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SFB 761 „Stahl ab initio“
02.09.2008„MSE“ Nürnberg
Uni. Prof. Dr.-Ing. D. SenkDipl.-Ing. A. Lob
Smelting and Soldification of Fe-Mn-C Steel
Senk, Lob
SFB 761 „Stahl ab initio“ Subarea B1
Smelting and Soldification of Fe-Mn-C SteelSubtask: Hydrogen Problem
No. 1
Abstract
- Presentation of the System Fe-Mn-C
- Hydrogen in Steel-making Prozess
- Hydrogen in Austenitic Steel
- Legality of Hydrogen Solubility
- Hydrogen Solubility Examinations
- Outlook for Further Examinations
Smelting and Soldification of Fe-Mn-C SteelSubtask: Hydrogen Problem
0.0240.02590.050.0020.0080.10.324.575.0Content [wt%]CrNiSiPSAlCMnFeElements
Chemical composition TRIP-Steel for SFB 761
System Fe-Mn-C
Steels of Interest
0.0240.02590.050.0020.0080.10.624.575.0Content [wt%]CrNiSiPSAlCMnFeElements
TRIP-Steel (TRansformation Induced Plasticity):strain-induced εhcp- and αbcc –martensite formation in the γfcc austenitic matrixunder plastic deformation*
Chemical composition TWIP-Steel for SFB 761
TWIP-Steel (Twinning Induced Plasticity):based on the formation of mechanical twins under plastic deformation
steelsystem Fe-Mn-C:
high strengthcombinedwith high ductility
No. 2 Senk, Lob
* for manganese contents > 15 wt%
Phase Diagram Fe-Mn
Hansen, M.; Anderko, K.: Constitution of binary alloys, McGraw-Hill Book Company, 2.Ed, New York Toronto (1958), pp 664-668
system Fe-Mn-C:440°C ≤ fcc ≤1430°CRT ≤ ε-hcp ≤ 440°C
Austenitic and Martensitic Structure
Characteristics of the System Fe-Mn-CNo. 3 Senk, Lob
Magnetic Transformation
γ Fe, γ Mn
Atome%
Weight%
Tem
pera
ture
(°C
)
Fe-Mn-Csystem;chemical
composition
Segregation-behaviour
Characteristics of the System Fe-Mn-C
18
20
22
24
26
28
30
0 50 100 150 200 250 300
Distance (µm)
wei
ght-
% (M
n,Fe
)
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
wei
ght-
% (C
)
MnFeC
system Fe-Mn-C:strong
segregations
No. 4 Senk, Lob
Segregation profile of Fe-Mn-C
Segregation coefficient of manganese
depending on:- melting parameters- casting format- distance to the surface- C-content
low Mn-distributionin interdendritic
micro areas
35,1...16,1min
max ==ccSMn
→ Segregation leads to inhomogeneous solidification structure affecting also [H] concentration
One Task of Subarea B1
Senk, LobHydrogen Examinations
Determinationof
Hydrogenin the liquid
System Fe-Mn-C
Chemically-inducedhydrogen crack formation
Crack formation in steel
No. 5
slagshydrated lime
atmospheric humidity
coolant decompositionCH4
rusty scrap
rusty scrap
residual humidity
deoxidiserslags
Steelmaking-Process
Sources for Hydrogen in Industrial WorkProblems and Treatment
refractory
from this, high contents
of hydrogenin steel induces
problems for thesteelmaking-process
break out (casting)
Senk, Lob
crack formation
in
out importantsteel
treatmentat this point
No. 6
Critical Values for Hydrogen Contents
Continuous Casting
Continuous Casting
Senk, Lob
breakout danger for hydrogen contents ≥ 10 ppm
Continuous Casting, schematic
Industrial hydrogenmeasurements in the tundish
No. 7
SolidificationTemperature (°C)
log
[H] (
ppm
)
104/T, T in K84 12 16
- 0,4
0
0,4
0,8
1,2
1,6
1000
800
600
400
1800
1600
1400
1200
Solubility of hydrogen in iron
Solubility switch of hydrogeninduces the followinghydrogen reactions
}{21][ 2HH →
dissolved hydrogenaccumulates at thesolid-liquid interfaceand will be movedthrough the liquidphase
dissolvedhydrogen
will getgaseous
anddiffuses
out of thesolid steel
hydrogen increasinghydrogen decreasing
Solid-liquid interface, schematic
HH
HH
H H
H H H
H
H
H
H
H
Senk, LobDiffusion of Hydrogen
hydrogen accumulation
in thesolid-liquidinterface
No. 8
lss HH −= ][][
Ratte, E.: Wasserstoffinduzierte verzögerte Rissbildung austenitischer Stähle auf CrNi(Mn)- und Mn-Basis. Berichte aus dem Institut für Eisenhüttenkunde, RWTH Aachen: Shaker Verlag, 2007
Hydrogensolubility:fcc > bcc
Dependence on Structure
Hydrogen solubility in the fcc (Austenite) is higher than in the bcc (Ferrite)octahedron places in the fcc are greater than the tetrahedrons places
Senk, LobHydrogen Solubility
Solubility of hydrogen in pure iron
No. 9
[Mn]
[C]
[Al]
12
14
16
18
20
22
24
26
28
30
0 2 4 6 8 10 12
Alloying Elements (wt%)
[H] m
ax (p
pm, w
t)
