Damage formation of a 2304 duplex stainless steel under hot working conditions

steel research international, 2019

The effect of warm rolling and annealing processes on the microstructure, microtexture, and mechanical properties of a 2205 duplex stainless steel was investigated in the present work. To evaluate the microstructure, scanning and transmission electron microscopy, and electron backscatter diffraction were used as main techniques. The mechanical properties were assessed through tensile tests. A transition from a bamboo type into a pearl structure was observed as the thickness reduction increased. Furthermore, the ferrite phase presented a weakening of -fiber, (<011>//RD), and a development of -fiber, (<111>//ND), while the austenite had a reduction in the intensity of {110}<112> Brass component and a strengthening of {110}<001> Goss and {112}<111> Copper components. Multi-stage work hardening behavior was observed by Jaoul-Crussard analysis, which indicated the presence of secondary deformation mechanisms during the plastic deformation of the steel. Post deformation SEM and TEM results revealed the formation of α' and ε-martensite at deformed regions. The orientation relationship developed between  and ε-martensite was Shoji-Nishiyama (S-N) <110>  //<2110> ε .

Journal of Materials Processing Technology, 2009

Materials research proceedings, 2023

The excellent performance of duplex and super duplex stainless steels due to their high corrosion resistance and high mechanical strength is directly related to their austeno-ferritic microstructure. However, these steels may suffer the formation of secondary brittle phases when they reach temperatures between 600°C and 950°C causing catastrophic service failure of components. In order to understand the influence of the mechanical history of the steel, the equal channel angular pressing was applied on UNS S32750 bar samples. ECAP is processed by using a hydraulic press (DE-80). Microstructural characterization was carried out on the severe plastic deformed samples by means of OM, SEM and EBSD. Ultimate tensile strength has improved with a low decreasing of elongation after the first pass. The ECAP process resulted to produce a faster precipitation of secondary phases if compared with the non-ECAP samples.

Materials Characterization, 2019

The effect of cold rolling deformation (4%-22%) on the microstructure, microtexture, and mechanical properties of a 2304 lean duplex stainless steel was investigated. The deformed microstructures were analyzed by electron backscattering diffraction and transmission electron microscopy. The results showed that after 4% thickness reduction, the strain produced phase transformation in austenite (γ), stacking faults (SFs), and mechanical twins. The orientation relationships of Kurdjumov-Sachs (KeS) and Nishiyama-Wassermann (NeW) were observed between the γ and α′-martensite. Moreover, Shoji-Nishiyama (SeN) and Pitsch-Schrader (PeS) were observed between γ and ε-martensite, and ε-martensite and α′-martensite, respectively. A further reduction in thickness (up to 22%) caused a reduction in total elongation and an increase in the yield and the ultimate tensile strength. 0.275%Mo, 0.20%Si, 4.2%Ni, 1.45%Mn, and balance Fe. The as

Rem: Revista Escola de Minas, 2013

Duplex stainless steels (DSS) involve two ductile phases, i.e. ferrite and austenite, with a proportion of each phase around 50%. The main advantage in comparison with other austenitic and ferritic stainless steels is the excellent combination of high strength and corrosion resistance together with good formability and weldability. Unfortunately, DSS present in general a poor hot workability. Standard hot ductility tests like hot tensile or hot torsion tests are always helpful to compare the fracture resistance of two very ductile materials. A new method based on the essential work of fracture (EWF) concept has been used in order to determine the hot cracking resistance. The EWF concept was introduced to address ductile fracture based on the entire load-displacement response up to the complete fracture of a specimen and not from the initiation measurements such as in classical fracture mechanics concepts. The aim of the method consists in separating, based on dimensional considerations, the work performed within the plastic zone from the total work of fracture in order to provide an estimate of the work spent per unit area within the fracture process zone to break the material. This method proved to be very well adapted to high temperature cracking. Two different duplex stainless steels have been characterized by the essential work of fracture method. Examination of the fracture micrographs and profiles match the EWF results. This method turns out to be a discriminating tool for quantifying hot cracking and to generate a physically relevant fracture index to guide the optimization of microstructures towards successful forming operations.

