High-carbon Martensitic Steel Research Articles

Effect of Spheroidizing Annealing Process on Microstructure and Properties of Quenching and Tempering 60Cr16MoMA Martensitic Stainless Steel

The effect of spheroidizing annealing on carbide characteristic parameters, mechanical properties and wear resistance of the quenching and tempering (Q&T) high carbon martensitic stainless steel is investigated. The microstructure of the steel is characterized and analyzed through various techniques, including scanning electron microscope (SEM), X‐ray diffraction (XRD), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM). Results show that the microstructure of the annealing steel is mainly composed of ferrite and M23C6 carbide. With the rise of austenitizing temperature, the average diameter of carbide of the annealed steel increases. The average diameter of carbides in the Q&T steel changes in the same way as that observed in the annealed steel. The steel has the lowest annealing hardness, highest Q&T toughness, and wear resistance at an annealed soaking temperature of 860 °C. The influence factor of the toughness and wear resistance can be identified that small‐sized carbides and low angle grain boundaries exhibit strong interface adhesive strength. This reduces the probability of cracking in the particle or at the interface.

Corrosion resistance of nitrogenated high-carbon martensitic stainless steel designed and produced at nitrogen low pressures

A new martensitic stainless steel with high nitrogen and carbon content at low pressures was designed using the CALPHAD method. The chemical composition of the steel was checked by optical emission spectrometry, obtaining 0.17 wt%-N and 1.33 wt%-C. Scanning electron microscopy (SEM) analyses were carried out for microstructural characterization. The properties of the steel were assessed by Rockwell hardness and potentiodynamic polarization tests in 0.6M NaCl. The steel showed maximum hardness values of 60 HRC, regarded as a hard material. However, the passive film formation was prevented by the high carbon content promoting excessive Cr-rich carbides.

Influences of partial substitution of C by N on the microstructure and mechanical properties of 9Cr18Mo martensitic stainless steel

Large eutectic carbides presenting in the matrix deteriorate the mechanical properties of high carbon martensitic stainless steel. In the present work, nitrogen-alloyed martensitic stainless steel with different C/N ratios were designed by partial substitution of C by N of 9Cr18Mo, and their microstructure and mechanical properties were investigated. The results show that, with increasing the content of N up to 0.15 wt% in the experimental steel, the quantity and the size of eutectic carbides decrease； and the net-work eutectic carbides are gradually eliminated. The microstructure of all the steels is composed of lath martensite, twin martensite and M23C6 carbides. With partial substitution of C by N, the morphology of martensite blocks evolves from a lath shape to a blocky one, the quantity of twin martensite increases, and the nano-scaled Cr2N nitrides precipitate in the martensite matrix. The steel containing 0.15 wt% N exhibits the hardness of 60.5 HRC, a fracture strength of 1900 MPa and an elongation rate of 1.6 % due to hot rolling and heat treatment, which is attributed to the refinement of carbides and grains, solid solution of C and N, as well as the dense dislocation.

Evolution of primary carbides during accelerated solidification process of high-carbon martensitic stainless steels

In order to evaluate the potential application advantage for development of sub-rapid cooling strip casting of high-carbon martensitic stainless steels, the effects of cooling rate on the solidification microstructure, solute element segregation, and primary carbide precipitation in high-carbon martensitic stainless steels were investigated using an association of high-temperature confocal laser scanning microscopy (HT-CLSM), optical microscopy (OM), scanning electron microscopy (SEM) and electro-probe microanalysis (EPMA). As a result, the microstructure becomes more refined and the secondary dendrite arm spacing (SDAS) decreases greatly by 51 μm from 65.9 μm as the increase of cooling rate from 30 to 6000 °C·min−1. The equation of SDAS versus cooling rate was formulated as λ2 = 191.62·RC−0.317. Solute elements are enriched in the inter-dendritic region, leading to the precipitation of primary carbides. The elemental segregation ratio reduces by more than 20 % for all elements, meanwhile, the size of primary carbides decreases significantly and the mean area fraction of the primary carbides decreases from 4.77 % to 0.82 % with increase of cooling rate from 30 to 6000 °C·min−1. Moreover, the reticulated carbides gradually become less continuous. Despite the type of carbide is not sensitive to the cooling rate, the content of Cr and Fe in the primary carbide is sensitive to cooling rate. Compared to the reported methods, sub-rapid cooling of strip casting shows great advantage in control of primary carbides of high-carbon martensitic stainless steels.

