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Modelling Plate Mill Rolling An Expert Practical System Approach M. - - PowerPoint PPT Presentation

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Modelling Plate Mill Rolling An Expert Practical System Approach M. Rebellato* and R. Barbosa** *Companhia Brasileira de Minerao e Metalurgia, **Universidade Federal de Minas Gerais The Charles Hatchett Seminar, 16 th July 2014, London

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Modelling Plate Mill Rolling An Expert Practical System Approach

  • M. Rebellato* and R. Barbosa**

*Companhia Brasileira de Mineração e Metalurgia, **Universidade Federal de Minas Gerais

The Charles Hatchett Seminar, 16th July 2014, London

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SLIDE 2

Introduction

Charles Hatchett Seminar Plate mill: an expert practical system 2

  • For structural steels, optimized mechanical

properties are heavily dependent on how fine and homogeneous the cross section ferrite grains become

  • The key is to determine how to apply basic

metallurgical fundamentals to the production line

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SLIDE 3

In the field

Charles Hatchett Seminar Plate mill: an expert practical system 3

  • Engineers face limitations such as plant

layout design, customer and societal specifications, costly downgrades

  • There is little time to decide; models must

give outputs very rapidly

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SLIDE 4

Motivation

Charles Hatchett Seminar Plate mill: an expert practical system 4

  • An expert, metallurgically sound, practical

system is necessary

http://www.industry.siemens.com/datapool/industry/industrysolutions/metals/siroll/en/Dongkuk-Plate-Mill-No.2-en.pdf

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SLIDE 5

This work

Charles Hatchett Seminar Plate mill: an expert practical system 5

  • In what follows the first steps of a larger

project aimed at building a practical expert system for industry rolling of microalloyed steels is presented

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SLIDE 6

Charles Hatchett Seminar Plate mill: an expert practical system 6

An industry case

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SLIDE 7

Rolling 300 mm slab to 16 mm plate

Charles Hatchett Seminar Plate mill: an expert practical system 7

Microstructure at ¼ thickness

Fine grains Coarse grain Mixed microstructure

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SLIDE 8

Rolling 300 mm slab to 16 mm plate

Charles Hatchett Seminar Plate mill: an expert practical system 8

Microstructure at ¼ thickness

Fine grains Coarse grain Mixed microstructure

Grain sizes Average ~ 10 μm However, grain sizes ranging from ~ 20-25 to ~ 5-6 μm

Very inhomogeneous structure

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SLIDE 9

Plate: chemical composition

Charles Hatchett Seminar Plate mill: an expert practical system 9

Element % weight C 0.046 Mn 1.08 Nb 0.04 Ti 0.014 V Cu Cr, Ni, Mo < 0.35 N2 0.0051

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SLIDE 10

Plate: possible precipitation

Charles Hatchett Seminar Plate mill: an expert practical system 10

Ti = 0.014 N2 = 0.0051 3.4 : 1 All Ti as TiN 0.0009 N2 available (almost no N2 left) N2 left ≈ 0 Nb = 0.040 7.75 : 1

  • 0.046 C takes 0.006

Nb

  • Nb left in solid

solution = 0.040 – 0.006 = 0.034 Form TiN + NbCN (few) + NbC , ie, mixed particles + leaving Nb in solid solution during rolling Most Nb in solution Low RLT and RST

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SLIDE 11

Hot rolling schedule

Charles Hatchett Seminar Plate mill: an expert practical system 11

Time Temperature

Broadsizing @ 1150oC Roughing R1 @ 1140oC and R8 @ 1130oC RLT @ 970oC RST @ 890oC Finishing F1 @ 940oC and F6 @ 855oC Acc Tstart @ 830oC and Tfinish @ 500oC Time = 25 s Holding period 240 s Possible partial recrystallization case due to low strain accumulation

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SLIDE 12

Finishing stands: Partial recrystallization of austenite

Charles Hatchett Seminar Plate mill: an expert practical system 12

Pass Recrystallized fraction after pass (%) Accumulated strain up to a given pass F1 17 0.33 F2 73 0.61 F3 90 0.50 F4 22 0.29 F5 18 0.46 F6 5 0.50 Model indicates:  possible partial recrystallization case  low strain accumulation before transformation

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SLIDE 13

Suggested alternative

Start finishing below RST, stop above Ar3

Charles Hatchett Seminar Plate mill: an expert practical system 13

Time Temperature

Broadsizing @ 1150oC Roughing R1 @ 1140oC and R8 @ 1130oC RLT @ 970oC RST @ 890oC Finishing F1 to F6 below RST and above AR3 Holding period 300 s Acc Tstart @ 830oC and Tfinish @ 500oC Time = 25 s

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SLIDE 14

Suggested improvement in finishing

Charles Hatchett Seminar Plate mill: an expert practical system 14

Reference temperature Temperature (oC)

RST 890 Finishing start temperature (F1) 910 (940 previous schedule) Finishing stop temperature (F6) 825 (855 previous schedule) AR3 810

Temperatures Possible outcome

 No partial recrystallization and  Increase in strain accumulation before transformation

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SLIDE 15

Finishing

Recrystallization and strain accumulation after changes

Charles Hatchett Seminar Plate mill: an expert practical system 15

Pass Recrystallized fraction after pass (%) Accumulated strain up to a given pass F1 Nil 0.38 F2 Nil 0.75 F3 Nil 1.08 F4 Nil 1.29 F5 Nil 1.51 F6 Nil 1.65 Model indicates:  no recrystallization in all passes  substantial increase in accumulated strain

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SLIDE 16

Charles Hatchett Seminar Plate mill: an expert practical system 16

Microstructure at ¼ thickness Grain sizes Average ~ 7 μm Grain sizes ranging from ~ 10-12 to ~ 3-6 μm

