Effect of carbon content on austenitic stability of as-cast Mn6 series steel
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Effect of carbon content variation on microstructure of as-cast Mn6 series steel was analyzed.The relationship between carbon content and austenite stability of as-cast Mn6 series steel was studied.The results show that when the carbon content is below 0.93%,pearlite and martensite can been partly observed in as cast solidification microstructure,when the carbon content is 1.19%,the solidification structure was whole austenite.Whereas when the carbon content reaches 1.28%,the secondary carbides are precipitated during the solidification.The 1.19% carbon content was an important demarcation point of austenite stability.Keywords:
Carbon fibers
High carbon
Content (measure theory)
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In order to investigate the evolution law of carbide in GCr15 bearing steel during heat treatment,the thermodynamic behavior of carbide precipitation was analyzed by Thermo-Calc software.The fine structure of the tested steel after different heat treatment was studied by means of OM,SEM,XRD and TEM.The results indicate that the microstructure is largely influenced by the combined effects of C and Cr content,the microstructure of GCr15 consists of acicular martensite with high density of twins,dispersed spheroidized carbide with the size of 200-500 nm,and retained austenite after quenching process.The content of austenite decreases with the increasing of tempering time,and carbides about 10 nm length are precipitated in the martensite because of the diffusion of interstitial carbon atoms.
Tempering
Acicular
Carbon fibers
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The microstructure of a new low carbon HSLA steel with a high tensile strength and a high toughness in the as-hot forged condition for automotive parts was observed in detail in an 0.12% C-2% Mn-1% Cr-0.25% Mo-0.12% Nb-0.021% Ti-0.0018% B steel. Lath-like microstructure observed at the cooling rate ranging from 250 to 6°C/s mainly was revealed to consist of bainitic-ferrite with retained austenite and auto-tempered martensite. Granular microstructure observed at the cooling rate ranging from 0.17 to 0.04°C/s was characterized to be martensite-austenite constituent islands in featureless matrix. This microstructure is considered to be formed the following process. The neighboring laths of bainitic ferrite coalesced and the length of untransformed austenite shortened and consequently its shape became to resemble islands during slow cooling. Toughness of granular microstructure was lowered by twinned martensite in islands and no boundaries in packets compared with lath-like microstructure. Toughness of the low carbon HSLA steel with as-transformed martensite and bainite microstructure is equivalent or superior to that of conventional medium carbon steels.
Lath
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Duplex stainless steels (d2s) are intended to present a microstructure composed of similar volume fractions of austenite and ferrite; this is the phase composition leading to the best compromise of mechanical and corrosion properties. To stabilize the austenite phase, nitrogen is added as an alloying element in the so-called second generation d2s; nitrogen is a cheap element (compared to nickel, the most common austenite stabilizer) that simultaneously increases the strength by a solid solution hardening effect; usually nitrogen contents in the second generation d2s vary from 0.15 to 0.25 weight %. The effect of a 0.14 % nitrogen addition to a cast d2s with a nominal composition corresponding to EN 10283 has been studied to evaluate its austenite stabilizing effect and its influence on the partition intensity of the elements contributing to the pitting corrosion resistance (chromium and molybdenum) between the two phases composing the microstructure. Two cast d2s have been prepared for this study: one without any nitrogen addition and another with 0.14% nitrogen; both had the same nominal composition. Specimens of the two cast d2s have been heat treated in a range of temperatures from 1050 to 1400°C, every 50°C; after a 2 hour soaking the specimens have been cooled in water. It is known that increasing the solution temperature increases the volume fraction of ferrite in the cast d2s microstructure. Both the volume fraction of each constitutional phase (austenite and ferrite) and the respective chromium and molybdenum content have been measured. The results of the volume fraction measurements showed an intense austenite stabilizing effect of the nitrogen. The results of the microanalysis of chromium and molybdenum showed that both elements present an ability to concentrate in the ferrite, although the molybdenum partition is clearly more intense than the chromium partition.
Volume fraction
Hardening (computing)
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This work aims at the development of carbon steel AISI 1536 through the microalloying addition of boron.Three grades of this steel with different content of boron up to 0.0055% were melted in 100 kg induction furnace.The produced steels were hardened at 960˚C for 30 min., followed by tempering at different temperatures and durations.All hardened steels have martensite phase as illustrated with microstructures and X-ray diffraction.Hardness of all tempered steel samples was measured to calculate the activation energies of carbon migration through martensite phase.The results indicated that the activation energies of carbon migration through martensite phase decreases with the increase of boron content due to its positive effect on the crystallinity of martensite phase.Also, the results showed that the addition of boron up to 0.0023% can improve the steel properties at the lowest temperature and tempered time.
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Heat treatments of DET(Divorced Eutectoid Transformation) and quenching+tempering were carried out to obtain the microstructure of ferrite with ultra-fine carbides for a 1.6%C ultra-high carbon steel.Simultaneously microstructure of quenched steel was observed by transmission election microscope.It is shown that the sub-structure is composed of dislocations and twins.When increasing the time of inducing-heat quenching,the steel shows that the quantity of lath martensite increases but decreases with twin martensite.The mechanical properties are measured to indicate that the ultra-high carbon steel has almost the same intensity as structure steels with moderate carbon and good plasticity,with extension rate 17%.
Lath
Tempering
Carbon steel
Carbon fibers
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The hot deformation process of low silicon TRIP steels with different Nb content was simulated by Gleebe-1500 hot mechanical simulator.The effects of niobium content on microstructures and properties of TRIP steel were studied.The results showed that microstructures of experimental steels were refined and bainite content was increased with the addition of Nb.If Nb content was added,retained austenite fraction and carbon contents of retained austenite decreased,and Vickers hardness and tensile strength increased.When Nb content was 0.014(mass,%),retained austenite fraction was 19.2%,carbon contents of retained austenite was 1.422%,Vickers hardness was 258HV and tensile strength was 851MPa,respectively.
TRIP steel
Vickers hardness test
Mass fraction
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Microalloyed steel
Lath
Carbon fibers
Elongation
Thermomechanical processing
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Volume fraction
Metallography
Pitting Corrosion
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Effect of Manganese on Microstructure and Mechanical Properties of Cast High Alloyed CrM nN i‐N Steels
The effect of the manganese content (0–11%) on the transformation temperatures, the mechanical properties and microstructure development of five highly alloyed 14Cr– X Mn–6Ni cast stainless steels with 0.1% nitrogen was studied. The examinations reveal that the M s , A s , and A f temperatures decrease with increasing manganese contents. As a result of low austenite stability, room temperature austenitic‐martensitic as‐cast microstructure was formed at manganese contents between 0 and 3%. At manganese levels of 6% and higher a fully austenitic as‐cast microstructure was observed. The temperature dependence of tensile properties in alloys was explained on the basis of varying contributions to the strength and ductility of deformation‐induced martensite and twin formation mechanisms. All investigated cast steel alloys achieved yield strengths above 200 MPa at room temperature. The increased proof stress is caused by solid solution strengthening due to the addition of nitrogen and manganese as well as phase hardening by as‐quenched martensite.
Diffusionless transformation
Ductility (Earth science)
Hardening (computing)
Solid solution strengthening
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