Vortrag_4_Influence_of_Surface_Defects
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Transcript Vortrag_4_Influence_of_Surface_Defects
Seminar: Metallography of casting alloys and metallurgical defects
Influence of surface defects and
metallurgical defects on the fatigue
strength of ductile iron
-1-
Seminar: Metallography of casting alloys and metallurgical defects
Characteristic surface of a fatigue fracture
Borderline between
the fast fracture area
and the fatigue
fracture area
Crack start point
-2-
Seminar: Metallography of casting alloys and metallurgical defects
Characteristic surface of fatigue fracture
Crack start point
Borderline between the fast fracture area and the fatigue fracture area
-3-
Seminar: Metallography of casting alloys and metallurgical defects
State of stress at different fatigue loadings
Push/pull
Bending
Torsion
Surface effect
-4-
Seminar: Metallography of casting alloys and metallurgical defects
Cast parts with different fatigue loadings
Push/pull
Piston rod
Bending
Axle arm
Torsion
Crankshaft
-5-
Seminar: Metallography of casting alloys and metallurgical defects
Damaging effects to the fatigue strength
Surface defects
• Roughness
• Pin holes
• Inclusions
• Blow holes
• Local depressions
(removed sand and slaginclusions)
Casting skin defects Microstructure defects
• Graphite flotation
• Ferritic skin
• Lamellar graphite skin
• Dross
• Surface zone
decarbonization
• Surface zone oxidation
• Inclusions of lustrous
carbon
• Degeneration of graphite
• Nonmetallic inclusions
• Grain boundary carbides
• Mikro / makro-porosity
-6-
Seminar: Metallography of casting alloys and metallurgical defects
Fatigue fracture caused by an inclusion in the surface
zone of GJS 600-3 with casting skin
Inclusion
-7-
Seminar: Metallography of casting alloys and metallurgical defects
Fatigue fracture caused by Dross
in the surface zone of GJS 400-15
-8-
Seminar: Metallography of casting alloys and metallurgical defects
Different fatigue testing machines
Resonant
testing
machine
Rotary bending testing machine
Source: Walter + Bai AG
Source: Russenberger Prüfmaschinen AG
-9-
Seminar: Metallography of casting alloys and metallurgical defects
Samples of specimen for fatigue testing by ASTM E 466
4 point bending equipment
Round specimen
Geometrical rated
break point
Constant
test area
Flat specimen
- 10 -
Seminar: Metallography of casting alloys and metallurgical defects
Microstructure of GJS 400 in as
cast condition
25x
Microstructure of GJS 400 with
graphite flotation
16x
- 11 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of the surface and the casting skin on the bending
fatigue strength of ferritic nodular iron
350
Stress Amplitude [MPa]
300
250
200
150
100
50
0
1,E+04
1,E+05
1,E+06
1,E+07
Cycles [N]
GJS 400 without defects & machined surface
GJS 400 with graphite flotation & casting skin
GJS 400 without defects & casting skin
- 12 -
Seminar: Metallography of casting alloys and metallurgical defects
Microstructure of GJS 400 with
61 % Nodularity
50x
Microstructure of GJS 400 with
70 % Nodularity
50x
- 13 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of structural defects on the compression-tension
fatigue strength of ferritic nodular iron
350
Stress Amplitude [MPa]
300
250
200
150
100
50
0
1,E+04
1,E+05
1,E+06
1,E+07
Cycles [N]
GJS 400 without defects
GJS 400 with 61% Nodularity
GJS 400 with 70% Nodularity
- 14 -
Seminar: Metallography of casting alloys and metallurgical defects
Microstructure of GJS 400 with nonmetallic inclusions
100x
- 15 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of structural defects on the rotary bending fatigue
strength of ferritic nodular iron
350
Stress Amplitude [MPa]
300
250
200
150
100
50
0
1,E+04
1,E+05
1,E+06
1,E+07
Cycles [N]
GJS 400 without defects
GJS 400 with 70% Nodularity
GJS 400 with 61% Nodularity
GJS 400 with nonmetallic inclusions
- 16 -
Seminar: Metallography of casting alloys and metallurgical defects
Microstructure of GJS 700
with 100 % pearlite
100x
Microstructure of GJS 700 with
20 % ferrite
100x
- 17 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of structural defects on the compression-tension
fatigue strength of pearlitic nodular iron
350
Stress Amplitude [MPa]
300
250
200
150
100
50
0
1,E+04
1,E+05
1,E+06
1,E+07
Cycles [N]
GJS 700 with 100 % pearlite
GJS 700 with 20 % ferrite
- 18 -
Seminar: Metallography of casting alloys and metallurgical defects
Microstructure of GJS 700 with 1,25 % spiky graphite
200x
- 19 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of graphite defects on the rotary bending
fatigue strength of pearlitic nodular iron
450
Stress Amplitude [MPa]
400
350
300
250
200
150
100
50
0
1,E+04
1,E+05
1,E+06
1,E+07
Cycles [N]
GJS 700 without defects
GJS 700 with 1,25 % spiky graphite
- 20 -
Seminar: Metallography of casting alloys and metallurgical defects
Abstract 1
>
The appearance of cracks at the casting skin normally are caused by single
defects like sand, dross or slag with an Ø < 1 mm.
