Papers by Keyword: Quenching

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: Gray cast iron has been one of the most widely used engineering materials since a long time ago. However, the development of casting techniques and methods to produce various models of cast iron products for the domestic market is not followed by improvements in product quality. The intriguing aspect of gray iron products is the diverse morphologies that graphite can assume, leading to distinct variations in mechanical and physical properties. Quenching is a typical heat treatment procedure performed to improve the mechanical properties of a material that entails the rapid cooling of the material from a high temperature to a low temperature. The aim of this study is to investigate the effect of water quenching effects on microstructure, crystal structure, hardness, and wear of gray iron, which undergoes quenching from the austenitizing temperature. Gray cast iron was obtained from the local foundry industry, then thermally treated at 900°C, held for 15 minutes, and rapidly quenched by water. The quenching procedure induces a significant alteration in the overall microstructure, where transition of most dendrite arms to the eutectic phase microstructure is observed. Moreover, the quenching process is attributed to the reduction of crystal size and growth of carbon crystal. The average crystal size of the sample was reduced from 47.833 nm to 17.97 nm, hence improving the hardness from 16.375 HRC to 48.04 HRC, which in turn improved wear resistance under high loading condition from 0.014 g/sec to 0.00042 g/sec.

Abstract: Nanoparticle addition into a fluid can increase the thermal conductivity. Such fluid is commonly called a nanofluid. Due to its improved heat transfer characteristic, nanofluid is widely used as coolant in engine or electronic equipment. In the steel heat treatment industry, nanofluid can be utilized as a quench medium. By controlling the amount of nanoparticle added in the nanofluid quench medium, the cooling rate can be adjusted. To preserve the heat transfer effectivity, the stability of the nanoparticle become very important. Hence, surfactant is quite essential to improve the particle stability and avoid particle agglomeration and sedimentation. In this study, a multiwalled carbon nanotube (MWCNT) was used as the nanoparticle in the distilled water. The concentration of the MWCNT was varied at 0.1, 0.3, and 0.5 % w/v. For the surfactant, Cetyl Trimethylammonium Bromide (CTAB) was chosen to disperse the particle better. In each of the three MWCNT variations, CTAB was added from 3 – 30% w/v. The maximum thermal conductivity obtained was in the nanofluid with 0.3% MWCNT and 5% CTAB at 0.72 W/mK. For the steel hardness, the value was roughly stable at 33 – 35 HRC in the nanofluid with no CTAB and 3 – 5% CTAB addition. Excessive surfactant addition at 30% CTAB decrease the hardness significantly up to 17 HRC.

Abstract: QP steels and other third generation AHSS possess outstanding combinations of strength and ductility, making them very attractive for the automotive sector. However, an Achilles heel of these materials is their rather limited weldability. Despite the obvious importance of this problem, very few works have been published characterising 3^rd generation AHSS welded joints. For the current contribution, 3 novel QP stainless steels were investigated. Resistance spot welded joints were prepared following QP treatment of sheets. Results following paint baking revealed a high nugget hardness and a microstructure of martensite, retained austenite and delta ferrite. Cross tension strength was highest for the alloy with an optimum dispersion of retained austenite which improved weld metal toughness despite the high hardness. A further improvement in cross tension strength was realised on tempering at high temperatures, leading to an 60% improvement in strength, thanks to improved toughness of the martensite constituent.

Abstract: In this work, the preparation and processing of aluminum-copper alloys, which added amounts of copper to aluminum in different parentages (2, 4, 5%) so that it does not exceed the saturation limit for aluminum (6% Copper). After adding these specific amounts of copper to aluminum, have been melting each alloy to thaw copper in aluminum fully and diffusion copper atoms in it, and after that the specimens were prepared and quenched at 8-30 hours and rapid cooling in the water, and then were studied parameters of heat treatment and different percentages of copper. It is clear from the schemes and experimental results that each weight ratio of copper in aluminum has a different approach to reach the best mechanical properties. After performing mechanical tests and tests, it was found that the highest hardness of the (aluminum-copper) alloy in the case of (2% Cu) amounted to (120 HB) and in the case of (4% Cu) the amount (211 HB) and in the case of (5% Cu) the amount (188 HB).

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: Tailored Tool Tempering (TTT) is an innovative method able to calibrate the strength and ductility characteristics of the components manufacture by means of Press-Hardening process. The process parameters that most influence the final mechanical properties of the soft zone are quenching time and temperature of the heated tools.In this work, with the aim of defining a process window to estimate the soft zone properties of an automotive B-pillar in Usibor^®2000 steel using TTT Press-Hardening approach, the strength and ductility of the soft zone are studied varying the quenching time and the temperature of the heated tools. Using a numerical-experimental approach, a Finite Element (FE) model is firstly developed in AutoForm to simulate the TTT Press-Hardening process and to define thermo-mechanical cycles that are characteristics of the soft zone as a function of quenching parameters (quenching time and temperature of the heated tools). FE thermo-mechanical cycles are then physically simulated on Usibor^®2000 specimens using Gleeble 3180 system. The treated specimens are subsequently subjected to micro-hardness and tensile tests. Experimental results are adopted to train an artificial neural network used to construct the process window.

Abstract: Taking ZL101A alloy as the research object, the ZL101A alloy test bar was solution treated at 535°C and kept for 5 hours, and then quenched at 25°C, 50°C, 70°C, 90°C water temperature conditions. And then aging the quenched alloy sample at 150°C and heat preservation for 3.5h. After tensile test, Brinell hardness test, using metallographic microscope, scanning electron microscope to observe the metallographic structure, fracture morphology and other methods of analysis, and summarized the changes in the structure and properties of ZL101A alloy under different quenching water temperature conditions. The results show that the elongation, reduction of area, and tensile strength of ZL101A alloy quenched at 70°C are the highest, and the Brinell hardness is the highest when the quenching water temperature is 25°C. Comprehensive practical application, the comprehensive mechanical properties of ZL101A alloy quenched at 70°C are the best.

Abstract: The relationship between the interaction of ferromagnetically ordered clusters in austenite with dislocations, twinning and nucleation of the martensite phase is considered. It is shown that the regions with short-range order existing in austenite affect the dislocation structure. In turn, dislocations are involved in the formation of twins and martensite nuclei. The imposition of an external magnetic field enhances the magnetic inhomogeneity of austenite and the effects of magnetoelastic interaction between clusters and dislocations.