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

No. 19

Thank you for your attention

Senk, Lob