scholarly journals Metallurgical Evaluation of an Additively Manufactured Nickel-Base Superalloy for Gas Turbine Guide Vanes

2020 ◽  
Author(s):  
Alex Bridges ◽  
John Shingledecker ◽  
Alex Torkaman ◽  
Lonnie Houck
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Rupture Strength ◽  
Creep Rupture ◽  
M23c6 Carbide ◽  
Nickel Base Superalloy ◽  
Creep Ductility ◽  
Cast Material ◽  
Guide Vanes ◽  
Significant Difference

Abstract In this paper, AM produced test samples of a IN939 derivative nickel-based alloy were tested for tensile, fatigue and creep properties at temperatures up to 871°C and compared to the traditional cast material. Initial results showed improved tensile and fatigue strength, but a reduction in both long-term creep rupture strength and creep ductility in the AM produced material compared to the cast baseline. Microstructural observations in the AM produced material showed a significant difference in the overall metallurgical characteristics beyond grain size compared to the castings. In addition to the laboratory studies and to provide a direct comparison between AM and traditional castings, both AM and cast components were tested in live engine trials exceeding 4,000 hours. Detailed scanning electron microscopy techniques were used to evaluate the evolution of grain size, gamma-prime, MC carbide and secondary M23C6 carbide size and distribution throughout a 5-step heat treatment process. Post-test evaluations for creep rupture specimens of the AM material showed creep cavitation near grain boundaries. The results from the AM produced material are discussed in comparison to expected properties and characteristics from traditional casting methods. Results have shown that material production and short-term metallurgical properties are sufficient to produce quality high temperature stationary guide vanes, but additional research and development is needed to optimize the AM process to achieve high-temperature creep behavior comparable to castings.

Progress in the Design of an Improved High-Temperature 1 Percent CrMoV Rotor Steel

1990 ◽  
Vol 112 (1) ◽  
pp. 99-115 ◽  
Author(s):  
R. L. Bodnar ◽  
J. R. Michael ◽  
S. S. Hansen ◽  
R. I. Jaffee
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Room Temperature ◽  
Rupture Strength ◽  
Temper Embrittlement ◽  
Creep Rupture ◽  
Rotor Steel ◽  
Creep Rupture Strength ◽  
Austenitizing Temperature ◽  
Creep Ductility

Silicon-deoxidized, tempered bainitic 1 percent CrMoV steel is currently used extensively for high-temperature steam turbine rotor forgings operating at temperatures up to 565°C due to its excellent creep rupture properties and relative economy. There is impetus to improve the creep rupture strength of this steel while maintaining its current toughness level and vice versa. The excellent creep rupture ductility of the low Si version of this steel allows the use of a higher austenitizing temperature or tensile strength level for improving creep rupture strength without loss in creep ductility or toughness. When the tensile strength of this steel is increased from 785 to 854 MPa, the creep rupture strength exceeds that of the more expensive martensitic 12CrMoVCbN steel currently used for high-temperature rotor applications where additional creep rupture strength is required. The toughness of 1 percent CrMoV steel is improved by lowering the bainite start (Bs) temperature in a “superclean” base composition which is essentially free of Mn, Si, P, S, Sb, As and Sn. The Bs temperature can be lowered through the addition of alloying elements (i.e., C, Ni, Cr, and Mo) and/or increasing the cooling rate from the austenitizing temperature. Using these techniques, the 50 percent FATT can be lowered from approximately 100°C to below room temperature, which provides the opportunity to eliminate the special precautionary procedures currently used in the startup and shutdown of steam turbines. The most promising steels in terms of creep rupture and toughness properties contain 2.5 percent Ni and 0.04 percent Cb (for austenite grain refinement and enhanced tempering resistance). In general, the creep rupture strength of the superclean steels equals or exceeds that of the standard 1 percent CrMoV steel. In addition, the superclean steels have not been found to be susceptible to temper embrittlement, nor do they alter the room temperature fatigue crack propagation characteristics of the standard 1 percent CrMoV steel. These new steels may also find application in combination high-temperature-low-temperature rotors and gas turbine rotors.

KUBOTA ALLOY KHR35C

Alloy Digest ◽  
1999 ◽  
Vol 48 (7) ◽  
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Tensile Properties ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Temperature Performance

Abstract Kubota alloy KHR35C is similar to HP alloy with the addition of niobium to increase its creep-rupture strength. Typical applications include components and assemblies for severe carburizing environments, such as ethylene pyrolysis coils. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance as well as casting and joining. Filing Code: SS-753. Producer or source: Kubota Metal Corporation.

scholarly journals Creep Rupture Analysis of Candidate Steels for the Traveling Wave Reactor

2018 ◽  
Author(s):  
Cheng Xu
Keyword(s):  
High Temperature ◽  
Yield Stress ◽  
Traveling Wave ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Thermal Creep ◽  
Uniaxial Tensile ◽  
Advantages And Disadvantages ◽  
Analysis Methods ◽  
Best Estimate

