Residual Austenite Content Research Articles

Manganese Effect on Q&P CMnSi Steels

The present study is focused on analyzing the effect of Mn amount in two experimental steel compositions, specially designed for Quenching and Partitiong (Q&P), 0.15C-2.5Mn-1.5Si and 0.15C-3Mn-1.5Si without significant contribution of Al. Two-Step Q&P thermal treatments were performed at laboratory scale in a quenching dilatometer Bähr DIL805A/D. The fractions of retained austenite were evaluated by X-ray diffraction techniques. The mechanical properties of the Q&P samples were evaluated, a strong dependence of strength, uniform elongation and strain hardening values on process parameters has been found. Higher uniform elongation were related to higher residual austenite contents. The 0.15C-3Mn-1.5Si steel showed systematically the largest mechanical values with respect to the 0.15C-2.5Mn-1.5Si steel.

Effects of temperature on fatigue limits and fracture morphologies of 40Cr steels formed by warm extrusion

AbstractA 40Cr steel was formed with warm extrusion under different temperatures, and the tensile fatigue limits after the warm extrusion were calculated according to the Roca rule. The metallographic microstructure and chemical compositions of the extrusion samples were analyzed with an optical microscope and photoelectric direct-reading spectrometer, respectively; the residual stress and residual austenite were investigated on a stress tester. The fracture morphologies were analyzed with a field-emission scanning electron microscope, and the mechanism by which the warm extrusion temperatures affected the fatigue fracture of the 40Cr steel was discussed. The results show that the grains are refined by warm extrusion at 550°C, the C weight fraction on the sample surface is 0.39%, and the compressive residual stress and content of residual austenite are −297 MPa and 5.3%, respectively, increasing the fatigue life of the samples. The grain sizes of the extrusion samples at 650 and 750°C are larger than those at 550°C, the corresponding C content of the sample surface is 0.39% and 0.38%, respectively, and the compressive residual stresses and contents of residual austenite decrease, leading to a decrease in the fatigue life. The fatigue strength of the samples by warm extrusion at 550, 650, and 750°C is 382, 412, and 385 MPa, respectively. The fracture morphology of the sample at 550°C is a dimple, while that at 650 and 750°C is a cleavage step and river pattern, respectively.

Factors Determining the Level of Mechanical 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 process parameters the structure of the chromium steels obtained may be martensitic with a minimum residual austenite content, martensitic with a greater content of residual austenite, or three-phase, consisting of martensite, residual austenite, and ferrite. The possibility is demonstrated of increasing steel martensite ductility by forming a specific amount of austenite within the steel structure.

Heat Treatment of Wear Resistant Steels for Mud Pumps

Influence of different type heat treatment including high temperature quenching on wear resistance has been investigated. The two investigated steels are widely used in production of mud pumps. It was shown that Kh12MFL had better wear resistance in comparison with 150KhNML. Martensitic-carbide structure of the steels formed by quenching from high temperatures (900 – 1000 °С) induced good hardness (61 – 64 HRC). Analysis of the residual austenite contents influence on wear resistance was also made. It was determined that residual austenite formed after high temperature quenching (900 – 1000 °С) was metastable and had tendency to transform into carbon containing martensite of deformation. This allowed steels to have maximum wear resistance because of providing high abilities to friction hardening of the work place of the sample.

Effect of Q&P Process on 0.15C-MnSi Steels

The present study is focused on analyzing the effect of Mn amount on two experimental steel compositions, specially designed for Q&P (Quenching and Partitioning), 0.15C-2.5Mn-1.5Si and 0.15C-3Mn-1.5Si without significant contribution of Al. Two-Step Q&P thermal treatments were performed at laboratory scale in a quenching dilatometer Bahr DIL805A/D. The fractions of retained austenite were evaluated by X-ray diffraction techniques. The mechanical properties of the Q&P samples were evaluated, a strong dependence of strength, uniform elongation and strain hardening values on process parameters has been found. Higher uniform elongation were related to higher residual austenite contents. The 0.15C-3Mn-1.5Si steel showed systematically the largest mechanical values with respect to the 0.15C-2.5Mn-1.5Si steel.

