Sandia Fracture Challenge
Microstructure Characterization
Yuxiong Mao, PhD
Mark Horstemeyer, CAVS Chair
Professor
Center for Advanced Vehicular
Systems Mississippi State University
1
15-5PH Stainless Steel Plate
•
•
Six samples were made from the received specimen to observe the LongitudinalTransverse (LT1&LT2), Longitudinal-Thickness (LS1&LS2), Transverse-Thickness
(TS1&TS2) sections.
Samples were mounted and polished. Then etched with Vilella's reagent for 90
seconds.
2
LT1 & LT2 Before Etch
LT sections are homogeneous. Very few inclusions can be found in these sections.
Note the lines here are polish scratches.
Inclusions
LT1 Overview
LT2 Overview
3
LT1 Before Etch
High Resolution View
4
LS1 Before Etch
Banding and inclusions can be observed in LS sections.
The inclusions are aligned along the longitudinal direction.
The bands run through the entire sample and are clustered
in the center region.
Near Surface
Inclusions
Center
Overview
High Resolution View
5
LS2 Before Etch
Near Surface
Center
Overview
High Resolution View
6
TS1 Before Etch
Near Surface
Banding and inclusions can also be observed in TS
sections. The bands are shorter compared to those in LS
sections.
Center
Overview
High Resolution View
7
TS2 Before Etch
Near Surface
Center
Overview
High Resolution View
8
Quantitative Analyses of the inclusions
observed in LS and TS un-etched sections
Area Fraction(%)
0.1014
0.0825
0.1534
0.1649
LS1
LS2
TS1
TS2
LS2
TS1
Average Area (um^2)
2.379
2.608
2.162
1.965
TS2
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
LS1
LS2
TS1
TS2
0.5
0.4
Fraction
Fraction
LS1
Number Density(/um^2)
4.261E-04
3.164E-04
7.093E-04
8.394E-04
Average
NND(um)
18.578
20.318
16.138
14.474
0.3
0.2
0.1
0
Area (um^2)
10
20
30
40
50
60
70
80
90 100 More
Nearest Neighbor Distance (um)
9
LT1 After Etch: Martensite
Dominated
Homogenous Martensitic matrix covers the entire LT sections.
Martensitic matrix
Overview
High Resolution View
10
LT2 After Etch
Overview
High Resolution View
11
LS1 After Etch: Ferrite Banding
is an Issue
Banding/segregations can be observed in LS sections.
The bands run through the entire sample and are
clustered in the center region. The bands are aligned
along the longitudinal direction. These segregations
may have detrimental effects on the mechanical
properties(a).
Near Surface
Ferrite
Stringer
Center
Banding
Overview
(a) B. Potter, “NDT of Precipitation Hardened Steels Using Fluorescent
Magnetic Particle Testing,” NDT Solution, December 2003
High Resolution View
12
LS2 After Etch
Near Surface
Center
Overview
High Resolution View
13
TS1 After Etch
Near Surface
Banding/segregations can also be observed in TS
sections. The bands are aligned along the transverse
direction and are shorter than those in LT sections.
Center
Banding
Overview
High Resolution View
14
TS2 After Etch
Near Surface
Center
Overview
High Resolution View
15
Grain Boundary Segmentation
16
Grain Size Distributions: Change
Hardening Behavior Locally
Sample
Average
Grain Size
(um)
LT1
LT2
LS1
LS2
TS1
TS2
4.54
4.80
4.01
4.30
3.71
3.56
LT1
LT2
LS1
LS2
TS1
TS2
35
30
Fraction
25
20
15
10
5
0
2.5
3.0
3.5
4.2
5.0
5.9
7.1
8.4
10.0 11.9 14.1 16.8
Grain Size (um)
17