Transformation Of Residual Austenite Research Articles

Multiphase Microstructure Optimization to Enhance the Mechanical Properties of AISI M35 High‐Speed Steel

It is crucial to conduct in‐depth research on the cryogenic‐treatment mechanism to promote the standardization and industrialization of cryogenic treatment in the high‐speed steel (HSS) industry. In this study, the microstructure and mechanical properties (microhardness and impact toughness) of AISI M35 HSS after deep‐cryogenic treatment (DCT) and conventional heat treatment (CHT) are investigated, and the microstructural characteristics at different stages of CHT and cryogenic treatment are studied. It is indicated in the results that DCT of the steel leads to the formation of fresh martensite from residual austenite, as well as the introduction of more dislocations due to plastic deformation. In addition, the deep‐cryogenic‐treated specimen that is tempered shows increased numbers of martensite blocks and secondary carbide precipitation. The carbides in the steel are mainly V‐rich (MC), W–Mo‐rich (M6C), and Cr‐rich (M23C6). The hardness of the deep‐cryogenic‐treated samples increases by approximately 50 HV1 because of the transformation of residual austenite and dislocation strengthening. Furthermore, specimens that are both deep‐cryogenic treated and tempered exhibit a 30% increase in impact toughness and a more uniform distribution in hardness, likely due to the more homogeneous precipitation of secondary carbides and refinement of martensite.

Comparison of the tribological behavior of quench-tempered ductile iron and austempered ductile iron with similar hardness

The tribological behavior of quench-tempered ductile iron (QTDI) and austempered ductile iron (ADI) with similar hardness was investigated. QTDI was composed of cementite particles, ferrite and spheroidal graphite, whilst ADI was consisted of acicular ferrite, retained austenite and spheroidal graphite. A higher yield strength was obtained for QTDI compared with ADI. Wear tests indicated that QTDI exhibited a lower friction coefficient than ADI. However, ADI had a better wear resistance than QTDI, which was because the transformation of residual austenite into martensite induced by friction stress resulted in the increase of surface hardness. Worn surface morphology indicated that the main wear mechanisms of QTDI was adhesive and abrasive wear. However, the surface fatigue wear was observed for ADI.

Effect of Stabilization Treatment on Size and Properties of Austempered M50 Steel

By using SU‐8010 thermal field scanning electron microscope, JEM‐2100 transmission electron microscope, MHRS‐150 Rockwell hardness tester and X‐ray diffractometer to observe the microstructure and detect residual stress, and the measurement of the hardness and the tensile properties, the effect of stabilization treatment on the microstructure, size change, and mechanical properties of the austempered M50 steel is studied. Results show that the residue of austenite and the carbides precipitated during the bainite transformation after austempering lead to lattice shrinkage, which reduces the size of the bearing ring. The release of quenching stress after tempering increases the size. During austempering and tempering, the size fluctuates between −0.29 and 0.23 mm. After the bearing ring is stabilized for 3 times, the precipitation of filamentous carbides reaches the maximum, and the number of carbides does not increase obviously after 5 times of stabilization. The size fluctuation range is −0.9 to 0.7 μm. After M50 steel is stabilized, the transformation of residual austenite to martensite and the precipitation of carbides increase the hardness, and the coarsening of carbides reduces the ductility. The tensile strength increases from 2550 to 2650 MPa, which is related to the dispersion strengthening of carbides and their pinning effect on dislocations.

Microstructural variations and mechanical properties of deep cryogenic treated AISI M35 high-speed steel tempered at various temperatures

Deep cryogenic treatment applied in high-speed steel yielded promising results, and it was found that tempering played a vital role. This paper systematically studied the effect of tempering temperatures on the microstructural composition (residual austenite, martensite, and carbides) and mechanical properties (Vickers hardness and impact toughness) of AISI M35 high-speed steel subjected to deep cryogenic treatment. An increase in the tempering temperatures facilitated the transformation of residual austenite and the formation of martensite blocks corresponding to a decrease in the number of dislocations. Moreover, the carbide precipitation (secondary carbides and nanoscale carbides) began at a tempering temperature of 350 °C, increased at 450 °C, and reached its maximum at 550 °C. The fracture mechanism on the micro-level could be interpreted as follows: cracks occurred in the carbides with larger sizes (primary carbides and large secondary carbides) and at the carbide/matrix interface, and small secondary carbides decohered at the interface, forming microvoids and facilitating plastic deformation. In addition, the specimen tempered at 150 °C exhibited the highest hardness of 880.4 HV1 due to the highest number of dislocations. The impact toughness of the sample tempered at 550 °C was the best, namely 2.50 MJ m−2, due to an increase in the number of martensite block boundaries and the more homogeneous carbide precipitation.

