Strengthening Mechanisms and Their Relative Contributions to the - PowerPoint PPT Presentation

Strengthening Mechanisms and Their Relative Contributions to the Yield Strength of Microalloyed Steels Junfang Lu 1 , Oladipo Omotoso 2 , J. Barry Wiskel 3 , Douglas G. Ivey 3 & Hani Henein 3 1 Enbridge Pipelines Inc., Edmonton, Alberta 2 Suncor Energy Centre, Calgary, Alberta 3 Dept. Chemical/Materials Engineering, University of Alberta, Edmonton, Alberta July 10, 2013 1/29

University of Alberta Facts • 105 years old • ~39,000 students • 80% undergraduate students • 20% graduate students • ~3,200 academic staff • $1.7B Cdn Budget • $0.46M Cdn Research http://geology.com/world/canada-satellite-image.shtml 2/29 http://centennial.eas.ualberta.ca

Outline I. Introduction II. Objectives III. Experimental Methods IV. Tests and Results  Grain size measurement  Precipitate size, morphology and chemistry  ICP analysis of the supernatant  Rietveld refinement of XRD data  Effect of microalloying content, CT/ICT on the amount of nano-sized precipitates  Strengthening contributions V. Conclusions VI. Acknowledgements 3/29

Thermomechanical controlled processing - to control microstructure evolution 1400 Reheating Recrystallized Austenite Rough Rolling T nr 1000 Pancaked Austenite Finish Rolling 800 A r3 Temperature, ºC Accelerated PF P Cooling 600 BF (or AF) Coiling M s 400 200  Grain size effect PF – Polygonal Ferrite P – Pearlite  Solid solution strengthening BF – Bainitic Ferrite  Precipitation strengthening AF – Acicular Ferrite Time 4/29 A schematic CCT diagram for microalloyed linepipe steels (Ref: D. Qi, Patent)

Objectives To understand the strengthening mechanisms of microalloyed steels I. To determine strengthening contribution due to grain size effect II. To determine strengthening contribution due to precipitation effect  To characterize precipitate size, morphology and chemistry  To quantify the amount of nano-sized precipitates  To understand the nano-sized precipitation as a function of steel chemistry and processing histories 5/29

Challenges associated with precipitate characterization  Fine sizes of precipitates  Wide particle size distribution  Low volume fraction  Precipitates have same crystal structure (NaCl-type), with similar lattice parameters 6/29

Chemical compositions & processing histories Steel chemistry and normalized FRT and CT/ICT Steel C N Si Nb Ti Mo V FRT* CT/ICT* CR (ºC/s) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) X70-564 0.0398 0.0118 0.23 0.069 0.023 0.2 0.001 0.94 1.04 15** X80-A4B 0.035 0.0058 0.283 0.094 0.017 0.305 0.003 1.05 0.93 15** X80-B4F 0.052 0.0061 0.128 0.077 0.009 0.299 0.002 1.00 1.00 15** X80-462 0.03 0.0098 0.27 0.091 0.013 0.297 0.002 0.94 1.04 15** X80-A4F 0.052 0.0055 0.115 0.044 0.009 0.404 0.003 1.00 0.90 15** Grade 100 0.08 0.011 0.244 0.094 0.06 0.301 0.047 1.07 1.09 15** X100-2A 0.039 0.005 0.11 0.037 0.013 0.41 0.003 1.00** 0.71 35 X100-2B 0.065 0.0059 0.22 0.047 0.009 0.4 0.07 1.00** 0.64 34 X100-3C 0.064 0.0063 0.33 0.05 0.009 0.4 0.003 1.00** 0.80 19.1 FRT* = normalized finish rolling temperature to that of X80-B4F steel CT/ICT* = normalized coiling/interrupted cooling temperature to that of X80-B4F steel ** = intended values For Grade 100 and X100 steels, steels were deformed by leveling or rolling at ICT temperature X100 steels are experimental, pilot scale steels 7/29

