Cr Martensitic Stainless Steel Research Articles

Effect of Nitrogen on the Hot Deformation Behavior of 0.4C–13Cr Martensitic Stainless Steel

The hot deformation behaviors of 0.4C–13Cr martensitic stainless steel at the nitrogen contents of 0.13% and 0.03%, respectively, are investigated at the deformation condition featuring the temperature range of 1223–1523 K and the strain rate range of 0.01–10 s−1. The variation of flow stress curves of experimental steels with different nitrogen contents is systematically analyzed. According to the flow stress curves, the activation energies determined by regression analysis are 472.77 and 411.58 kJ mol−1 for 0.4C–13Cr steel with N contents of 0.13% and 0.03%, respectively. It demonstrates that the deformation resistance of 0.4C–13Cr steel improves with the increase in nitrogen content. The reason is related to the pinning effect of solid solution nitrogen atoms, and Cr2N particles on dislocations and grain boundaries. The dynamic recrystallization (DRX) kinetics models of experimental steels are established. Furthermore, the microstructures of experimental steels are also analyzed. The result shows that the pinning effect caused by nitrogen also plays an important role in the development of DRX and microstructure evolution. The more nitrogen addition in 0.4C–13Cr steel, the earlier achievement of DRX onset, the slower the DRX kinetics and the finer the microstructure.

Effect of Tempering on Tribological Properties of 13Cr Martensitic Stainless Steel and Alumina Material Pair in Dry Sliding

This present study seeks to understand tribological properties of 13Cr martensitic stainless steel (MSS) in austenitizing and tempering conditions (300, 550, and 700 °C). A ball-on-plate configuration with an alumina ball as the counterface was employed for dry sliding experiments. Complementary analytical techniques such as 3D optical profilometry, optical microscopy, scanning electron microscopy/energy-dispersive spectroscopy, and microhardness measurements were used to elucidate the operating wear mechanism. The results showed that the coefficient of friction (COF), wear rate, and wear mechanism changed significantly with tempering temperature. Austenitized and 300 °C tempering condition exhibited stable COF variations with time, whereas fluctuating and increasing COFs with time were observed in 550 and 700 °C tempering conditions, respectively. Wear resistance for the tempering condition was lower than that for the austenitizing condition, with the least wear resistance for the 550 °C tempering condition. The wear resistance of the alumina ball also followed the same trend as for 13Cr MSS. The least wear resistance of the counterface material was observed against the 550 °C tempering condition. These observations were attributed to the (a) formation of large amount of nanosized carbides and (b) embedment of the counterface material during sliding. The austenitizing and 300 °C tempering conditions showed abrasive plus mild oxidation wear mechanism, whereas tempering at 550 and 700 °C showed delamination plus the presence of adhesion traces and a compacted tribolayer plus severe oxidational wear mechanism, respectively. The present results clearly highlight the changes in wear mechanism of 13Cr MSS against the counterface alumina ball with the developed microstructural changes during tempering treatments.

Structure and Property Modulations of 13Cr Stainless Steel Through Microgravity Solidification and Minor Ce Addition

Both rare‐earth doping and microgravity solidification processing bring significant influences upon the structure formation and mechanical properties of various alloys. Herein, the microstructure and performance of 13Cr martensitic stainless steel are modulated by adding minor Ce content and microgravity solidification by means of drop tube technique. The lattice structure of constituent phase α(Fe) is deformed evidently by microgravity solidification, and the lattice parameter variation is 1.8 times of that caused by Ce addition. The microstructures of this steel processed by arc melting consist of lath‐shaped martensites and a few feather‐shaped bainites whose volume fraction increases with the Ce content. The bainite is replaced by ferrite in the rapidly solidified microstructure of 13Cr steel under microgravity condition. Although both microgravity solidification and Ce addition induce the microstructure refinement and inclusion spheroidization, the former effect plays the dominant role. The compressive properties and microhardness decrease moderately with Ce addition due to the slight increase in bainite, however, the microgravity solidification brought the hardening effect and thus the microhardness of the steel droplets increases with undercooling.

