Supermartensitic Stainless Steel Research Articles

Kinetics analysis of two-stage austenitization in supermartensitic stainless steel

The martensite-to-austenite transformation in X4CrNiMo16-5-1 supermartensitic stainless steel was followed in-situ during isochronal heating at 2, 6 and 18Kmin−1 applying energy-dispersive synchrotron X-ray diffraction at the BESSY II facility. Austenitization occurred in two stages, separated by a temperature region in which the transformation was strongly decelerated. The region of limited transformation was more concise and occurred at higher austenite phase fractions and temperatures for higher heating rates. The two-step kinetics was reproduced by kinetics modeling in DICTRA. The model indicates that the austenitization kinetics is governed by Ni-diffusion and that slow transformation kinetics separating the two stages is caused by soft impingement in the martensite phase. Increasing the lath width in the kinetics model had a similar effect on the austenitization kinetics as increasing the heating-rate.

The effect of titanium on pitting corrosion resistance of welded supermartensitic stainless steel

ABSTRACTThis study evaluated the effect of Ti in the supermartensitic stainless steel (SMSS) on the pitting corrosion in welded joints using gas tungsten arc welding. In the welded SMSS sample, there was martensite grain coarsening in the heat-affected zone (HAZ), and d-ferrite formation at the interface between the base metal and HAZ regions. The presence of Ti in the SMSS prevented grain coarsening and promoted the formation of retained austenite in the HAZ regions. The values of the pitting potentials of SMSS + Ti and SSMS using a cell-pen (designed to reveal the behaviour of localised microstructure in a narrow area) were 0.347 and 0.286 V in the non-welded condition, and 0.374 and 0.183 V in the welded condition, respectively. The corresponding values using the conventional cell were 0.349 and 0.257 V in the non-welded condition and 0.230 and 0.089 V in the welded condition, respectively.

<i>In Situ</i> Techniques for the Investigation of the Kinetics of Austenitization of Supermartensitic Stainless Steel

The austenitization and inter-critical annealing of X4CrNiMo16-5-1 (1.4418) supermartensitic stainless steel were investigated in-situ with synchrotron X-ray diffraction (XRD), dilatometry and differential scanning calorimetry (DSC) under isochronal heating conditions. Austenitization occurred in two stages: the austenitization started at approx. 600 °C, decelerated at approx. 700 °C at 60 to 75 v.% of transformed austenite, and first resumed after heating for approx. 100 °C. This plateau in the transformation curve was more dominant for faster heating rates. Inter-critical annealing at 675 and 700 °C revealed, that austenite can to a certain extent be stabilized to room-temperature. There was good agreement for the transformation curves yielded by dilatometry and XRD. Some deviation occurred due to the different applied heating principles, different temperature monitoring and the impact of surface martensite formation on the XRD measurement. The applicable temperature range for DSC as well as the close proximity of the Ac1- and the Curie-temperature limited the usage of the technique in the present case.

SHIELDING GAS AND HEAT INPUT EFFECTS ON THE MECHANICAL AND METALLURGICAL CHARACTERIZATION OF GAS METAL ARC WELDING OF SUPER MARTENSITIC STAINLESS STEEL (12Cr5Ni2Mo) JOINTS

This paper deals with the effects of shielding gas mixtures (100% CO2, 100% Ar and 80 % Ar [Formula: see text] 20% CO[Formula: see text] and heat input (3.00, 3.65 and 4.33[Formula: see text]kJ/mm) on the mechanical and metallurgical characteristics of AISI 410[Formula: see text]S (American Iron and Steel Institute) super martensitic stainless steel (SMSS) by gas metal arc welding (GMAW) process. AISI 410[Formula: see text]S SMSS with 1.2[Formula: see text]mm diameter of a 410 filler wire was used in this study. A detailed microstructural analysis of the weld region as well as the mechanical properties (impact, microhardness and tensile tests at room temperature and 800[Formula: see text]C) was carried out. The tensile and impact fracture surfaces were further analyzed through scanning electron microscope (SEM). 100% Ar shielded welds have a higher amount of [Formula: see text] ferrite content and due to this fact the tensile strength of the joints is superior to the other two shielded welds.

Sulfide stress corrosion study of a super martensitic stainless steel in H2S sour environments: Metallic sulfides formation and hydrogen embrittlement

Thanks to their high corrosion resistance, super martensitic stainless steels are commonly used in the oil and gas industry, particularly in sour environments. Some grades are however susceptible to undergo hydrogen and mechanically-assisted corrosion processes in the presence of H2S, depending on the pH. The martensitic stainless steel EN 1.4418 grade exhibits a clear protective passive behavior with no sulfide stress corrosion cracking when exposed to sour environments of pH≥4, but undergoes a steep decrease in its corrosion resistance at lower pH conditions. The present paper investigated this abrupt loss of corrosion resistance with electrochemical measurements as well as different physicochemical characterization techniques. Results indicated that below pH 4.0 the metal surface is covered by a thick (ca 40μm) porous and defect-full sulfide-rich corrosion products layer shown to be straightforwardly related to the onset of hydrogen and sulfide mechanically-assisted corrosion phenomena.

