Papers by Keyword: Tempered Martensite

Abstract: This study investigates the impact of varied heat treatment parameters on the mechanical and metallurgical characteristics of 9254 steel. Different cylindrical specimens underwent controlled heat treatments targeting three different phases. The interplay of time and temperature was systematically explored to understand their influence on bending strength, bending deflection, hardness, and microstructural evolution. The results revealed that a partially tempered martensitic structure exhibiting an exceptional ultimate strength of 4308 MPa. Achieving this involved a heat treatment, starting at 900°C for 30 minutes, followed by rapid cooling in an oil bath, quenching at 165°C for 5 minutes, annealing at 180°C for 60 minutes, and gradual air-cooling. This treatment regimen produced a specimen with a desirable combination of mechanical properties, showcasing its potential significance in advanced engineering applications.

Abstract: The strengthening effect due to high-temperature tempering (HTT) at 700 °C on the microstructure and mechanical properties of welded joints between medium-Mn stainless steel (MMnSS) and high-strength carbon steel (CS) was studied. The microstructure of the weldments was investigated using Laser and scanning electron microscopes. An Electron probe microanalyzer (EPMA) was used to assess quantitatively the elemental distribution profiles of alloying elements within the weld zone. The strengthening precipitates induced during welding and HTT were characterized by transmission electron microscopy (TEM). Uniaxial tensile tests and microindentation hardness (H_IT) measurements of the weld joints were conducted to evaluate the strengthening effect. Fully fresh-martensite and fine-tempered martensitic structures were promoted in the as-weld and HTT processes, respectively. The HTT structure exhibited a remarkable improvement in mechanical properties (a better combination of yield and tensile strength together with moderate ductility) compared to its weld counterpart. TEM investigation revealed that various types of precipitates have been promoted in the structures of the weld and HTT, e.g., nanosized vanadium and chromium carbides. It is apparent that the proposed HTT of the joints is an effective treatment for improving the mechanical properties due to inducing the formation of fine interphase precipitates, resulting in enhanced mechanical strength of the joints.

Abstract: AISI H13 material finds wide use as screw shafts and screw elements in Twin Screw Extruders for Polymer Compounding applications owing to its high strength, excellent thermal shock resistance, high wear resistance and good fatigue strength. However, two AISI H13 shafts used in the Twin Screw Extruder supplied for fluoropolymer application experienced breakage after two years of service. Visual examination of broken shafts revealed deposits of processing material, rust marks and grooves at multiple locations on the shaft spline at the element to element butting zone. The location of breakage of the shaft was noted at Barrel No.5, which happens to be the vent zone of the extruder. The fracture surface was observed to be almost perpendicular to the rotating axis of the shaft. Macro-examination of the shafts showed abnormal wear at the groove areas and significant reduction in the diameter of the screw shafts with complete absence of spline in the zone adjacent to fracture. Hardness survey revealed values of 25-27 HRC that was 18-20 HRC lower than the hardness in supply condition. Microstructural examination on the failed shafts showed fine spheroidized carbides with ferrite in tempered martensitic matrix. SEM Analysis on samples from fracture surface revealed presence of multiple micro-voids and indicated coalescence of these voids. Based on the investigation & analyses it was inferred that the predominant mode of failure of the shafts had been “Corrosion Assisted Ductile Rupture” in elevated temperature operating conditions. Finally, recommendation to prevent occurrence of such failures has been proposed.

Abstract: AISI D3 material finds wide use as Dies in Tableting Machines for Pharmaceutical applications owing to its good strength, toughness and moderate corrosion resistance combined with cost effectiveness. However, 10-15% of AISI D3 Dies used in rotary Tableting Machines were found to fail within 4-6 months of service resulting in frequent disruption of regular production and loss in overall productivity besides having potential long-term risks such as metal contamination in the output product. Visual examination of the failed Die showed 180^o crack across the top Die face with rust marks, but no such crack was found on the bottom face. Also, the crack on the top Die face had a jagged morphology and those cracks on the Outer Diameter (OD) surface oriented in the axial direction were found to be straight and sharp. Macro-examination of Die sectioned diametrically and perpendicular to the crack on the Die face revealed jagged axial cracks on the Internal Diameter (ID) surface. Cluster pitting marks centered around mid-height of the Die were observed on the ID surface and the cut open sections of the Die along the crack revealed extensive corrosion. While microstructural examination of samples taken on the ID surface showed presence of banded carbides oriented axially in tempered martensite matrix, the same examination carried out on samples taken on Die face revealed fine needle like carbides in tempered martensite matrix. Fractography analysis conducted in the cluster pitting zone on the ID surface clearly showed presence of micro-cracks having multiple points of origin with clear indications of propagation into the cross section of the Die. Scanning Electron Microscopy (SEM) carried out in the aforementioned zone near ID surface also showed the presence of multiple micro-cracks. The SEM-EDX analysis in the referred zone at specific locations in the vicinity of microcracks confirmed inadequate Chromium oxide content leading to lack of corrosion resistance in the material. Based on the investigation & analyses and the detailed study of the Tableting Process in rotary Tableting Machines that revealed the nature of applied load to be cyclic, a comprehensive failure mechanism was arrived at, and it was inferred that the predominant mode of AISI D3 Die failure was Corrosion Fatigue. Finally, recommendation has been proposed to prevent such failures during service.