Influence of microstructure on the corrosion behavior of super 13Cr martensitic stainless steel under heat treatment

The effect of microstructure on the corrosion characteristics of super 13Cr martensitic stainless steel (S13Cr MSS) under heat treatment was investigated. The results revealed that the Ni enriched reversed austenite content in the tempered steel increased as the tempering temperature increased. No Mo-rich intermetallic compounds and reversed austenite were found in the quenched steel. The Mo-rich intermetallic compounds adversely affected the protective properties of the corrosion film because the Mo-depleted regions adjacent to the compounds had approximately 7 mV Volta potential lower than steel matrix, destroying the corrosion film stability. However, the reversed austenite benefitted on the corrosion film due to it inhibiting further corrosion of S13Cr MSS and enhancing the corrosion film stability. Accordingly, the quenched steel without Mo-rich intermetallic compounds had the highest corrosion resistance and the corrosion resistance of the tempered steel increased with an increasing tempering temperature.

Corrosion resistance of 13wt.% Cr martensitic stainless steels: Additively manufactured CX versus wrought Ni-containing AISI 420

The corrosion resistance of heat-treated additively manufactured (AM) precipitation hardening martensitic stainless steel (SS) CX and wrought components of AISI 420-SS with lower Ni content, were compared. The microstructure of heat-treated AM-CX comprised of a martensitic matrix and a few nano-scale particles, while the wrought AISI 420-SS contained approximately 8% of austenite and Cr-rich carbides in a martensitic matrix. Superior corrosion resistance was detected for the AM-CX part as compared to the AISI 420-SS ascribed to nearly absence of Cr-rich carbides and martensite-retained austenite interfaces in the AM-CX SS, while their presence in the AISI 420-SS destabilized the passive film.

Effect of Austenitization-Cooling on Microstructure and Localized Corrosion Behavior of 13Cr Martensitic Stainless Steel

The present study investigates the microstructural changes and corrosion behavior of 13Cr martensitic stainless steel (MSS), austenitized at 1040 °C followed by cooling to room temperature through oil-quenching, air-cooling and furnace-cooling. Oil-quenching and air-cooling produced a lath martensitic microstructure, while, the oil-quenched condition showed δ-ferrite stringers and quench cracks. The slow furnace-cooling produced a widmanstatten type ferrite with Cr-rich carbides. Air-cooled condition developed a higher hardness than that for the oil-quenched and furnace-cooled conditions due to martensitic structure and fine carbide precipitation along the prior austenitic grain boundaries (PAGB) during cooling from austenitization temperature. Double loop-electrochemical potentiokinetic reactivation (DL-EPR) tests and immersion tests followed by scanning electron microscope examination indicated that furnace-cooled and air-cooled conditions are susceptible to intergranular corrosion (IGC). Slow cooling is highly detrimental to IGC. Air-cooled condition showed preferential attack along the PAGB boundaries in both DL-EPR and immersion tests whereas furnace-cooled condition showed combined heavy uniform corrosion and IGC. No preferential attack is observed in oil-quenched condition, and it exhibited uniform corrosion. The present results show that the austenitization followed by cooling in air is sufficient to cause sensitization in 13Cr MSS. However, controlled (fast) air-cooling (avoiding sensitization during cooling) would be better a choice for austenitization heat treatment of 13Cr MSS.

The mechanism of thermal oxide film formation on low Cr martensitic stainless steel and its behavior in fluoride-based pickling solution in conversion treatment

(Attention for corrosion science, the abstract must not exceed more than 100 words)In this research, first a multi-analytical approach was carried out to propose a mechanistic model for the formation of the thermal oxide film on low Cr stainless steel. It describes the effects of kinetically and thermodynamically driven phenomena on the growth of a Fe-Cr complex oxide film at 950℃. Second, the behavior of the thermal oxide film in the presence of fluoride ions, as a relevant pickling agent in conversion treatment, was investigated. It was shown that fluoride ions enter the oxide film and form a complex with Fe and preferentially dissolve hematite islands through a complexation mechanism.

