Decarburized Layer Research Articles

Enhanced bending fatigue resistance of a 50CrMnMoVNb spring steel with decarburized layer by surface spinning strengthening

Surface decarburization directly influences the service performance of spring steel, which is an important scientific issue. The bending fatigue behavior of 50CrMnMoVNb spring steel with surface decarburization as well as treated by surface spinning strengthening (3S) was systematically investigated in this study. The results show that the decarburized layer was significantly modified by turning into a strengthened layer with gradient microstructure after 3S treatment, and the bending fatigue life of spring steel was effectively extended. Furthermore, a fatigue risk model and the Basquin equation were used to predict the crack initiation site and evaluate the fatigue life respectively. Moreover, the 3S treatment can significantly decrease the fatigue risk of the spring steel surface, which makes the fatigue crack initiation site migrate into the subsurface layer and extend the bending fatigue life. Accordingly, some recommended principles were proposed finally to enhance the fatigue resistance of the surface decarburized spring steel, including surface strengthening, removing decarburized layer, decreasing the size and quantity of inclusion, and homogenizing microstructure.

Meso and microscale clad interface characteristics of hot-rolled stainless steel clad plate

Stainless steel clad plate containing corrosion-resistant 304 stainless steel cladding and Q235 carbon steel substrate has been successfully fabricated by vacuum hot rolling at 1150 °C. The interface characteristics, microstructure, alloy element distribution and precipitation phases of clad plate were investigated by SEM, EPMA and TEM analysis in detail. Due to the carbon element diffusion, a decarburized layer (60–80 μm) and a carburized layer (20–40 μm) were formed at the carbon steel substrate and stainless steel cladding beside the interface, respectively. The uphill diffusion and interface peak value of carbon element are attributed to the differences in the diffusion velocity and solubility of carbon element in the substrate and cladding. Concentration gradient and diffusion coefficient between Cr and Ni elements are different, leading to different diffusion distances. Meanwhile, the grain boundaries of carburized layer were surrounded by Cr23C6 particles. The interface with a thickness of 300–400 nm contains refined grains accompanying with many Cr23C6 and MnSi2O4, SiO2 particles. The sufficient alloy element diffusion behavior and interface oxides, precipitation phases lead to a high interface bonding shear strength (389 MPa).

Mechanism of Carbon Diffusion in the Iron Sheet During Gas–Solid Decarburization

To investigate the diffusion of carbon in the iron sheet during gas–solid decarburization in a weak oxidative atmosphere (Ar + H2 + H2O), the microstructures of iron sheets following decarburization were observed through SEM. The carbon gradient following decarburization in the iron sheet along the thickness direction was detected in this study. The results showed that the iron sheet along the thickness direction following decarburization consisted of three layers: the L1 layer (ferrite phase) that was near the surface, the L2 layer (cementite phase) that was between the L1 + L3 layers, and the L3 layer (cementite + ferrite + graphite phase) that was in the center of the sample. The depth of the decarburization layer (L1 + L2) showed a good linear relation with the square root of the decarburization time. The carbon gradient in iron sheet along the thickness direction was of ladder type during decarburization. The carbon content in the center of iron sheet was influenced by the decarburization time or the temperature. The carbon migration in iron sheet consisted of stable carbon decomposition and free carbon diffusion. The carbon migration in the S2 stage of iron sheet was the controlling step of the entire decarburization process.

Effect of Surface Decarburization on Corrosion Behavior of GH3535 Alloy in Molten Fluoride Salts

Corrosion test of a Ni–16Mo–7Cr alloy with a decarburized layer was conducted in FLiNaK salt at 700 °C. A detailed microstructure study was performed to investigate the corrosion behavior and mechanisms. The results show that the Fe-rich layers were formed on the corroded alloys with and without decarburization. The surface decarburization had little influence on the corrosion resistance of the alloy, whereas it caused more M2C carbide formation beneath the corrosion layer. That is attributed to the higher concentration of C gradient near the alloy surface, which was resulted from the increase in C content liberated from graphite crucible wall during the corrosion process.

