Supermartensitic Stainless Steel Research Articles

In situ evaluation of sensitization in the heat affected zone of supermartensitic stainless steel welded with superduplex filler metal

Supermartensitic stainless steels (SMSS) are high strength corrosion resistant alloys used in oil and gas production in deep water. Failures related to sensitization and excessive hardness in the heat affected zone (HAZ) are prone to happen in harsh environments, such as those found in oil production. To avoid dangerous types of failure, post weld heat treatments (PWHT) are necessary. Temperature and duration of PWHTs are fundamental parameters to be adjusted. In the present work, a minicell was developed to perform DL-EPR tests in different regions of a multipass welded joint of SMSS with superduplex stainless steel as filler metal. The welded joint was submitted to PWHT at 650 °C for 5 and 15 min. The effects of these short duration PWHT on the HAZ and base metal were analyzed using a minicell for double loop electrochemical tests (DL-EPR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicate that both PWHTs (5 and 15 min) caused the increase in the degree of sensitization of HAZ without the reduction of hardness to acceptable values.

The new design to improve the stability of retained austenite and mechanical properties in super martensitic stainless steel

The quenching and partitioning (QP) process has proven to be an effective technique for stabilizing retained austenite (RA). The N element partitioning process has replaced the traditional C element partitioning method, resulting in improved stability of RA in super martensitic stainless steel. To enhance these benefits, an innovative combination of intercritical annealing (A) and QP has been developed, known as the QAP process. This technique utilizes interstitial N atoms and substitutional Ni, Mn atoms to co-stabilize RA, leading to excellent comprehensive mechanical properties. The findings indicate that the QAP samples display a yield strength (YS) that is 75–121 MPa higher than the QP sample. At intercritical annealing temperatures of 500 °C and 550 °C, the QAP steel demonstrates a product of strength and elongation (PSE) of 36.61 GP·% and 31.51 GP·%, respectively, surpassing the QP steel (26.52 GP·%). Furthermore, the presence of secondary martensite increases with higher intercritical annealing temperatures in QAP samples. However, excessive secondary martensite significantly diminishes toughness.

Postweld Heat Treatment of 15Cr-6Ni-2Mo-1Cu Supermartensitic Stainless Steel Welds

Supermartensitic stainless steels with 15Cr-6Ni- 2Mo-1Cu and 135 ksi minimum yield strength (15Cr- 135 SMSS) offer high strength and good toughness through a complex hierarchical microstructure of nanoscale precipitates, tempered martensite, and reverted austenite. Upon welding and postweld heat treatment, substantial changes to heat-affected zone microstructure and hardness may occur. Here, we reveal spatially heterogeneous microstructure and microhardness in the HAZ of 15Cr-135 SMSS; correlate these changes to measured phase transformation temperatures; and demonstrate that HAZ hardness changes depend strongly on postweld heat treatment (PWHT) temperatures. Furthermore, we demonstrate that PWHT may lead to undesired reductions in base metal yield strength and formulate a design guide for PWHT that quantifies the trade-offs in desired reductions of HAZ hardness with undesired changes to base metal yield strength. These findings have important practical implications for welding procedure design and qualification.

Effect of heat treatment processes on the microstructure and mechanical properties of 00Cr13Ni5Mo super martensitic stainless steel (SMSS)

The effects of quenching and tempering temperatures on the microstructure and mechanical properties of super martensitic stainless steel (SMSS) 00Cr13Ni5Mo were studied. The SMSS after heat treatment is composed of martensite (α phase) and a small amount of austenite. When the quenching temperature is 930 °C, with the increase of tempering temperature, the enrichment of Ni in martensite leads to the formation of reverse austenite, the content of martensite phase decreases from 84.9 % to 80.0 %, and the average grain size increases from 23.23 μm to 27.07 μm. When tempering at 580 °C, the content of martensite phase decreases from 80.0 % to 83.7 % with the increase of quenching temperature. The average grain size increased from 25.23 μm to 35.01 μm. When the quenching temperature is 930 °C, the hardness and yield strength of SMSS decrease, and the hardness and yield strength are the highest at 530 °C, which are 275 HV and 873 MPa. The plasticity increases first and then decreases, and the plasticity is the best at 580 °C. The elongation and reduction of area were 22.87% and 71.41%. These changes in mechanical properties are mainly related to the content of martensite and reversed austenite in the microstructure. The tensile strength and elongation of SMSS under different process conditions were compared. The results show that when the quenching temperature is 930 °C and the tempering temperature is 580 °C, the comprehensive performance of SMSS is the best, reaching 18700 MPa•%. This value is 31% higher than that of forgings. Finally, the formation mechanism of reversed austenite was discussed, and the strengthening model of SMSS 00Cr13Ni5Mo was established.