Tool life and wear mechanism analysis of carbide tools used in the machining of martensitic and supermartensitic stainless steels

In this study, the wear mechanisms present on the surfaces of carbide tools coated with TiC/TiCN/TiN by CVD were investigated during the turning of two stainless steels: martensitic S41000 and supermartensitic S41426. Tool life tests were performed under several cutting conditions. The flank wear was monitored throughout the tests and at the end the wear mechanisms were investigated using a scanning electron microscope (SEM) equipped with EDS. The results showed that at high cutting speeds and high depth of cut the supermartensitic stainless steel presented a shorter tool life than the martensitic stainless steel. In the machining of martensitic stainless steel abrasion and diffusion were the prevailing wear mechanisms, while for the supermartensitic stainless steel attrition and abrasion were dominant.

A study of the function mechanism of a corrosion inhibitor package for martensitic stainless steel tubulars

Purpose The purpose of this investigation was to study the function mechanisms of a corrosion inhibitor package used for martensitic stainless steel tubulars in acid solution at high temperatures. Design/methodology/approach The inhibition performance was evaluated by means of an acid corrosion test at high temperature and high pressure, and the functional mechanism of the inhibitor package at different temperatures was investigated using polarization curve and electrochemical impedance spectroscopy measurements. Findings The results showed that the corrosion inhibitor package chosen for high-temperature and high-pressure gas well applications was very suitable for use with 13Cr super martensitic stainless steel. At lower temperatures, the function mechanism of the corrosion inhibitor package was characterized as a type of negative catalytic effect. As the temperature was increased, the effect of the intensifier in the package became more significant and the function mechanism changed to be the geometric covering effect type. Originality/value This study has the important practical value for guiding the oil field to conduct reasonable screening and using the acidizing corrosion inhibitor for martensite stainless steel tubulars.

Hot Deformation of Martensitic and Supermartensitic Stainless Steels

The deformation behavior of supermartensitic and martensitic stainless steels was investigated through compression test using Gleeble-3800 thermo-mechanical simulator within the temperature range of 900 – 1200 оС and the strain rates range of 0.01 – 10 s-1. The results showed that the flow stress and the peak strain increase with the drop in the deformation temperature and the rise in the strain rate. Flow stress of SMS steel exceeds flow stress of MS steel for same regimes of deformation. The difference in flow stress increases with the increase in Zener-Hollomon parameter, but does not exceed 15 MPa. The critical deformation, required to start dynamic recrystallization, for supermartensitic stainless steel is slightly lower than for martensitic stainless steel. The hot deformation activation energy of steels is also investigated, their values are similar and equal to 432 and 440 kJ/mol for MS and SMS steel, respectively.

Hydrogen Embrittlement of Welded Joint Made of Supermartensitic Stainless Steel in Environment Containing Sulfane

Abstract The work is focused on evaluation of resistance of the welded joint made of supermartensitic 13Cr6Ni2.5Mo stainless steel to sulfide stress cracking. Testing method A and solution B in accordance with NACE TM 0177 were used. All the testing samples were ruptured in a very short time interval but welded joint samples were fractured primarily in the weld metal or in heat affected zone and not in the basic material. Material analysis of samples were made with use of a ZEISS NEOPHOT 32 light microscope and a JEOL 6490LV scanning electron microscope.

Properties, weldability and corrosion behavior of supermartensitic stainless steels for on- and offshore applications

Abstract Stimulated material-environment interactions inside and around flowlines of deep or ultra deep wells during oil and gas exploration, and fabrication economy of pipelines have been the major challenges facing the oil and gas industries. Presumably, an extensive focus on high integrity, performance and material economy of flowlines have realistically made supermartensitic stainless steels (SMSS) efficient and effective material choices for fabricating onshore and offshore pipelines. Supermartensitic stainless steels exhibit high strength, good low temperature toughness, sufficient corrosion resistance in sweet and mildly sour environments, and good quality weldability with both conventional welding processes and modern welding methods such as laser beam welding, electron beam welding and hybrid welding approaches. In terms of economy, supermartensitic stainless steels are cheaper and they are major replacements for more expensive duplex stainless steels required for tubing applications in the oil and gas industry. However, weld areas of SMSS pipes are exposed to sulphide stress cracking (SSC), so intergranular stress corrosion cracking (IGSCC) or stress corrosion cracking can occur. In order to circumvent this risk of cracking, a post-weld heat treatment (PWHT) for 5 minutes at about 650 °C is recommended. This paper provides detailed literature perusal on supermartensitic stainless steels, their weldability and corrosion behaviors. It also highlights a major research area that has not been thoroughly expounded in literature; fatigue loading behaviors of welded SMSS under different corrosive environments have not been thoroughly detailed in literature.

