Papers by Keyword: Tempering

Abstract: Mechanical tests and electron microscopic structural studies of low-carbon copper-steels quenched after austenitization and tempered at different temperatures are carried out to clarify the decomposition mechanism of α-Fe based substitution solid solutions. With the onset of decomposition, limited nanosize (4–7 nm) precipitates of so-called ε-phase (solid solution of iron in copper with fcc structure) appear on dislocations. The substructure formed from the austenitic region during quenching determines the nature of such decomposition. In alloys with martensitic structure, the decomposition is heterogeneous. Both the formation of precipitates of the copper-rich ε-phase and their growth primarily occur on dislocations and grain boundaries. In supersaturated alloys with polyhedral ferrite structure, on the contrary, the decomposition is homogeneous, and the growth of the copper-rich phase occurs mainly in the defect-free part of the bcc matrix. Supersaturated iron begins to decompose, forming copper-rich zones isomorphic α-Fe. When a sufficiently high copper concentration is reached, these zones create mechanical stresses that cause local tetragonal distortions of the crystal lattice leading to its reconstruction. When a dislocation loop is formed around this zone, compensating for the elastic deformation, the coherence of the structure is destroyed and fcc precipitates are formed in the matrix. Satisfactory agreement between the theoretical estimate of 8 nm of the critical displacement required for the formation of a dislocation of inconsistency and the initial incoherent precipitates size determined experimentally – by electron microscopy, confirms the proposed mechanism based on the nucleation of nanoinclusions of the ε-phase copper in the bcc iron matrix.

Abstract: This study investigated the evolution of microstructure, hardness, and toughness in nodular cast iron following quenching and tempering at 450°C. The research explored how the heat treatment process impacts these mechanical properties, to identify an optimal balance between hardness and toughness. Untreated nodular cast iron displayed a microstructure comprising ferrite, pearlite, and spheroidal graphite, resulting in moderate hardness (24.33 HRC) and toughness (0.082 J/mm²). Quenching at 850°C, followed by rapid cooling in water, induced the formation of martensite, a hard and brittle phase, which significantly increased hardness to 56.73 HRC but decreased toughness to 0.068 J/mm². Tempering at 450°C transformed the martensite into tempered martensite, reducing hardness to 41.37 HRC while improving toughness to 0.11 J/mm². These findings highlighted the importance of tempering in achieving a better balance between hardness and toughness, making the material suitable for industrial applications requiring both wear resistance and impact durability. The results offered valuable insights for optimizing heat treatment procedures to enhance the performance and durability of nodular cast iron components in various industries.

Abstract: Armour steel products developed in various forms, function and materials. The usage of steel as bulletproof material has many advantages i.e. easy to transport, easy to be formed and has competitive price compared to other material. The mechanical properties of steel which can be used as bulletproof material must meet certain criteria which can be improved through heat treatment process. The aim of this research is to determine the most suitable heat treatment parameter of SKD 11 modified steel material to improve its hardness and the effect of thickness SKD 11 modified as requirement for bulletproof material. This research processed the SKD 11 modified steel material using heat treatment with 1030°C quenching parameter with 3 hours holding time followed by tempering temperature parameter which vary of 400°C, 500°C, 530°C and 600°C with 4 hours holding time for each tempering. The tempering process is done twice for each sample. Result showed that the highest hardness properties was achieved at 1030°C quenching parameter with 3 hours holding time followed by tempering temperature parameter of 530°C with 4 hours holding time. From the best parameter resulted in highest hardness then SKD 11 modified material for ballistic test varied into 5, 7.5 and 10 mm thickness. TheBallistic performance test level III and level IV showed that hardened SKD 11 modified steel material with 10 mm thickness has the lowest BFS value of 3.32 mm and 7.54 mm with a shattered phenomenon present on the experiment. The experiment result confirm that the SKD 11 modified material meet the BFS allowed limit which 46 mm based on NIJ0101.06 standard.

Abstract: The effect of heat treatment process on the microstructure and hardness of train wheel material was investigated. The railway wheel material was prepared by a casting process from used train wheel and followed by heat treatment processes namely normalizing, flame hardening, and tempering. The normalizing process at a temperature of 850 °C with a holding time of 120 minutes followed by air cooling has resulted in hardness of 24 HRC. The flame hardening process at a temperature of 800 °C with a holding time of 1 minutes followed by water quenching has resulted in hardness of 57.33 HRC. The tempering process at a temperature of 500 °C with a holding time of 60 minutes followed by air cooling has resulted in a final surface hardness of 34 to 37 HRC that complies with the standards.