Experimental methods – combination of different techniques Carbon replicas Matrix dissolution Steel Thin foils Steel Steel Dissolve sample in solution Steel Carbon replicas SEM TEM Centrifuge, remove portion of liquid Precipitate Dilute solution Precipitate Grain size SEM/TEM Centrifuge again distribution Mass balance in matrix Size; Solution morphology; Residues ICP analysis chemistry SEM/TEM XRD Rietveld refinement Relative amounts of crystallographic phases 8/29

X70-564 X80- 462 X100- 3C Grade 100 9/29

Hall-Petch equation 10/29

Grade 100 – thin foil {220} {111} {200} BF-TEM DF-TEM 11/29

300 C Grade 100 Grade 100 – carbon replica Cu Mo 200 Cu Intensity Nb O 100 Ti Nb Cu Ti Mo V Fe Nb 0 0 2 4 6 8 10 12 14 16 18 20 Energy (keV) {220} {111} {200} 12/29

350 Cu Nb Mo 300 Grade 100 – matrix dissolution 250 Ti Nb Intensity 200 150 Ti Mo 100 Si Cu Fe Ca Nb V 50 Mo Fe Kb1 0 0 2 4 6 8 10 12 14 16 18 20 Energy (keV) Nb/Mo- rich {220} {111} {200} Matrix dissolution using 10% AA Matrix dissolution using HCl (10% acetylacetone + 1% TMAC (tetramethylammonium chloride) + methanol) 13/29

X100-3C – carbon replica 100 nm 20 nm 14/29

Wt% of Nb - based on steel chemistry and ICP analysis 0.12 Nb amount in solid solution Nb amount in precipitate 0.10 0.08 wt% of Nb 0.06 0.04 0.02 0.00 X70-564 X80-462 X80-A4B X80-B4F X80-A4F Grade100 X100-2A X100-2B X100-3C Steel 15/29

Wt% of Mo - based on steel chemistry and ICP analysis 0.50 Mo amount in solid solution Mo amount in precipitate 0.40 wt% of Mo 0.30 0.20 0.10 0.00 X70-564 X80-462 X80-A4B X80-B4F X80-A4F Grade100 X100-2A X100-2B X100-3C Steel 16/29

XRD analysis of residues (preliminary analysis) 8000 (111) Grade 100 NbC-rich X70-564 (200) TiN-rich X80-462 X80-B4F 6000 Intensity (Counts) 4000 (111) (220) (200) (311) (220) 2000 (400) (311) 0 20 40 60 80 100 120 2θ • Ti, Nb and V carbides, nitrides or carbonitrides have NaCl-type, fcc structure • Lattice parameters are similar, making it difficult to identify specific precipitates 17/29

Rietveld refinement of XRD pattern Rietveld refinement: Least squares profile fitting (minimization procedure)  To minimise a function S which represents the difference between y(calc) and y(obs)  Full pattern profile refinement  Simultaneous crystal structure refinement  Quantitative phase analysis     2 S w ( y ( obs ) y ( calc )) Minimum i i i i SF ( MZV )  a a w  a SF ( MZV ) j j j y i : observed (and calculated) intensities at each step w i : weighting factor for each observation w a : relative weight fraction of phase a in a mixture of j phases SF : refined scale factor, which is proportional to the number of unit cells of phase a in the specimen M : mass of the molecular formula Z : number of formula units per unit cell V : volume of the unit cell 18/29