Cr Segregation and Impact Fracture in a Martensitic Stainless Steel

The fracture surfaces of a 10.5 wt.% Cr martensitic stainless steel broken in Charpy tests have been investigated through X-ray photoelectron spectroscopy (XPS). The specimens have been examined in two different conditions: as-quenched and heat treated for 10 h at 700 °C. The trends of Fe/Cr ratio vs. test temperature are similar to the sigmoidal curves of absorbed energy and, after both ductile and quasi-cleavage brittle fractures, such ratio is always significantly lower than the nominal value of the steel chemical composition. Cr segregation does not occur on a macroscopic scale but takes place in microscopic zones which represent weaker spots in the steel matrix and a preferred path for moving cracks. Small area (diameter 300 µm) XPS measurements evidenced a higher density of such microscopic zones in the inner part of probes; this is explained by the different diffusion length of Cr atoms in the external and inner parts during quenching from austenitic field which has been calculated through FEM simulations. No significant differences of Cr concentration were observed in fracture surfaces of probes with and without heat treatment. The results highlight how Cr segregation plays a role not only in the intergranular mode of fracture but also in the quasi-cleavage and ductile ones.

Effect of Uniaxial Tension-Induced Plastic Strain on the Microstructure and Corrosion Behavior of 13Cr Martensitic Stainless Steel

This study aims to understand the correlation between the manufacturing process-induced plastic deformation, microstructure, and corrosion behavior of a 13Cr martensitic stainless steel tubing material (UNS S42000). Comparisons were made between the microstructure, crystallographic orientation, and corrosion performance of a texture-free, heat-treated sample and uniaxially tensioned samples to the elongations of 5% and 22%. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopy were performed on all samples in aerated 3.5 wt% NaCl electrolyte at room temperature. Overall, the corrosion resistance of the samples was found to decrease with increasing deformation level. A more stable and higher corrosion potential and pitting potential values with a better stability of the passive film were derived for the nondeformed sample, whereas the 5% and 22% elongated samples exhibited lower corrosion and pitting potential values and were characterized by having a less stable passive layer. All samples consistently revealed micropit formation on the lath boundaries where a high concentration of chromium carbide precipitates was detected. Increasing the level of plastic strain in 13Cr stainless steel was found to enlarge the size of sensitized regions along the matrix/coarse chromium carbide precipitates interface, leading to more regions susceptible to initiation and propagation of pitting.

Corrosion and repassivation of Super 13Cr stainless steel in artificial 1D pit electrodes at elevated temperature

Repassivation behavior of Super 13Cr martensitic stainless steel was investigated using a one-dimensional artificial pit electrode in deaerated NaCl solutions at 85 °C. Critical potentials for pit repassivation (Ecrit) were measured by downward potential scans. Ecrit and the final current density (if) at the end of the scan can be correlated to the pit repassivation, showing that repassivation is more probable with smaller if and higher Ecrit. Pit repassivation at a constant potential was correlated with if and average current density (iavg). A combination of lower if and iavg suggests a higher probability for pit repassivation.

Electrochemical Behavior and Passive Property of 13Cr Martensitic Stainless Steel in Nitric Acid Solution

Intergranular corrosion behavior of a 13Cr martensitic stainless steel (MSS) in tempered condition was studied. Tempering was done in the temperature range of 300-700 °C after austenitization, and microstructure was established using scanning and transmission electron microscopy. Electrochemical characterizations to establish localized corrosion susceptibility were performed in 5% HNO3 solution. The MSS tempered at 550 °C showed sensitization and significant localized attack during tests in HNO3. Characterization of surface film on this condition revealed an oxide with a higher defect density (through electrochemical impedance spectroscopy–Mott–Schottky analysis) and Fe content (x-ray photoelectron spectroscopy) as compared to that for the austenitized condition. The inability of sensitized MSS tempered at 550 °C to form a protective surface film was attributed to the formation of considerable nano-sized Cr-rich carbide precipitates associated with narrow Cr depletion zones. On the other hand, the MSS tempered at 300 and 700 °C did not show any localized attack in HNO3 and this was attributed to lack of sensitization at 300 °C and de-sensitization at 700 °C.

On the microstructural evolution in 12% Cr turbine steel during low cycle fatigue at elevated temperature

In order to better understand the physical process of deformation and cyclic softening a 12% Cr martensitic stainless steel FV566 has been cyclically tested at high temperature in strain control. Increase in temperature was found to increase the cyclic life, softening rate and viscous stress magnitude. An increase in the dwell time led to the acceleration of the material degradation. The microstructure changes and dominating deformation mechanisms were investigated by means of scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results have revealed a gradual sub-grain coarsening, transformation of lath structure into fine equiaxed subgrains, and misorientation angle development in blocks and packets until material failure. The softening behaviour was attributed to the mutual annihilation of the dislocations and rearrangement of the residual dislocation in the low energy structures.