Corrosion behavior of SMSS 13Cr and SS 316L under chloride solution and H2S/CO2 environments

Abstract Corrosion resistant alloys (CRAs) include a range of different stainless steels and nickel alloys that are used in corrosion-aggressive environments encountered in oil and gas operations. Supermartensitic stainless steel (SMSS 13Cr) has been used in the manufacture of steel tubes for use in oil drilling due a more financially viable option to replace the austenitic stainless steel (SS 316L) in the oil and gas market. This present work estimate the effect of the hydrogen sulphide (H2S) on SMSS 13Cr and SS 316L, in saline solution, simulating the operating conditions in the oil and gas industry. Corrosion behavior was monitored using Potentiodynamic-Potentiostatic-Potentiodynamic (PD-PS-PD) technique in order to obtain pitting potential (Ep) or crevice potential (Ecrev)) and repassivation potential (Erp) while the long-term Open Circuit Potential (OCP) technique was applied to estimate the stable corrosion potential (Ecorr*). A Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and Optical Microscopy were used for surface characterization. With all analysis carried out was possible to propose a trend regarding the pitting probability. The pitting increases with increasing H2S concentration on SSSM 13Cr, consequently, large, and deeper pits were observed, making possible to develop into cracks if there are mechanical stresses. On the contrary, the pitting probability for the SS 316L is low (compared with SMSS 13Cr) for all environments reproduced here in this research.

The performance of grooved turning tools under distinct cooling environments

This work investigates the performance of modified tungsten carbide inserts when turning supermartensitic stainless steel with cutting fluid and/or air jet applied in two directions: either cutting fluid under high pressure or compressed air under low pressure supplied on the back of the chip (through a hole produced near the principal cutting edge), together with either cutting fluid or compressed air, both under low pressure, directed at the clearance face. Tool performance is evaluated by means of the principal cutting force, temperature distribution (using FEM), visual evaluation of the rake face, morphology of the chips and the quality of the machined surface. The findings indicate that the groove reduces the cutting force when dry cutting. Cutting fluid applied under low pressure at the clearance face is more efficient in decreasing both the cutting force and chip temperature than cutting fluid at high pressure supplied at the back of the chip. A chrome oxide layer is formed on the chip when air jet is applied, thus leading to an unfavorable cutting condition. The simultaneous application of cutting fluid under high pressure to reach the back of the chip and compressed air supplied through the clearance face provides the best surface quality.

Finite element simulation analysis of flow heat transfer behavior and molten pool characteristics during 0Cr16Ni5Mo1 laser cladding

0Cr16Ni5Mo1 super martensitic stainless steel has excellent weldability and is an economical material with a high life cycle and low cost, but there are few researches and applications of this material in additive manufacturing. In order to realize the application of 0Cr16Ni5Mo1 large-area laser cladding technology, the multi-track lap cladding of the material was studied. In this work, a multi-physical finite element model of multi-layer multi-track laser cladding was established, taking into account thermodynamic processes such as phase transition, Marangoni convection, and buoyancy. The flow and heat transfer behavior of 0Cr16Ni5Mo1 in multi-layer multi-track laser cladding process and the characteristics of the molten pool are studied. The research focused on the flow heat transfer behavior and molten pool characteristics of 0Cr16Ni5Mo1 during multi-layer multi-track laser cladding. The discussed aspects include the evolution history of the temperature field within the molten pool, flow field characteristics, molten pool dimensions, and dilution ratio under various laser powers and overlap rates. The results show that with the increase of overlap rate, the morphology of molten pools in different clad tracks will also change, and the flow rate, dilution ratio, and length of molten pools in the second track are negatively correlated, while the temperature and height of molten pools are positively correlated. As the laser power increases, all the characteristic quantities are positively correlated with it.

