Fracture Toughness After Long-Term Aging in 9Cr-1Mo-V Steel for Pressure Vessels

2014 ◽  
Author(s):  
Takeo Miyamura ◽  
Shigenobu Nanba ◽  
Tomoaki Nakanishi ◽  
Masato Yamada
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Aging Time ◽  
Charpy Impact ◽  
Pressure Vessels ◽  
High Temperature Strength ◽  
Boiler Tube ◽  
Treatment Conditions ◽  
The Impact

9Cr-1Mo-V steel with excellent high temperature strength is one of candidate materials for advanced pressure vessels in oil-refining plants, whose process temperature is expected to be around 500°C. Although 9Cr-1Mo-V steel has been applied as boiler tube material in power generation for a few decades, it was reported that embrittlement occurred after long-term aging around 600°C which is accelerated condition for pressure vessel operation. Since pressure vessels are more sensitive in stress-concentration around crack tip than boiler tube because of its large wall thickness, fracture toughness is an important property of concern when 9Cr-1Mo-V steel is applied to pressure vessels. In this research, 9Cr-1Mo-V steel with tempered-martensitic microstructure was aged up to max. 10000 hr at 500, 550 and 600°C, and fracture toughness was evaluated after the aging by Charpy impact test. The influence of heat treatment conditions such as austenitizing, tempering and PWHT were also investigated, because the heat treatment conditions used in pressure vessels are different from those of boiler tube. In case of samples treated under the conditions for pressure vessels, Charpy impact values at 0°C were sufficient around 200J before aging, and decreased after aging depending on its conditions, and longer time and higher temperature led to more severe degradation. When the aging time at 550°C and 600°C was converted to the equivalent aging time at 500°C by Larson-Miller-equation, the impact value was estimated to keep over 50J after several decades at the operating temperature for pressure vessels. In contrast to the conditions for pressure vessels, the heat treatment conditions used in boiler tube made initial impact value decreased significantly, because tempering and PWHT were shorter than those of pressure vessels. Therefore, the samples heat treated under boiler tube conditions showed lower impact values around 50J in the earlier stage of aging. Considering all obtained results, it was suggested that the serious degradation of fracture toughness in 9Cr-1Mo-V after long term aging would not occur in actual service time for pressure vessels.

Evaluation of Fracture Toughness for P355NH Steel Subjected to Thermal Cycles Simulation

2015 ◽  
Vol 1111 ◽  
pp. 193-198
Author(s):  
Sergiu Valentin Galaţanu ◽  
Doru Romulus Pascu ◽  
Nicolae Faur
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Welded Joints ◽  
Thermal Cycle ◽  
Pressure Vessels ◽  
Thermal Cycles ◽  
Butt Welding ◽  
Cycle Simulation ◽  
Complex Equipment ◽  
The Impact

The thermal cycles simulator of welding is a complex equipment that reproduces in a specimen thermal cycles of the type caused in the HAZ by welding processes.In this paper, it is presented a comparison between the results obtained by welded joints and thermal cycle simulator specimens, from the material P355NH of 22 mm thickness for pressure vessels. Two types of thermal cycle simulator specimens were used: one specimen without post-simulation heat treatment and one specimen with post-simulation heat treatment.For the welded specimens Mn3Ni1CrMo filler material was used.This paper offers information about the impact energy of specific areas of the welded joints, both for butt welding and thermal cycle simulator specimens.A good correlation was observed between the results of thermal cycle simulation with post-simulation heat treatment and the results obtained by welding.

Effect of Postweld Heat Treatment Conditions on Microstructure of 9Cr-1Mo-V Steel Welds for Pressure Vessel

2017 ◽  
Author(s):  
Hidenori Terasaki ◽  
Tomohiro Tanaka ◽  
Masamitsu Abe ◽  
Mitsuyoshi Nakatani
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Weld Metal ◽  
Postweld Heat Treatment ◽  
Pressure Vessels ◽  
Dislocation Network ◽  
Precipitation Behavior ◽  
Treatment Conditions ◽  
Scanning Transmission ◽  
The Difference

We investigated the effects of post-weld heat treatment conditions on the microstructure of the multi-pass submerged arc weld metal of 9Cr-1Mo-V steel used in pressure vessels. The microstructural properties were analyzed under three conditions (as-weld, Larson-Miller parameter (LMP) = 21.38 × 103, and LMP = 21.99 × 103). The precipitation behavior was observed using scanning electron microscopy, and the difference in precipitation behavior in the “as-welded” and “reheated” regions of the prepared multi-pass weld metal was clarified at the different LMP values. The precipitate was analyzed using scanning transmission electron microscopy. An oxide and two types of precipitates were identified, and a dislocation network pinned by MX-type carbides was visualized under the low-LMP condition. The effects of LMP on the effective grain size and dislocation amount were also evaluated using electron back-scattering diffraction. All microstructural change along the LMP had a positive effect on the toughness of weld metal.

