skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS

Abstract

Synchrotron diffraction experiments were conducted to examine the real-time transformation behaviours of an ex-perimental 9Cr-3W-3Co-NbV steel with high B and low N (N130B), and the commercial P92 steel under simulated weld heat-affected zone thermal cycles. When heated to peak temperatures near 1100 C, both steels rapidly trans-formed from ferrite to 100% austenite. During cooling, both transformed to martensite near 400 C. Both steels also retained untransformed austenite: 1.7% in N130B, and 5.8% in P92. The N130B was also heated to about 60 C above its A3 of 847 C. About 56% of the original ferrite never transformed to austenite. During cooling an additional 21% of ferrite and 23% of martensite formed. It retained no austenite. The P92 was heated to just above its A3 of 889 C. About 15% of the original ferrite never transformed to austenite. During cooling an additional 22% of ferrite and 60% of martensite formed. This steel retained about 2.3% austenite. Metallographic examina-tions indicated that the M23C6 in N130B was much more stable than that in P92 for heating to the lower peak tem-peratures. Analysis using equilibrium thermodynamics suggested that the more stable M23C6 in N130B could raise its apparent A3 by sequestering C. This couldmore » cause the ferrite-austenite transformation to appear sluggish. Ther-modynamic analysis also indicated that the M23C6 in N130B contained about 3.9 at% B compared to about 0.08 at% B in that of P92. In contrast, the refractory metal element content of the M23C6 was predicted to be higher in P92.« less

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
FE USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
981759
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 7th International Charles Parsons Turbine Conference, Glasgow, United Kingdom, 20070911, 20070913
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 43 PARTICLE ACCELERATORS; AUSTENITE; DIFFRACTION; FERRITE; HEATING; MARTENSITE; REFRACTORY METALS; STEELS; SYNCHROTRONS; THERMODYNAMICS; TRANSFORMATIONS; TURBINES; 9Cr steel; boron; heat-affected zone; phase transformations; Type IV failure

