Supermartensitic Stainless Steel Research Articles

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

Supermartensitic stainless steels with 15Cr- 6Ni-2Mo-1Cu with 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 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.

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.

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.

Effect of Cu on the Formation of Reversed Austenite in Super Martensitic Stainless Steel.

We investigated the effect of Cu on the formation of reversed austenite in super martensitic stainless steel by using X-ray diffraction (XRD), a transmission electron microscope (TEM) and an energy-dispersive spectrometer (EDS). Our results showed that the microstructure of the steels comprised tempered martensite and diffused reversed austenite after the steels were quenched at 1050 °C and tempered at 550-750 °C. The volume fraction of reversed austenite in the steel with 3 wt.% of Cu (3Cu) was more than that with 1.5 wt.% of Cu (1.5Cu). The transmission electron microscope results revealed that the reversed austenite in 1.5Cu steel mainly had the shape of a thin strip, while that in 3Cu steel had a block shape. The nucleation points and degree of Ni enrichment of reversed austenite in 3Cu steel were higher than those in 1.5Cu steel. The reversed austenite was more likely to grow in ε-Cu enriched regions. Therefore, Cu can promote reversed austenite nucleation and growth. The mechanical properties of 3 Cu steel are obviously better than those of 1.5Cu steel when tempered at 550-650 °C.

Influence of Abrasion on Corrosive Behavior of a Supermartensitic Stainless Steel in Saline Medium

Abstract Supermartensitic stainless steels, with moderate wear and corrosion resistance, are commonly used in the petroleum and gas industry. A setup configured with a potentiostat and a tribometer was developed to study tribocorrosion behavior of a supermartensitic stainless steel. The electrochemical evaluation indicated that under abrasion, the breakdown potential shifted from 73 V toward lower values, reaching −76 mV(Ag/AgCl) by using larger particles. Using the smallest particles, the breakdown potential was the highest. Because of the synergetic effect of wear and corrosion, the concentration of pits was higher with rubbing, but the pit growth was inhibited. The effects of particle size on wear and corrosion were evaluated using diamond particles with a size range of 10–20 μm, 30–40 μm, 40–60 μm, and 140–170 μm. The smallest particles promoted the highest pit growth inhibition and the highest breakdown potential but also the highest passivation current density. The larger abrasive diamond particles decreased the breakdown potential of the supermartensitic stainless steel in a saline solution.

Mechanical Properties and Strain-Hardening Models of Supermartensitic Stainless Steels Alloyed to Nitrogen and Vanadium

Mechanical Properties and Strain-Hardening Models of Supermartensitic Stainless Steels Alloyed to Nitrogen and Vanadium

Effects of microstructure on crack initiation in super martensitic stainless steel under very‐high‐cycle fatigue at elevated temperature

AbstractThe present study envisaged the behavior and relevant crack initiation mechanism of super martensitic stainless steel (0Cr13Ni5Mo) at elevated temperature (ET) under very‐high‐cycle fatigue (VHCF). Fractographic analysis revealed that all the VHCF cracks of the failure specimens initiated from the surface and formed fine granular area (FGA) morphology at ET in an absence of vacuum. The initiation characteristic area (ICA) consisted of an initiation site, a relatively smooth area, and the annular continuous FGA. FGA was formed in the peaks and valleys of local microstructures, and the smooth regions connected these peaks and valleys dominated by shear stress. It was observed that the FGA was unevenly distributed on the crack surface related to the local microstructure and below the grain surface relevant to local strain distribution. The stress intensity factor (SIF) and the crack tip plastic zone of the ICA slightly changed with temperature.

Electrochemical characterization of 13Cr low-carbon martensitic stainless steel - corrosion study with a mini-cell setup

13Cr low-carbon martensitic stainless steels also known as supermartensitic stainless steels (SMSS) have superior properties than conventional martensitic stainless steels. The SMSS have better weldability and corrosion resistance. Nevertheless, corrosion resistance depends on phases transformations which are induced generally by heat treatments. In this work, the electrochemical properties of a SMSS were evaluated as a function of the tempering temperature (400 °C–700 °C). The susceptibility to intergranular corrosion was determined throught the degree of sensitization (DOS) using the Double Loop - Electrochemical Potentiokinetic Reactivation technique (DL-EPR) in a conventional three electrodes corrosion cell. On the other hand, the pitting susceptibility was evaluated by potentiodynamic polarization using a homemade corrosion mini-cell (based on a sessile electrolyte droplet), thus avoiding crevice problems typically seen with conventional arrangements. Imaging the microstructure with SEM, XRD analysis and thermodynamic and kinetic simulations were performed to understand the microstructural transformations and their relationship with corrosion resistance. The most severe sensitization occurs at the temperature where reversed austenite transformation is highest.

Optimizing mechanical properties of 15Cr supermartensitic stainless steel by enhanced stability of retained austenite

The effect of annealing temperature below austenite start transformation temperature on the mechanical properties of martensitic stainless steel was investigated. The annealing treatment can transform the anisotropic compressive stress of retained austenite into hydrostatic pressure, which stabilizes the retained austenite and increases the elongation of the martensitic stainless steel.