Lower corrosion resistance of the nitrocarburized layer formed on two supermartensitic stainless steel types

Lower corrosion resistance of the nitrocarburized layer formed on two supermartensitic stainless steel types

Wire-arc directed energy deposition super martensitic stainless steel with excellent strength and plasticity

Super martensitic stainless steel (SMSS) is wildly used in hydroelectric, petrochemical, and nuclear power industries relying on high strength and sound weldability. While the low ductility and high strength make it difficult to be deformed and machined. The wire-arc directed energy deposition (DED) process allows a high deposition rate and can produce high-quality parts. In this study, the SMSS thin-wall parts were fabricated through wire-arc DED with the cold metal transfer technique. This research aims to investigate the microstructural evolution regulation and mechanical performance improvement mechanism of the additive manufacturing SMSS parts and achieve good comprehensive performance. The microstructure of the as-deposited wall consists of full lath martensite with columnar and fine equiaxed grains in periodic alternation layer by layer. By regulating the temperature between each layer, the overall wall's microstructure is kept consistent. The yield strength and ultimate tensile strength of the as-deposited wall are 1046 and 903 MPa with total elongation of 9 % and impact energy of 16 J. Thus, the toughness and plasticity needed to be improved by heat treatment. Based on the energy dispersive spectroscopy (EDS) technique and diffraction pattern analysis using transmission electron microscopy (TEM), the phases formed during the intercritical tempering process were identified as tempered martensite and reversed austenite. The enhancement of toughness is associated with austenitic transformation-induced plasticity. The amount of reversed austenite is 29.5 % at 600 °C and then disappeared at 700 °C. The best comprehensive mechanical properties were obtained at a temperature of 550 °C with an ultimate tensile stress of 927 MPa, yield stress of 850 MPa, impact energy of 33 J, and elongation of 18 %, comparable to the rolled parts.

Investigation on microstructure and mechanical properties of boron-modified 13Cr5Ni2Mo by powder-pack boriding

ABSTRACT The main objective of the present paper is to investigate the effect of pack boriding treatment at 950°C/4 h on surface 13 Cr supermartensitic stainless steel. Scanning electron microscopy and X-ray diffractometry were used to characterise the grown boride layers microstructures. In addition, we performed 3D profilometry, microhardness measurements, nanoindentation tests with a Berkovich diamond tip, Daimler-Benz Rockwell-C adhesion, and ball-on-disk wear tests in order to evaluate the mechanical properties. After boriding, the phases were found to be iron borides (FeB/Fe2B), chromium borides (CrB), nickel borides (Ni2B), and molybdenum borides (Mo2B). The results showed that the use of the powder-pack boriding process on 13Cr SMSS at 950°C/4 h conducted in the presence of dual phases (FeB/Fe2B) improved the mechanical properties compared to untreated material.

Evaluation of post weld heat treatments and susceptibility to sulfide stress corrosion cracking of simulated HAZ in forged supermartensitic stainless steel UNS S41427

Supermartensitic stainless steels (SSMSs) with 12–13%Cr, 5%Ni, 2%Mo and microadditions were developed to casings, tubullars and mandrels used in the oil and gas off-shore production. These materials have great resistance to aqueous medium containing large amounts of CO2 and can withstand high temperatures and large amounts of chloride as well. However, SMSSs have a limited resistance to H2S containing solutions, and may fail due to sulfide stress cracking (SSC). This limit is even lower for forged and welded components that used in mandrels. Recent studies have been developed to find an operational envelope for safe use of SMSSs in sour production systems. The present study shows the results of slow strain rate testing (SSRT) of a forged V-alloyed SMSS submited to thermal simulation in Gleeble machine to produce a coarse grain heat affected zone (HAZ). The microstructure of the HAZ is characterized by fresh martensite, intergranular delta ferrite and fine precipitates which increase the hardness to a level above the maximum limit for sulfide stress corrosion cracking. The effects of two post weld heat treatments (PWHT) on the mechanical properties and susceptibility SSC were evaluated. Single and double tempering treatments provoked the decrease of hardness and the increase of ductility parameters. However, specimens representative of the HAZ, base metal, and HAZ with single and double tempering presented high SSC susceptibility parameters in SSRT in saline solution (200,000 ppm NaCl) with 1.0 psia of H2S partial pressure, and pH 4.5.

Study on the mechanical stability of reversed austenite in super martensitic stainless steel via in-situ synchrotron high energy X-ray diffraction

This study investigated the mechanical stability of two types of reversed austenite, film-like and blocky reversed austenite, which were obtained after tempering for different time at 620 °C in 16%Cr-5%Ni super martensitic stainless steel. Herein, synchrotron high-energy X-ray diffraction combined with in-situ tensile testing was performed. The results indicate that most of the blocky reversed austenite transformed into martensite early at the elastic stage, while the stress induced martensitic transformation of film-like reversed austenite mainly occurred after yield. The increase in chemical driving force caused by the lower degree of Ni enrichment, the decrease in strain energy due to matrix softening, and the lower interfacial energy due to the smaller specific surface area were considered possible reasons for the poor mechanical stability of blocky reversed austenite.