Microstructural transformation and precipitation of an ultra-high strength steel under continuous cooling

We investigated phase transition and precipitation of ultra-high strength steel (UHSS) in a new “short process” with controlled rolling and controlled cooling. Thermal expansion test combined with metallographic observation was used to research the continuous cooling transformation (CCT) curve. Moreover, the microstructural transformation and precipitation law was revealed by morphological observation and alloying elements by electron probe micro-analyzer (EPMA). Transmission electron microscopy (TEM) was utilized to analyze the composition and grain orientation of microstructure. The study showed that the measured critical transformation temperatures of Ac1 and Ac3 were 746 and 868 °C, respectively. The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate of 1 °C•s−1. When subjected to a cooling rate of 1 °C•s−1, the undercooled austenite was divided into small-sized blocks by formed martensite. With further increase of cooling rate, micro-hardness increased dramatically, the microstructure of specimen was mainly lathe bainite(LB), granular bainite(GB), lath martensite (LM) and residual austenite. By diffraction test analysis, it was identified that there was K-S orientation relationship between martensite and austenite for {110}α//{111}γ, {111}α//{101}γ. EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 °C•s−1. Phase transition drive force was lower and the residual austenite existed in the block form of Martensite austenite island (M-A). With the increase of cooling rate to 10 °C•s−1, the block residual austenite reduced, the carbon content of residual austenite increased and α phase around the residual austenite formed into a low carbon bainite form.

The Heat Treatment Influence of 1.3343 High Speed Steel on Content of Residual Austenite

The heat treatment applied to high speed steel is in large measure dictated by the necessity of decreasing the residual austenite content. After hardening, a large amount of residual austenite it is found in the structure; this is unwanted because it is less hard than practical necessities and also unstable in time. As a result, the heat treatment has the purpose to conferee to tools mechanical properties that are required in exploitation, and in the same time, stable from structural point of view and of mechanical characteristics. In this purpose there are known several processes, as for example multiple tempering and treatment below zero degrees. In this paper, it is proposed the analysis of residual austenite from 1.3343 high steel speeds subject to multiple heat treatment operations, by determining after each, the quantity of residual austenite; this was made with X ray diffraction using a software package program. Research has revealed the decrease of residual austenite content with the number of tempering as well as with the treatment below zero degrees.

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 laser heat treatment on salt spray corrosion of 1Cr5Mo heat resistant steel welding joints

The surface of 1Cr5Mo heat-resistant steel welding joint was processed with CO2 laser, and the corrosion behaviors before and after laser heat treatment (LHT) were investigated in the salt spray corrosion environments. The microstructures, phases, residual stresses and retained austenite content of 1Cr5Mo steel welding joint before and after LHT were analyzed with optical microscope and X-ray diffraction, respectively. The cracking morphologies and chemical compositions of corrosion products after salt spray corrosion were analyzed with field emission scanning electron microscopy (FESEM) and energy disperse spectroscopy (EDS), respectively, the polarization curves were measured on a PS-268A type electrochemical workstation, and the mechanism of corrosion resistance by LHT was investigated as well. The results show that the passive film of original sample is destroyed owing to the corrosive media penetrating into the subsurface, resulting in the redox reaction. The content of residual austenite in the surface and the self-corrosion potential are increased by LHT, which is contributed to improving the capability of salt spray corrosion resistance.

HEAT TREATMENT OF WEAR RESISTANT STEELS FOR DRILLING RIG PUMPS

The influence of heat treatment different options on wear resistance of steels of trademarks Kh12MFL and 150KhNML applied in manufacturing of mud pumps is reviewed. It is shown that the steel Kh12MFL is superior in wear resistance than the steel 150KhNML at abrasion. The martensite-carbide structure of both steels obtained at quenching at normal temperatures, from 900 to 1000 0С, ensures a good hardness (61-64 HRC). The analysis of the residual austenite contents influence on wear resistance was also made. It was determined that residual austenite formed after high temperature quenching (110-1170 0С) was metastable and had a tendency to transform into carbon containing martensite of deformation in the process abrasive wearing. This allowed steels to have a maximum wear resistance because of ensuring a high ability to frictional hardening of the working surface.

Magnetic and acoustic techniques for determining the phase composition and destruction dynamics of plastically deformed cobalt-free martensite-aging steel

The results of investigating the magnetic properties and phase composition (using the X-ray diffraction method) of specimens of cobalt-free ChS5VI (03N18M3TU) martensite-aging (maraging) steel that were subjected to a plastic tensile deformation are presented. It was established that all of the studied specimens can be divided into two groups depending on their heat treatment: specimens that were aged at T 550°C, in which the magnetic properties and the phase composition abruptly change at the initial deformation stages (up to 4–6%). The phase composition (the content of the residual austenite) in specimens of both groups, regardless of their degree of deformation, can be tested on the basis of the saturation induction and the N′ parameter, which correlates with the internal demagnetization factor. The acoustic-microscopy method showed that in specimens with the highest content of residual austenite, microflaws with minimum dimensions occurred during deformation, and cracks were not observed up to the specimen rupture. The location of the future neck nucleation at early deformation stages was predicted on the basis of acoustic images of subsurface layers for a specimen that was aged at T = 580°C.