Interfacial microstructure and mechanical properties of stainless steel clad plate prepared by vacuum hot rolling

A stainless steel clad plate composed of stainless steel and carbon steel was prepared by vacuum hot rolling process, and its microstructure, especially the bonding interface, was evaluated using an optical microscope, a scanning electron microscope and a transmission electron microscope (TEM). The corresponding mechanical properties were also assessed by means of hardness and shear tests. The results showed a bonding interface formed between stainless steel and carbon steel, which was relatively straight in macroscope but serrated in microscope. Decarburization layer and carbon-enriched layer were distinguished at the side of carbon steel and stainless steel near the interface, respectively, which should be related to diffusion of carbon and alloying elements. The carbon-enriched layer could also be identified as a recombination region, whose microstructure was mainly recognized as martensite by TEM. Consequently, the hardness was the highest at this region. Furthermore, the result of shear test at the bonding interface showed that the shear strength was 395 MPa and the fracture mode was dominated as ductile fracture, indicating the bonding interface with good quality.

Influence of Dew Point on the Selective Oxidation, Microstructure and Mechanical Properties of a High-Al Low-Si Dual Phase Steel during Hot-Dip Galvanizing Process

The effect of dew point on the selective oxidation behavior, microstructure and mechanical properties of a high-Al low-Si dual phase steel is elucidated. The results showed that as dew point is increased from–30°C to +5°C, internal oxidation of alloying elements occurs, and consequently the mass of external oxides decreases, which improves the galvanisability of steel sheets. It was also observed that the dew point had an impact on the microstructure and mechanical properties of the experimental steel. With the increase of dew point, the decarburization layer on the surface was increased, leading to inferior mechanical properties. Compared with the industrial steel, the high-Al-low-Si DP steel exhibited excellent galvanisability under identical annealing conditions.

Influence of hot rolling on microstructure and mechanical characteristics of explosive-welded FSS/CS laminate

The influence of hot rolling on the microstructure and subsequent mechanical characteristics of explosive-welded ferritic stainless steel (FSS)/carbon steel (CS) laminate was investigated. The results indicate that by hot rolling, decarburization layer disappears and a uniform structure is gained in CS side, but ferrite grains and carbides in constituent FSS form an uneven band microstructure which is denser at superficial zone than near the interface. The transmission electron microscopy results indicate that the layers adhering to the interface show typical deformed microstructure features, i.e., stream-like strips and elongated grains in FSS plates, carbide precipitates and bended cementite fragments in CS plates; and high-density dislocations in both plates. With hot rolling, various mechanical strengths and hardness are increased, while the elongation percentage is diminished. Examination of fractographs from tensile tests reveals predominately small dimples for explosive-welded specimens, whereas both big dimples and cleavage fracture for rolled specimens. Stereomicroscopic fractographs taken on shear samples indicate that the surfaces of explosive-welded specimens exhibit uniform deformation, but uneven deformation is displayed for that of rolled specimens. These results indicate that hot rolling is beneficial to improve the strength of explosive-welded FSS/CS laminate but not good for enhancing its plasticity.

A Method to Control the Transverse Corner Cracks on a Continuous Casting Slab by Combining Microstructure Analysis with Numerical Simulation of the Slab Temperature Field

In the current article, a method based on analysis of the microstructure combined with numerical simulation of the temperature field of a continuous casting slab is proposed to eliminate the transverse cracks occurred in slab corners. The microstructures near the cracks will be varied as the phase‐transformation conditions change. Thus, the cracking temperature range can be effectively estimated by analyzing the microstructures near the cracks. The different behaviors of microstructures near cracks in three conditions are presented and discussed. These behaviors include the following: the decarburization layer is symmetrically distributed on both sides of the cracks; the microstructures are refined near the cracks; the cracks “open” the ferrite along the austenite grain boundaries, which results in the ferrite being symmetrically distributed on both sides of the cracks. The variation of the slab corner temperature during a continuous casting process is calculated and discussed. Then, a secondary cooling adjustment scheme is proposed to eliminate the occurrence of transverse corner cracks on the slab surface. Results from industrial practice show that the method can effectively avoid the generation of slab surface cracks without damage to the internal quality of the slab. The method can also be applied to other studies of crack control.

