Duplex Stainless Steel Type Research Articles

Sliding Wear Behavior of a Duplex Stainless Steel

Duplex stainless steels contain similar amounts of austenite  and ferrite α. This two-phase microstructure leads to an excellent combination of mechanical properties and corrosion resistance. However, there are few works dealing with the wear behaviour of these steels. This paper aims to determine the sliding wear mechanisms of a duplex stainless steel type 2205. In order to do it, three different sliding velocities (0.2, 0.7 and 1.2 m/s) and six sliding distances (500, 1000, 2000, 3000, 4000 and 5000 m) were selected. The results show that wear rate depends on both sliding velocity and sliding distance. The wear mechanisms detected were plowing, microcracking and microcutting (typical mechanisms of fatigue wear). These mechanisms evolve according to sliding velocity and sliding distance, highlighting a transition zone in which wear rate is reduced.

Activated slip systems and microcrack path in LCF of a duplex stainless steel

A low-cycle fatigue test was carried out at room temperature on a forged duplex stainless steel type 25-07 alloyed with 0.17% nitrogen. From EBSD measurements performed before the test and in-situ microscopic observations performed during the test, activated slip systems were identified in austenite and ferrite, respectively. Crystallographic Kurjumov–Sachs (K–S) relationships were rarely observed between the austenitic and ferritic phases and thus the flow of plasticity was nearly inhibited between them. Although the cyclic plastic activity begins firstly in the austenite and then continues to the ferrite, a strong relief was developed rapidly in the ferrite. As a consequence, microcracks initiate preferentially at α/α grain boundaries and then propagate along slip markings formed successively in the austenitic and ferritic grains. Microcracks seldom nucleate at phase boundaries because they lay mainly perpendicular to loading axis.

Precise Resistance Welding with Wire Insert

Butt resistance welding of super duplex stainless steel type 329J4L with inserting type 316L stainless steel wires was investigated. When the base material temperature was increased from room temperature to 1373 K at the heating rate of 550 K /sec, base materials were jointed through the insert wires. HAZ (heat affected zone) of the joint interface were less than 80 μm. In this jointing technique, the insert wires played an important role of concentrating current on the wires and increasing their temperature up to melting point or near melting point. Thermal analysis using thermography revealed that insert wires were adequately heated just after current started at a load of 10 N. When the welding was performed at a load of 70 N, joint area was increased by plastic deformation of the base material. That led to decrease of current concentration. Consequently insert wires were jointed in the solid state.

Microstructural Evolution of Secondary Phases in the Cast Duplex Stainless Steels CD3MN and CD3MWCuN

The isothermal formation behavior of secondary phases in two types of duplex stainless steels (DSS), CD3MN and CD3MWCuN, was characterized. Samples were heat treated from 1 minute to 30 days at temperatures from 700°C to 900°C. Small carbide (M23C6) and nitride (Cr2N) precipitates, together with the intermetallic phases sigma and chi, were observed using scanning electron microscopy (SEM) and confirmed by transmission electron microscopy (TEM) analyses. Based on SEM analysis, time-temperature-transformation (TTT) curves for the sigma and chi phases were determined by measuring their volume fractions from backscattered electron micrographs of heat-treated and quenched sample cross sections. Resulting TTT curves showed that the maximum formation temperature for chi is lower than that for sigma, while the time to reach 1 vol pct formation is much less for sigma than it is for chi. The thermodynamic driving forces associated with the sigma and chi formation were assessed using Thermo-Calc.

EFFECT OF ARTIFICIAL AGING TIME AND TEMPERATURE ON TENSILE STRENGTH OF DUPLEX STAINLESS STEELS SAF 2205 AND SAF 2304 USING (ABI) TECHNIQUE.

Two types of duplex stainless steels SAF 2205 and SAF 2305 have been selected in this study to investigate the effect of aging time and temperature on the tensile strength using (ABI) technique. Metallographic studies were conducted on heat treated duplex stainless steels to examine the phase relation ship with tensile strength. The results showed that with increasing the aging temperature from 400cº to 800cº the tensile strength of duplex stainless steels increased and reached its maximum value at 600cº for 72 hrs. At 1000cº the tensile strength decreased with increasing the aging time. For both types of duplex stainless steels these results attributed to metallurgical aspects like carbide precipitation, sigma phase, change in grain size, etc.

