Papers by Keyword: Tempering

Abstract: The article deals with the problems of withstanding harsh temperatures by steel and iron. The authors of the work discuss iron denser high-temperature of γ modification and maximums and minimums of impact. In addition, the article analyses the transformations of iron and anomalies of properties: peak of heat capacity, acceleration of diffusion, etc. The authors take into account the consensus on the causes of polymorphism and the theoretical model of ferromagnetism. Besides, there is a consideration of "transformation" in interaction between Fe atoms that produce anomalies of steel properties. It is necessary to note the transformation detected by anomalies of any properties including mechanical. In the presented work the authors have made an attempt to prove transformations in iron at ~650 °C on the basis of extreme values of hardness and microhardness, metallographic structure, parameters of fine structure, precipitation resistance force depending on temperature. Therefore, the analysis of literature sources on physical and mechanical properties of iron and its derivatives has been made.

Abstract: Currently, hard alloys are common tool materials; they are widely used in the tool manufacturing industry. Due to the presence of refractory carbides in its structure, hard-alloy tools feature a high hardness of 80 to 92 HRA (73 to 76 HRC); a high heat resistance (from 800 °С to 1,000 °С); therefore, they can be used at speeds that are several times higher than cutting speeds of high-speed steel grades. Hard alloys are used in the form of plates that are either mechanically fixed on or soldered to tool holders. The main operational parameters, that determine the hard-alloy tool operation mode, are hardness, wear resistance, and bending strength. The operational parameters of alloy are highly dependent on its structure, phase composition, lattice block sizes, and micro-stress values [1-20]. The main methods to enhance physical and mechanical properties of hard-alloy plates are improvement of manufacturing technology, including production of fine-grained alloys and microalloying, as well as applying composite coating by vacuum deposition, which allows to increase the tool resistance 1.5 to 2 times.

Abstract: The quantitative microstructure - impact toughness relationships in two batches of the same steel grade subjected to quenching and tempering (Q&T) have been established via characterization using EBSD technique and FIB visualization. The EBSD-based criterion for separation of structural constituents in microstructure of Q&T low carbon low alloy steels is proposed. Impact toughness differences between two steel batches subjected to nominally identical Q&T are caused by the changes in the volume fraction of structural constituents caused by various cooling conditions at quenching stage. High volume fraction of bainite containing more distorted bainitic ferrite and the highest amount of brittle cementite precipitates leads to the increase in strength and to the decrease in impact toughness.

Abstract: The sharp side of a steel axe is often broken. This part is usually forged into a tapered shape until the front edge is thin and sharp. The purpose of this study was to determine the effect of tempering on the structure and hardness of a steel axe made of AISI 5160 leaf spring steel which has undergone a forging and hardening process. The as-received samples were obtained from a commercial market after undergoing a forging process to reduce their thickness from 10 mm to 5.5 mm in the base part and 1 mm in the front edge part. The hardening process was carried out by heating the samples at a temperature of 850 °C followed by rapid cooling in an isorapid oil. The samples were then tempered with tempering temperatures of 300 °C, 350 °C, and 400 °C. The hardness of the tempered samples was evaluated using a Vickers microhardness tester in three different locations; the base, the middle, and the front edge of the tapered samples. To analyze the property change, the microstructure of the tempered samples was observed using SEM and EDS. The result showed that the hardness of the samples decreased with the increase in tempering temperature. The hardness of the front edge was higher than that of the middle and base part of the tempered samples. The faster cooling rate inside the thinner part was responsible for the higher hardness. The microstructure showed that the martensitic structure that emerged after the hardening process turned into fine tempered martensitic and secondary carbides. The size and amount of carbides increased with increasing tempering temperature

Abstract: The present work is a contribution in investigating the effect of heat treatment on microstructure, hardness and friction wear of A105N steel. Samples of 25x25 mm2 cross-section and 15mm thickness have been prepared from the as-received material and then heat-treated. The samples were austenitized at 1050°C for 60 minutes followed by water quenching, then tempered at 500 and 700°C for 120 minutes. Microstructural changes and their effect on the wear resistance and hardness were investigated according to the applied heat treatments. The main results show that after quenching the structure is mostly composed of quenched martensite, which confers high hardness and friction resistance to the steel. While the tempered structure is composed of tempered martensite and ferrite. As the temperature rises to 700°C, the tempered martensite decreases and is fully transformed to ferrite and cementite. A good wear resistance expressed by a low friction coefficient and a low wear rate is achieved by tempering at 500°C.