Reduction of Wustite Scale by Dissolved Carbon in Steel at 650–900 °C

The reduction behaviour of wustite-type iron oxide scale on a low-carbon, low-silicon steel by dissolved carbon in the steel at 650–900 °C under pure nitrogen was studied. It was found that dissoved carbon in the steel examined was able to react with the wustite scale on the surface, leading to reduction of this scale. It was also found that the scale reduction rate was the most rapid within 750–800 °C, followed by that at 700 °C and then at 850 °C, whereas the rates were essentially zero at 650 and 900 °C. Decarburization occurred to the steel as a result of scale reduction, and the degree of decarburization at 750–800 °C was also the most severe. The rate of scale–carbon reaction was primarily controlled by carbon diffusion through the decarburization layer as the calculated carbon permeability, defined as the product of carbon diffusivity and the carbon concentration difference across the decarburization layer, also reached its maximum within 750–800 °C. Scale reduction led to the formation of pores at the scale–steel interface as a result of volume shrinkage when wustite was reduced to iron, but the porosity volume was smaller than calculated at 800–850 °C, which could have an inhibiting effect on the scale–carbon reaction. The calculated volume of CO + CO2 gases generated as a result of scale–carbon reactions was about 100 times the calculated porosity volume. It was believed that the wustite scale was permeable to CO and/or CO2, allowing the much larger volume of CO and CO2 gases to escape through the scale layer.

Using architectured materials to control localized shear fracture

A medium carbon steel was partially decarburized to create a compositionally graded material consisting of a surface layer with 0.1 wt% C and a core with 0.4 wt% C. The graded material was heat-treated to produce a martensitic microstructure which was subsequently cold-rolled in the as-quenched state. Localized shear bands developed within the core region during the rolling process. The shear bands did not, however, penetrate the outer decarburized layer. In this way, it was possible to roll 0.4 wt%C martensite, in the as-quenched state, to equivalent strains in excess of 2. The microstructure evolution of the cold-rolled martensite was followed using optical microscopy, Electron Back Scatter Diffraction (EBSD), Transmission Electron Microscopy (TEM) and nano-indentation. The development of shear bands is interpreted in terms of the collapse of martensite blocks during deformation, leading to geometric softening and shear localization within the high carbon core.

Formation and evolution of macro inclusions in IF steels during continuous casting

The evolution of macro inclusions during continuous casting was investigated by large-area inclusion characterization using ASPEX and analysis of nozzle blockage deposits. Six kinds of inclusions over 5 μm were observed in samples taken from the tundish and the slabs: single alumina particles, alumina dendrites, refractory-related alumina, alumina associated with bubbles, alumina clusters and Al–Ti complex oxides. By examining the morphology of the nozzle blockage deposit, it was concluded that the refractory-related alumina in the slabs came from the decarburization layer washed away by the steel stream. Some of the alumina clusters that came from the nozzle blockage deposit dislodged by the steel flow, were formed by the agglomeration and sintering of 5–20 μm inclusions that were carried over from the tundish. Two kinds of Al–Ti oxides were found in the tundish, and their evolution mechanisms during the casting process were proposed.

Public Traffic Type Escalator Driving Chain Broken: A Failure Analysis

The main drive chain of escalator is an important part of power transmission. In this paper, combined with an Escalator driving chain failure case, by taking a variety of analytical methods, such as visual inspection, chemical composition analysis, and microstructure, analysis on the cause of driving chain failure. According to analysis, we can conclude that the fracture of the drive chain is caused by the stress concentration effect of the bending stress of the transition plate, and the decarburization layer on the surface of the chain plate reaches 3. 5% of the plate thickness, which accelerates the occurrence of fatigue cracking. So in the process of design and manufacture, the rationality of material, manufacturing and assembly process should be fully considered. Also in the use of the drive chain due to wear, impact, etc., to achieve the service life should be replaced in a timely manner.

Failure analysis of an exploded CO2 gas cylinder

Abstract This paper presents the analysis and subsequent recommendations towards prevention of failure in an IS 7285 type 2 cylinder which is seamless gas cylinder grade steel. The region of fracture showed the presence of an oxidized zone in the inner walls of the CO2 gas cylinder along with a fresh surface. Visual observation showed presence of multiple small cracks at the inner surface. Microstructural examination with optical and scanning electron microscopes revealed that the cracks were associated with scale indicating their pre-existence. A decarburized layer was also observed at the inner surface. The stress intensity factor (K1C) estimated at the crack tip upon consideration of the pressure inside the cylinder surpassed the fracture toughness of the material. Exposure to direct sunlight elevated the temperature of the CO2 gas wherein it behaved as a supercritical fluid occupying the entire volume of the cylinder with a pressure higher than ambient. At a particular density, above 48–54 °C, this pressure increased abruptly, beyond the limit offered by the pressure valve resulting in explosion. Periodic checking of pressure valves and proper quality assurance system enabled by NDT techniques were recommended for the prevention of such catastrophic failures.