Rietveld refinement of XRD data (Grade 100) Overall XRD pattern profile fitting 9,000 9,000 8,000 8,000 7,000 7,000 6,000 6,000 5,000 5,000 4,000 4,000 3,000 3,000 2,000 2,000 1,000 1,000 0 0 -1,000 -1,000 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75 80 80 85 85 90 90 9,000 9,000 Ti 0.9 Nb 0.1 N 9,000 9,000 Nb 0.7 Ti 0.3 C 0.5 N 0.5 8,000 8,000 8,000 8,000 7,000 7,000 7,000 7,000 6,000 6,000 6,000 6,000 5,000 5,000 5,000 5,000 4,000 4,000 4,000 4,000 3,000 3,000 3,000 3,000 2,000 2,000 2,000 2,000 1,000 1,000 1,000 1,000 0 0 0 0 -1,000 -1,000 -1,000 -1,000 -2,000 -2,000 -2,000 -2,000 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75 80 80 85 85 90 90 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75 80 80 85 85 90 90 9,000 9,000 9,000 9,000 Ti 0.5 Nb 0.5 C 0.5 N 0.5 Nb 0.48 Mo 0.28 Ti 0.21 V 0.03 C 8,000 8,000 8,000 8,000 7,000 7,000 7,000 7,000 6,000 6,000 6,000 6,000 5,000 5,000 5,000 5,000 4,000 4,000 4,000 4,000 3,000 3,000 3,000 3,000 2,000 2,000 2,000 2,000 1,000 1,000 1,000 1,000 0 0 0 0 -1,000 -1,000 -1,000 -1,000 -2,000 -2,000 -2,000 -2,000 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75 80 80 85 85 90 90 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 75 80 80 85 85 90 90 19/29

Precipitate information Steel Precipitate chemistry Precipitate size (nm) Nb 0.52 Ti 0.43 Mo 0.05 C 0.5 N 0.5 20-40 X70-564 Nb 0.79 Ti 0.15 Mo 0.06 C 0.5 N 0.5 20-40 Nb 0.58 Mo 0.42 C 5 Ti 0.52 Ti 0.48 C 0.5 N 0.5 60-80 X80-A4B Nb 0.9 Ti 0.1 C 0.5 N 0.5 25-70 Nb 0.68 Mo 0.32 C 5 Ti 0.72 Nb 0.28 N 80-100 X80-B4F Nb 0.57 Ti 0.43 C 0.5 N 0.5 85-135 Nb 0.92 Ti 0.08 C 0.5 N 0.5 40-100 Nb 0.78 Mo 0.22 C 4.5 Ti 0.76 Nb 0.24 N 100-200 X80-A4F Ti 0.51 Nb 0.49 C 0.5 N 0.5 20-30 Nb 0.86 Ti 0.14 C 0.5 N 0.5 20-30 Nb 0.74 Mo 0.26 C 4 Ti 0.76 Nb 0.24 N 100-200 X80-462 Ti 0.55 Nb 0.45 C 0.5 N 0.5 80-100 Nb 0.86 Ti 0.14 C 0.5 N 0.5 40-90 Nb 0.8 Mo 0.2 C 5 20/29

Precipitate size and chemistry Steel Precipitate chemistry Precipitate size (nm) Ti 0.9 Nb 0.1 N 500-3000 Grade 100 Ti 0.77 Nb 0.23 C 0.5 N 0.5 100-500 Ti 0.5 Nb 0.5 C 0.5 N 0.5 100-200 Nb 0.7 Ti 0.3 C 0.5 N 0.5 100-200 Nb 0.48 Mo 0.28 Ti 0.21 V 0.03 C 4.5 X100-2A Ti 0.70 Nb 0.26 Mo 0.04 C 0.5 N 0.5 30 Ti 0.54 Nb 0.41 Mo 0.05 C 0.5 N 0.5 20 Ti 0.66 Nb 0.29 V 0.05 C 0.5 N 0.5 80 X100-2B Nb 0.53 Ti 0.42 V 0.05 C 0.5 N 0.5 60 Nb 0.85 Ti 0.13 V 0.02 C 40 X100-3C Ti 0.5 Nb 0.47 Mo 0.03 C 0.5 N 0.5 40 Nb 0.67 Ti 0.3 Mo 0.03 C 0.5 N 0.5 20 Phases NbN NbC TiN TiC MoC VN VC Lattice parameter (nm) 0.43927 0.44698 0.42417 0.43274 0.428 0.41392 0.41820 21/29