Comparison of slip-rolling behaviour between 20MnCr5 gear steel, 36NiCrMoV1-5-7 hot working tool steel and 45SiCrMo6 spring steel

The automotive industry places significant importance on downsizing components to achieve greater efficiency. The goal of reducing CO2 emissions has led to the development of lightweight materials that are also able to enhance performance. In light of these aspirations, the aim of this study is to characterize two novel, high-performance steels, as well as a “classical” gear steel for comparison with each other and currently applied materials. The gear steel underwent carburization and subsequent deep freezing treatments in an attempt to yield discrete sample groups with respect to residual austenite. The high-performance steels were heat treated as recommended by their respective manufacturers, and were not carburized. Elemental analyses were conducted by multiple methods to ensure accurate results. Residual austenite contents of the steels and the depth profiles of residual stresses were determined by X-ray diffraction (XRD). Hardness profiles were taken from the testing surfaces into the material core. The carburization of 20MnCr5 led to higher hardness and the greater concentration of carbon in the carburization zone more representative of a hardened SAE E52100, or 100Cr6/102Cr6, than of a non-carburized 20MnCr5. Residual austenite contents ranging from approximately 6–14vol% were generated, though effectively providing only two, rather than the desired four discrete sample groups. Residual stresses from machining and carburization were measured directly at the sample surface, and from carburization alone below the surface. The high-performance steels fulfilled manufacturer expectations in terms of elemental content, hardness between 50 and 55 HRC and strongly martensitic microstructure character. Finally, slip-rolling endurance testing (T=+120°C, 10,000,000 cycles, approximately 19 days in a factory fill engine oil) was carried out on all materials, whereby coefficient of friction distributions during testing and wear coefficients after testing were calculated. Testing was performed up to and including P0Mean=1.94GPa (P0Max=2.91GPa, FN=2000N). Ultimately, the non-carburized high-performance steels showed competitive wear performance and better friction behaviour than the carburized 20MnCr5, which has been attributed to their work hardening capability.

Thermal Fatigue Resistance of Bionic Compacted Graphite Cast Iron Treated with the Twice Laser Process in Water

For enhancing the thermal fatigue resistance of bionic compacted graphite cast iron (CGI) laser-treated in water, the bionic units are treated twice with the laser to form an uneven bionic surface imitating the alternately soft and hard structure of a plant leaf, which can resist the tearing wind. The results show that this method, without changing the phase composition of the bionic unit, makes the austenite-to-martensite transformation more complete and the content of residual austenite is reduced, in addition, the microstructure coarsens and microhardness slightly turns lower. The twice laser process in water can effectively enhance the thermal fatigue resistance of bionic CGI by reducing the number of cracks in bionic units since the number of cross cracks on the bionic unit surface is the key factor, which affects their resistance to thermal crack propagation.

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.

The Influence of Vibration on the Microstructure of the Wear-Resistant Layer Made with the Welding Wire MSG-6-GZ-C-60G

In the production of steel parts exigent of high durability to abrasive wear at high temperatures and / or corrosive environment, the method is used for the deposition welding with the addition material MSG-6-GZ-C-60G. With this material layer it is made of 55-60 HRC hardness, corrosion and wear resistant, with properties that are kept up to temperatures of 5000 C. There can be manufactured new parts (pressure casting forms, components for dies, molds, etc.), or dynamically and abrasion-torn reconditioned parts may be required. Deposits have been made with wear-resistant layer on the steel 42CrMo4, with and without the generation of vibration during welding. For the samples swing, a device was used with an electrodynamic exciter to generate vibrations with frequencies up to 20 kHz. Vibration tests were performed at a frequency of 50 Hz, because the frequency can be applied in industrial conditions, by means of excitation of electromagnetic or vibration driven motor. There have been registered horizontal and vertical accelerations which lead to changes in the conditions of crystallisation of the melt, respectively the formation of a microstructure with superior features. Microstructures and hardness recorded on specimens welded with and without vibration are comparatively presented. Micrographs which were made demonstrate the favourable influence of the vibration on the quality of the deposited layer and the base material. Whith the vibration with accelerations of ax= 55 m/s2and az= 70 m/s2resulted: much lower deformation of the base material, HAZ - a lower content of residual austenite, in the TZ there was a great interlock of the two materials, in the deposited material the dendritic crystals strongly fragmented and the grain was finished.