Influence of tempering treatments on mechanical properties and hydrogen embrittlement of 13 wt% Cr martensitic stainless steel

The influence of tempering treatments on mechanical properties and hydrogen embrittlement (HE) of 13 wt% Cr martensitic stainless steel (MSS) have been investigated by Charpy impact tests and slow strain rate tensile (SSRT) tests followed by fracture surface examination. The austenitized and quenched specimens were tempered at 300, 550 and 700 °C for 2.5 h. The MSS tempered at 550 °C showed brittle intergranular (IG) fracture after impact tests indicating its susceptibility to temper embrittlement. The experimental results showed that the 13 wt% Cr MSS is sensitive to HE. The as-quenched condition showed cracking during hydrogen pre-charging itself. Hydrogen pre-charging duration increased the susceptibility to HE of tempered MSS. The maximum HE susceptibility was observed for specimen tempered at 550 °C with a drastic reduction in strength and strain to failure. Tempering at 300 and 550 °C showed brittle IG fracture with hydrogen pre-charging in SSRT tests whereas increased IG region with ductile dimples was observed for specimen tempered at 700 °C with increase of pre-charging duration. The reason for maximum susceptibility to HE of specimen tempered at 550 °C is due to synergistic interaction of hydrogen and impurities segregated at prior austenitic grain boundaries.

A Comparative Study of Localized Corrosion and Stress Corrosion Cracking of 13Cr Martensitic Stainless Steel Using Acoustic Emission and X-ray Computed Tomography.

An accurate evaluation of stress corrosion cracking (SCC) in 13Cr martensitic stainless steel (MSS) is still missing due to the lack of an in-situ insight into the process evolution and full characterization of the corrosion morphology. In this work, two main regimes involved in the SCC progression, including localized corrosion and cracking, were comparatively studied using in-situ acoustic emission (AE) monitoring and three-dimensional (3D) X-ray computed tomography (XCT) scanning. The stress corrosion tests were conducted with u-bent smooth specimens subjected to a single droplet of 1 μL 1% neutral NaCl solution. Localized corrosion and cracking evolution were controlled in tempered and quenched steel specimens, respectively. From XCT scanning, localized corrosion was featured by an irregular corrosion pit with deposited corrosion products containing cracks. The single dominant SCC crack was observed to initiate from corrosion pit and propagate with a 3D tortuous and discontinuous morphology. AE signals were detected in both cases. Correlated with in-situ observations and clustering analysis, source identification of AE signals was proposed. AE signals during localized corrosion were assessed to be mainly from cracking within the deposited corrosion products. Comparatively, hydrogen-bubble evolution, plastic deformation, and crack-branches coalescence were proposed as the AE sources of cracking evolution.

Effect of heat treatment on the stress corrosion cracking (scc) susceptibiliy of the 13Cr martensitic stainless steel for steam turbine blade

Two different constant loads have been used to evaluate the effect of heat treatment on susceptibility to stress corrosion cracking (SCC) of 13 Cr martensitic stainless steel in 3.5% NaCl. The steel specimens were austenitized at 1050°C for 1 hour followed by oil quench to obtain martensite structure. Then, specimens were tempered at 400, 500, 600, 650 and 700°C for 1 hour. To investigate the SCC susceptibility, SCC tests were carried out at two different constant loads of 40% and 80% of ultimate tensile strength (UTS) in accordance with the method developed by Nishimura et.al. After the SCC tests, scanning electron microscope (SEM) observations of the fracture surface on the fractured specimens were conducted to investigate fracture mode. The experimental results showed that the 13Cr martensitic stainless steel was highly susceptible to SCC in a solution 3.5% NaCl at high constant load (80% of UTS) in almost tempered conditions. The least susceptible steel was the tempered one at 700°C. At lower constant load (40% of UTS), the highly susceptible steels were the tempered ones at 400 and 500°C. Steels which were tempered at high tempering temperature were not failed for 240 hours of SCC testing. The mechanism responsible for this susceptibility is thought to be secondary phenomenon where carbide precipitation of M7C or M23C6 occurs. The fracture surfaces exhibited intergranular cracks and dimple rupture fracture for steels tempered at 400, 600 and 650°C and transgranular cracks and cleavage fracture for steels tempered at 500°C.