Evolution of M7C3 carbides near the solidus and the influence of Mn element on the formation of M23C6 carbides in a high carbon martensitic stainless steel 90Cr18MoV

The evolution behavior of M7C3 carbides in a 90Cr18MoV martensite stainless steel during high temperature diffusion annealing treatments at temperatures near the solidus was investigated. Results showed that only M7C3 carbides dissolved, and the dissolution of large-sized M7C3 carbides was limited when the temperature was below the solidus. However, when the temperature was above the solidus, a certain amount of liquid phase appeared around the grain boundaries. Meanwhile, two different types of precipitates appeared within the grains. And these two types of precipitates were eutectic products that mainly consisted of M7C3 carbides and bcc phase, and divorced eutectic products that mainly consisted of M23C6 carbides, respectively. Thermodynamic calculations indicated that with the increase of Mn content, the Gibbs free energy of M23C6 carbides would be lower than that of M7C3 carbides. Thus, the difference in Mn content was the main reason for the formation of those two types of precipitates, i.e., M7C3 carbides were formed in regions with low Mn content and M23C6 carbides were observed in areas with high Mn content.

Effect of Quenching and Tempering Processes on Sharpness of Knives Made from 6Cr13 High-Carbon Martensitic Stainless Steel

Effect of Quenching and Tempering Processes on Sharpness of Knives Made from 6Cr13 High-Carbon Martensitic Stainless Steel

Mapping of lattice distortion in martensitic steel—Comparison of different evaluation methods of EBSD patterns

To visualize the varying tetragonal distortions in high carbon martensitic steels by EBSD, two different approaches have been applied on backscattered Kikuchi diffraction (BKD) patterns. A band-edge refinement technique called Refined Accuracy (RA) (Oxford Instruments) is compared with a technique called Pattern Matching (PM), which optimizes the fit to a simulated BKD signal. RA distinguishes between hypothetical phases of different fixed c/a, while PM determines a best fitting continuous c/a by projective transformation of a master pattern. Both techniques require stored BKD patterns.The sensitivity of the c/a-determination was tested by investigating the microstructure of a ferritic steel with an expected c/a=1. The influence of the Kikuchi pattern noise on c/a was compared for a single or 40 averaged frames per measuring point, and turned out to be not significant. The application of RA and PM on the martensitic microstructure delivered qualitatively similar maps of c/a. The comparison of RA and PM shows that RA is suitably fast and precise during mapping the martensite c/a ratio in analyses of high carbon martensite, especially for fast initial surveys. As RA leads quantitatively to higher noise in c/a, the PM analysis can be used for higher precision results.

Numerical Investigation on the Electroslag Remelting of High Carbon Martensitic Stainless Steels