A Study on Austenite Catalytic Cryogenic Treatment of Cr-W-Mo-V High Alloy Medium-Upper Carbon Steel

The processing of austenite catalytic cryogenic treatment of two components of Cr-W-Mo-V high alloy medium-upper carbon steels and the effect on the retained austenite transformation and tempering hardness were studied in this paper. The results show that, the effect of austenite catalytic cryogenic treatment of Cr-W-Mo-V high alloy medium-upper carbon steel is better than that of direct cryogenic treatment after quenching, and the content of residual austenite reduced to below 5%, and the hardness improved by 1.5HRC than that of conventional quenching and tempering. The retained austenite catalytic temperature of Cr-W-Mo-V high alloy medium-upper carbon steel merely is higher than 10°C~20°C of the temperature for the highest tempering hardness. Catalytic temperature Tc can be determined by experimental method of conventional quenching and tempering of the steel, in which the microstructure feature is precipitation of M3C carbide particle of 0.01μm~0.03μm in martensite matrix, and the content of retained austenite decreases evidently. By cryogenic treatment after the austenite catalyzed the retained austenite of quenching are transformed into more martensite, and in the subsequent tempering processing the original quenching martensite and the martensite from retained austenite transformation almost will form synchronous precipitation hardening. Thus the tempering hardness improves evidently as well.

Study on the Mechanical Stability of Retained Austenite in Cold-Rolled Medium-Mn Steel

The mechanical stability of the retained austenite in the cold-rolled medium-Mn steel was studied. Tensile tests were carried out to measure the mechanical properties of the annealed steel. Scanning electron microscopy was applied to characterize the microstructure evolution during the tensile process; X-ray diffraction analysis was used to determine the residual austenite content in the deformed steel. It was found that the volume fraction of retained austenite gradually decreases with strain .The value of the stability coefficient of retained austenite k was small in the test steel, which indicated high mechanical stability of retained austenite. Due to TRIP effect, the high mechanical stability of the retained austenite strongly delays the onset of necking, which resulted in good comprehensive mechanical properties with ultrahigh strength and plasticity.

Characterization of the structural details of residual austenite in the weld metal of a 9Cr1MoNbV welded rotor

The existence of residual austenite in weld metal plays an important role in determining the properties and dimensional accuracy of welded rotors. An effective corrosive agent and the metallographic etching process were developed to clearly reveal the characteristics of residual austenite in the weld metal of a 9Cr1MoNbV welded rotor. Moreover, the details of the distribution, shape, length, length-to-width ratio, and the content of residual austenite were systematically characterized using the Image-Pro Plus image analysis software. The results revealed that the area fraction of residual austenite was approximately 6.3% in the observed weld seam; the average area, length, and length-to-width ratio of dispersed residual austenite were quantitatively evaluated to be (5.5 ± 0.1) μm2, (5.0 ± 0.1) μm, and (2.2 ± 0.1), respectively. The newly developed corrosive agent and etching method offer an appropriate approach to characterize residual austenite in the weld metal of welded rotors in detail.

Effect of Austenitizing Processes on Isothermal Quenching Microstructure in Bearing Steel

Austempering was applied to bearing steel to improve the performance. The effect of austenitizing temperature and time on isothermal quenching microstructure in bearing steel was investigated via microstructure observation and fracture analysis. The results show that with the increase of austenitizing temperature, the size of bainite plate and residual austenite content increase. Austenitizing at lower temperature, the samples has a fracture composite fracture morphology of polygon cleavage unit and even small dimple.The fracture morphology of sample austenitized at 1050 °C is quasi-cleavage fracture with bar cleavage unit which is corresponding to the coarse acicular microstructure. the size of bainite plate increase with increasing the austenitizing time. As the result of comprehensive effect of fine grain strengthening and dispersion strengthening, that the microhardness firstly increases, and then obviously decreases with the increase of austenitizing time.

Influence of the quenching temperature on the phase composition, structure, and wear resistance of 150XHM steel

The influence of the quenching temperature on the quantity of residual austenite, its stability, and its ease of deformational martensitic transformation in 150XHM steel is studied. In the addition, the hardening and abrasive-wear resistance of the steel are studied as a function of the quenching temperature. The dependences of the steel’s hardening and wear resistance on the quenching temperature are of opposite form. The drop in hardness with increase in quenching temperature is due to increase in the content of residual austenite. At the same time, the relative ease of deformational martensitic transformation in the metastable residual austenite results in increase in wear resistance and microhardness of the worn surface.