Heat treatment temperature influence on ASTM A890 GR 6A super duplex stainless steel microstructure

Duplex and super duplex stainless steels are ferrous alloys with up to 26% chromium, 8% nickel, 5% molybdenum and 0.3% nitrogen, which are largely used in applications in media containing ions from the halogen family, mainly the chloride ion (Cl −). The emergence of this material aimed at substituting Copper–Nickel alloys (Cupro-Nickel) that despite presenting good corrosion resistance, has mechanical properties quite inferior to steel properties. The metallurgy of duplex and super duplex stainless steel is complex due to high sensitiveness to sigma phase precipitation that becomes apparent, due to the temperatures they are exposed on cooling from solidification as well as from heat treatment processes. The objective of this study was to verify the influence of heat treating temperatures on the microstructure and hardness of ASTM A890/A890M Gr 6A super duplex stainless steel type. Microstructure control is of extreme importance for castings, as the chemical composition and cooling during solidification inevitably provide conditions for precipitation of sigma phase. Higher hardness in these materials is directly associated to high sigma phase concentration in the microstructure, precipitated in the ferrite/austenite interface. While heat treatment temperature during solution treatment increases, the sigma phase content in the microstructure decreases and consequently, the material hardness diminishes. When the sigma phase was completely dissolved by the heat treatment, the material hardness was influenced only due to ferrite and austenite contents in the microstructure.

Corrosion Behavior of Heat-Treated Duplex Stainless Steels in Saturated Carbon Dioxide-Chloride Solutions

Abstract Sweet and/or sour service environments require the use of corrosion resistant materials since conventional steels usually exhibit general corrosion, pitting attack, and stress corrosion cracking (SCC) under these conditions. Long term performance and cost effectiveness must be considered when evaluating material selection. Duplex stainless steels (DSSs) may be considered useful materials under corrosive conditions. These materials are highly resistant to general corrosion and resistant to pitting attack. The low nickel content is an advantage from a SCC stand-point. In this study, the pitting corrosion behavior of a lean duplex stainless steel (type Fe-15Cr-5Ni-1.9Cu) alloy as well as medium grade (type 3RE60 DSS) were evaluated in NaCl solutions saturated with CO2 (sweet environment), containing little or no thiosulfate species at 50°C. The effect of inappropriate heat treatment (e.g., formation of sigma phase in the 3RE60 alloy and sensitization in the lean grade DSS type) is also studied under such conditions. The results revealed that these alloys are susceptible to chloride pitting corrosion with better performance for the 3RE60 alloy. The intensity of the chloride attack is remarkably increased with the addition of CO2, the presence of thiosulfate species, and with the application of inappropriate heat treatment. Although chloride solutions containing saturated dissolved CO2 are more corrosive than those containing thiosulfate species, the presence of both species (CO2 and S2O32) has a more negative effect on the chloride pitting resistance than on each component separately. More severe attack was obtained for heat-treated samples immersed in chloride solutions containing both dissolved carbon dioxide and thiosulfate ions.

Influence of the sigma phase in the cold rolling of duplex stainless steels

One of the steps in the industrial rolling process of duplex stainless steels is the annealing heat treatment after hot rolling. If this annealing is performed in a temperature range that favours the precipitation of intermetallic phases, the mechanical properties can be modified considerably. The formation of these precipitates has a detrimental effect on the DSS ductility and toughness, so it will be a drawback for further cold rolling. In the present investigation, the effect of the sigma phase during cold rolling of a duplex stainless steel type EN 1.4462 has been studied. To simulate this process, compression tests up to a thickness reduction similar to that performed at industrial level have been done. The testing samples were studied by optical microscopy, SEM (scanning electronic microscopy) and TEM (transmission electronic microscopy). Afterwards, some of the annealing conditions were selected in order to carry out cold rolling, using a laboratory scale machine, with the aim to observe if they offered a similar behaviour as that experienced in the compression tests. The results show that only the annealing condition at 975°C during 10 minutes allows to produce sheets without rolling defects.