Control of solidification structure and segregation is crucial to improve the service performance of high carbon martensitic stainless steels. Design of the electroslag remelting (ESR) process based on the essential parameters of melting rate, filling ratio, and slag thickness is a precondition to achieve optimal control of solidification structure and segregation of the steels. However, there is still a lack of coupled works giving deep insight into the overall effect of the parameters on the expected control. With this background, a 2D numerical model was established to probe into the effect of process parameters. The results showed that: (1) With the increase of melting rate from 90 kg/h to 180 kg/h, the molten metal pool depth increased by about 4 cm. Meanwhile, the center LST, PDAS, and SDAS increased by about 450 s, 100 μm, and 12 μm. The segregation index of C and Cr increased by about 0.15 and 0.09. (2) As the filling ratio increased from 0.16 to 0.43, the depth of the metal pool decreased by about 4.5 cm, LST and SDAS received a slight increase of about 41 s and less than 5 μm, but PDAS had little change. The segregation index of C had an increase of about 0.03, but the segregation index of Cr demonstrated tiny changes. (3) As the slag thickness increased from 0.08 to 0.14 m, the metal pool depth presented a first increase of about 1 cm and then a slight decrease. The center LST, PDAS, and SDAS first increased by 148 s, 30 μm, and 4 μm and then decreased slightly. The changes of the segregation index of C and Cr presented a similar tendency than that of LST, but the changes are extremely small. (4) A low melting rate less than 120 kg/h, a filling ratio of about 0.23–0.33, and a slag thickness of 0.08–0.10 m were appropriate to obtain good performance for ESR of high carbon stainless steels in this study.

Underlying Mechanism for “Loss of Passivation” Effect of a High-Carbon Martensitic Stainless Steel Coating via Laser Cladding

Recently, laser cladding (LC) technology has become a cost-effective and convenient method to protect metal substrate from corrosion by producing metal coating with high corrosion resistance. In order to fully investigate the pitting mechanism for high carbon martensitic stainless steel (HMSS) coating, the microstructure and pitting performance of high-carbon martensitic stainless steel (HMSS) samples, which were produced via laser cladding (LC) and hot isostatic pressing (HIP) were comparatively investigated via electrochemical measurements and electron microscopies. Dendritic and network connected M23C6 carbides are the main precipitates in the HMSS coating, while the M23C6 carbides in HMSS bulk are spherical or elongated in shape. Pitting resistance of the HMSS coating is dramatically deteriorated. The massive and continuously distributed dendritic M23C6 carbides could form a large-area cathode and cause the micro-galvanic corrosion of the HMSS-LC coating matrix, thus can be considered as underlying factor for the “loss of passivation (LOP)” effect of the HMSS coating.

Investigation on carbide dispersion modified by magnesium and rare earth in high-carbon martensitic stainless steel

Fine and uniform carbides play a beneficial role in the high hardness and wear resistance of martensitic stainless steel. This paper investigates the effect of magnesium and rare earth(RE) on the dispersion of carbides in a high-carbon martensitic stainless steel. The results show that RE-Al-O and RE-Al-O-S inclusions were generated in RE-containing steel, while Mg-Al-O+(Ca, Mn)S and MgO+CaS inclusions were in Mg-containing steel. MC, M7C3, and M23C6 types of carbides were detected in both RE-containing and Mg-containing steels, which is consistent with thermodynamic calculation. The RE-Al-O inclusion can act as heterogeneous nuclei for carbides, while Mg-containing inclusions do not promote carbide precipitation for sulfur enrichment. The three-dimensional etching test suggests that RE-containing steel has more serious network carbides and larger carbide sizes than Mg-containing steel. The carbon segregation ratio presents an “M” shape due to δ→γ phase transformation. Rare earth is easy to combine with S and weaken the inhibiting effect of carbon segregation. Thus, magnesium has a stronger inhibitory effect on carbon segregation than rare earth.

Formation and evolution of primary carbides in high-carbon martensitic stainless steel

Formation and evolution of primary carbides in high-carbon martensitic stainless steel

Wear resistance of an additively manufactured high-carbon martensitic stainless steel

The dry sliding wear behaviour of a high carbon martensitic stainless steel (HCMSS) consisting of ~ 22.5 vol% of chromium (Cr)- and vanadium (V)-rich carbides processed by electron beam melting (EBM) has been captured. The microstructure consisted of martensite and retained austenite phases with a homogeneous distribution of sub-micron-sized V-rich and micron-sized Cr-rich carbides, leading to relatively high hardness. The CoF decreased ~ 14.1% with increasing load in the steady-state, due to the material transferred from the wear track over the counterbody. The wear rate of the HCMSS compared to martensitic tool steel processed in the same manner, and it was nearly identical under low applied load. The dominant wear mechanism was removal of the steel matrix through abrasion, followed by the oxidation of the wear track, while three-body abrasive wear occurred with increasing load. A plastically deformed zone beneath the wear track was revealed through cross-sectional hardness mapping. Specific phenomena occurred with increasingly aggressive wear conditions were described with carbide cracking, pull-out of V-rich carbides and matrix cracking. This study revealed the wear performance of the additively manufactured HCMSS, which could pave the way for producing components for wear-related applications ranging from shafts to plastic injection moulds via EBM.

