scholarly journals Microstructure Evolution and Surface Cracking Behavior of Superheavy Forgings during Hot Forging

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Zhenhua Wang ◽  
Hongpeng Xue ◽  
Deli Zhao
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Nuclear Power ◽  
Power Plants ◽  
Hot Forging ◽  
Model Material ◽  
Grain Structure ◽  
High Angle ◽  
Cracking Behavior

In recent years, superheavy forgings that are manufactured from 600 t grade ingots have been applied in the latest generation of nuclear power plants to provide good safety. However, component production is pushing the limits of the current free-forging industry. Large initial grain sizes and a low strain rate are the main factors that contribute to the deformation of superheavy forgings during forging. In this study, 18Mn18Cr0.6N steel with a coarse grain structure was selected as a model material. Hot compression and hot tension tests were conducted at a strain rate of 10−4·s−1. The essential nucleation mechanism of the dynamic recrystallization involved low-angle grain boundary formation and subgrain rotation, which was independent of the original high-angle grain boundary bulging and the presence of twins. Twins were formed during the growth of dynamic recrystallization grains. The grain refinement was not obvious at 1150°C. A lowering of the deformation temperature to 1050°C resulted in a fine grain structure; however, the stress increased significantly. Crack-propagation paths included high-angle grain boundaries, twin boundaries, and the insides of grains, in that order. For superheavy forging, the ingot should have a larger height and a smaller diameter.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

The Effects of Ion Implantation on the Surface Features of Inconel 600

1985 ◽  
Vol 43 ◽  
pp. 288-289
Author(s):  
John D. Rubio
Keyword(s):  
Grain Boundary ◽  
Ion Implantation ◽  
Nuclear Power ◽  
Power Plants ◽  
Surface Region ◽  
Selective Dissolution ◽  
Boundary Region ◽  
Near Surface ◽  
Inconel 600 ◽  
Steam Generator Tubing

The degradation of steam generator tubing at nuclear power plants has become an important problem for the electric utilities generating nuclear power. The material used for the tubing, Inconel 600, has been found to be succeptible to intergranular attack (IGA). IGA is the selective dissolution of material along its grain boundaries. The author believes that the sensitivity of Inconel 600 to IGA can be minimized by homogenizing the near-surface region using ion implantation. The collisions between the implanted ions and the atoms in the grain boundary region would displace the atoms and thus effectively smear the grain boundary.To determine the validity of this hypothesis, an Inconel 600 sample was implanted with 100kV N2+ ions to a dose of 1x1016 ions/cm2 and electrolytically etched in a 5% Nital solution at 5V for 20 seconds. The etched sample was then examined using a JEOL JSM25S scanning electron microscope.

Study on the Influence of Strain Rate on Crack Initiation and Growth in Simulated Reactor Coolant Environment of Type 316 Stainless Steel

2018 ◽  
Author(s):  
Takahisa Nose ◽  
Takao Nakamura ◽  
Takanori Kitada
Keyword(s):  
Crack Initiation ◽  
Strain Rate ◽  
Nuclear Power ◽  
Power Plants ◽  
Fatigue Crack Initiation ◽  
Crack Size ◽  
Strain Rates ◽  
3 Dimensional ◽  
Reactor Coolant ◽  
Cumulative Fatigue Damage

In order to conduct effective and rational maintenance activity of components in nuclear power plants, it is proposed to manage fatigue degradation based on crack size corresponding to an extent of cumulative fatigue damage. The purpose of this study focuses on the influence of strain rate in simulated reactor coolant environment for fatigue crack initiation and growth. 3-dimensional replica observations were conducted for environmental fatigue test specimens in different strain rates. Crack initiation and growth were observed in the experiments. It is clarified that low strain rate influences crack propagation and coalescence and increases crack growth rate that finally decrease fatigue life.

Strain Rate Effects in SA-106 Carbon Steel Pipe

1982 ◽  
Vol 104 (1) ◽  
pp. 31-35 ◽  
Author(s):  
D. Peterson ◽  
J. E. Schwabe ◽  
D. G. Fertis
Keyword(s):  
Carbon Steel ◽  
Yield Strength ◽  
Strain Rate ◽  
Tensile Properties ◽  
Nuclear Power ◽  
Power Plants ◽  
Experimental Modeling ◽  
Steel Pipe ◽  
Strain Rate Effects ◽  
Rate Effects

Experiments were performed to measure the effect of strain rate on the tensile properties of SA-106 carbon steel pipe, in support of analysis and experimental modeling of postulated pipe whip in nuclear power plants. It was observed that increasing the strain rate from 4 × 10−4 to 4 s−1 raised the yield strength by approximately 30 percent.

Critical Strain Model of Cr4 Steel for Heavy Supporting Roller

2011 ◽  
Vol 117-119 ◽  
pp. 1770-1773
Author(s):  
Xue Wen Chen ◽  
Qi Zhang
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Deformation Temperature ◽  
Critical Strain ◽  
Hot Forging ◽  
Forming Process ◽  
Supporting Roller ◽  
The Mathematical Model ◽  
Strain Model ◽  
Hot Forging Process

Critical strain is the basis to determine whether the dynamic recrystallization occurs during hot deformation process, it is important for designers to control hot forming process and microstructure of final product. In order to investigate the influence of deformation temperature and strain rate on critical strain of Cr4 steel, hot compression simulation experiment was conducted for Cr4 steel in the temperature range of 750～1200°C and strain rate of 0.002～5S-1 by means of Gleeble−1500D thermo-simulation machine. The results showed that the critical strain increase with decreasing deformation temperature and increasing strain rate. Based on the experimental data and regression analysis method, the mathematical model of the critical strain of Cr4 steel is constructed. The critical strain model provides data support to predict the dynamic recrystallization during Cr4 heavy supporting roller hot forging process.