Abstract: Effects of pre-strain and tempering on mechanical properties in high-strength martensitic steels were investigated. In this study, strain tempering (ST) and quenching and tempering (QT) martensitic steels were prepared, and their mechanical properties were studied. In the tensile tests at the deformation temperatures between 296 and 573 K, the ST sample increased both of tensile strength (TS) and uniform elongation (U.El) from 473 to 523 K whereas the QT sample increased U.El with little change of TS. From the in situ neutron diffraction experiments, stress partitioning to the bcc phase increased with an increase in the deformation temperature from 296 to 523 K. The difference of phase stress between the bcc and cementite phases decreased with increasing the temperature because of a decrease in the cementite strength. In the ST sample, Pre-straining of 0.5% increased YS at 296 K with slight work hardening. The initial value of dislocation density (ρ) decreased at 523 K but ρ increased significantly after yielding, leading to better combination of TS and U.El. The combinations of pre-strain, tempering, and deformation temperatures have changed ρ before deformation and the increase of ρ after yielding of the martensitic steels.

Abstract: Rapid induction can be utilized to decrease the time and energy used for heat-treatment of steels. In the present study, a commercial 500 HB grade wear-resistant steel was subjected to rapid induction tempering and compared to conventionally furnace tempered samples. The martensitic ultra-high strength steel was cut to narrow thin sheets, which were tempered at 200, 300, 400, and 500 °C with both methods. The rapid tempering was applied with an in-house built induction line, in which the samples were moved through an induction coil. The velocity of the samples was adjusted to ensure constant temperature control. The applied heating rate was 1000–1100 °C/s resulting in extremely rapid tempering times. The conventionally tempered samples were heated in a pre-heated furnace for 45 min and cooled in still air. The samples were tested for tensile and hardness properties and microstructural characterization was conducted. Results revealed only minor differences between the differently treated steels. Elongation was slightly improved with the induction treatment. Therefore, the induction tempering appeared to result in similar or even slightly better tensile properties and can be considered a promising alternative for tempering processes in future steelmaking.

Abstract: Requirements for high service life and mechanical strength of components undergoing cyclic deformation and abrasive resistant, identification of quantitative relationships between material properties and its microstructure very important. In the previous study, Hardness and toughness properties are usually obtained by combining quenching and tempering. The other studies, to increase the hardness by adding Cr on the material. The application of heat treatment in austenizing can provide a microstructure change with refining carbides. In this study, 2.085Cr 2.418Ni low carbon steel casting were heat treated with a reheated in various temperature without quenching. The changes in the microstructure in the last step after passing through the temperature experienced respectively 750 ° C, 650 ° C and 350 ° C were very significant. The phase that appears is tempered martensit surrounding refinement fine tempered martensite and decreasing hardness from 496 HvN to 257 HvN.

Abstract: Nodular cast iron is usually used for components that require good mechanical properties such as strength, toughness, and ductility. Heat treatment is applied to the components made from the nodular cast iron to improve their mechanical properties. This study aimed to investigate the influence of tempering time on the microstructure, hardness, and wear rate of nodular cast iron. The heat treatment was performed by austenitizing to 850 °C with a holding time of 1 hour and quenched in the oil medium. After quenching, it was tempered at a temperature of 450 °C by varying the tempering time to 15, 30, 45, and 60 min. The investigation consists of microstructure observation, hardness, and wear rate measurements. The results show that the highest hardness was 55.3 HRC at a tempering time of 15 min, and the lowest hardness was 54 HRC at a tempering time of 60 min. The lowest wear rate was 0.00476 g/min at a tempering time of 15 min, and the highest wear rate was 0.00574 g/min at a tempering time of 60 min. It can be concluded that the longer the holding time of tempering, the lower the hardness and the higher the wear rate.

Abstract: Recent past witnessed the widespread use of High Strength Low Alloy steels in several structural applications, including pressure vessels, line-pipe transportation of crude oil in the oil industry and many more. API X-65 grade is widely used as a promising material for line-pipe applications in the oil industry. HSLA X-65 plate steels are produced by normalising, Controlled Rolling (CR), Direct Quenching & Tempering (DQT) or Quenching & Tempering (Q&T) techniques. These steels are characterised by their low carbon concentration while maintaining low alloy additions. Micro alloy additions such as V, Ti, and Nb provide substantial precipitation strengthening effect. Strengthening, hardness and microstructural examinations are conducted in all the stages to ascertain X-65 HSLA steel's ageing behaviour.

Abstract: The paper compares the technical characteristics of two thermochemical treatment (TCT) lines for self-tapping screws at OJSC MMK-Metiz. Quenching on TCT line 1 is carried out in the furnace by AUTOMATION SERVICE, while quenching on TCT line 2 is carried out in the furnace by KOHNLE. The authors described quenching and tempering schedules in these two furnaces, studied the microstructure of screws at all process stages, determined technical parameters and properties of finished products after thermochemical treatment. The research showed that the best performance had TCT 2 by KOHNLE. The metallographic analysis indicated more stable parameters of the layer thickness after nitrocarburizing, core and surface hardness, which was in full compliance with regulatory documents. By introducing a better structure of a new TCT line by KOHNLE, a TCT process period became shorter, and a range of self-tapping screws might be extended entailing a higher output of finished products.