Effect of Heat Treatment on Microstructure, Mechanical Properties, and Corrosion Performance of 410NiMo Super Martensitic Stainless Steel Cladded on 21CrMoV5-11 by Submerged Arc Welding Process

Effect of Heat Treatment on Microstructure, Mechanical Properties, and Corrosion Performance of 410NiMo Super Martensitic Stainless Steel Cladded on 21CrMoV5-11 by Submerged Arc Welding Process

Effects of tempering temperature on the microstructure evolution and mechanical properties of 16%Cr–5%Ni super martensitic stainless steel

The effects of tempering temperature on the microstructure evolution and mechanical properties of 16%Cr–5%Ni super martensitic stainless steel (SMSS) were investigated in the present study. Reversed austenite was detected via X-ray diffraction when the as-quenched samples with full martensite were tempered above 500 °C, and its volume fraction attained a maximum of ∼17% at 620 °C. When tempered below 620 °C, all the reversed austenite formed was able to keep stable at room temperature, while partial or even entire reversed austenite formed above 640 °C with Ni content less than 8 wt% transformed back into fresh martensite during cooling, demonstrating that the enrichment of Ni determined the thermal stability of reversed austenite. EDS results revealed that the precipitation of M23C6 carbides caused Ni enrichment in the adjacent regions, promoting the nucleation of reversed austenite, and the growth of reversed austenite was mainly controlled by Ni diffusion. The results of tensile tests and instrumented impact tests indicated that stable reversed austenite effectively improved the ductility and toughness, and offset the deterioration of toughness caused by the M23C6 precipitating at grain boundaries. Tempering at 540 °C achieved an excellent combination of strength and toughness, while the best plasticity of samples was obtained by tempering at 620 °C.

Study on Effect of Tempering Temperature on Microstructure and Properties of Super Martensitic Stainless Steel Welded Joints

The ultra-martensitic stainless steel ZG06Cr13Ni4Mo, due to its excellent corrosion resistance, good tensile property and excellent weldability, is widely used in many occasions of hydropower, thermal power, and nuclear power, especially as the preferred material for pump impeller. This type of steel has good weldability due to its low carbon content, but the low content of reversed austenite in the weld will lead to poor plastic toughness of the welded joint. The effect of different tempering processes on the microstructure transformation and mechanical properties of welded joints of ultra-martensitic stainless steel was studied. The 20 mm thick test plate was MIG welding and then tempered at 560 °C, 600 °C, and 640 °C for 2 h. The results show that after increasing tempering temperature, the microstructure gradually decreases from the base metal to the weld and gradually transforms from lath martensite to tempered sorbite; When tempering at 600 °C, the microstructure in the weld is the finest, and the size of grain size is 0.274 μm. The highest content of reversed austenite is 9.39%; In the welded joint, compared with the untempered joint, the hardness of the welded joint area decreases after tempering, and the tensile strength first decreases and then increases. The yield strength and elongation gradually increase.

Insight on microstructure and mechanical properties of 40 mm thick-walled ferromagnetic super-MSS by magnetic-field-assisted narrow gap GTAW

In this work, the welding of 40 mm thick-walled ferromagnetic super martensitic stainless steels (super-MSS) welded by magnetic-field-assisted (MFA) narrow gap-gas tungsten arc welding (NG-GTAW) is reported and a defect-free joint is successfully obtained. The variations trends of microstructure and mechanical properties at different positions along the thickness direction of the joint are analyzed. The results show that there are obvious differences in microstructure and properties between different layers of the MSS joint. The strength level of the joint is comparable to that of the base metal. The impact toughness of the middle and bottom layers is much higher than that of the base metal. This is mainly due to the differences in microstructure, such as austenite content, refinement and grain boundary characteristics of martensite observed by OM, SEM, and EBSD. A two-pass filling test is employed to understand the evolution of microstructure and properties of thick-walled super-MSS joint and clarify the self-heat-treatment (SHT) effect between the weld passes by simulation. It is found that during the welding process of thick-walled super-MSS, the adjacently later pass can exert an obvious SHT effect on the bottom layer, which leads to significant refinement of martensitic lath in the weld. Finally, the relation between microstructure and properties of the thick-walled super-MSS joint is revealed.