Hydrogen solubility in Fe-X-systems depending on chemical composition
Weinstein, E.; Elliot, J. F.: Trans. Met. Soc., AIME 227 (1963), pp. 382-393
for the systemFe-Mn-C
the elements Mn, Al, Care of great
interest
Senk, LobHydrogen Solubility
Dependence on Chemical Composition
No. 10
shrinkagehole
cracks
pores
Hydrogen in Microstructure
Hydrogen „Trapping“
Graphic representation of typical lattice defects
Cavities in as-cast
Multi phase steel
- H is free to move in the lattice, till H crosses a trap- strong interaction between Fe atom and hydrogen at trap- exothermal reaction bonds H at this position
Energy of bonding for hydrogen, to leave the trap:
plane traps ( )= active traps → (-) mechanical qualities
deep traps ( )= innocent for mechanical qualitiesmolH
kJG Tf 30−≥∆
molHkJG T
f 6155 −≥≥−
Senk, LobNo. 11
negative influence from hydrogen on solid
steel depends on microstructure
mechanical problems→ cracks→ blowholes
K = equilibrium constanta = activityf = activity coefficient
Hydrogencontent depends on:
- chemical composition- temperature
- pressureto calculate with measured temperature
to be adjusted
to calculate with analysed chemical composition
to measure withHydris® orpin tube
(4) Gmelin, L.; Durrer, R.; Trenkler, H.; Krieger, W.: Gmelin-Durrer Metallurgie des Eisens. Weinheim: Verlag Chemie, (1978) (5a/b)
Senk, LobLegality for Hydrogen Solubility
No. 12
Sieverts
0.023Si
0.008S
0.015P
-0.002Ni
-0.001Mn
-0.002Cr
0.060C
0.011Al
Interaction parameter ejHAlloy element j Dependence on chemical composition
K = equilibrium constantT = temperature (K)A = -1900 (K-1); constantB = 0,9201; constant
Stone, R. P.; Plessers, J.; Turkdogan, E. T.: Die Genauigkeit der Bestimmung des Wasserstoffgehaltes in flüssigem Stahl mit dem Hydris-System. Stahl und Eisen 110 (1990), 11, pp. 65 – 71
Frohberg, M. G.: Thermodynamik für Werkstoffingenieure und Metallurgen. Leipzig: Deutscher Verlag für Grundstoffindustrie (1994)
Senk, LobNo. 13
Temperature dependence
examinations of the dependence on
chemical composition for hydrogen solubiltiy
at first
Sieverts; Parameters
Legality for Hydrogen Solubility
Senk, Lob
Hydrogen Solubility Trials for the System Fe-Mn-C
50 kg medium frequency induction furnace
exhaust duct
refractory
Hydris®-lance
hood for inerting(protection againstthe atmospheric
humidity)
at the bottom:porous plug
Ar and Ar/H flooding
Hydris® Measurements
Hydris®-probe
Functional principle of Hydris®
No. 14
Senk, LobPin Tube Measurements
Hydrogen Solubility Trials for the System Fe-Mn-C
1) sample extraction from
the melt
2) quenchingthe sample
into cold water
3) removing the fused quartzfrom the solidified sample 4) leaving the solidified sample
into liquid nitrogen
rapid treatment of every
step
Analysing
Pin Tube
Storage the sample in liquid nitrogen
Steps for pintube sample taking
No. 15
4 cm
Hydris
Pin Tubes
Temperature
3
4
5
6
7
8
9
10
11
12
13
14
0 5 10 15 20 25
Manganese Content (wt%)
Hydr
ogen
Con
tent
(ppm
, wt)
1550
1600
1650
1700
1750
1800
1850
1900
1950
2000
Tem
pera
ture
(°C
)
Comparison between Hydris® - and Pin Tubes measurement for increasing manganese contents
Senk, Lob
critical hydrogen content for
casting breakout
Hydrogen Solubility Trials for the System Fe-Mn-C
Own Results of RWTH Metallurgie
at firstthe dependence
of chemicalcomposition
will be checked
No. 16
→ Both measurement techniques give conformable results
Further Hydrogen Solubility Trials
Determination on:- temperature dependence- pressure dependence- examination of interaction parameter
No. 17
Vacuum-Induction-Furnace 4 at IEHK
frequency: 3 kHzmaximum power input: 150 kWvacuum: ≥ 3·10-3 mbar capacity: 100 kgspecial features: adjustable atmosphere
programmable temp.charging during vacuum
upcoming features: online and clean measurement = Hydris®-System
LookoutSenk, Lob
Senk, LobNo. 18
- System Fe-Mn-C: - austenitic structure- segregation behaviour
- Hydrogen = - poor mechanical qualities for steel- casting break out for high [H] contents- high solubility in austenitic structure- accumulation at sold-liquid interface
- First experiments: - chemical composition dependence- Hydrogen solubility above critical
values for casting break-out
- Further experiments: - temperature dependence- pressure dependence
Summary
Project B1