Grain Structure Refinement in Nickel Alloy Welds by Magnetic Arc Stirring

2011 ◽  
Author(s):  
Steven L. McCracken ◽  
X. Yu ◽  
Y. C. Lim ◽  
D. F. Farson ◽  
S. S. Babu
Keyword(s):  
Nickel Alloy ◽  
Weld Pool ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Structure Refinement ◽  
Grain Structure ◽  
High Chromium ◽  
Dilution Effects ◽  
Alloy Weld

Nickel alloys with high chromium content provide optimum resistant to stress corrosion cracking for service in the reactor coolant system of commercial nuclear power plants. High chromium nickel-base alloys however present many challenges, such as less than ideal weldability and susceptibility to solidification cracking or solid-state cracking depending on welding conditions and dilution effects with dissimilar metals. Moreover, the presence of large solidification grains, typical of nickel alloy weld metals, makes ultrasonic examination of the weldment difficult. Magnetic stirring of the nickel alloy weld pool has the potential to address these challenges and improve joining, overlay welding, cladding, and repair of critical components in commercial nuclear power plants. This study evaluates use of magnetic arc stirring to modify weld pool solidification conditions in order to promote a fine solidification grain structure in nickel alloy welds.

Hot Workability of Ultrafine-Grained Aluminum Alloy Produced by Severe Plastic Deformation of Al6063 Powder and Consolidation

2010 ◽  
Vol 667-669 ◽  
pp. 979-984 ◽  
Author(s):  
Hamed Asgharzadeh ◽  
Abdolreza Simchi ◽  
Hyoung Seop Kim
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Hot Deformation ◽  
Grain Structure ◽  
Al Alloy ◽  
Strain Rates ◽  
Hot Workability ◽  
Ultrafine Grained

Al6063 powder was subjected to severe plastic deformation via high-energy mechanical milling to prepare ultrafine-grained (UFG) aluminium alloy. Uniaxial compression test at various temperatures between 300 and 450 °C and strain rates between 0.01 and 1 s-1 was carried out to evaluate hot workability of the material. Microstructural studies were performed by EBSD and TEM. The average activation energy and strain rate sensitivity of the hot deformation process were determined to be 280 kJ mol-1 and 0.05, respectively. The deformation temperature and applied strain rate significantly affected the grain structure of UFG Al alloy. A finer grain structure was obtained at lower temperatures and higher strain rates. The formation of highly misoriented and equiaxed grains also revealed that dynamic recrystallization occurred upon hot deformation. Furthermore, elongated grains with high dislocation density were observed that disclosed partial dynamic recrystallization of the aluminum matrix.

Corrosion Behavior of Si3N4 Ceramics under High-Temperature and High-Pressure Water Condition

2007 ◽  
Vol 26-28 ◽  
pp. 259-262 ◽  
Author(s):  
Weon Ju Kim ◽  
Seok Min Kang ◽  
Ji Yeon Park
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Grain Boundary ◽  
Corrosion Behavior ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Boundary Phase ◽  
Pressure Water ◽  
Si3n4 Ceramics

Silicon nitride (Si3N4) ceramics have been considered for various components of nuclear power plants such as mechanical seal of reactor coolant pump (RCP), guide roller for control rod drive mechanism (CRDM), and seal support, etc. Corrosion behavior of Si3N4 ceramics in high-temperature and high-pressure water must be elucidated before they can be considered for components of nuclear power plants. In this study, the corrosion behaviors of Si3N4 ceramics at hydrothermal condition (300°C, 9.0 MPa) were investigated in pure water. The grain-boundary phase was preferentially corroded and the corrosion reaction was controlled by the diffusion of the reactive species and/or products through the corroded layer. Results of this study imply that the variation of sintering aids and/or the control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of Si3N4 ceramics in high-temperature water.

scholarly journals Effect of twinning and Al-Nd phase on dynamic recrystallization in rolled Mg-Al-Zn-Nd alloy at the moderate strain rate

2021 ◽  
Author(s):  
Xiaoming Cui ◽  
Zhengguang Wang ◽  
Zhilei Yu ◽  
Fei Liu ◽  
Xueping Zhao ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Hot Rolling ◽  
Electron Backscatter Diffraction ◽  
Energy Dispersive Spectrometer ◽  
Strain Rate Range ◽  
Nucleation Effect ◽  
Backscatter Diffraction ◽  
Rolling Deformation

Abstract The dynamic recrystallization of Mg-Al-Zn-Nd alloy during moderate strain rate rolling was studied using electron backscatter diffraction (EBSD) and an energy dispersive spectrometer (EDS). The results showed three kinds of twinnings produced in the alloy in the strain rate range of 4.2 s-1 ~ 7.3 s-1, including {101 ̅2} extension twinning, {101 ̅1} contraction twinning, and {101 ̅1}-{101 ̅2} double twinning. The extension twinnings decreased gradually with the increase of strain rate. The dynamic recrystallization mechanisms during hot rolling under moderate strain rate conditions mainly include grain boundary nucleation, twinning nucleation, and secondary particle assistant nucleation. The dynamic recrystallization mechanism induced by twinning is mainly {101 ̅1}-{101 ̅2} double twinnings. In addition, the strain value near the Al-Nd phase and grain boundary is higher than in grain. The Al-Nd particles in Mg-Al-Zn-Nd alloy play an auxiliary nucleation effect on dynamic recrystallization during hot rolling deformation.

Sign in / Sign up

Export Citation Format

Share Document