Creep Deformation Property and Creep Life Evaluation of Super304H

2021 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Rupture Strength ◽  
Rupture Life ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Rupture Ductility ◽  
Time To Rupture ◽  
Life Evaluation ◽  
Creep Exposure

Abstract Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increase in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C and above. In the short-term, at 600°C, creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing the maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C. Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into accounts of the change in slope of stress vs. time to rupture curves was demonstrated.

Creep Deformation Property and Creep Life Evaluation of Super304H

2020 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada
Keyword(s):  
Creep Rate ◽  
Creep Deformation ◽  
Rupture Strength ◽  
Rupture Life ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Rupture Ductility ◽  
Time To Rupture ◽  
Life Evaluation ◽  
Creep Exposure

Abstract Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increases in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C (1292°F) and above. In the short-term, at 600°C (1112°F), creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing this maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C (1112°F). Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into account the change in slope of stress vs. time to rupture curves was demonstrated.

Creep Deformation, Rupture Strength, and Rupture Ductility of Grades T/P92 Steels

2014 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Hideaki Kushima
Keyword(s):  
Creep Deformation ◽  
Deformation Property ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Allowable Stress ◽  
Analysis Method ◽  
Creep Rupture Strength ◽  
Rupture Ductility ◽  
Region Splitting

Creep and creep rupture strength property of Grades T/P92 steels are investigated. Assessment of creep rupture strength is examined by region splitting analysis method with the use of three type time-temperature parameters (TTP) of Larson-Miller, Orr-Sherby-Dorn, and Manson-Succop parameters. According to the evaluated creep rupture strength, the current allowable stress of Grades T/P92 steels is reviewed. Remarkable drop in creep rupture ductility of the steels is recognized in the low-stress and long-term regime where the ratio of stress to 0.2% offset yield stress is 50% and below, and it is discussed in consideration of change in creep deformation property. Paper published with permission.

Influence of Oxidation on Long-Term Creep Strength of ASME Grade 23 Steel

2009 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Masakazu Fujitsuka ◽  
Hideaki Kushima
Keyword(s):  
Creep Strength ◽  
Rupture Strength ◽  
Rupture Life ◽  
Microstructural Change ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Gas Atmosphere ◽  
Helium Gas ◽  
Term Creep

Creep test of ASME Grade 23 steel has been conducted at 625 and 650°C in helium gas atmosphere. Long-term creep strength of the steel in helium gas was compared with that in air and the influence of oxidation on long-term creep strength was investigated. Creep rupture strength drop was observed in the long-term at 625 and 650°C in air, and the same creep rupture strength drop was observed also in helium gas at 625°C. On the other hand, although creep rupture strength drop was observed in the long-term at 650°C in helium gas, creep rupture life in the long-term in helium gas was slightly longer than that in air at 650°C. Creep rupture life in the long-term at 650°C in air is reduced by not only degradation due to microstructural change, but also marked oxidation, however, that at 625°C is considered to be shortened mainly by a degradation caused by microstructural change. Long-term creep strength of ASME Grade 23 steel at 600°C and above should be reevaluated in consideration of strength drop due to microstructural change.

Creep Rupture Ductility of Creep Strength Enhanced Ferritic Steels

2010 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Hideaki Kushima
Keyword(s):  
Yield Stress ◽  
Creep Strength ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Ferritic Steels ◽  
Creep Rupture Strength ◽  
Stress Regime ◽  
Rupture Ductility ◽  
Strength And Ductility

Creep rupture strength and ductility of Creep Strength Enhanced Ferritic steels of Grades 23, 91, 92 and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in creep rupture strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of creep rupture strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of creep rupture ductility. Higher creep rupture ductility of Grade P23 steel was considered to be caused by its lower creep strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in creep rupture ductility of Grade 91 steel was observed only in the very low stress regime at 650°C. Alloying elements including impurities and changes in precipitates may influence on creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low stress regime is derived from a concentration of creep deformation into a tiny recovered region formed at the vicinity of grain boundary.

Influence of Data Scattering on Estimation of 100,000 hrs Creep Rupture Strength of Alloy 617 at 700 °C by Larson–Miller Method

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Fujio Abe ◽  
M. Tabuchi ◽  
M. Hayakawa
Keyword(s):  
Regression Analysis ◽  
Rupture Strength ◽  
Large Data ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Alloy 617 ◽  
Time To Rupture ◽  
Reciprocal Temperature ◽  
Rupture Data ◽  
C Value

The 100,000 hrs creep rupture strength of Alloy 617 at 700 °C is estimated by Larson–Miller method using the rupture data of longer duration than 500 hrs in the temperature range between 593 and 816 °C, corresponding to 700 ± 100 °C. The maximum time to rupture was 40,126.7 hrs. The rupture data exhibit large scattering, especially at 760 °C. After eliminating the shorter time to rupture data at 760 °C, the regression analysis gives us the Larson–Miller constant C = 12.70 and the 100,000 hrs creep rupture strength of 100 MPa at 700 °C, by Swindeman program. The present regression analysis underestimates the constant C and 100,000 hrs creep rupture strength. The linear extrapolation of log tr versus reciprocal temperature 1/T plots to 1/T = 0 gives us an average C value of Cav = 18.5, which is much larger than the constant C of 12.70 obtained by the Swindeman program. It is concluded that the origin of underestimation of the constant C and corresponding 100,000 hrs creep rupture strength is large data scattering. Using an appropriate constant C of 18.45, the 100,000 hrs creep rupture strength at 700 °C is estimated to be 123 MPa. Using the rupture data including the shorter time to rupture data at 760 °C and using C = 18.45, the 100,000 hrs creep rupture strength at 700 °C is estimated to be 116 MPa.