Variations in Fracture Toughness for Alloy 718 Given a Modified Heat Treatment

1990 ◽  
Vol 112 (1) ◽  
pp. 116-123 ◽  
Author(s):  
W. J. Mills ◽  
L. D. Blackburn
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Fracture Mechanisms ◽  
Alloy 718 ◽  
Percent Confidence Level ◽  
Heat Treated ◽  
Curve Method ◽  
Heat Treated Condition ◽  
The Impact ◽  
Product Forms

Heat-to-heat and product-form variations in the JIC fracture toughness for Alloy 718 were characterized at 24, 427, and 538°C using the multiple-specimen JR-curve method. Six different material heats along with three product forms from one of the heats were tested in the modified heat treated condition. This heat treatment was developed at Idaho National Engineering Laboratory to improve the impact toughness for Alloy 718 weldments, but it has also been found to enhance the fracture resistance for the base metal. Statistical analysis of test results revealed four distinguishable JIC levels with mean toughness levels ranging from 87 to 190 kJ/m2 at 24°C. At 538°C, JIC values were 15 to 20 percent lower than room temperature toughness levels. Minimum expected values of JIC (ranging from 72 kJ/m2 at 24°C to 48 kJ/m2 at 538°C) and dJR/da (27 MPa at 24 to 538°C) were established based on tolerance intervals bracketing 90 percent of the lowest JIC and dJR/da populations at a 95 percent confidence level. Metallographic and fractographic examinations were performed to relate key microstructural features and operative fracture mechanisms to macroscopic properties.

Fracture Toughness of Highly Irradiated Pressure Vessel Steels in the Upper Shelf Temperature

2006 ◽  
Author(s):  
Hiroshi Matsuzawa ◽  
Toru Osaki
Keyword(s):  
Fracture Toughness ◽  
Chemical Composition ◽  
Reference Material ◽  
Fast Neutron ◽  
Pressure Vessel ◽  
Charpy Impact ◽  
Pressure Vessels ◽  
Shelf Energy ◽  
Pressure Vessel Steels ◽  
Reactor Pressure

Nine Reactor Pressure Vessel (RPV) Steels and four RPV weld were irradiated up to 1.2 × 1024n/m2 fast neutron fluence (E>1MeV), and their fracture toughness and Charpy impact energy were measured. As chemical compositions, such as Cu, are known to affect the fracture toughness reduction due to neutron exposure, the above steels were fabricated by changing chemical composition widely to cover the chemical composition of the RPV materials of the operating Japanese nuclear power plants. 2.7 mm thick compact specimens were used to measure the upper shelf fracture toughness of highly irradiated materials, and their Charpy upper shelf energy was also measured. By correlating Charpy upper shelf energy to fracture toughness, the upper shelf fracture toughness evaluation formulae for highly irradiated reactor pressure vessel steels were developed. Both compact and V-notched Charpy impact specimens were irradiated in a test reactor. The fast neutron flux above 1MeV was about 5 × 1016n/(m2s). Charpy impact specimens made of Japanese PWR reference material containing 0.09w% Cu were irradiated simultaneously. The upper shelf energy of the reference material up to the medium fluence level showed little difference in the reduction of upper shelf energy to that which had been in the operating plant and which was irradiated to the same fluence. The developed correlation formulae have been adopted in the Japan Electric Association Code as new formulae to predict the fracture toughness in the upper shelf region of reactor pressure vessels. They will be applied to time limited ageing analysis of low upper shelf reactor pressure vessels in Japan, on a concrete technical basis in very high fluence regions.

Numerical Simulation of CrMo Steels Thick Welds Intermediate Postweld Heat Treatments

2005 ◽  
Author(s):  
Maryline Clerge´ ◽  
Christian Boucher ◽  
Sylvain Pillot ◽  
Philippe Bourges
Keyword(s):  
Heat Treatment ◽  
Complex Shape ◽  
Heat Treatments ◽  
Pressure Vessels ◽  
Post Weld Heat Treatment ◽  
Treatment Conditions ◽  
Stress Relieving ◽  
Creep Resistant Steels ◽  
Postweld Heat ◽  
Hydrogenation Treatment

During manufacturing, complex shape welded pressure vessels are submitted to numerous intermediate heat treatments after each weld (de-hydrogenation treatment - DHT and/or intermediate stress relieving treatment - ISR) before final Post Weld Heat Treatment (PWHT). The present study aims at analysing and optimising the intermediate heat treatment conditions regarding the resulting mechanical properties (tensile strength and impact. strength) of CrMo and CrMoV creep resistant steels. Hydrogen behaviour in weld metal and HAZ, and residual stresses evolution have been assessed by numerical modelling and experimental measurements on welded specimens representative of big pressure vessels: butt welds and set in nozzle welds of 150 mm wall thickness. The optimised conditions are compared to usual construction codes and buyer’s requirements.