Kinetics of martensite decay during tempering

The microstructure of steel after quenching consists of martensite and residual austenite. Depending on the tempering temperature and the carbon content in the hardened steel, the following structural changes occur: the transformation of residual austenite into martensite, the decay of martensite into troostite or sorbitol, and with prolonged high—temperature tempering and annealing — into a ferrite-perlite structure. This article describes the kinetics of the decay of martensite during tempering using computer metallography, based on the obtained photos of the microstructure. The article will be useful for a deeper understanding of the process of decomposition of martensite during tempering.

Investigation of the Effect of Boundary Condition on the Property of TRIP Steel by Finite Element Simulation

TRIP (Transformation induced plasticity) steel combined high strength and high plasticity perfectly, which depend on the micro structure of the material greatly. Residual austenite plays an important role on the micro material transformation and macro property. Different boundary condition makes different stress and strain field of the TRIP steel and induced different residual austenite transformation. Under different compression stress, the residual austenite transformation was different, to predict the micro transformation behavior, investigation of the macro stress character was necessary. Finite element simulation was carried out in this paper to investigate the stress filed of TRIP steel under different boundary condition to predict the micro residual austenite transformation and macro property development.

Change in Properties of Pipe Steel with Two-Phase Structure During Low-Temperature Heating and Subsequent Plastic Deformation

Results are given for evaluation of the effect of longitudinal deformation on the change of the mechanical properties and steel properties with a two-phase pipe metal structure previously given low-temperature heat treatment simulating application of an anticorrosion coating. A reduction in steel deformation capacity to the minimum permissible level is evaluated by a criterion δun ≥ 3% and σy(Rt0.5)/σu ≤ 0.96–0.98. As a result of testing plates subjected to longitudinal tension with plastic deformation ep = 1.5–7.0%, it is shown that exhaustion of steel deformation capacity is predicted in the transverse direction with preliminary deformation ep ≈ 5%, and in the longitudinal direction with ep ≈ 4–5%. SEM and TEM methods are used to study the effect of steel main structural characteristics whose presence facilitates retention of capacity for steel strain hardening after heating (200–220°C, 5 min): fine islands of twinned martensite, fine cementite particles and abundant precipitation of nanosize particles of Nb and V carbonitrides. During branch pipe bending deformation (ep ≤ 3.0%) in a two-phase steel structure (main components are ferrite and lath martensite) includes transformation of residual austenite from the MA-component in twinned martensite.

Features of Formation of the Structure and Properties of Chromium Corrosion-Resistant Steels Alloyed with Nitrogen

Chromium corrosion-resistant steels alloyed with nitrogen are studied by experiment. It is shown that depending on chemical composition and production parameters the steel’s structure may be martensitic with a minimum residual austenite content, martensitic with a higher residual austenite content, or threephase consisting of martensite, residual austenite, and ferrite. The possibility is demonstrated of residual austenite transformation into martensite during cooling after tempering at 400°C, which leads to an increase in steel hardness and correspondingly strength.

Effects of Different Heat Treatments on Transformation of Residual Austenite in Bearing Steel

The effect of heat treatment on transformation of residual austenite in bearing steel is studied, by adding the cryogenic treatment into the normal heat treatment process. The results indicate that the residual austenite content is decreased and the hardness is improved obviously, when putting the cryogenic treatment at -70°C or lower directly behind the quenching process. While when the tempering is added between quench and cryogenic treatment, the temperature of cryogenic treatment must be much lower than -70°C to offset the thermal stability of residual austenite, which is given by tempering.