Long-Term Creep Rupture Strength of Individual Heats and Restriction of Al Concentration in 304HTB and 316HTB Stainless Steels for Gen IV Application

2014 ◽  
Author(s):  
Fujio Abe
Keyword(s):  
Rupture Strength ◽  
Nitrogen Concentration ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Available Nitrogen ◽  
Time To Rupture ◽  
Using Data ◽  
Gen Iv ◽  
Term Creep

The long-term creep rupture strength has been investigated for 9 heats of JIS SUS 304HTB (18Cr-8Ni) and for 9 heats of JIS SUS 316HTB (18Cr-12Ni-Mo) steels at 600 to 750 °C, using data in NIMS Creep Data Sheets. The heats with high Al exhibit the significant degradation in creep strength at long times. The formation of AlN and TiN during creep reduces the beneficial effect due to nitrogen. The heat-to-heat variation in time to rupture is analyzed using available nitrogen concentration Nav, which is defined as the concentration of nitrogen free from AlN and TiN, and also using nitrogen to soluble Al ratio (N/sol Al). The Nav clearly explains the observed heat-to-heat variation in time to rupture of 304HTB and 316HTB at long times. The precipitation hardening due to fine NbC carbides and the effect of small amount of Cu cause additional heat-to-heat variation in time to rupture for 304HTB at short times and for 316HTB at long times, respectively. The restriction of soluble Al concentration is proposed to be below 0.038 and 0.033 mass % for 304HTB and 316HTB, respectively, so that the creep rupture strength of 304HTB and 316HTB is larger than the ASME Sec.III-NH values for up to 300,000 h at 650 to 700 °C. At long times above 300,000 h, such as 500,000 h, the concentration of soluble Al should be further lowered.

Region Splitting Analysis on Creep Strength Enhanced Ferritic Steels

2007 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Hideaki Kushima ◽  
Kota Sawada ◽  
Yoshiaki Toda
Keyword(s):  
Creep Strength ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Ferritic Steels ◽  
Creep Rupture Strength ◽  
Delta Ferrite ◽  
Time To Rupture ◽  
Term Creep ◽  
Region Splitting

Overestimation of long-term creep strength of creep strength enhanced ferritic steels is caused by inflection of a relation between stress and time to rupture. Creep rupture strength of those steels has been re-evaluated by a region splitting analysis and allowable tensile stress of some steels regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code in Japan has been reduced. A region splitting analysis method evaluates creep rupture strength in the short- and the long-term individually, which is separated by 50% of 0.2% offset yield stress. Inflection of stress vs. time to rupture curve is attributable to longer creep rupture life with a stabilized microstructure of creep strength enhanced ferritic steels, since tensile strength property, which determines short-term creep rupture strength, remains the same level. Accuracy of creep rupture strength evaluation is improved by region splitting analysis. Delta ferrite produces concentration gap due to difference in equilibrium composition of austenite and ferrite at the normalizing temperature. It increases driving force for diffusion and promotes recovery of tempered martensite adjacent to delta-ferrite. Concentration gap may be produced also in heat affected zone (HAZ), especially in fine grain HAZ similar to that in dual phase steel, and it has possibilities to promote recovery and, therefore, to decrease creep strength.

Creep Deformation Analysis of Grade 91 Steels and Prediction of Creep Strength Properties

2014 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Kota Sawada ◽  
Hideaki Kushima
Keyword(s):  
Creep Deformation ◽  
Empirical Equation ◽  
Rupture Strength ◽  
Rupture Life ◽  
Strength Properties ◽  
Creep Rupture ◽  
Deformation Analysis ◽  
Grade 91 ◽  
Term Creep ◽  
Rupture Strain

Creep deformation behavior was analyzed on Grade T91 steels and an empirical equation was derived to express creep strain as a function of time. Creep rupture life prediction was investigated by means of the derived empirical equation. Influence of creep rupture strain on creep rupture life predicted by the derived equation was small over a range of creep rupture strain from 0.05 to 0.30, especially creep rupture strain of 0.10 and above. Prediction accuracy of creep rupture life of the equation was better than that of creep rupture data analysis with a Larson-Miller parameter. Heat-to-heat variation of long-term creep rupture strength was appropriately observed. Minimum creep rate, onset of tertiary creep, and time to specific strain are easily predicted by the equation.

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