Materials Research, 2019

Duplex stainless steel (DSS) has been considered as an excellent alternative for applications where high corrosion resistance and high mechanical strength are required. Therefore, microstructure and properties of DSS remain topics of much interest. For this purpose, the effect of warm-rolling was studied in a duplex stainless steel. The focus of this work was 2205 which is one of the most useful type of DSS. Although evolution of microstructure, texture and tensile properties during warm rolling of DDS have been reported, there is no study on the effect of warm rolling on corrosion resistance of 2205 DSS. In this context, the objective of this work is to evaluate microstructure, texture and mechanical and corrosion properties of UNS S32205 DSS after warm rolling. The duplex stainless steel was warm-rolled at 600°C up to 60 and 80% thickness reduction and submitted to electrochemical tests. The electrochemical behaviour of warm-rolled 2205 in the chlorine ion environment was evaluated using cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS). The samples exhibited an excellent corrosion resistance in 3.5% NaCl solution. The study showed that the thermomechanical treatment used favoured the formation of the passive film and led to a greater polarization resistance. This behaviour is consistent with the pits density observed by scanning electron microscopy (SEM) and the crystallographic microtexture of the steel.

Rem: Revista Escola de Minas, 2016

The need for materials with higher strength and corrosion resistance in corrosive environments, such as in the oil extraction in saline media, has led to the use of super duplex stainless steels in projects such as the Pre-sal. The manufacture of these materials involves the step of thermomechanical processing, whose performance depends on the workability of the material. Processing conditions in which the super duplex stainless steel UNS S32760 can be worked safely and in which the material can fail were investigated in this presentation. The physical simulation was performed by means of hot torsion testing. The tests were performed at temperatures ranging from 900°C to 1200°C and strain rates of 0.01s-¹ to 10s-¹. The evolution of strain rate sensitivity of flow stress (m) for deformation of 0.5 at all temperatures investigated here was determined. After attaining the values of m for each deformation condition, the values of the power dissipation efficiency (η) were calculated, an instability criterion (ξ) was applied, and processing maps were constructed. Using these maps, the effects of deformation conditions on the power dissipation efficiency and the material plastic instability were discussed. The domains of processing maps, the observed microstructures and the shape of plastic flow stress curves were associated.

2010

High temperature behavior of 2205 duplex stainless steel was studied by considering behavior of each constituent phase. The specimens were subjected to hot compression tests at temperatures of 800-1100°C and strain rates ranging from 0.001 to 1 s À1 at intervals of an order of magnitude. The flow stress analysis showed that hot working empirical constants are different at low and high temperatures. The strain rate sensitivity m was determined and found to change from 0.12 to 0.21 for a temperature rise from 800°C to 1100°C. The apparent activation energy Q was calculated as 554 and 310 kJ/mol for low and high temperature, respectively. The validity of constitutive equation of hyperbolic sine function was studied and stress exponent, n, was assessed to be 4.2. Assuming the hyperbolic sine function for determination of strain rate and application of the rule of mixture, the interaction coefficients of d-ferrite, P, and austenite, R, were estimated at different hot working regimes. It was found that the interaction coefficients are functions of Zener-Hollomon parameter Z and obey the formulas P = 1.4Z À0.08 and R = 0.76Z 0.005. Therefore, it was concluded that at low Z values d-ferrite almost accommodates strain and dynamic recovery is the prominent restoration process which may even inhibit dynamic recrystallization in austenite. Otherwise, at high Z, austenite controls the deformation mechanism of material and dynamic recrystallization leads in finer microstructure.

Metallurgical and Materials Transactions A, 1998

Tecnologia em Metalurgia, Materiais e Mineração

The deformation mechanism of lean duplex stainless steel (LDSS) is overly complex not only by their dual phase microstructure, but also due to metastable austenite, which can deform by different mechanisms and transform to martensite by strain. The purpose of this study was to investigate the mechanisms of deformation by tensile test on low deformed cold-rolled samples (4%-22%) of a 2304 LDSS. The microstructure was analyzed by X-ray diffraction, optical microscopy, electron backscattered diffraction and transmission electron microscopy. It was observed the formation of mechanical twinning, ε-martensite, and α'-martensite which evidenced the TRIP effect. The strain hardening rate was calculated and analyzed by Holomon and Crussard-Jaoul modeling together with instantaneous strain hardening exponent, and three operating mechanisms were observed: twinning, dislocations slipping, and strain induced martensite formation (SIM). Brass texture had compromised SIM transformation. The fractography analysis of tensile specimens showed quasi-cleavage occurrence, and dimples formation for this range of pre-deformation.