Abstract: The effect of tempering time on the microstructure and mechanical properties of SA738 Gr.B nuclear power steel was studied using SEM, TEM and thermodynamic software, and its precipitation and microstructure evolution during tempering were clarified. The results showed that SA738 Gr.B nuclear power steel has better comprehensive mechanical properties after tempering at 650 °C for 1h. With the extension of the tempering time, M₃C transformed into M₂₃C₆ with increasing size, which affected the yield strength and impact energy. When the tempering time is 8h ~ 10h, due to the transformation of M₃C to M₂₃C₆, the composition of matrix around the carbide changed, causing the temperature of A_c1 dropped, forming twin-martensite which deteriorated the impact toughness of the steel.

Abstract: The effect of thermo-mechanical treatment on the microstructural evolution of low carbon micro-alloyed high strength steel was studied by combining prestrain with tempering (PST) in this paper. It was found that the prestrain causes the dislocation to plug up around the grain boundary and carbide, resulting in carbide boundary fragmentation. Moreover, it breaks the thermo-dynamic equilibrium between the matrix and carbide, induces the dissolution of carbon in the high energy state, and then changes the distribution of carbon in the matrix. In the subsequent tempering process, the precipitation regularity of carbide was changed, which promoted the precipitation carbide at low temperature. The influence of carbide precipitation on dislocation can be divided into two stages: the first stage was precipitation induced creep, which promoted stress relaxation; the second stage was precipitation pinning dislocation, which improved material strength and inhibited stress relaxation.

Abstract: This paper considers the effect of hardening of throwaway cutting inserts made of hard alloy T15K6 using continuous laser impact at various modes. Tests were carried outon inserts made of hard alloy T15K6. The cutting properties of the inserts were determined by cutting on a T612 vertical milling machine. A face mill with a diameter of 100 mm with mechanical mounting of tested inserts was used as a tool.Dry milling was performed using two inserts. At that, cutting mode was of impact natureas the mill diameter was larger than the width of machined workpiece. Number of passes – 5. Cutting modes:v = 197 m/min, h = 1 mm, S = 160 mm/min, b = 90 mm. Machiningwasperformedonworkpieces made of 40X grade steel (GOST 4543-71). Workpiecedimensions– 160x60x90 mm. During the machining, hard alloy inserts moved beyond the workpiece edge and cut into it from the other side. One of the main performance characteristics of hard alloys is material rigidity (modulus of elasticity, Е). Tests were carried out after various types of laser impact at bending and material rigidity was determined by strain gauging. Decreasein the slopeofstraight-lineportionofrelativestrain-versus-stress curve at bending indicates the decrease in hard alloys’ modulus of elasticity after laser processing. Small defect structure is being formed.

Abstract: Performance characteristics of hard-alloy tools are largely depends on the structure. The hard-alloy tool structure can be influenced by various factors. The main factors influencing the structure and properties of hard alloys at heat treatment are ВаCl₂ salt bath deoxidation degree, heating temperature, holding time, rate of cooling and cooling medium, temperatures and holding time. Oxidation at temperatures more than 500-600^оС and relatively low thermal conductivity of λ = 27.214 W/(m×K) are characteristic for hard alloys under heating.In this regard, it became necessary to study the salt baths deoxidation processes occurred in the course of heat treatment. Insufficient study of hard alloy heat treatment processes is associated with peculiarity of their structure and large assortment, difficulty of setting heat treatment modes.Research of hard alloy sample heating with the subsequent air cooling (normalization) was carried out in a salt baths in thermal area of tool shop.X-ray diffraction analysis was performed by Williamson-Hall method. In our experiments, coherent scattering regions size and WC phase micro-distortions magnitude were defined using MD-10 microdiffractometer. It was found out that phase structure of hard alloys is not change as a result of heat treatment. There are only reflections from carbide phase planes in the diffraction pattern. A quantitative analysis of diffraction reflection broadening using Williamson-Hall method showed that size of the coherent scattering regions for VK8 and T14K8 hard alloys subjected to hardening procedure is more than for sintered alloys.Relevance of the study is due to the fact that heat treatment involved heating in salt baths can be a promising method of improving mechanical and operational properties of hard alloys. This approach ensures necessary strength and performance characteristics of hard alloys without significant economic expenses.The purpose of this paper is to define effect of ВаCl₂ salt bath deoxidation degree on physical and mechanical properties of VK8 and T14K8 hard alloys.

Abstract: High-carbon high-strength JIS-SUJ2 bearing steel is one of the alloys used as rolling contact applications which need high wear resistance. This high hardness material is broken from non-metallic inclusions under fatigue stress. In this work, we developed a new observation method “fracture surface etching (FSE)” in order to observe the material microstructure on the fracture surface. We succeeded to draw clear grain boundaries on the fracture surfaces and closely observed the material microstructure around the crack origins by the FSE method. We concluded that the crack initiation area boundary is not formed by only the grain boundary, and the grain size around the Al2O3 inclusion on the fracture surface was similar to that of the flat surface which does not have inclusions before fatigue testing.