Effect of Heat Treatment on the Damage Tolerance Properties of Ti-6Al-2Zr-2V-1.5Mo ELI Alloy Plate

2011 ◽  
Vol 690 ◽  
pp. 282-285
Author(s):  
Xiao Xiang Wang ◽  
Song Xiao Hui
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Fatigue Crack ◽  
Annealing Temperature ◽  
Damage Tolerance ◽  
Phase Zone ◽  
Alloy Plate ◽  
Β Phase ◽  
Α Phase ◽  
Treatment Conditions

Effect of heat treatment on the damage tolerance properties of a newly developed middle strength high damage tolerance Ti-6Al-2Zr-2V-1.5Mo ELI alloy plate has been investigated in this paper by testing fracture toughness and fatigue crack-extending rate of the plate under three heat treatment conditions and fractograph inspection of the samples. It has been found that with the increasing of the primary annealing temperature from 900°C to 950°C, the fracture toughness increased and the fatigue crack extending rate decreased significantly. Microstructural observation has found that the crack expanded through the α beaming and mainly are perpendicular to the α orientation in the lamellar structure which annealed in α+β phase zone. For the Widmanstaten structure, which can be obtained from annealing in single β phase zone, the continuous grain boundary α phase and α beaming boundary hinder the crack expanding significantly.

Long-Term Gamma Prime Phase Stability after Various Heat Treatment Conditions with Temperature Dropping during Solution Treatment in Cast Nickel Base Superalloy, Grade Inconel-738

2017 ◽  
Vol 891 ◽  
pp. 420-425
Author(s):  
Sureerat Polsilapa ◽  
Aimamorn Promboopha ◽  
Panyawat Wangyao
Keyword(s):  
Heat Treatment ◽  
Turbine Blades ◽  
Solution Treatment ◽  
Nickel Base Superalloy ◽  
Gamma Prime ◽  
Nickel Based Superalloy ◽  
Treatment Conditions ◽  
Nickel Base ◽  
Base Superalloy

Cast nickel based superalloy, Grade Inconel 738, is a material for turbine blades. Its rejuvenation heat treatment usually consist of solution treatment condition with temperature range of 1125-1205 oC for 2-6 hours. Then it is following with double aging process including primary aging at 1055oC for 1 hour and secondary aging at 845oC for 24 hours. However, the various selected temperature dropping program were performed during solution treatment to simulate the possible error of heating furnace. The maximum number of temperature dropping during solution treatment is varied from 1-3 times From all obtained results, the various temperature dropping during solution treatment conditions showed extremely the significant effect on the final rejuvenated microstructures and long-term gamma prime stability after heating at temperature of 900oC for 200 hours.

Fracture Toughness Properties of a Modern Ni-Mo-Cr High Temperature Alloy

2000 ◽  
Author(s):  
R. R. Seeley ◽  
D. L. Klarstrom
Keyword(s):  
Fracture Toughness ◽  
Impact Toughness ◽  
Tensile Ductility ◽  
Charpy Impact ◽  
Thermal Exposure ◽  
Strong Relationship ◽  
Fracture Toughness Test ◽  
Temperature Fracture ◽  
Nickel Base

The Ni-Mo-Cr alloy (HAYNES® 242™) is an age-hardenable alloy that can be significantly strengthened by a simple aging heat treatment at 650°C (1200°F). Long-term thermal exposures at moderate temperatures increase the strength and decrease the ductility and Charpy V-notch impact toughness. Tensile ductility and Charpy impact toughness have traditionally been used to study the effect of long-term thermal exposure on mechanical properties. However, there has been little or no work reported on the effect of long-term thermal exposures on the fracture toughness of nickel-base alloys. The room temperature fracture toughness (KJc) properties have been evaluated for Ni-Mo-Cr plate material in the annealed, annealed and aged, and annealed plus long-term thermal exposed condition. The microstructural and fracture mode characteristics of this alloy were examined as well. The tensile ductility, impact toughness and fracture conditions of the toughness properties were decreased by a long-term thermal exposure at 650°C (1200°F). The fracture toughness test data revealed the crack extension during the KJc tests to be stable throughout the test. The mechanical property data suggest a strong relationship between fracture toughness and tensile ductility. The microstructures and fracture surface morphologies for three metallurgical conditions of the Ni-Mo-Cr alloy are presented.

Modelling Chi-Phase Precipitation in High Molybdenum Stainless Steels

2006 ◽  
Vol 15-17 ◽  
pp. 531-536 ◽  
Author(s):  
W. Xu ◽  
D. San Martin ◽  
Pedro E.J. Rivera-Díaz-del-Castillo ◽  
Sybrand van der Zwaag
Keyword(s):  
Heat Treatment ◽  
Stainless Steels ◽  
Chromium Content ◽  
High Strength ◽  
Processing Parameters ◽  
Nucleation And Growth ◽  
Phase Precipitation ◽  
Treatment Conditions ◽  
Highly Sensitive

High molybdenum high strength stainless steels can contain the so-called Chi phase (Fe36Cr12Mo10). The presence of this phase, which normally occurs at grain boundaries, depletes the chromium content leading to intergranular corrosion. This may cause alloy embrittlement during long term use. The presence of such phase has proven to be highly sensitive to alloy processing parameters such as the cooling rate after a final heat treatment. The present work provides a model to quantify the effects of processing parameters aimed at controlling the Chi phase. The model is based on nucleation and growth classical theories involving capillarity effects for the early stages; it is applied to a range of heat treatment conditions and compared to experimental results.

Sign in / Sign up

Export Citation Format

Share Document