Grain refinement to improve impact toughness in 9Cr–1Mo steel through a double austenitization treatment

Karthikeyan, T.; Paul, V. Thomas; Saroja, S.; Moitra, A.; Sasikala, G.; Vijayalakshmi, M.

doi:10.1016/j.jnucmat.2011.08.010

Cited by 64 publications

(13 citation statements)

References 29 publications

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“…Tempering is one of the methods for PWHT that is able to release the welding stress and stabilize the microstructure of the welded rotor steel [21][22][23][24]. Generally, the welded rotor is heated to a higher temperature with a certain heating speed and then the welded rotor is insulated for a period of time followed by a cooling process with a lower cooling rate in the furnace or air because of the large size and high thickness of the welded rotor [25,26].…”

Section: Introductionmentioning

confidence: 99%

Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment

Liu

Cai

Yang

et al. 2018

Metals

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The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel low-pressure steam turbine welded rotor under different post-weld heat treatment (PWHT) conditions are investigated. The fractography and microstructure of weld metal after PWHT are characterized by optical microscope, SEM, and TEM, respectively. The Charpy impact test is carried out to evaluate the toughness of the weld. The optical microscope and SEM results indicate that the as-welded sample is composed of granular bainite, acicular ferrite and blocky martensite/austenite (M-A) constituent. After PWHT at 580 • C, the blocky M-A decomposes into ferrite and carbides. Both the number and size of precipitated carbides increase with holding time. The impact test results show that the toughness decreases dramatically after PWHT and further decreases with holding time at 580 • C. The precipitated carbides are identified as M 23 C 6 carbides by TEM, which leads to the dramatic decrease in the toughness of TIG weld metal of 25Cr2Ni2MoV steel.

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Section: Introductionmentioning

confidence: 99%

Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment

Liu

Cai

Yang

et al. 2018

Metals

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“…Then, grains could either be refined or coarsened depending on the holding time and temperatures [ 2 ]. It was reported by Karthikeyan et al [ 3 ] that the grain size of 9Cr-1Mo steel was refined from 26 to 12 μm via high temperature holdings. The grain size of 22MnB5 carbon steel was significantly refined by short austenization at 900 °C for 2 s, and the tensile properties and hardness were greatly enhanced [ 4 ], whereas, high temperature holdings for a long period of time could lead to grain coarsening of steels.…”

Section: Introductionmentioning

confidence: 99%

In Situ Investigation of Grain Evolution of 300M Steel in Isothermal Holding Process

Chen

Zheng

et al. 2018

Materials

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The relationships between initial microstructures, process parameters, and grain evolutions in isothermal holdings have drawn wide attention in recent years, but the grain growth behaviors of 300M steel were not well understood, resulting in a failure in precise microstructure controlling in heat treatment. In this work, in situ observations were carried out to characterize the grain evolutions of 300M steel with varying holding time, holding temperatures, and initial microstructures. The intriguing finding was that the grain refinement by austenization of 300M steel was followed by a dramatic grain growth in the initial stage of holding (≤~600 s), and with increasing time (~600–7200 s), the average grain size appeared to have a limit value at specific temperatures. The austenization process accelerated the grain growth by generating large quantity of grain boundaries at the initial stage of holdings, and the growth rate gradually slowed down after holding for ~600 s because the driven force was weakened due to the reduction of grain boundary energy. The initial structure and the initial grain size of 300M steel had no obvious influences on the grain size evolutions. The mechanisms of grain growth were analyzed based on in situ observations and transmission electron microscope (TEM) characterizations. A grain evolution model considering the grain boundary migration of 300M steel was established for the isothermal holding process. Good agreement was obtained between the in situ observation results and the model calculation results. This investigation aimed to understand fundamentally the grain evolutions of 300M steel in the isothermal holding process.

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“…Table 4 shows the statistical results for misorientation angles in the alloys. Wang et al [29] and Karthikeyan et al [30] classified original austenite grain boundaries in martensitic steels as HABs, and sub-grain and martensite lath boundaries as LABs. The increase in the proportion of LABs indicated that sub-grains gradually formed during aging at 550 • C. The coarsening and growth of austenite grains would be responsible for the reduction in HABs in steel during aging and the reduction of the unit volume of HABs.…”

Section: Microstructurementioning

confidence: 99%

Effects of Yttrium on Microstructure Stability and Tensile Properties of China Low Activation Martensitic Steel

Qiu

Zhan

et al. 2019

Metals

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This study investigated the microstructural stability and mechanical properties exhibited by China low activation martensitic (CLAM) steels with different yttrium (Y) contents over 3000 h of aging at 550 °C. Scanning electron microscopy, electron backscatter diffraction analysis, and transmission electron microscopy were employed to investigate the microstructural evolution of the steels. Results indicated that grain boundary migration was slow and the Laves phase precipitation was delayed in Y-containing steels. Grain boundaries at different angles in 0Y and 6Y CLAM steels were significantly affected, and those in 36Y and 71Y alloys exhibited negligible changes during the long-term thermal aging. Moreover, Y contents had appreciable effects on the strength and toughness of the aged steels. The stable microstructure of Y-containing CLAM alloys is responsible for improved strength and impact toughness during aging.

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Grain refinement to improve impact toughness in 9Cr–1Mo steel through a double austenitization treatment

Cited by 64 publications

References 29 publications

Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment

Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment

In Situ Investigation of Grain Evolution of 300M Steel in Isothermal Holding Process

Effects of Yttrium on Microstructure Stability and Tensile Properties of China Low Activation Martensitic Steel

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