Localized Corrosion of Corrosion Resistant Alloys in H2S-Containing Environments

Corrosion resistant alloys (CRAs) are widely used in harsh oil and gas production environments where low-alloy steels cannot be used. It is recognized that stress corrosion cracking (SCC) of stainless steels and Ni-based alloys can occur at potentials above the repassivation potential (Erp) for localized corrosion. This paper focuses on experimental work that has been conducted to determine Erp of six CRAs, i.e., super-martensitic stainless steels S13Cr (UNS S41425) and S15Cr (UNS S42625), super-duplex stainless steel 2507 (UNS S32750), and solid solution Ni-based Alloys 2535 (UNS N08535), 29 (UNS N08029), and 28 (UNS N08028) in chloride-H2S environments. A generalized approach is applied to determine Erp values from electrochemical polarization results at temperatures ranging from 85°C to 232°C. The use of completely deaerated solutions and ensuring the stable growth of localized corrosion are both critical to obtain conservative Erp values for CRAs in environments that are similar to downhole conditions...

Quantification of retained austenite by X-ray diffraction and saturation magnetization in a supermartensitic stainless steel

The good performance of supermartensitic stainless steels is strongly dependent on the volume fraction of retained austenite at room temperature. The present work investigates the effect of secondary tempering temperatures on this phase transformation and quantifies the amount of retained austenite by X-ray diffraction and saturation magnetization. The steel samples were tempered for 1h within a temperature range of 600–800°C. The microstructure was characterized using scanning electron microscopy and electron backscatter diffraction. Results show that the amount of retained austenite decreased with increasing secondary tempering temperature in both quantification methods.

Effect of Heat Input on Mechanical and Metallurgical Properties of Gas Tungsten Arc Welded Lean Super Martensitic Stainless Steel

Welding of 6mm thick AISI: 410S lean super martensitic stainless steel (LSMSS) under different heat input of 7.97, 8.75 and 10.9 kJ/cm was carried out by gas tungsten arc welding process. The influence of heat input on metallurgical and mechanical properties in weld and HAZ region was studied. The tensile tests were carried out at different temperatures, namely at room temperature, at 600oC, 7000C and 8000C. It is observed that rise in the heat input and temperature decreased the tensile strength of the weld joint. Further it is noticed that rise in the heat input enhanced the toughness of weld deposit but hardness of weld joints showed insignificant variation in it. This was primarily due to the increase in ferrite content in the matrix of martensite by enhancement of the heat input. In general, the microstructures of weld consisted of mixture of martensite and austenite as well as some amount of ferrite. Whereas, HAZ near to the fusion line consisted of larger and more elongated bright phase of banded delta ferrite in a matrix of martensite irrespective of change in heat input.

Influence of tempering treatment on microstructure and pitting corrosion resistance of a new super ferritic–martensitic–austenitic stainless steels with 17%Cr

Supermartensitic stainless steels (SMSSs) allow high mechanical strength with better corrosion resistance and toughness than conventional martensitic stainless steels. The SMSS steels with 12–13%Cr have been studied and applied in the oil and gas offshore production. The increase of Cr content, and the addition of Mo and W is now being investigated to increase mechanical and pitting corrosion resistance. In this work, a new 17%Cr steel, with Mo and W additions was studied. Depending on the final tempering treatment, the steel has a complex microstructure of austenite, ferrite, martensite and precipitates. The pitting corrosion resistance also depends on the microstructure produced by tempering. It was found that the pitting potential slightly decreases with the increase of tempering temperature and is further decreased by the double-tempering treatment. The pits initiate and grow preferentially in the martensite or tempered martensite islands, due to the lower Cr, Mo and W contents of these areas.

Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

Abstract The influence of austenitization treatment of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) on austenite formation during reheating and on the fraction of austenite retained after tempering treatment is measured and analyzed. The results show the formation of austenite in two stages. This is probably due to inhomogeneous distribution of the austenite-stabilizing elements Ni and Mn, resulting from their slow diffusion from martensite into austenite and carbide and nitride dissolution during the second, higher temperature, stage. A better homogenization of the material causes an increase in the transformation temperatures for the martensite-to-austenite transformation and a lower retained austenite fraction with less variability after tempering. Furthermore, the martensite-to-austenite transformation was found to be incomplete at the target temperature of 1223 K (950 °C), which is influenced by the previous austenitization treatment and the heating rate. The activation energy for martensite-to-austenite transformation was determined by a modified Kissinger equation to be approximately 400 and 500 kJ/mol for the first and the second stages of transformation, respectively. Both values are much higher than the activation energy found during isothermal treatment in a previous study and are believed to be effective activation energies comprising the activation energies of both mechanisms involved, i.e., nucleation and growth.