TerraPower has developed sophisticated computational analysis tools to support the design and fabrication of high temperature components to be used in the Traveling Wave Reactor (TWR). One of the key material properties required to predict material damage and remaining lifetime of key in-reactor components is the thermal creep rupture time. Although TerraPower optimized ferritic-martensitic (FM) HT9 steel has shown consistent improvement in yield stress and creep rupture strength through uniaxial tensile tests, extrapolations of existing test data are still needed to fully support the complex analysis used in the TWR design. Traditional Larson-Miller analysis for creep rupture was used to compare the TerraPower optimized HT9 steel to the existing historical database. The results of the Larson-Miller analysis were compared to the results from the Wilshire analysis to explore the relative advantages and disadvantages of each method. The best estimate values for fitting constants and activation energies were determined for both methods, taking into account the effects of the higher yield stress observed in TerraPower optimized HT9 compared to historic HT9. Likewise, the best estimate creep rupture stresses for TerraPower optimized HT9 at various times and temperatures were determined by extrapolations using both the Larson-Miller and Wilshire analysis. The allowable stresses of historical and TerraPower optimized HT9 steels were compared to those of existing materials (9Cr-1Mo-V) in the ASME high temperature code. The comparison of analysis methods and rupture stresses demonstrate that TerraPower FM steel thermal creep performance and analysis methods are comparable to existing ASME qualified materials for high temperature applications.

Evaluation of Short Term Creep-Rupture Strength of High Temperature P122 Boiler Material

2003 ◽  
Author(s):  
John Pumwa
Keyword(s):  
High Temperature ◽  
Fracture Mode ◽  
Life Prediction ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Short Term ◽  
Boiler Material ◽  
Term Creep ◽  
Short Term Creep

The complex thermal-mechanical loading of power-generating plant components usually comprises of creep, high-cycle and low-cycle fatigue which are thermally induced by start-ups, load changes and shut-downs, producing instationary temperature gradients and hence creating strain as well as stress fields. In order to select the correct materials for these hostile environmental conditions, it is vitally important to understand the behaviour of mechanical properties such as creep rupture properties of these materials. This paper reports the results of standard creep rupture tests of P122 (HCM12A or 12Cr-1.8W-1.5Cu) high temperature boiler material. P122 is one of the latest developed materials for high temperature environments, which has the potential to be successful in hostile environments. The tests were conducted at temperatures ranging from 550°C to 700°C at 50°C intervals with stress levels ranging from 80–400 MPa using a locally made creep rupture testing machine. The results are found to have stable creep-rupture strength at short term creep stage for over 800-hours at elevated temperatures. Creep life prediction from Larson-Miller relationship was also carried out and the accuracy of life prediction is demonstrated. Moreover, the fracture mode assessments strongly revealed a typical ductile transgranular fracture mode with dimples and voids.

Development of a New Austenitic Stainless Steel (Low-C-18Cr-11Ni-3Cu-Mo-Nb-B-N) With High Sensitization Resistance and High Temperature Strength

2019 ◽  
Author(s):  
Yuhei Suzuki ◽  
Shogo Aota ◽  
Etsuo Dan ◽  
Masaki Ueyama ◽  
Takahiro Osuki ◽  
...  
Keyword(s):  
High Temperature ◽  
High Ratio ◽  
M23c6 Carbide ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Low Carbon ◽  
Intergranular Stress Corrosion ◽  
Creep Ductility ◽  
Acid Environment ◽  
Intergranular Stress Corrosion Cracking

Abstract Austenitic materials with high sensitization resistance and high temperature strength are required for furnace and reaction tower of desulfurizing plants in the petroleum refinery industry. For these requirements, a new steel (LowC-18Cr-11Ni-3Cu-Mo-Nb-B-N) has been developed. The steel shows no intergranular stress corrosion cracking in polythionic acid environment after aging in the temperature range from 565 to 700 °C for up to 10,000 hours. This excellent PTA-SCC resistance is attributed to the prevention of M23C6 carbide precipitation along grain boundary due to extra low carbon content with high ratio of niobium to carbon. The maximum allowable tensile stress of this steel is estimated to be more than 30% higher than that of ASME SA213 Type347H. This excellent strength is based on the precipitation strengthening effect due to fine precipitates of a copper rich phase which are coherent with the austenite matrix in addition to Z-phase (NbCrN). Moreover, boron addition improves creep strength and creep ductility of the steel. From these results, it is concluded that the newly developed steel is a promising material not only for refinery processes but also for other elevated temperature usages.