Investigation of corrosion rate on the modified 410 martensitic stainless steel in tempered condition

Martensitic stainless steels were usually used for turbine blade. Their properties can be improved in various ways, such as by heat treatment. This paper reports the influences of tempering temperature and holding time in various concentration and temperature of NaCl solution on corrosion rate of the modified 13Cr martensitic stainless steels. Samples were austenized at 1050°C for 1 hour followed by oil quenching. The austenized sample were tempered at 600°C, 650°C, and 700°C for 1, 3, and 6 hours. All tempered specimens were immersed in 20% NaCl concentration for 120 hours and tempered specimen at 700°C for 6h was prepared for another corrosion test. Samples were immersed in different concentration of NaCl solution 3.5%; 10%; and 20% at room temperature, 60°C, and 80°C. Increasing temperature and concentration of solution will lead to corrosion rate increased. However, corrosion rate slightly decreases at higher temperature due to dissolved oxygen was decreased.

Passivity breakdown of 13Cr stainless steel under high chloride and CO2 environment

Herein, the effect of high chloride ion (Cl−) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO2 environment was demonstrated. The Cl− concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl− concentration on the corrosion potential (Ecorr), passive breakdown potential (Epit), and repassivation potential (Erep). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl− concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl− concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model (PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl− concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.

Passivity of martensitic stainless steel in borate buffer solution: Influence of sulfide ion

Upon performing electrochemical measurements, XPS and TEM characterizations, the influence of sulfide on the passive behavior of Super 13Cr martensitic stainless steel was deciphered. Mechanism interpretation is performed by optimizing the Point Defect Model based upon the impedance data. It is revealed that the passive film display n-type semiconductivity, and the donor density dropped with increasing concentration of sulfide ion. Sulfide ion can induce a current peak at −250 mVSCE (Epeak). The addition of Na2S generates a continuous outer layer which is comprised of Cr(OH)3, FeS2 and FeS at potential lower than Epeak, and Cr(OH)3 at potential higher than Epeak. This result leads to the thinner barrier layer and lower charge transfer resistance, implying a weaker protection of the substrate by the passive film.

Effects of solution composition on corrosion behavior of 13 mass% Cr martensitic stainless steel in simulated oil and gas environments

The effects of CH₃COONa and CO₂ on the corrosion behavior of 13 mass% Cr martensitic stainless steel in simulated oil and gas environments were investigated with electrochemical and surface analysis techniques. The electrochemical results showed that a plateau region and sudden increase in the current density of the anodic polarization curves. The current density of the plateau region decreased with increasing CH₃COONa concentrations. The pitting corrosion potential shifted to the positive direction with increasing CH₃COONa concentrations, and shifted to a negative value by adding CO₂. From the surface analysis, a Cr enriched layer had formed on the sample surface after immersion tests, and the thickness of this layer became thinner with increasing CH₃COONa concentration. The surface analysis results after the immersion tests suggested the presence of CH₃COO⁻ or HCO₃⁻ on the surface.

Effects of Heat Treatments on the Corrosion Behavior of 13Cr Stainless Steels in Chloride Solutions Containing Carbon Dioxide

Various electrochemical measurements were adopted to explore the effects of heat treatments on the corrosion resistance of 13Cr martensitic stainless steels in Cl– solutions containing carbon dioxide. Phase contents and lattice strains were measured by Matlab image processing and X-ray diffraction, respectively. The compositions of passive film were tested by X-ray photoelectron spectroscopy. The results showed that the enhancement of austenitized temperature can improve the pitting resistance, whereas uniform corrosion resistance can be injured by the formation of retained austenite. The quenched specimen exhibited enhanced passivation stability in long-term immersion tests. Tempering at 280°C as the optimum process can guarantee 13Cr stainless steel a refined microstructure with reasonable internal stress and easy to obtain an intact protective passive film, which can serviced in complicated CO2 and Cl– corrosion environment.