Abstract: A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life.

Abstract: Different types of carbide phases and regions of their precipitation in tempered martensite of austenitic steel have been investigated with orientation microscopy (EBSD) and electron microprobe analysis. The steel structure consisted of large grains of high-temperature ferrite (~ 15%), without visible mesostructured, and martensite packages with a great number of low-angle boundaries. High-angle boundary spectrum with the most prominent coincidence site lattice (CSL) boundaries, Σ3, Σ11, Σ25b, Σ33с Σ41с, is typical for martensite. This spectrum, resulted from austenite transformation by shear mechanism according to orientation relationships (OR), intermediate between Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). In the structure two types of carbide precipitates were observed: large MC [~ NbC] along the boundaries of former austenite grains, and dispersed M₂₃C₆ [~ (W,Mo)₂(Cr,Fe)₂₁C₆] predominantly along the boundaries in martensite packages. It has been shown that under martensite tempering M₂₃C₆ precipitation was mainly at high-angle intergranular boundaries. Carbide almost did not precipitate at low-angle and special CSL Σ3 boundaries. A few carbides were detected at special CSL boundaries, Σ11, Σ25b, Σ33с Σ41с.

Abstract: Two types of steels which are different in Ni content were tested in three groups of different quenching temperatures and same tempering temperature respectively under the same conditions, and then tested the mechanical properties and observated the microstructure, comparing with the effects of different Ni content on the microstructure and properties. When 1Ni-steel is under the different quenching temperature, its tensile strength range is 1269-1290MPa and changes subtlely. The yield strength and impact energy reach the highest at 910°C, and the mircostructure is fine and uniform. With the quenching temperature increasing, the strength of 3Ni-steel decreases ,but the toughness increases comparing with both kinds of the steels, the microstructure of 3Ni-steel has much more hard phases in its tempered martensite microstructure. Its tensile strength, yield strength and toughness are higher than 1Ni-steel at the lower quenching temperature. The inclusions of 3 Ni-steel are characterized by spheroidization and refinement. In the NACE-A test, the SSC resistance of 3Ni-steel is better than that of 1Ni-steel, which indicates that the high Ni steel has better comprehensive properties.

Abstract: Microstructures, Vickers depth profiles and low-temperature toughness of the tempered direct water quenched steels have been evaluated in the experiment. Martensite dominates the direct quenched specimen, and it is brittle at low-temperature toughness test. The toughness of direct quenched steel is improved when it is tempered at 500 °C for 1800 s. However, increasing the tempering temperature from 500 °C to 660 °C has little effect on low-temperature toughness of the steel. The application of offshore steel must avoid bainite formation. Tempering treatment is very effective to improve low-temperature toughness of the martensite dominated structure.

Abstract: In this investigation, the characteristics of bulky retained austenite in an austempered ductile iron are evaluated in two tempered conditions. which were intially tempered at 200oC for 1h before cooling to room temperature, and then tempered at 350oC for 1h. The result shows that the hardness within retained austenite areas is distributed unevenly with a range from 423 HV to 897 HV, which is attributed to the transformation from austenite to martensite during austempering. Also, the mechanism regarding the quenched marteniste formation is discussed. The poor fatigue resistance of ADI is hypothesized to be due to the amount of austenite transformed to martensite.

Abstract: The demand for new materials that provide excellent structural performance while reducing weight and being cost-effectively manufactured is increasing. For applications with high strength requirements, ultra-high strength steels (UHSS) have been widely used. However, with such a high strength level, UHSS are very sensitive to the hydrogen that could be ease by the tempering process. In this research, the correlation of hydrogen and tempering process on commercial UHSS 15B30 has been studied. Results show that the tensile strength (TS) of as-quenched 15B30 is about 1900MPa. After tempering treatment of the quenched 15B30, the TS decreases from 1600MPa to 1200MPa with tempering temperature increased from 200°C to 400°C. The 15B30 specimens, being subjected to hydrogen charge, exhibit the dramatic reduction of mechanical strengths.