Effect of Alloying Elements on the Sharpness Retention of Knife Blades Made of High Carbon Martensitic Stainless Steels

Blades usually become blunt as the blade tip suffers wear during cutting, and improving the sharpness retention of steel blades has become an attractive prospect in various industries. In this study, blades were fabricated from commercial high carbon martensitic stainless steels (154CM, 440C and N690) with different contents of alloying elements. 154CM with higher Mo content demonstrated superior capability in sharpness retention to 440C and N690, although these steels exhibit similar chemical composition, carbide phases, microstructure and HRC hardness. Further investigations via SEM and nanoindentation indicated that the faster deterioration of sharpness in 440C and N690 may result from the fatigue peeling of the carbides, which was aggravated by the modulus mismatch between carbide particles and the martensitic steel matrix.

Microstructure and mechanical properties of a continuous carbon-gradient sheet steel

To take advantage of the high strength of high-carbon martensitic steel and simultaneously avoid insufficient plasticity, a novel continuous carbon-gradient sheet steel (CGSS) with a high-carbon surface and medium-carbon core was developed as a gradient material using surface carburizing and warm rolling. An exceptional strength–ductility combination was achieved. On the premise of carbides precipitation in high-carbon martensitic matrix, tempered CGSS at 200 °C exhibits excellent mechanical property with an ultimate tensile strength of 2440 MPa and a total elongation of 4.6%. Enlarged-strain-component in the tensile direction is the primary cause for higher plasticity in the high-carbon surface. Inhomogeneous fracture mode indicates the typical restraint of crack propagation in the core, suggesting greater toughness for the tempered CGSS.

Effect of heat treatment on the chromium‐depleted zones of a high carbon martensitic stainless steel

AbstractHeat treatments are commonly applied in the martensitic stainless steels to achieve high wear resistance and hardness; however, they can lead to a decrease in corrosion resistance due to the precipitation of chromium‐rich carbides. The present work investigates the effect of austenitizing and tempering parameters on the microstructure, hardness, and passivation and reactivation currents of AISI 440C. A double‐loop electrochemical potentiodynamic reactivation test is performed to evaluate the dissolution and precipitation of chromium‐rich carbides. The volume fraction of phases after heat treatment is estimated by X‐ray diffraction. Results show that an increase in the austenitizing temperature leads to an increase in the carbide dissolution, and also in the amount of retained austenite. As a consequence, low passivation and reactivation currents are obtained. When austenite is the main phase, the increase of austenitizing time contributed to an increase in the degree of sensitization due to austenite grain boundary carbon enrichment. However, the presence of austenite after tempering kept part of the carbon in a solid solution resulting in low passivation and reactivation currents.

The effect of quench cracks and retained austenite on the hydrogen trapping capacity of high carbon martensitic steels

Hypereutectoid martensitic steels possess excellent hardness levels which make them attractive materials for specific industrial applications. However, they can contain cracks and/or retained austenite after quenching which show a particular interaction with hydrogen (H). Hence, this work evaluates the interaction between H and a martensitic Fe-1.1C alloy by combining a wide variety of (H) characterization techniques with a systematic approach for specially designed H charged and heat treated samples. A detailed analysis of the microstructure for every condition serves as the basis for the interpretation. The results show that the presence of H leads to additional cracking and branching or growth of pre-existing quench cracks. Moreover, it is shown that when the temperature exceeds the retained austenite decomposition temperature while the austenitic grains contain H, additional cracking occurs which increases the amount of reversible H trapping sites thus raising the HE susceptibility.