Study of Creep Strength for P91 Steels after Short Term Overheating above Ac3 Temperature

2013 ◽  
Vol 393 ◽  
pp. 94-101
Author(s):  
Ng Guat Peng ◽  
Badrol Ahmad ◽  
Mohd Razali Muhamad ◽  
M. Ahadlin
Keyword(s):  
High Temperature ◽  
Creep Strength ◽  
Rupture Strength ◽  
Rupture Life ◽  
Creep Rupture ◽  
Tempered Martensite ◽  
Short Term ◽  
Creep Tests ◽  
Rupture Stress ◽  
Limited Creep

Advanced ferritic steels containing 9 wt% Cr are widely used in the construction of supercritical and ultra supercritical boiler components. The microstructure of the as supplied 91 materials consists of a tempered martensite matrix, a fine dispersion of intergranular chromium rich M23C6 precipitates and intragranular carbonitrides MX particles rich in V and Nb. This steel requires post weld heat treatment (PWHT) to produce a tempered microstructure after welding to develop excellent creep strength for high temperature service. Based on past experience, situations may arise whereby the components are subjected to an accidental overshoot in temperature during PWHT. The short excursion to high temperature beyond Ac3 would have resulted in the formation of deleterious phases, for example, soft α-ferrite which has poor creep strength and hard martensite which has a low toughness. In this study, the degraded specimens with soft α ferrite as a result of cooling transformation from 900°C are proven to have a limited creep rupture life where the creep rupture strength dropped remarkably after 1000 hours. As the peak temperature increased to 950°C and 1000°C, hard and brittle martensite was formed on cooling. The creep specimens were found to exhibit better creep strength; most probably the creep behavior was improved by the tempering effect at 600°C during creep tests. Nevertheless, despite the tempering which might have improved the toughness slightly, the high temperature creep rupture stress still had dropped approximately 40%, as compared to the virgin alloys in the range of rupture time from 1,000 hours to 10,000 hours.

Fracture Behavior of Inconel 718 at High Temperature

2011 ◽  
Vol 462-463 ◽  
pp. 1244-1249 ◽  
Author(s):  
Omar Bapokutty ◽  
Zainuddin Sajuri ◽  
Junaidi Syarif ◽  
A.R. Said
Keyword(s):  
Tensile Strength ◽  
High Temperature ◽  
Inconel 718 ◽  
Elevated Temperatures ◽  
Solution Treatment ◽  
Nickel Base Superalloy ◽  
Creep Properties ◽  
Heat Treated ◽  
Significant Difference ◽  
Nickel Base

The effect of heat treatment on tensile and creep properties of nickel-base superalloy, Inconel 718 in room and at high temperature was investigated. Solution treatment was applied on the as-received material at 980oC for 1 hour before water quenched followed by double aging treatments at 720oC and 621oC for 8 hours, respectively and then cooled in air. The tensile strength at elevated temperatures of 550oC and 650oC were slightly deteriorated for heat treated and as-received materials. Beside strength, significant difference was observed in the elongation. The elongation of heat treated samples drastically reduced to 4 to 5% only compared to that of the as received materials which exhibited more than 30% elongation. The significant increased in tensile strength is suspected due to the present of γ’, γ” and δ precipitates which pinned the movement of grain boundary and sliding. However, the present of these precipitates caused the material to become harder and brittle. Moreover, the increase in load from 70% to 90% UTS and in temperature significantly accelerated the creep rate.

scholarly journals Microstructural Modeling During Multi-Pass Rolling of a Nickel-Base Superalloy

2009 ◽  
Author(s):  
Kannan Subramanian ◽  
Harish P. Cherukuri
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Strain Rate ◽  
Nickel Base Superalloy ◽  
Alloy 718 ◽  
Process Variables ◽  
Shape Rolling ◽  
Microstructural Modeling ◽  
Nickel Base ◽  
Base Superalloy

Superalloys are metallic alloys used for high temperature applications such as encountered in the aircraft industry and where resistance to deformation is a primary requirement. Alloy 718 is one such Nickel-base superalloy that resists deformation at elevated temperatures and is therefore difficult to hot work. One of the major hotworking operations is multi-pass shape rolling in which Alloy 718 undergoes multiple deformations in several passes along with reheating between passes. For a given composition of alloy, the high temperature flow stress is influenced to a large extent by the grain size of the microstructure. In the case of shape rolling in which the cross section changes from circular to oval in alternate passes, the correct working forces, which relate to gauge and shape control as well as to power requirements, can be estimated accurately only if the microstructure relevant to the specific pass of rolling is known. In addition, the microstructure present at the end of the rolling and cooling operations controls the product properties. Control of grain size is an increasingly important characteristic in hotworking. The narrow temperature range (980°C and 1120°C [1]) for hotworking of Alloy 718 makes the grain size control more difficult. During hotworking, Alloy 718 undergoes microscopic and mesoscopic events such as dynamic recrystallization (DRX), metadynamic recrystallization (MDRX) and static grain growth (SGG) depending on the temperature, strain rate and retained strain. Modeling these microstructural events is important in designing the rolling process. Due to the tremendous amount of time, cost and effort associated with experiments and industrial trials, numerical methods are resorted to because of the complexity of the variables involved in multi-pass rolling. One such popular numerical technique, finite element (FE) method can predict process variables such as strain, strain rate and temperature for the deformation process. In general, microstructural modeling relates these process variables to microstructural evolution. During microstructural modeling, constitutive equations describing the microstructural evolutions are developed using experiments, which can then be readily implemented in an FE package capable of modeling rolling processes.

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