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1、2024/7/21Equilibrium and Stress-induced Non-Equilibrium Grain Boundary Segregations of Phosphorus in a 2.25Cr1Mo SteelSong Shenhua2.25Cr1Mo钢中磷的平衡及应力引钢中磷的平衡及应力引起的非平衡晶界偏聚起的非平衡晶界偏聚2024/7/21Preface (1)Grain boundary segregation (GS) Effects of grain boundary segregation on the properties of materials Me
2、chanical, corrosion, electrical, and magnetic propertiese.g., in structural materials, such as steel and Ni alloysSegregation of detrimental elements such as S, P, Sn, and Sb decreasing the grain boundary cohesion grain boundary weakeningSegregation of beneficial elements such as B, C and Be increas
3、ing the grain boundary cohesion grain boundary strentheningPreface (2)2024/7/21Preface (3)GSEGSNEGS NEGS induced by high temperature deformationStress induced NEGSIrradiation induced NEGSThermally induced NEGS2024/7/21Preface (4)2.25Cr1Mo steelApplied stress2024/7/21Outline (1)Equilibrium grain boun
4、dary segregationSegregation of phosphorus and molybdenumIntroduction, experiment, results and discussion, summaryRelationship between phosphorus boundary concentration and ductile-to-brittle transition temperature (DBTT)Introduction, experiment, results and discussion, summaryEffect of phosphorus gr
5、ain boundary segregation on intergranular fractureIntroduction, experiment, results and discussion, summary2024/7/21Outline (2)Stress-induced non-equilibrium grain boundary segregationIntroduction, experiment, results and discussion, summaryConclusions2024/7/21Outline (1)Equilibrium grain boundary s
6、egregationSegregation of phosphorus and molybdenumIntroduction, experiment, results and discussion, summaryRelationship between phosphorus boundary concentration and ductile-to-brittle transition temperature (DBTT)Introduction, experiment, results and discussion, summaryEffect of phosphorus grain bo
7、undary segregation on intergranular fractureIntroduction, experiment, results and discussion, summary2024/7/21Equilibrium grain boundary segregation (1)(McLean, 1957)(Seah, 1977)(Guttmann, 1975)Segregation thermodynamics2024/7/21Equilibrium grain boundary segregation (2)Segregation kinetics(McLean,
8、1957)erfc(x) = 1 erf(x)2024/7/21Equilibrium grain boundary segregation (3)Ageing timeSolute boundary concentrationThermal equilibrium concentration2024/7/21OutlineEquilibrium grain boundary segregationSegregation of phosphorus and molybdenumIntroduction, experiment, results and discussion, summaryRe
9、lationship between phosphorus boundary concentration and ductile-to-brittle transition temperature (DBTT)Introduction, experiment, results and discussion, summaryEffect of phosphorus grain boundary segregation on intergranular fractureIntroduction, experiment, results and discussion, summary2024/7/2
10、1IntroductionP-Mo interactionWeak or strong?2024/7/21Experiment (1)IngotPlateBlock 2NormalizationAustenizationTemperHot rollingVacuum inductionRaw materialCuttingBlock 1Sample processing and pretreatment2024/7/21Experiment (2)AESPretreated samplesExperimental procedureAging at different temperatures
11、 for different times and quenchingBoundary concentrationFraction of Intergranular fractureSEM Impact testMachiningDBTTHardness testMetallographic analysis HardnessGrain zize2024/7/2192050minTimeTemperature98030min6502hAir coolingOil quenchingWater quenching(Normalization)(Austenization)(Termper)(Agi
12、ng under different stresses for different time)Quenching520Heat treatment procedureExperiment (3)520480Water quenching560(Ageing)2024/7/21Experiment (4)Auger electron spectrometerAuger specimen2024/7/21Experiment (5)AES scanning positionFracture surface of AES specimen2024/7/21Results and discussion
13、 (1)Typical AES spectra2024/7/21Results and discussion (2)Ageing timeSolute boundary concentrationThermal equilibrium concentration480oC2024/7/21Results and discussion (3)520oC560oC2024/7/21Results and discussion (4)Equilibrium boundary concentrations at different temperaturesSegregation energies at
14、 different temperatures2024/7/21Results and discussion (5)P-Mo interaction is very week2024/7/21SummaryThe interaction between phosphorus and molybdenum is very weak.The segregation enthalpies of phosphorus and molybdenum are about 38 and 17 kJmol-1, respectively.The segregation entropies of phospho
15、rus and molybdenum are both about 0.2024/7/212024/7/21Outline (1)Equilibrium grain boundary segregationSegregation of phosphorus and molybdenumIntroduction, experiment, results and discussion, summaryRelationship between phosphorus boundary concentration and ductile-to-brittle transition temperature
16、 (DBTT)Introduction, experiment, results and discussion, summaryEffect of phosphorus grain boundary segregation on intergranular fractureIntroduction, experiment, results and discussion, summary2024/7/21Introduction (1)-150 -100-500500204060Impacct temperature% ductile fracture80100DBTT2024/7/21Intr