Microstructure and corrosion resistance of radial friction welded supermartensitic stainless steels

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their corrosion behaviours were studied based on potentiodynamic polarisation and double-loop electrochemical potentiokinetic reactivation tests. Measurements were performed on samples taken from the base metal (BM), weld interface and consumable ring (CR) of the RF weldment. The corrosion properties are discussed in terms of their resulting metallurgical microstructure. The precipitation of Cr carbides that takes place during the tempering treatment induces a substantial Cr depletion value (Ir/Ia = 54.22%). On the other hand, CR and weld interface regions, which had their microstructure transformed and their Cr carbide precipitates redissolved by the RF welding thermomechanical cycle, present a low level of Cr depletion (Ir/Ia < 1%). The AC microstructure, which is composed of a mixture of virgin martensite and stable retained austenite, presents an increase in pitting corrosion resistance compared to the tempered structure of the BM region. It was also observed that the δ-ferrite decreases the pitting resistance of the weld interface region.

Деформационное поведение коррозионностойкой супермартенситной стали в условиях горячей осадки

The deformation behavior of supermartensitic stainless steel 02Cr13Ni4Mo was investigated through compression test using Gleeble-3800 thermo-mechanical simulator within the temperature range of 900–1200 °C and strain rate range of 0,01–10 s –1 . The results showed that the flow stress increases with the drop in the temperature and increasing strain rate. Flow stress of supermartensitic steel exceeds the flow stress of martensitic steel 20Cr13 for same regimes of deformation. Critical strain required to start dynamic recrystallization has similar values for supermartensitic and martensitic steel. The activation energy of hot deformation of supermartensitic steel (442 kJ/mole) is slightly higher than that of martensitic steel (430 kJ/mole). Apparently, this difference is due to a decrease in the carbon content and addition of molybdenum in the supermartensitic steel, which dramatically increases the activation energy of self-diffusion of g-iron.

Passivation Behaviors of Super Martensitic Stainless Steel in Weak Acidic and Weak Alkaline NaCl Solutions

The passivation behaviors of super martensitic stainless steels (SMSS) were studied by polarization curves at passive potential of −0. 1 V and in various NaCl solutions, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) analysis. Electrochemical test results showed that, in alkaline solutions, passivation region width was wider, passivation current was smaller, and polarization resistance was greater; thus, the passive film of SMSS in alkaline solutions had better passivation behaviors than that in acidic solutions. The polarization curve and EIS of samples SMSS1 and SMSS2 were also used to study which sample had better passivation behaviors. All results demonstrated that passive film structure of SMSS1 sample was more stable, and capacity of passive film was enhanced. The impact of alloying elements on the passive film (SMSS) passivation capability was also discussed by XPS depth profiling, and XPS depth profiling showed that the composition of the passive film was mainly composed of Fe-oxide and Cr-oxide. So the passive film structures were mixed layers of Fe-oxide and Cr-oxide. Fe oxidation product and Cr oxidation product would help to improve the protective property of passive film, which could promote the formation of a passive film structure more stably and densely.

Solidification Sequence of Spray-Formed Steels

Solidification in spray-forming is still an open discussion in the atomization and deposition area. This paper proposes a solidification model based on the equilibrium solidification path of alloys. The main assumptions of the model are that the deposition zone temperature must be above the alloy’s solidus temperature and that the equilibrium liquid fraction at this temperature is reached, which involves partial remelting and/or redissolution of completely solidified droplets. When the deposition zone is cooled, solidification of the remaining liquid takes place under near equilibrium conditions. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to analyze the microstructures of two different spray-formed steel grades: (1) boron modified supermartensitic stainless steel (SMSS) and (2) D2 tool steel. The microstructures were analyzed to determine the sequence of phase formation during solidification. In both cases, the solidification model proposed was validated.

Effect of 0.2 and 0.5% Ti on the microstructure and mechanical properties of 13Cr supermartensitic stainless steel

The effect that a 0, 0.2, and 0.5 wt.% titanium content has on the microstructure and mechanical properties of 13Cr supermartensitic stainless steel was investigated using an optical microscope, transmission electron microscope, and X-ray diffraction. The resultant microstructures of the three steels were tempered martensite with a reversed austenite dispersed throughout the matrix. Additionally, the formation of Cr-rich carbides was suppressed by stable Ti(C, N), which improved the strength without severely decreasing in the Ti-microalloyed steel toughness. Nano-precipitation of Ni3Ti was found for the 0.5 wt.% Ti steel during tempering, which significantly increased the strength, but decreased the toughness. The reversed austenite volume fraction also significantly influenced the mechanical properties.