Decarburization mechanism during hydrogen reduction descaling of hot-rolled strip steel

The removal of the oxide scales using hydrogen reduction will become a promising process compared to traditional pickling descaling due to its advantage for eliminating environmental pollution. However, decarburization occurs with the reduction of oxide scales and degrades the microstructures and properties of strip steel. To understand why decarburization occurs, a reduction experiment and a decarburization experiment on plain carbon steel were performed using a tubular furnace. The surface morphologies and microstructures of the cross-sections of the samples were observed by OM and SEM, and the weight losses of the samples were measured using a precision balance. The weight loss curves for hydrogen reduction and decarburization were plotted based on the experimental data. The decarburization mechanism is discussed in detail. The results show that the oxide scales reduce to pure ferrite and form a reduction layer on the surface of the strip steel after hydrogen reduction. A decarburized layer forms between the reduction layer and steel substrate. Decarburization is mainly caused by water vapor from the reduction of the oxide scales in a hydrogen atmosphere. Decarburization occurs simultaneously with the reduction of the oxide scales. The overall weight losses include deoxidation losses as well as decarburization losses.

Effects of decarburization on the wear resistance and damage mechanisms of rail steels subject to contact fatigue

Decarburization can remain on the surfaces of rail head steels and affect their wear and damage processes. The current research explored the influence of a decarburized layer on wear resistance and damage behavior of rail materials using a rolling–sliding wear testing machine. A decarburized layer decreases the hardness and wear resistance of rail steels, and the wear rate of a decarburized rail is over twice that of the same steel without decarburization. Multi-layer peeling appears on rail rollers without decarburization, but a decarburized layer changes the damage mechanism of the rail steel. With an increase in the depth of decarburization, the damage of rail roller turns from major spalling to pitting and peeling. In addition, surface fatigue cracks become more serious as depth increases. By contrast, shallow decarburization has little effect on rolling contact fatigue (RCF) of the rail material. Only when the depth of the decarburization exceeds a certain thickness (i.e., about 0.5mm based on the present results), RCF damage sharply worsens as decarburization depth increases. Furthermore, adhesive wear features are obvious on the rail roller only when a decarburized zone remains at the wear surface.

High-Temperature Oxidation and Decarburization of 14.55 wt pct Cr-Cast Iron in Dry Air Atmosphere

The oxidation and decarburization behavior of 14.55 wt pct Cr-cast iron at 1273 K to 1423 K (1000 °C to 1150 °C) in a dry air atmosphere was studied. A gravimetric investigation showed that intensive oxidation of cast iron takes place at temperatures above 1273 K (1000 °C). It is found that oxidizing heating is accompanied by decarburization, which manifests itself in secondary and eutectic carbide dissolution. The volume fraction of carbides decreases with temperature and holding duration increasing. Decarburization results in the formation of a decarburized layer up to 4 mm in depth. A carbide-free layer in depth up to 100 μm appears in the free surface after 6 to 8 hours holding at 1373 K to 1423 K (1100 °C to 1150 °C). Preliminary activation energy calculations suggested that the eutectic carbide dissolution at the depths of 50 to 400 μm is controlled by carbon diffusion in austenite. The dissolution of eutectic carbides involves a capillarity-induced mechanism, which consists of formation and growth of capillary cavities inside carbides.

