A Scheil-Gulliver model dedicated to the solidification of...

A Scheil-Gulliver model dedicated to the solidification of steel

Aachen, the 11th of September 2014

P. Schaffnit, J. Konrad, M. Weinberg

ED

WW

, Sch

affn

it, S

lide

3, 1

9 S

epte

mbe

r, 20

14


Steel production and continuous casting

Steel production: Continuous casting (~ 90%!) “Batch” casting (ingot, precision) Sintering

Source: World Steel Association (worldsteel)

ED

WW

, Sch

affn

it, S

lide

4, 1

9 S

epte

mbe

r, 20

14


Continuous casting and solidification interval

Continuous casting: solidification range Liquidus Solidus

Benefits Safety margins can be reduced (precise prediction of solidification range) Improve quality, efficiency Reduce energy consumption, environmental footprint

ED

WW

, Sch

affn

it, S

lide

5, 1

9 S

epte

mbe

r, 20

14


Validation

Sample: 25 industrial heats (wide span of composition: solidification range from 5°C to 135°C)

Experimental procedure Slab material Optical emission spectrometry DTA measurements

ED

WW

, Sch

affn

it, S

lide

6, 1

9 S

epte

mbe

r, 20

14


Discrepancies for prediction of liquidus temperature

TCFE6 predicts liquidus temperature with an accuracy of ± 5°C

Liquidus: “TCFE6 – DTA”

ED

WW

, Sch

affn

it, S

lide

7, 1

9 S

epte

mbe

r, 20

14


Discrepancies for prediction of solidus temperature

“Scheil-Gulliver” shows significant scatter: See Kozeschnik, Rindler et Buchmayr, Int. J. Mater. 98 (9), 2007 Zero ductility temperature estimated with an accuracy of ± 30°C

Solidus: “TC’s SG – DTA” (95% solidified)

ED

WW

, Sch

affn

it, S

lide

8, 1

9 S

epte

mbe

r, 20

14



Both equilibrium and “Scheil-Gulliver” show significant scatter

Solidus: “TC’s SG – DTA”

“Equilibrium – DTA”

ED

WW

, Sch

affn

it, S

lide

9, 1

9 S

epte

mbe

r, 20

14


State of the art

Adequate prediction of liquidus temperature (± 5°C)

Prediction of solidus temperature requires special attention Equilibrium (± 20°C) Scheil-Gulliver with “back diffusion” and “back transformation” (± 35°C)

See Chen and Sundman, Mat. Trans., Vol. 43 No. 3 (2002) Scheil-Gulliver for austenitic solidification Equilibrium for ferritic solidification (diffusion of substitutional components in ferrite significantly faster than in austenite)

ED

WW

, Sch

affn

it, S

lide

11, 1

9 S

epte

mbe

r, 20

14


Measurement and available models

See Chen and Sundman, Mat. Trans., Vol. 43 No. 3 (2002) Scheil-Gulliver for austenitic solidification (e.g.: “steel Q”) Equilibrium for ferritic solidification (e.g.: “steel L”) (diffusion of substitutional components in ferrite significantly faster than in austenite)

Low alloyed

Ferritic solidification

Austenitc solidification

Peritectic solidification

ED

WW

, Sch

affn

it, S

lide

12, 1

9 S

epte

mbe

r, 20

14


Modeling of solidification

„Original model“ Ds=0, DL=¥ k=CS/CL

Analytical solution

„Explicit implementation“ Computer aided Several solid phases and components No assumption on phase diagram (partition coefficient) Diffusion of interstitials in solid (C, N: Ds

C,N= ¥) Transformation (d à g)

Source: MatCalc handbook

Source: University of Cambridge http://www.doitpoms.ac.uk/tlplib/

solidification_alloys/scheil.php

Scheil-Gulliver model

ED

WW

, Sch

affn

it, S

lide

14, 1

9 S

epte

mbe

r, 20

14


„Classical“ Scheil-Gulliver model :

„State-of-the-art“ Scheil-Gulliver : (+ “back transformation”!)

Scheil-Gulliver for steel:

Modelling of solidification

Overview of Scheil-Gulliver models with regard to diffusion:

Liquid d g, ... Interstitials: (DC,N,..)

¥ ¥

Substitutionals: (DMn,Si,...) 0


¥ ¥

Substitutionals: (DMn,Si,...) 0


¥ 0 Substitutionals: (DMn,Si,...)

ED

WW

, Sch

affn

it, S

lide

16, 1

9 S

epte

mbe

r, 20

14


Diffusion coefficients in ferrite and austenite

Databases: TCFE6 and MOB2

ED

WW

, Sch

affn

it, S

lide

17, 1

9 S

epte

mbe

r, 20

14




Infinite diffusion

No diffusion Scheil-Gulliver with back diffusion

ED

WW

, Sch

affn

it, S

lide

18, 1

9 S

epte

mbe

r, 20

14




Infinite diffusion

No diffusion

Scheil-Gulliver for steel

ED

WW

, Sch

affn

it, S

lide

19, 1

9 S

epte

mbe

r, 20

14


Scheil-Gulliver for steel: flow chart

ED

WW

, Sch

affn

it, S

lide

20, 1

9 S

epte

mbe

r, 20

14


Solidification “steel P”: DTA

ED

WW

, Sch

affn

it, S

lide

21, 1

9 S

epte

mbe

r, 20

14


Solidification “steel P”: SGS

Liquidus (DTA)

Solidus (DTA)

Ferritic solidification

Peritectic

reaction

Austenitic solidification

Database: TCFE6

ED

WW

, Sch

affn

it, S

lide

23, 1

9 S

epte

mbe

r, 20

14



SGS consistently reconciles equilibrium (ferrite) and Scheil-Gulliver (austenite) Complete redistribution in ferrite (equilibrium) Only interstitial elements redistribute in austenite (Scheil-Gulliver)

SGS model predicts solidus temperatures of technical steels reliably

ED

WW

, Sch

affn

it, S

lide

24, 1

9 S

epte

mbe

r, 20

14



SGS consistently reconciles equilibrium (ferrite) and Scheil-Gulliver (austenite) Complete redistribution in ferrite (equilibrium) Only interstitial elements redistribute in austenite (Scheil-Gulliver)

SGS model predicts solidus temperatures of technical steels reliably

ED

WW

, Sch

affn

it, S

lide

26, 1

9 S

epte

mbe

r, 20

14



Model (with TCFE6) adequately predicts solidus temperature

Solidus: “SGS – DTA”

ED

WW

, Sch

affn

it, S

lide

27, 1

9 S

epte

mbe

r, 20

14


Overview

Model (with TCFE6) adequately predicts solidification range

ED

WW

, Sch

affn

it, S

lide

28, 1

9 S

epte

mbe

r, 20

14


Conclusions, outlook

Adequate prediction Liquidus: ± 5°C Solidus : ± 15°C Narrow down safety on casting window

Model Robust, easy to use (production environment!) Bridges predictions of equilibrium and Scheil-Gulliver with “back diffusion” and “back transformation”

Further improvements Segregation in alloys with ferritic solidification Threshold temperature for diffusion of substitutional components (empirical length scale and diffusion database)

A Scheil-Gulliver model dedicated to the solidification of...

Documents

Transcript of A Scheil-Gulliver model dedicated to the solidification of...