

R. M. Davison

Papers

Practical guide to using duplex stainless steels

A guide to using duplex stainless steels

A review of worldwide developments in stainless steels

Practical guide to using 6 Mo austenitic stainless steels

Critical review of testing methods applied to duplex stainless steels