Effects of Ca and B on the Strip Deformation of Cold Rolled Duplex Stainless Steel Type 2205 during Continuous Annealing

The effects of Ca and B on the strip deformation of duplex stainless steel Type 2205 under continuous annealing conditions were investigated. For the creep test, the stresses were calculated from the line tension applied to hot rolled and cold rolled Type 2205 strip during continuous annealing. It was found that the cold rolled Type 2205 steel showed more prominent superplasticity as compared with the hot rolled steel, which could be attributed to the fine grain size of the cold rolled steel. The creep rate of cold rolled Type 2205 steel decreased with the Ca and B additions due to the grain boundary segregation of B. It is suggested that the rate controlling mechanism for the strip deformation of cold rolled Type 2205 steel seems to be grain boundary diffusion in γ phase.

Analysis of creep deformation behaviors of type 2205 duplex stainless steel under continuous annealing conditions

The objective of this study is to investigate the effects of temperature and line tension on the creep deformation behavior of duplex stainless steel strip under continuous annealing conditions. For the creep tests, the stresses were calculated from the line tension applied to hot-rolled and cold-rolled duplex stainless steel (Type 2205) strip during continuous annealing. It was found that Type 2205 steel exhibited the superplastic-like deformation behaviors with a high strain rate sensitivity value ( m) and a large uniform elongation. The cold-rolled Type 2205 steel showed more prominent superplasticity as compared to the hot-rolled steel, which could be attributed to the fine grain size of the cold-rolled steel. It is suggested that the rate controlling mechanisms for the creep deformation of hot-rolled and cold-rolled Type 2205 steels are seem to be power law creep and grain boundary diffusion in γ phase, respectively.

Microstructure evolution during isothermal annealing of a standard duplex stainless steel type 1.4462

Small alterations in chemical composition, even within the boundaries of the international standards, can drastically alter the formation kinetics of intermetallic phases in a stainless steel. Therefore, by means of isothermal annealing experiments, the time-temperature-precipitation (TTP) diagram was constructed for an industrially cold rolled and annealed standard duplex stainless steel of type 1.4462 (X2CrNiMoN22-5-3), having a distinct composition. Temperature was varied from 600 to 1050 °C, with annealing times from 10 to 3-10 5 s Two intermetallic phases were observed with scanning electron microscopy (SEM): a phase and X phase, a precipitation occurred in a slightly higher temperature range than X precipitation. In addition, at high temperatures a was the first phase to appear, while at lower temperatures X was the first. This could be explained by the driving force for transformation, which is larger for a at high temperatures and larger for X at low temperatures. The microstructural changes during the heat treatment were studied in detail in order to provide a complete overview of all the phenomena that occur during annealing. At temperatures between 750 and 900 °C precipitation was fastest and all the a was replaced by y and a after prolonged times. The presence of neighbouring ferrite seems to be a necessary condition for the X phase to be stable. The appearance of large volume fractions of a above 700 °C was accompanied by a strong growth of the austenitic phase resulting in a more isotropic microstructure. Beneath 700 °C, the precipitated volume fractions of a were relatively small and consequently the original banded structure remained clearly visible. At these lower temperatures the mobility of alloying elements is limited and a Widmannstatten like austenite was observed to grow into the ferrite in a needle-like manner.

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Two types of duplex stainless steels were deformed by torsion at a temperature range of 900 to 1200 °C and strain rate of 1.0 s-1 and their final microstructures were observed. The austenite volume fraction of steel A (26.5Cr - 4.9Ni - 1.6Mo) is approximately 25% at room temperature, after conventional annealing, while that of steel B (24Cr - 7.5Ni - 2.3Mo) is around 55%. Experimental data show that steel A is ductile at high temperatures and displays low ductility at low temperatures, while steel B has low ductility in the entire range of temperatures studied. At high temperatures, steel A is essentially ferritic and shows dynamic recrystallized grains after deformation. When steel A is strained at low temperatures and displays low austenite volume fraction, microstructural observations indicate that failure is triggered by grain boundary sliding due to the formation of an austenite net structure at the ferrite grain boundaries. At intermediate volume fraction, when austenite forms a dispersed second-phase in steels A and B, failure begins at the ferrite/ferrite boundaries since some of the new ferrite grains may become immobilized by the austenite particles. When steel B is strained at volume fraction of around 50% of austenite and both phases percolate the microstructure, failure occurs after low straining as a consequence of the different plastic behaviors of each of the phases. The failure characteristics of both steels are correlated not only with the volume fraction of austenite but also with its distribution within the ferrite matrix, which limits attainable strain without failure.