Effects of Welding Parameters on Sigma Phase Precipitation in 25Cr-5Ni-1Mo-2.5Cu-1Mn-0.18N Duplex Stainless Steel

Recently, a new grade of duplex stainless steel, UNS S82551 (25Cr-5Ni-1Mo-2.5Cu-0.18N), has been developed to overcome the drawbacks in super martensitic stainless steel, conventional 22Cr and 25Cr super duplex stainless steels in terms of productivity and cost. The characteristic of the alloy design of UNS S82551 is to use Cu, instead of Mo, to ensure comparable corrosion resistance and strength. In addition, due to the significant decrease in Mo content, UNS S82551 is expected to be less sensitive to sigma phase precipitation during single or multi-pass welding compared with conventional and super duplex stainless steels. There is a trade-off between achieving better properties and avoiding sigma phase precipitation when increasing alloying elements such as Mo, Cr and Cu. In order to utilize the new UNS S82551 steel in industry for welding in a similar manner to conventional and super duplex stainless steels, the prevention of sigma phase precipitation is important. This work investigated the effect of weld thermal cycling on sigma phase precipitation behaviour in UNS S82551 welds. During thermal cycling in the tests, the amount of sigma phase for UNS S31803 and UNS S32750 increased with increasing the number of thermal cycles, and lower cooling rate, but it was not observed for UNS S82551. Based on the isothermal kinetics of sigma phase precipitation, the amount of sigma phase precipitated during thermal cycle can be predicted by applying the additivity rule to the physical model. The area fractions of sigma phase calculated have a good fit to the experimental ones.

Hydrogen embrittlement of high-strength steels in thiosulphate solutions

ABSTRACT The susceptibility to hydrogen embrittlement of supermartensitic stainless steel (S13Cr), martensitic-ferritic stainless steel (17Cr), carbon steel (P110) and austenitic-ferritic stainless steels (2205 and 2507) was evaluated by slow strain rate tests using a modified NACE TM-0177 solution, with 10–3M NaS2O3 substituting the saturated H2S standard solution. Tests were conducted at 25°C, pH 2.7 and under galvanostatic polarisation with a cathodic charging of 10 mA/cm2. S13Cr, 17Cr, P110 and 2507 steels were susceptible to hydrogen embrittlement inthiosulphate, with S13Cr and 17Cr being the most sensitive to this mechanism, while 2205 showed no sign of ductility loss. This harmful effect was attributed to the hydrogen sulphide generated from thiosulphate.

Electrochemical Noise of SCC Inhibition of a Supermartensitic Stainless Steel in Sour Solution

In this work, the inhibition effect of a non-ionic gemini surfactant, named bis(2-((2-palmitoamidoethyl)amino)ethyl)1H-imidazole4,5-dicarboxylate, on the stress corrosion cracking (SCC) behavior of a supermartensitic stainless steel (SMSS) was studied in sour environment. The slow strain rate stress tests (SSRT) results and fractographic analysis revealed that the corrosion inhibitor was able to inhibit the SCC process using a concentration above than 5ppm. At concentrations of 0 and 5 ppm, the steel showed a brittle fracture with susceptibility to SCC, whereas at concentrations of 25 and 100 ppm, the fracture was ductile, and the steel was practically immune to SCC. The EN measurements showed transients associated with pits and microcracks, which were confirmed by SEM examination. The EN analysis using the shot noise theory indicated that localized corrosion was the dominant corrosion process at the concentrations of inhibitor in which the SMSS was susceptible to SCC.

Effect of Heat Treatment on the Corrosion Behavior of a Supermartensitic Stainless Steel in Sour Solution.

In the present research work, the influence of heat treatment on the corrosion behavior of a supermartensitic stainless steel (SMSS) in sour solution (H2S gas was replaced by sodium thiosulfate) was studied using polarization curve electrochemical techniques (CP) and Electrochemical Impedance Spectroscopy (EIS), along with microstructural characterization using optical microscopy and X-ray diffraction (XRD) measurements. The CP results revealed that the samples subjected to quenching and tempering process exhibited the formation of a more protective corrosion product layer. However, the EIS results showed that this layer accelerated the corrosion process as immersion time increased. Finally, according to XRD and electrochemical test results, the lower the percentage of volume fraction of retained austenite in the microstructure of SMSS, the lower the corrosion resistance.