Hydrogen Desorption Behavior Trapped in Various Microstructures of High-Strength Steels Using Thermal Desorption Analysis

The relationship between different microstructures and hydrogen trapping states of cold-drawn pearlitic (CD-P) steel, medium-carbon martensitic (MC-M) steel, and high-carbon martensitic (HC-M) steel was studied based on the hydrogen desorption profile, activation energy of hydrogen desorption (Ea), and hydrogen release behavior at room temperature by means of thermal desorption analysis (TDA). The TDA results revealed that hydrogen in CD-P and HC-M was present as both Peak 1H and Peak 2H, but only as Peak 1H in MC-M. Hydrogen release behavior indicated that Peak 1H for all three types of steel was diffusible (Ea ≤ 34 kJ/mol). For CD-P, Peak 2H was non-diffusible (Ea = 62 kJ/mol), but diffusible for HC-M (Ea = 43 kJ/mol). TDA results combined with SEM and/or TEM observation and XRD analysis clarified that the former hydrogen was desorbed from strained incoherent α/θ interfaces in a detrapping-controlled process. The latter hydrogen was desorbed via trapping sites involved in retained austenite in a diffusion-controlled process. It is essential to judge hydrogen trapping states as either diffusible or non-diffusible by analyzing not only hydrogen desorption profiles but also hydrogen release behaviors and Ea values, taking into account microstructure characteristics related to hydrogen trapping and diffusion processes.

Advanced quantification of the carbide spacing and correlation with dimple size in a high-strength medium carbon martensitic steel

Interparticle spacing in materials science is a key parameter controlling ductile fracture. It is generally evaluated as the distance between particle centers of mass. High strength medium carbon martensitic steels contain a high density of carbides, whose size is non-negligible with respect to the distance between them. Current microstructural quantification methods do not take the shape of analyzed particles into account, thus being not necessarily relevant to materials containing a high density of particles that trigger void nucleation and ductile fracture.This work reports on the potency of a simple full field particle quantification method based on a watershed algorithm that takes the shape and spatial distribution of particles into account. Three microstructures were produced by heat treating a hot-rolled 40CrMo4 steel bar. Cementite carbide populations of each microstructure were quantified using carbon extractive replicas, conventional image processing and application of the developed algorithm. A comparison of results from a full field Voronoi tiling algorithm revealed pronounced differences in the shape of distributions. The watershed-based method was shown to allow efficient interpretation of the relationships between carbide distribution and ductile fracture features.

Carbide Evolution in High-Carbon Martensitic Stainless Cutlery Steels during Austenitizing

The carbide phase is critical in high-carbon martensitic stainless steels (HCMSS) used for cutlery. In this study, carbide evolution during the austenitizing of different HCMSS (5Cr15MoV, 7Cr17MoV, 9Cr14MoV, and 9Cr18MoV) and its effect on the microstructure and mechanical properties are investigated. The statistical analysis of carbides suggests that the dissolution of small-sized secondary carbides ( 0.5 μm). Due to the influence of the elemental diffusion distance, the interfacial energy, and directional dissolution, small-sized carbides are more soluble than large-size carbides, which can be determined by the change of the ratio of Cr/Fe (wt.%) of carbides.

Rolling Contact Fatigue Resistance of Cryogenically Treated AISI 440C Steel

AISI 440C is a high carbon martensitic stainless steel, primarily used in bearing applications. For this study, one group of AISI 440C steel disks was quenched in oil and tempered. Another group was soaked in liquid nitrogen (− 196 °C) immediately after quenching for 5 h and then tempered. The resulting microstructures were analyzed as well as the rolling contact fatigue (RCF) performance using two methodologies, with and without artificial defects. It was found that the microstructural modifications generated by the cryogenic treatments did not improve significantly the RCF resistance of the material. However, this work supports the use of artificial defects as a valid methodology for conducting accelerated rolling contact fatigue experiments.