Heat-to-Heat Variation in Creep Life and Fundamental Creep Rupture Strength of 18Cr-8Ni, 18Cr-12Ni-Mo, 18Cr-10Ni-Ti, and
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UCTION
NATIONAL Institute for Materials Science (NIMS) has been conducting the Creep Data Sheet Project since 1966 primarily to obtain the 100,000 hours-creep rupture strength data for principal heat-resistant steels and alloys, which were produced in Japan.[1] The allowable stress for designing high-temperature components is usually determined on the basis of 100,000 hours-creep rupture strength at operating temperature.[2] The establishment of reliable methods for determining the remaining creep life has also been desired for components being operated for a long time because there is an economic advantage in using components beyond the design life. The NIMS Creep Data Sheets have provided long-term creep and creep FUJIO ABE, Research Fellow, is with the Materials Reliability Unit, Environment and Energy Materials Division, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Japan. Contact e-mail: [email protected] Manuscript submitted January 25, 2016. Article published online June 15, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
rupture data available for both safe designing and reliable creep life assessment of high-temperature components. In the NIMS Creep Data Sheet Project, long-term creep and creep rupture tests have been carried out using multiple heats in each material, e.g., 12 heats for 2.25Cr-1Mo ferritic-pearlitic steel,[3] 10 heats for 9Cr-1Mo-VNb tempered martensitic steel specified as ASME Grade 91,[4] and 9 heats for 18Cr-8Ni austenitic stainless steel,[5] to obtain typical and average test data. The heat means different ingots and different products. The materials such as tubes, pipes, plates, and so on, from which the creep test specimens were taken, were sampled at random from commercial stocks produced in Japan. It should be noted that the creep test results sometimes exhibit large scattering as shown by about a one order of magnitude difference in creep life or more between the strongest and weakest heats because the creep strength widely depends on production procedures and quality of materials, e.g., heat treatment conditions and impurity contents, and the creep strength is sometimes much lower than that just as one intends, even if VOLUME 47A, SEPTEMBER 2016—4437
4438—VOLUME 47A, SEPTEMBER 2016
METALLURGICAL AND MATERIALS TRANSACTIONS A
C
Si
Mn
P
S
Ni
Cr
0.04–0.1 0.06 0.05 0.05 0.058 0.078 0.066 0.07 0.06 0.06
Requirement AAA AAB AAC AAD AAE AAF AAL AAM AAN
Requirement ACA ACB ACC ACG ACH ACJ
£0.75 0.62 0.54 0.57 0.53 0.47 0.55
£2.00 1.49 1.59 1.46 1.60 1.59 1.65
Mn £0.040 0.023 0.023 0.023 0.023 0.023 0.023
P
18.70 18.34 18.50 18.70 18.95 18.25 18.16 18.24 18.18
£0.030 0.006 0.006 0.006 0.007 0.015 0.006
S
Ni
0.17 0.19 0.16 0.06 0.07 0.05 0.14 0.16 0.12
Cu
0.040 0.064 0.054 0.006 0.062 0.020 0.031 0.036 0.040
Ti
0.040 0.005 0.006 0.004 0.008 0.008 0.008 0.008 0.008
Sol Al
0.007 0.005 0.006 0.006 0.006 0.005 0.007 0.006 0.006
Insol Al
0.07 0.14 0.17 0.17 0.16 0.13 0.26 0.24 0.26
Cu
0.011 0.011 0.055 0.028 0.037 0.055 0.043 0.06
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