17、oduction (2)DBTTGrain sizeHardnessP boundary concentration2024/7/21ExperimentPretreated samplesExperimental procedureAging at different temperatures for different times and quenchingBoundary concentrationFraction of Intergranular fractureSEM Impact testMachiningDBTTHardness testMetallographic analys
18、is HardnessMicrostructure,Grain sizeAES2024/7/21Results and discussion (1)A: 650oC2h B: 560oC100hC: 480oC500hD: 480oC800hE: 480oC1200h 2024/7/21Results and discussion (2)650oC2h480oC1200h 100 m(a)100 m(b)2024/7/21Results and discussion (3)R-square = 0.9972024/7/21Results and discussion (4)Temperatur
19、e-time embrittlement diagram2024/7/21SummaryThere is a linear relationship between DBTT and phosphorus boundary concentration.A temperature-time embrittlement diagram was established. From the diagram, the DBTT of the material aged for any time at any temperature can be predicted. 2024/7/212024/7/21
20、Outline (1)Equilibrium grain boundary segregationSegregation of phosphorus and molybdenumIntroduction, experiment, results and discussion, summaryRelationship between phosphorus boundary concentration and ductile-to-brittle transition temperature (DBTT)Introduction, experiment, results and discussio
21、n, summaryEffect of phosphorus grain boundary segregation on intergranular fractureIntroduction, experiment, results and discussion, summary2024/7/21Introduction (1)2024/7/21Introduction (2)Does low temperature facilitate intergranular fracture?Christiens results in 17-4 PH martensitic stainless ste
22、el:The specimen experienced ductile fracture, intergranular fracture, cleavage fracture when impact-fractured from 300oC to -196oC. (Christien, 2003)2024/7/21ExperimentPretreated samplesExperimental procedureAging at different temperatures for different times and quenchingBoundary concentrationFract
23、ion of Intergranular fractureSEM Impact testMachiningDBTTHardness testMetallographic analysis HardnessMicrostructure,Grain sizeAES2024/7/21Results and discussion (1)480oC1200h 650oC2h Intergranular fracture is not observed at all test temperatures 2024/7/21Results and discussion (2)StressTemperature
24、OIntergranular fracture stressCleavage fracture stressYield strengthTcTaTb2024/7/21SummaryPhosphorus grain boundary segregation facilitates intergranular fracture.The specimen experienced ductile fracture, intergranular fracture, and cleavage fracture when impact-fractured from high to low temperatu
25、re.2024/7/212024/7/21OutlineStress-induced non-equilibrium grain boundary segregationIntroduction, experiment, results and discussion, summaryConclusions2024/7/21Introduction (1)343 MPa(Shinoda and Nakamura, 1981)(Misra, 1996)2024/7/21Introduction (2)Diffusional creepGrain interiorGrain boundarySolu
26、te atoms2024/7/21Introduction (3)Xus modelGrain interiorGrain boundarySolute atomsVacancyVacancy-solute complex2024/7/21Experiment (1)Creep test Pretreated samplesExperimental procedureAgeing without stress for 1000 h and quenchingCreep curvesStress ageingMachiningSegregation kineticsTensile testYie
27、ld strengthAES analysis2024/7/21920 50minTimeTemperature980 30min6502hAir coolingOil quenchingWater quenching(Normalization)(Austenization)(Termper)(Aging under different stresses for different time)Quenching520Heat treatment procedureExperiment (2)520480Water quenching(Aging without stress for 1000
28、h)5602024/7/21Experiment (3)2024/7/21Results and discussion (1)Yield strength:462 MPa 2024/7/21Results and discussion (2)Creep curves and segregation kinetics40 MPa40 MPa200 MPa200 MPa350 MPa350 MPa2024/7/21Results and discussion (3)Stress ageing timeP boundary concentrationComplex effectCreep effec
29、tCombined effectSegregation kinetics under high stress2024/7/21Results and discussion (4)Grain boundary is deformed preferentiallyDeformation can produce vacancy ( )Strain hardeningDeformation spreads to grain interiorSegregation kinetics under medium stress2024/7/21SummaryStress can induce differen
30、t kinds of segregation kinetics. Elastic deformation and creep deformation can both affect phosphorus segregation kinetics.2024/7/212024/7/21ConclusionsThe interaction between phosphorus and molybdenum is very weak.There is a linear relationship between DBTT and phosphorus boundary concentration.A t
31、emperature-time embrittlement diagram was established. From the diagram, the DBTT of the material aged for any time at any temperature can be predicted. Phosphorus grain boundary segregation facilitates intergranular fracture. The specimen experienced ductile fracture, intergranular fracture, and cleavage fracture when impact-fractured from high to low temperature.Elastic deformation and creep deformation can both affect phosphorus segregation kinetics during stress ageing.