Dimensional Stability Analysis of Unconventional Treated Steel Bearings

One of the most important characteristics of the element bearings behaviour evaluation is the dimensional stability in time. The structures resulting in conventional thermal treatments are characterized by a major instability along time. Structural changes cause dimensional changes for both austenite and martensite transformations. Residual austenite transformation generates an increase in volume while the martensite transformation decomposes when volume decreases. Research has shown that cryogenic treatment and steel tempering in ultrasonic field applied to bearing steels have a positive influence on the dimensional stability. In what the dimensional stability concerns, the heat treatment below 0°C acts specifically on those sources of strain that have a maximum contribution to further parts dimension modification, especially on the transformation of austenite into martensite. It would have been better if the amount of austenite that remained after quenching at room temperature had been higher and the steel contained more carbon and alloying elements [.

Effect of the Heat Input in the Transformation of Retained Austenite in Advanced Steels of Transformation Induced Plasticity (TRIP) Welded with Gas Metal Arc Welding

The effect of heat input on the transformation of retained austenite steels transformation induced plasticity (TRIP) was investigated in the heat affected zone (HAZ) of the Gas Metal Arc Welding GMAW process. The determination of retained austenite of the HAZ is important in optimizing the welding parameters when welding TRIP steels, because this will greatly influence the mechanical properties of the welding joint due to the transformation of residual austenite into martensite due to work hardening. Coupons were welded with high and low heat input for investigating the austenite transformation of the base metal due to heat applied by the welding process and was evaluated by optical microscopy and the method of X-Ray Diffraction (XRD). Data analyzed shows that the volume fraction of retained austenite in the HAZ increases with the heat input applied by the welding process, being greater as the heat input increase and decrease the cooling rate, this due to variation in the travel speed of the weld path.

The Simulation of Influence of Quenching Temperature on Properties of Bearing Rings

Roller bearings are a very important part of modern machineries and equipments. They have a significant impact on the smooth running, reliable performance and durability. Replacing worn or damaged roller bearings often require extensive disassembly of the machine and the costs often exceed the price of the replaced bearings. There is an influence of the correct bearing construction and dimensional accuracy on the durability, but the grade and quality of used steel and its heat treatment are very important, too. Tempering is an important chapter. Tempering has the effect to modifying the properties of martensite after quenching and transformation of residual austenite, which is related to the change of bearing rings dimensions, growth, roundness and hardness. Decrease in hardness of bearing steel is associated with a reduction in the basic dynamic load rating of rolling bearings and thus durability. In this article there is analysed the influence of quenching and tempering on their mechanical properties after heat treatment. There was also used simulation software to verify the possibility of modeling of bearing rings quenching.

Tempering Process to Improve Hardness Uniformity of Plastic Mould Steel

A new design of copper-bearing non-quenched plastic mold steel is presented and explained. Two kinds of microstructure can be obtained from this new type copper-bearing steel via cooling with different cooling rates, bainite and a mixed microstructure consisting of ferrite and bainite. It is found that, after proper tempering process, the hardness will be increased. Moreover, the hardness difference between different microstructures will be reduced. For further investigation, the samples tempered at different temperatures were examined by XRD and 3DAP (three dimensional atom probe) analysis. Results show that the improvement is contributed mainly by the precipitation of Cu phase and transformation of residual austenite.

Fe-Co기 고인성 고강도강의 반복 열처리 거동 - Part 1. 조직제어

In this study, microstructural evaluation was carried out on secondary hardening type ultrahigh strength steel, Fe-Co-Ni composition. This paper as a first part of whole research presented the microstructural behavior by cyclic heat treatment. The cyclic heat treatment method includes normalizing, stress relieving, solution treatment and aging. Especially, solution treatments performed triple times to get maximized solution hardening. Phase transformation and microstructure were observed by using optical microscope (OM), Electron back-scattered diffraction (EBSD) and X-ray stress analyzer. During the triple solution treatment, size of grain boundary was dramatically decreased by generating a packet from the martensite transformation of residual austenite in the inner part of grain, whereas the hardness increase was not significant.

Study on the Law of Phrase Transformation of High-Carbon Matrix Steel 4Cr-3Mo-3V-2W

The study on the phase transformation law of High-Carbon Matrix steel 4Cr-3Mo-3V-2W-Ni-Nb, which is processed in different heat treatment, is conducted by means of metallographic observation, hardness determination and phase analysis conducted with the help of X-ray diffraction. The results indicate what is as follow: through quenching at 970°C, the main precipitations of alloy carbide are V4WC5, Cr7C3 and Fe3W3C at 200~300°C, V4WC5 and Cr7C3 at 400°C, V4WC5 and Cr7C3 at 500°C, V4WC5, Cr7C3 and Mn23C6 at 600°C. The transformation of residual austenite is thorough completed above 400 °C and the cause of secondary hardening is the precipitation of V4WC5 and V4C2.67.