Влияние плазменной резки на микроструктуру и твердость высокопрочной стали

The application of high-strength steels during the creation of products satisfying all the modern requirements of the market is one of the most promising areas of modern engineering. The use of these steels reduces metal consumption of produced constructions due to reducing the thickness of the metal while maintaining the same structural strength, increases the service life of products thanks to increasing durability, as well as improves the reliability of the produced product. The processing of high-strength steel has a number of features associated with increased sensitivity of such steels to a thermal effect. The aim of this study is to research the influence of plasma-arc cutting on the microstructure and hardness in the heat-affected zone of high-strength steel having hardness of 500 HBW. To do that, the research of microstructure in the heat-affected zone of plasma-arc cutting of high-strength steel with 500 HBW hardness was performed. The results of research showed the presence of parts with different structures and properties in the heat-affected zone of plasma-arc cutting: decarburized layer, hardening layer, incomplete quenching layer, tempering layer, and the base metal. While moving off the boundary of the cut the cooling rate and temperature of metal are reduced. It is the cause of lowering steel hardness. The microstructure of the base metal has a needle form, and consists of strips of different orientation and size. The structure of different parts of the heat-affected zone are: hardening layer – martensite, incomplete quenching layer – martensite + ferrite, tempering layer – tempered martensite. The total length of the heat-affected zone and the length of its individual sections were also determined.

The Evolution of the Surface Morphologies and Microstructures of an Unleveled Hot-Rolled Steel Strip During Cold Rolling After Hydrogen Reduction

The removal of oxide scale from a hot-rolled strip surface can completely eliminate environmental pollution if performed by hydrogen-reduction descaling instead of traditional pickling descaling. However, a large number of cracks appear on the surface of a leveled hot-rolled steel strip after hydrogen reduction. This effect is likely to impede the application of reduction descaling to cold-rolled products. Nevertheless, there are almost no cracks on the surface of an unleveled hot-rolled steel strip if the hot-rolled steel strip is not subjected to repeated bending by the leveler machine. The surface quality of a reduced steel strip will be better than that of a pickled steel strip. To investigate the evolution of the surface morphologies, microstructures, and properties of an unleveled strip steel during cold rolling, unleveled strip steel samples were rolled using a four-high mill after hydrogen reduction and after pickling. The surface morphologies and cross-sectional microstructures of the samples were observed by SEM, and the surface-roughness values were measured using a TR200 profilometer before and after cold-rolling deformation. The evolution of the surface morphologies and cross-sectional microstructures of the sample after cold rolling were analyzed. The results show that the oxide scale formed on the surface turns into a metallic iron layer, and a decarburization layer appears between the metallic iron layer and the steel matrix after hydrogen reduction. Few cracks, besides pores, and bubbles, appeared on the surface of the sample after hydrogen reduction. The pores and bubbles were roll-flattened after five passes of cold rolling. The work hardening degree and mechanical properties of the reduced sample are similar to those of the pickled sample after cold rolling. Compared with the rolled sample after pickling, the surface qualities of the reduced samples are better than those of the pickled samples and better than those of the reduced samples that were subjected to leveling prior to reduction.

Heat treatment of rollers in the ShPS 30-80 ball-rolling mill at JSC DMPZ

In the production of steel rollers, surface decarburization may occur in the course of heating before quenching. Means of more effective protection against such decarburization are considered in the case of the 35X CA steel barrel of wrapped rollers for the ShPS 30-80 ball-rolling mill. A technological protocol for the heat treatment of the rollers is developed. It is shown that protection by means of nitrogen + a carburizing agent + a muffle increases the likelihood of the desired outcome (no decarburized surface layer and hardness no less than 45 HRC) by 31.9% in comparison with protection by means of Barier protective compound + a carburizing agent + a muffle. On average, 450–470 t of grinding balls (diameter 40 mm; hardness groups III and IV) may be rolled in a complete run (to regrinding) on rollers heat-treated by the proposed protocol.

Skin effect of WC–8 wt% Co alloy by microwave sintering

To investigate the microwave effect on the WC–Co alloys, WC–8 wt% Co alloy was fabricated by microwave sintering (MWS) in this paper. The results show that decarburization layer forms on the surface of the microwave-sintered samples. WC grain coarsening in the core area is strongly suppressed by the decarburization effect. In addition, the microstructure of the MWS-fabricated alloy was compared to that of the alloy sintered by vacuum sintering (VS). Microstructural investigations by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) show that more tungsten (29.50 wt%) is dissolved in the cobalt binder phase in microwave-sintered alloy than that in the vacuum-sintered samples. Finally, the formation mechanism of the surface layer by skin effect was discussed.