Metallurgical Assessment of the Softened HAZ Region During Multipass Welding

1997 ◽  
Vol 122 (2) ◽  
pp. 310-315 ◽  
Author(s):  
D. Wojnowski ◽  
Y. K. Oh ◽  
J. E. Indacochea
Keyword(s):  
Heat Affected Zone ◽  
Thermal Cycle ◽  
High Stress ◽  
Life Extension ◽  
Limiting Factor ◽  
Weld Repair ◽  
Tem Analysis ◽  
Pressure Steam ◽  
Good Creep Resistance ◽  
Softening Region

CrMoV steels are used in high temperature and high stress sections of power plant members; their good creep resistance is impaired by welding done during fabrication of assemblies and weld repair of service damaged rotors. Occurrence of a “softening” (“tempered”) region in the grain refined heat-affected zone/intercritical heat-affected zone, has become the limiting factor in the life extension of weld repaired high pressure/intermediate pressure steam turbine rotors. This study focuses on the effect that multiple thermal cycles have on the development of this softened region. Work was conducted on real weldments and with simulated heat-affected zones produced with the Gleeble thermomechanical simulator and by isothermal furnace heat treatments. The thermal cycle at the softening region in the actual weldment was measured and reproduced during simulation; it was estimated that the peak temperature at this location was just above the intercritical A1 temperature. Softening occurred before any changes in microstructure could be detected with the light microscope. Carbide coarsening, shown by limited TEM analysis, and the likely dissolution of some of the carbides, most probable, contributed to reduce the microhardness values. [S1087-1357(00)70202-4]

scholarly journals EBSD and TEM Analysis of the Heat Affected Zone of Laser Welded AISI 304/308 Stainless Steel

2017 ◽  
Vol 23 (S1) ◽  
pp. 2212-2213 ◽  
Author(s):  
Keyou Mao ◽  
Yaqiao Wu ◽  
Janelle P. Wharry
Keyword(s):  
Stainless Steel ◽  
Heat Affected Zone ◽  
Tem Analysis ◽  
Aisi 304

scholarly journals Comparative Study of Laser-Arc Hybrid Welding for AA6082-T6 Aluminum Alloy with Two Different Arc Modes

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 407 ◽  
Author(s):  
Xiaohui Han ◽  
Zhibin Yang ◽  
Yin Ma ◽  
Chunyuan Shi ◽  
Zhibin Xin
Keyword(s):  
Aluminum Alloy ◽  
Heat Affected Zone ◽  
Metal Transfer ◽  
Inert Gas ◽  
Hybrid Welding ◽  
Cold Metal Transfer ◽  
Melted Zone ◽  
Cold Metal ◽  
Fracture Features ◽  
Softening Region

The effects of arc modes on laser-arc hybrid welding for AA6082-T6 aluminum alloy were comparatively studied. Two arc modes were employed: pulsed metal inert gas arc and cold metal transfer arc. The results indicated that joints without porosity, undercutting, or other defects were obtained with both laser-pulsed metal inert gas hybrid welding (LPMHW) and laser-cold metal transfer hybrid welding (LCHW). Spatter was reduced, and even disappeared, during the LCHW process. The sizes of equiaxed dendrites and the width of the partially melted zone in the LPMHW joint were larger than those in the LCHW joint. The microhardness in each zone of the LPMHW joint was lower than that of the LCHW joint. The softening region in the heat-affected zone of the LPMHW joint was wider than that of the LCHW joint. The tensile strength of the LCHW joint was higher than that of the LPMHW joint. For the two joints, the fractures all occurred in the softening region in the heat-affected zone, and the fracture morphologies showed ductile fracture features. The dimples in the fractograph of the LCHW joint were deeper than those of the LPMHW joint.

Microstructure and Properties of Heat-Affected Zones in X100 Steel Grade Line Pipes

2009 ◽  
Author(s):  
Chuanjing Zhuang ◽  
Na Li ◽  
Shipeng Wang ◽  
Weiping Lin ◽  
Jicheng Ren
Keyword(s):  
Heat Affected Zone ◽  
Thermal Cycle ◽  
Deleterious Effect ◽  
Ferrite Matrix ◽  
Steel Grade ◽  
Peak Temperature ◽  
Coarse Grained ◽  
Microstructure And Properties ◽  
The Relationship ◽  
Second Peak

The relationship between microstructure and properties of weld heat-affected zones in X100 grade pipeline steels was studied. It was found that the intercritically reheated coarse-grained heat-affected zone (IRCGHAZ) of experimental steels has the lowest toughness values when the second peak temperature is at the intercritical (α + γ) region during multi-pass welding. The local embrittlement is attributed to the morphology, amount, and size of the M-A constituent. It is also found that the microstructural inheritance at IRCGHAZ has a deleterious effect on toughness. On the basis of the experimental results, it is suggested that the local embrittlement could be prevented by using pre-heating or post-heating thermal cycle. Pre-heating thermal cycle would eliminate the microstructural inheritance and meliorate M-A constituent. Furthermore, the use of a post-heating thermal cycle will improve the morphology, amount and size of the M-A constituent, and improve the conformation of ferrite matrix.

