Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment
To improve the microstructure and mechanical properties of heat-resistant 12Kh1MF steel after long-term operation in the stretched bend zone of the main steam pipeline of a thermal power plant, restorative heat treatment (RHT) was proposed. The RHT mode consisted of two normalization stages (from te...
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2024-12-01
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| author | Halyna Krechkovska Ivan Tsybailo Ihor Dzioba Oleksandra Student Robert Pała |
| author_facet | Halyna Krechkovska Ivan Tsybailo Ihor Dzioba Oleksandra Student Robert Pała |
| author_sort | Halyna Krechkovska |
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| description | To improve the microstructure and mechanical properties of heat-resistant 12Kh1MF steel after long-term operation in the stretched bend zone of the main steam pipeline of a thermal power plant, restorative heat treatment (RHT) was proposed. The RHT mode consisted of two normalization stages (from temperatures of 1100 and 960 °C, respectively) followed by tempering at a temperature of 740 °C. The RHT mode, regulated for steel in the initial state, was applied only after its normalization from a significantly higher temperature (1100 °C). It was shown that the proportion of fine grains in the steel structure increased to 55% over the entire pipe wall thickness after using RHT. At the same time, the proportion of large grains in the restored steel decreased significantly (to 10%), while in exploited steel, their proportion reached almost 50%. The proposed RHT mode increased the hardness, strength, plasticity, and resistance to brittle fracture of the restored steel relative to the corresponding characteristics of the operated steel. The maximum positive effect of the RHT was obtained during impact testing. The fractographic features of the exploited and restored steel were studied on fractures of samples tested by tension. The main fractographic feature of the operated steel was nanosized particles at the bottom of large dimples. These tiny particles were considered to be fragments of large carbides formed due to their final decohesion from the matrix during tensile testing. However, such nanosized particles were not found on the samples’ fracture surfaces in the steel after restorative heat treatment. In addition, the ductile dimples on the fractures of the restored steel were more prominent, which indicated high energy costs for their formation. Thus, all the obtained research results suggest the possibility of using the proposed RHT mode to extend the service life of long-operated critical elements of a thermal power plant’s steam pipelines. |
| format | Article |
| id | doaj-art-84838270b97448a0a415628fc291e127 |
| institution | Kabale University |
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| language | English |
| publishDate | 2024-12-01 |
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| series | Metals |
| spelling | doaj-art-84838270b97448a0a415628fc291e1272025-01-24T13:41:25ZengMDPI AGMetals2075-47012024-12-011512110.3390/met15010021Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat TreatmentHalyna Krechkovska0Ivan Tsybailo1Ihor Dzioba2Oleksandra Student3Robert Pała4Department of Diagnostics of Materials Corrosion-Hydrogen Degradation, Karpenko Physico-Mechanical Institute of the National Academy of Science of Ukraine, 5 Naukova Str., 79060 Lviv, UkraineDepartment of Diagnostics of Materials Corrosion-Hydrogen Degradation, Karpenko Physico-Mechanical Institute of the National Academy of Science of Ukraine, 5 Naukova Str., 79060 Lviv, UkraineFaculty of Mechatronics and Mechanical Engineering, Kielce University of Technology, Av. 1000-An. of Polish State 7, 25-314 Kielce, PolandDepartment of Diagnostics of Materials Corrosion-Hydrogen Degradation, Karpenko Physico-Mechanical Institute of the National Academy of Science of Ukraine, 5 Naukova Str., 79060 Lviv, UkraineFaculty of Mechatronics and Mechanical Engineering, Kielce University of Technology, Av. 1000-An. of Polish State 7, 25-314 Kielce, PolandTo improve the microstructure and mechanical properties of heat-resistant 12Kh1MF steel after long-term operation in the stretched bend zone of the main steam pipeline of a thermal power plant, restorative heat treatment (RHT) was proposed. The RHT mode consisted of two normalization stages (from temperatures of 1100 and 960 °C, respectively) followed by tempering at a temperature of 740 °C. The RHT mode, regulated for steel in the initial state, was applied only after its normalization from a significantly higher temperature (1100 °C). It was shown that the proportion of fine grains in the steel structure increased to 55% over the entire pipe wall thickness after using RHT. At the same time, the proportion of large grains in the restored steel decreased significantly (to 10%), while in exploited steel, their proportion reached almost 50%. The proposed RHT mode increased the hardness, strength, plasticity, and resistance to brittle fracture of the restored steel relative to the corresponding characteristics of the operated steel. The maximum positive effect of the RHT was obtained during impact testing. The fractographic features of the exploited and restored steel were studied on fractures of samples tested by tension. The main fractographic feature of the operated steel was nanosized particles at the bottom of large dimples. These tiny particles were considered to be fragments of large carbides formed due to their final decohesion from the matrix during tensile testing. However, such nanosized particles were not found on the samples’ fracture surfaces in the steel after restorative heat treatment. In addition, the ductile dimples on the fractures of the restored steel were more prominent, which indicated high energy costs for their formation. Thus, all the obtained research results suggest the possibility of using the proposed RHT mode to extend the service life of long-operated critical elements of a thermal power plant’s steam pipelines.https://www.mdpi.com/2075-4701/15/1/21heat-resistant steelrestorative heat treatmentmicrostructuremechanical propertiesfractographic features |
| spellingShingle | Halyna Krechkovska Ivan Tsybailo Ihor Dzioba Oleksandra Student Robert Pała Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment Metals heat-resistant steel restorative heat treatment microstructure mechanical properties fractographic features |
| title | Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment |
| title_full | Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment |
| title_fullStr | Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment |
| title_full_unstemmed | Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment |
| title_short | Restoration of Properties of Heat-Resistant Steel After Long-Term Operation in Steam Pipeline Bends of TPP by Heat Treatment |
| title_sort | restoration of properties of heat resistant steel after long term operation in steam pipeline bends of tpp by heat treatment |
| topic | heat-resistant steel restorative heat treatment microstructure mechanical properties fractographic features |
| url | https://www.mdpi.com/2075-4701/15/1/21 |
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