Citation Formats

Santella, Michael L, Specht, Eliot D, Shingledecker, John P, and Abe, Fujio. A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS. United States: N. p., 2007. Web.
Santella, Michael L, Specht, Eliot D, Shingledecker, John P, & Abe, Fujio. A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS. United States.
Santella, Michael L, Specht, Eliot D, Shingledecker, John P, and Abe, Fujio. Mon . "A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS". United States. doi:.
@article{osti_981759,
title = {A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS},
author = {Santella, Michael L and Specht, Eliot D and Shingledecker, John P and Abe, Fujio},
abstractNote = {Synchrotron diffraction experiments were conducted to examine the real-time transformation behaviours of an ex-perimental 9Cr-3W-3Co-NbV steel with high B and low N (N130B), and the commercial P92 steel under simulated weld heat-affected zone thermal cycles. When heated to peak temperatures near 1100 C, both steels rapidly trans-formed from ferrite to 100% austenite. During cooling, both transformed to martensite near 400 C. Both steels also retained untransformed austenite: 1.7% in N130B, and 5.8% in P92. The N130B was also heated to about 60 C above its A3 of 847 C. About 56% of the original ferrite never transformed to austenite. During cooling an additional 21% of ferrite and 23% of martensite formed. It retained no austenite. The P92 was heated to just above its A3 of 889 C. About 15% of the original ferrite never transformed to austenite. During cooling an additional 22% of ferrite and 60% of martensite formed. This steel retained about 2.3% austenite. Metallographic examina-tions indicated that the M23C6 in N130B was much more stable than that in P92 for heating to the lower peak tem-peratures. Analysis using equilibrium thermodynamics suggested that the more stable M23C6 in N130B could raise its apparent A3 by sequestering C. This could cause the ferrite-austenite transformation to appear sluggish. Ther-modynamic analysis also indicated that the M23C6 in N130B contained about 3.9 at% B compared to about 0.08 at% B in that of P92. In contrast, the refractory metal element content of the M23C6 was predicted to be higher in P92.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • This research program was undertaken to provide fundamental and basic metallurgical information on the behavior of the heat affected zone (HAZ) in Cr-Mo steel welds as well as practical information on their relative weldability. The principal work was the evaluation of the post weld heat treatment (PWHT) cracking of Cr-Mo steels ranging in Cr content from 2-1/4% to 9%. Differences in observed cracking behavior were contrasted with composition, on cooling transformation behavior and HAZ microstructure. Hydrogen assisted cracking (HAC) studies using a large scale cracking test were conducted on 2-1/4 Cr and 3 Cr steels. Soft zone studies were conductedmore » on 9 Cr NKK steel to determine the reason for the development of a low hardness region (''Soft Zone'') at the outer boundary of the HAZ. The literature review provides a concise historical review and the basis of theories for PWHT cracking and HAC in Cr-Mo steels which were employed to explain the weld cracking susceptibility of various Cr-Mo alloys. PWHT cracking susceptibility was investigated using Gleeble simulated heat affected zone (HAZ) specimens. A new test was developed at the University of Tennessee, The C-ring test, to evaluate the PWHT cracking behavior. The C-ring test was found to be an extremely useful test for PWHT cracking susceptibility and for verifying the results obtained from Gleeble tsting. An excellent correlation was obtained for the two tests. The standard Y-groove test was selected for HAC susceptibility testing. This test is very suitable for evaluating the HAC of the base metal and is defined in Japanese Industrial Standard JIS Z 3158.« less
  • This research program was undertaken to provide fundamental and basic metallurgical information on the behavior of the heat affected zone (HAZ) in Cr-Mo steel welds as well as practical information on their relative weldability. The principal work was the evaluation of the stress-relief cracking (SRC) and hydrogen assisted cracking (HAC) susceptibility of Cr-Mo steels ranging in Cr content from 2 1/4% - 12%. Differences in observed cracking behavior were contrasted with differences in composition, on cooling transformation behavior and weld microstructure.
  • Basic investigations of the weldability of modern 9--10% Cr creep resistant steels for application in high efficiency and low emission thermal power generation plants were performed on a pipe P91 and a W-containing cast steel G-X 12 CrMoWVNbN 10 1 1. Gleeble simulation, representing the manual metal arc welding process, were applied to produce HAZ-simulated microstructures. They were exposed to different PWHT-treatments and tested using hardness tests, metallographic investigations, constant strain rate tests, creep tests and toughness tests. Primary attention was given to the softening effect in the HAZ and its influence on the creep resistance of the welded material.more » The decrease shown by the W-modified version seems to be less pronounced than that observed in the P91 material. The preheating temperature during welding can be selected through determination of the M{sub s}-transformation behavior of the base materials and the welding deposit.« less
  • Creep strength-enhanced ferritic (CSEF) steels such as the 9 Cr steel [ASTM A387 Grade 91] are widely used as tubing and piping in the new generation of fossil fired power plants. Microstructures in the fine-grained heat affected zone (FGHAZ) may significantly reduce creep strength leading Type IV failures. Current research suggest that reducing pre-weld tempering temperature from 760 C (HTT) to 650 C (LTT) has the potential to double the creep life of these welds. To understand this improvement, time-resolved X-ray diffraction (TRXRD) measurement with synchrotron radiation was used to characterize the microstructure evolution during fine grained heat-affected zone (HAZ)more » thermal cycling of grade 91 steel. The measurements showed both M23C6 (M=Fe, Cr) and MX (M=Nb, V; X=C,N) are present in the sample after the HTT condition. Near equilibrium fraction of M23C6 was measured in high temperature tempering condition (HTT, 760 C). However, the amount of M23C6 in LTT condition was very low since the diffraction peaks are close to the background. During simulated FGHAZ thermal cycling, the M23C6 partially dissolved in HTT sample. Interestingly, MX did not dissolve in both LTT and HTT samples. Hypothesis for correlation of M23C6 carbide distribution and pre-mature creep failure in FGHAZ will be made.« less
  • During operation of oil- and gasfields the new developed weldable low carbon martensitic 13%Chromium steels may be subjected to local corrosion by chloride containing wet phases. Crevice corrosion at defective welds, coatings or flanges may contribute to unexpected failures and shutdowns at temperatures and potentials below that of local pitting corrosion. In addition to established standardized test methods, crevice corrosion susceptibility can be quantified by measured corrosion starting times and corrosion currents. In the present investigation, both parameters are monitored by a Remote Crevice Assembly (RCA) providing quantitative consistence between local corrosion rates and measured net corrosion currents at amore » cathode/anode area ratio of 45000/l. Two materials with different nickel and molybdenum contents are tested at free corrosion conditions in CO{sub 2} purged formation water and nitrogen purged artificial seawater. Increasing potentials at test start are providing reduced crevice corrosion incubation times and increased corrosion currents, depending on fluid and type of steel. Weld simulating quenching from 1000 C of the anode provided stronger crevice corrosion only at the steel with higher Ni and Mo alloy content, which, otherwise was less crevice corrosion sensitive in the as delivered state as compared to the lower alloyed steel. Increasing temperatures of the cathode and the anode resulted in strong increases of corrosion currents. However, at temperatures above 40 C, pitting corrosion started at the cathode which resulted in reduction of crevice corrosion net currents. As a conclusion, the susceptibility to crevice corrosion of 13%Cr martensitic steels should be considered, also in possibly unintended pipeline operations and can be quickly established by short RCA tests.« less