Characterization of the Ni–Mo–Cr superalloy subjected to simulated heat-affected zone thermal cycle treatment

2015 ◽  
Vol 643 ◽  
pp. 7-16 ◽  
Author(s):  
Yanming He ◽  
Jianguo Yang ◽  
Chunjie Qin ◽  
Shuangjian Chen ◽  
Zengliang Gao
Keyword(s):  
Heat Affected Zone ◽  
Thermal Cycle

scholarly journals Effects of Water Stress on Boron Partitioning and Glucosinolate Composition in Two Hydroponically Grown Canola Cultivars

HortScience ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 673b-673
Author(s):  
Barbara Kocourkova ◽  
Craig S. Charron ◽  
Charles Graves ◽  
Norman K. Lownds ◽  
Carl E. Sams
Keyword(s):  
Water Stress ◽  
Inductively Coupled Plasma ◽  
Block Design ◽  
High Stress ◽  
Emission Spectrometry ◽  
Glucosinolate Content ◽  
Limiting Factor ◽  
Inductively Coupled ◽  
Indole Glucosinolate ◽  
High Stress Level

High glucosinolate content in brassica meal is a limiting factor in consumption of rapeseed. In recent years canola cultivars of rapeseed with decreased glucosinolate content have been developed. However, environmental and nutritional factors are also believed to influence glucosinolate content. This study was conducted to determine the relationships among water stress, B nutrition, and glucosinolate content in canola. Two canola cultivars (`Cyclone' and `American A112') were grown in a continuously recirculating hydroponic system with modified Hoagland solution (0.6 ppm B). Water stress was induced gradually (2% per day using polyethylene glycol 8000) starting when plants were 4 weeks old. Osmotic potential was maintained at –0.1 MPa (high stress level), –0.085 MPa (medium stress), or 0.05 MPa (control). Treatments were arranged in a randomized incomplete-block design, with three blocks, four replications, two cultivars, and three treatments. Upper leaves (no. 15 and higher) were collected and analyzed by inductively coupled plasma emission spectrometry for B content. Total and indole glucosinolate content of seeds were measured colorimetrically and by HPLC. The leaf B content of stressed plants decreased by 55% in `Cyclone' and 29% in `American A112'. Total glucosinolate content increased 28% and 12%, respectively, in stressed plants of `Cyclone' and `American A112'. Indole glucosinolate content was 44% and 13% higher in the same plants. The interaction between cultivar and water stress was not significant for glucosinolate content but was significant for B content of the leaves.

Rotor Welding: TVA Experience

2008 ◽  
Author(s):  
H. G. Best ◽  
M. E. Koss
Keyword(s):  
High Stress ◽  
Base Material ◽  
Turbine Rotor ◽  
Third Party ◽  
Fossil Plant ◽  
Weld Repair ◽  
Stress Region ◽  
Turbine Rotors ◽  
Additional Base ◽  
Single Flow

TVA has a fleet of 59 units with 187 large steam fossil turbine rotors, 68 fossil generators, and 27 auxiliary turbine rotors, in-service. The original equipment manufacturers (OEM) rotors have three designs some welded, others are shrunk on disk, but the majority of the rotors are mono-block. TVA has worked with OEM’s, third parties, and with-in TVA to perform weld repairs on rotors. Rotor Problems requiring welding: 1. Journal/gland damage due to lubrication failure and/or wear. 2. Attachment area damage due to cracks or distortion. 3. Attachment area due to changes in design. In the TVA fleet there are approximately 20 rotors that have been welded. Most of these have been successfully operated, but there have been 3 failures of welded rotors that will be discussed. Allen Fossil Plant Unit 3 Intermediate Pressure–Low Pressure Single Flow Turbine Rotor: In 1992 this rotor had a failure of the Curtis Stage. The decision was made to have the rotor welded and change the number of blades. Westinghouse (the OEM) performed the design and weld repair. In 2000 the unit experienced vibration, the unit was disassembled, and the weld repair had failed at the fusion line. An investigation of the failure revealed the weld had not been located at the designed location and the actual location of the weld was in a high stress area. Gallatin Fossil Plant Unit 4 High Pressure Turbine Rotor: TVA designed an upgrade to the Rateau Stage to change from axial entry to a tri-pin attachment. This required the welding of the disk. During welding, with a third party, cracks resulted that extended into the base material. This failed and additional base material was removed before welding. After 8 years of operation the rotor experienced vibration, the unit was inspected, and the weld was found with creep cracks in the heat affected zone (HAZ). An investigation of the failure revealed the expanded weld build-up relocated the HAZ into a high temperature, high stress region of the rotor. Widows Creek Fossil Plant Unit 7 Boiler Feed Pump Turbine Rotor: The rotor experienced stress corrosion cracking (SCC) of the fifth stage during operation in 2003. The rotor was weld repaired and returned to service in 2006. After 5 months of operation the rotor experienced vibration, was inspected, and the welded fifth stage and the sixth stage had experience SCC failures.

scholarly journals How Nanoscale Dislocation Reactions Govern Low- Temperature and High-Stress Creep of Ni-Base Single Crystal Superalloys

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 134 ◽  
Author(s):  
David Bürger ◽  
Antonin Dlouhý ◽  
Kyosuke Yoshimi ◽  
Gunther Eggeler
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
High Stress ◽  
Shear Stresses ◽  
Creep Tests ◽  
Shear Creep ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Crystallographic Shear ◽  
Shear System

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

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