Retained Austenite and Residual Stress Evolution in Carbonitrided Shot-Peened Steel

Carbonitriding followed by shot peening is an important industrial process to improve the mechanical properties of components, especially by producing compressive residual stresses. In addition, a high hardness and strength produced by this process enhances the surface properties and leads also a high resistance to fatigue. In this study, shot peening with different parameters have been employed to treat the carbonitrided specimens. The measurements of residual stress and residual austenite were performed by X-ray diffraction. It is shown, with a simple eigenstrain model, that residual austenite transformation under shot impact contributes to a significant fraction of residual stresses. When the material (750 HV) is peened with 800 HV shot, it represents about 50%, the remaining is due to plasticity. When it is peened with 640HV shot, 100% of residual stresses can be explained by austenite transformation.

Surface hardening by strain induced martensitic transformation

The hardness and fatigue strength achieved by strain hardening are normally noticeable lower than those attained by thermal or thermochemical heat treatments. Strain or deformation induced martensitic transformation of residual austenite can increase the strength achieved by mechanical surface hardening processes considerably. In this paper, an approach is presented where workpieces with a high content of metastable austenite are used for hardening the surface layer. The microstructure has to be sufficiently stable, in order to ensure that the material can be machined without being changed by strain induced transformation of the residual austenite. After machining, high Hertzian contact stresses are introduced by deep rolling, so that a strain induced martensitic transformation of the residual austenite takes place. At the same time deep rolling produces the surface finish of the part. By this method, a surface hardening without a heat treatment process within the production line can be realized. A conceivable use of this method could be the production of bearings or guideways.

Effect of Niobium on Isothermal Transformation of Austenite to Ferrite in HSLA Low-Carbon Steel

Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA low-carbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage. the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.

Transformation of residual austenite under thermomechanical variations

The austenite to martensite transformation seems to have an influence an the resistance to micropitting Then. the residual austenite transformation was studied for different thermal and thermomechanical conditions. Three homogeneous steels (80, 50 and 27MnCr5) exhibiting three y res fractions at room temperature were studied since their composition correspond respectively to the surface layer, the Hertz zone and the bulk material of a carbonized part. In this paper we only, present the 80MnCr5 results. Tempering under tensile stress tests and compression fatigue tests were performed on samples initially treated according to four heat treating procedures (in order to get different residual austenite amounts and stabilities). The compression fatigue test results, revealed the influence of the initial γ res amount, the applied stress and the internal stress state on the γ res transformation kinetics. The tempering under tensile stress experiments showed that the start temperature of transformation as well as the transition carbides precipitation kinetics are not modified by the applied stress, whereas they do in the case of the austenite transformation. Moreover they, allowed us to establish a destabilisation criterion residual austenite transforms when the applied stress is close to the yield stress of the austenic (depending on the deformation rate).

ALMAZLA HAMARLAMA ZAMANI STRUKTUR- FAZA ÇEVRİLMƏLƏRİ

Abstract. The obtained results show that the plastic deformation of the tempered 15XГ2СМФР and 12ГН2МФАЮ steels with polishing is observed with an increase in the density of dislocations and a fragmentation of the structure. Due to the fact that the density of dislocations in the local zones of the surface reaches a critical level during polishing under the conditions of forces greater than the optimal force, in some cases, the appearance of submicroscopic cracks and a decrease in strength may occur in the deformed metal layer. Due to the increased pressure on the surface of the part, the metal layer strengthened by diamond polishing is characterized by microdistortions. After polishing, the crystal lattice of steel is distorted and the density of dislocations increases. As a result of surface-plastic deformation, intensive splitting of residual austenite and its transformation into martensite occur. After polishing and tempering, a significant amount of residual austenite is observed in the upper layers of the studied steel. The initial 16-20% amount of residual austenite decreases to 4-7% after polishing with a force of 270 N. As a result of diamond polishing, the microstructure of the steel is crushed, the density of dislocations increases, and the transformation of residual austenite into martensite leads to additional strengthening of 15XГ2СМФР and 12ГН2МФАЮ steels.