>
Single defects in the cast skin are more significant than anomalies in the
microstructure at the casting skin and in the cast wall.
>
The blasting of the cast skin improve the bending fatigue strength up to 50 %
compared to non-blasted cast surfaces.
>
Blasted surfaces have a 25 % reduced bending fatigue strength compared to
machined surfaces.
>
The prevention of “big defects” is state of the art, but the producing of castings
completely without failures are unrealistic. The design of the castings have to
tolerate different micro structural and surface defects.
- 21 -
Seminar: Metallography of casting alloys and metallurgical defects
Tested ADI modifications
Microstructure
Metallurgy / Moulding sand
Base material (graphite types VI)
Optimized process
Non metallic inclusions
Increasing level of residual Mg-content
Graphite type VI V III
Decreasing of residual Mg-content
Carbidic inclusions
Alloying with Mo
Graphite degeneration in the surface zone
High S-level in the molding sand
- 22 -
Seminar: Metallography of casting alloys and metallurgical defects
Temperatur in °C
ADI heat treatment of the samples
1000
900
800
700
600
500
400
300
200
100
0
0
100
200
300
400
Austenitizing:
890°C / 210 min
Quenching:
salt bath
Holding:
380°C / 150 min
500
Zeit in min
Microstructure of base material after
heat treatment (500 : 1)
- 23 -
Seminar: Metallography of casting alloys and metallurgical defects
Non metallic inclusions caused by high Mg-contents
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,57
2,14
0,23
0,019
0,004
-
1,72
0,75
0,065
Nodularity
84,6 %
Particle density
155 1/mm²
Non metallic
inclusions
0,41 %
- 24 -
Seminar: Metallography of casting alloys and metallurgical defects
Non metallic inclusions caused by high Mg-contents
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,62
2,11
0,21
0,020
0,003
-
1,71
0,83
0,075
Nodularity
78,7 %
Particle density
121 1/mm²
Non metallic
inclusions
0,74 %
- 25 -
Seminar: Metallography of casting alloys and metallurgical defects
Non metallic inclusions (%)
Influence of Mg-content on the volume of
non metallic inclusions
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
0,040
Reference
0,045 0,050
0,055
0,060 0,065
0,070 0,075
Mg-content in %
- 26 -
0,080
Seminar: Metallography of casting alloys and metallurgical defects
Influence of the Mg-content on the graphite typ
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,63
2,20
0,27
0,018
0,006
-
1,84
0,82
0,019
Nodularity
72,6 %
Particle density
188 1/mm²
- 27 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of the Mg-content on the graphite typ
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,56
2,21
0,21
0,006
0,007
-
1,84
0,84
0,011
Nodularity
48,1 %
Particle density
212 1/mm²
- 28 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of the Mg-content
on the nodularity and graphite type III
100
Percentage
80
60
Typ III (1)
Reference
40
20
Typ III (2)
0
0
0,01
0,02
0,03
0,04
Mg-content (%)
Nodularity (%)
Graphite type III (%)
- 29 -
0,05
Seminar: Metallography of casting alloys and metallurgical defects
Influence of Mo-content on carbide formation
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,52
2,29
0,26
0,023
0,004
0,33
1,85
0,76
0,041
Nodularity
85,2 %
Particle density
230 1/mm²
Carbide
0,21 %
- 30 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of Mo-content on carbide formation
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,62
2,24
0,26
0,030
0,008
0,74
1,74
0,78
0,036
Nodularity
87,7 %
Particle density
257 1/mm²
Carbide
0,38 %
- 31 -
Seminar: Metallography of casting alloys and metallurgical defects
Influence of Mo-content on carbide formation
Carbide content (%)
0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,00
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
Mo-content (%)
- 32 -
0,8
Seminar: Metallography of casting alloys and metallurgical defects
Lamellar graphite-zone in ductile iron
%C
% Si
% Mn
%P
%S
% Mo
% Ni
% Cu
% Mg
3,62
2,13
0,25
0,019
0,008
-
1,76
0,81
0,040
Nodularity
86,8 %
Particle density
149 1/mm²
Lamellar zone
1 mm
- 33 -
Seminar: Metallography of casting alloys and metallurgical defects
Mechanical values of all test variants
1000
7
900
Strength (MPa)
800
700
5
600
4
500
3
400
300
2
200
1
100
0
0
Base
material
Non
metallic
(1)
Non
metallic
(2)
Graphite typ III
(1)
(2)
Carbides
(1)
Variants
Rm [MPa]
Rp0,2 [MPa]
A [%]
- 34 -
Carbides
(2)
Fracture elongation (%)
6
Seminar: Metallography of casting alloys and metallurgical defects
Fatigue strength
350
Stress amplitade (MPa)
300
250
200
150
100
50
0
Base
material
Non metallic inclusions
(1)
(2)
Graphite type III
(2)
(1)
Carbides
(1)
Carbides
(2)
Casting skin defect
(as cast)
(shot blasted)
Variants
Compression-tension fatigue strength [MPa]
Rotary bending fatigue strength [MPa]
Bending fatigue strength [MPa]
- 35 -