More homogeneous structure

Rolling 300 mm slab to 16 mm plate

New trial

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SLIDE 17

Charles Hatchett Seminar Plate mill: an expert practical system 17

Microstructure at ¼ thickness

Rolling 300 mm slab to 16 mm plate

After Before

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SLIDE 18

Charles Hatchett Seminar Plate mill: an expert practical system 18

The model

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SLIDE 19

Description

Charles Hatchett Seminar Plate mill: an expert practical system 19

  • Two modules: reheating and hot rolling
  • Sellars’ type model
  • Uses equations available in the literature
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SLIDE 20

Reheating module

Charles Hatchett Seminar Plate mill: an expert practical system 20

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SLIDE 21

Reheating module

Charles Hatchett Seminar Plate mill: an expert practical system 21

Inputs Outputs

 Alloy design  Process parameters

  • Slab thickness
  • Furnace geometry
  • Furnace temperatures

 Nb content in solution  Time needed to dissolve Nb

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SLIDE 22

Hot rolling module

Charles Hatchett Seminar Plate mill: an expert practical system 22

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SLIDE 23

Hot rolling module

Charles Hatchett Seminar Plate mill: an expert practical system 23

Inputs Outputs

 Process parameters

  • Pass temperatures
  • Strain
  • Strain rate
  • Grain size
  • Delay times

 Recrystallization data  Precipitation data  Ferrite grain size  Schedule optimization  Nb in solution (from reheating module)

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SLIDE 24

Schedule optimization

Schedule thicknesses, mm

Stage at rolling Slab 300 End broadsizing 227 Hold 64 Final 16

Reduction %

Stage at rolling Reduction (%) Recommended Sizing + broadsizing 24 Roughing 70 ≥ 50 – 60% Finishing 75 ≥ 20%

5 10 15 20 25 30 35 B1 B2 B3 R1 R2 R3 R4 R5 F1 F2 F3 F4 F5 F6

Reduction [%] Pass Number

Suggested schedule

Heaviest thickness reduction applied at last roughing pass

BS Roughing Finishing Obs.: a) Heaviest thickness reduction at last roughing pass; b) Pass reductions are progressive along metallurgical roughing phase.

Charles Hatchett Seminar 24 Plate mill: an expert practical system

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SLIDE 25

Charles Hatchett Seminar Plate mill: an expert practical system 25

Is this a reasonable type of model?

Proposed and other types of models

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SLIDE 26
  • Physically based
  • Physically based +

Numerical

  • Numerical models
  • Empirically based +

Numerical

  • Empirically based

Plate mill: an expert practical system

There are several types

Charles Hatchett Seminar 26

Wide plate mill

http://www.danieli.com/products/Flat-Products- Hot-Rolling-Mills/Plate-Mills/PLATE-MILLS/Wide- Plate-Mill on April, 12, 2014.

Type of models (not exhaustive)

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SLIDE 27
  • They render a better

understanding of the physical variables and metallurgical phenomena behind the process

Plate mill: an expert practical system

Physically based models

Among strong points…

Charles Hatchett Seminar 27

C.L. MIAO, C.J. SHANG, H.S. ZUROB, G.D. ZHANG, and S.V. SUBRAMANIAN, Recrystallization, Precipitation Behaviors, and Refinement of Austenite Grains in High Mn, High Nb Steel, METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME 43A, FEBRUARY 2012—66

Predicted results showing evolution of net drive force of recrystallization with time.

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SLIDE 28
  • They rely on many

variables that are difficult to obtain with a specific degree of accuracy

Plate mill: an expert practical system

Physically based models

…however…

Charles Hatchett Seminar 28

  • S. Hore, S.K. Das, S. Banerjee, S. Mukherjee, A multiscale coupled Monte Carlo model to characterize microstructure evolution during hot rolling of Mo-

TRIP steel, Acta Materialia 61 (2013) 7251–7259.

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SLIDE 29
  • Still provides better

understanding however,

  • Difficulty in
  • btaining key

variables persists and

  • It is usually time

consuming

Plate mill: an expert practical system

Physically based + Numerical models

Possible strong and weak points

Charles Hatchett Seminar 29

  • S. Hore, S.K. Das, S. Banerjee, S. Mukherjee, A multiscale coupled Monte Carlo model to characterize microstructure evolution during hot rolling of Mo-

TRIP steel, Acta Materialia 61 (2013) 7251–7259.

Multiscale model

Obs: Model uses a continuum dislocation density evolution model coupled with a heat transfer model integrated with a mesoscale Monte Carlo (MC) simulation technique.

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SLIDE 30
  • Usually very easy to

use

  • Lack of

generalization

  • Must be tuned by

numerical algorithm

Plate mill: an expert practical system

Empirical + Numerical models

Possible strong and weak points

Charles Hatchett Seminar 30

Average prediction errors for MFS values calculated using equations available in the literature

Antonella DIMATTEO, Marco VANNUCCI and Valentina COLLA , Prediction of Mean Flow Stress during Hot Strip Rolling Using Genetic Algorithms, ISIJ International, Vol. 54 (2014), No. 1, pp. 171–178

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SLIDE 31

Plate mill: an expert practical system

Empirical models

Charles Hatchett Seminar 31

  • V. V. Orlov and E. I. Khlusova , SIMULATION OF THROUGH PRODUCTION PROCESSES FOR MANUFACTURING THICK-WALLED PLATE IN HOT ROLLING

REVERSING MILLS, Metallurgist, Vol. 56, Nos. 11–12, March, 2013 (Russian Original Nos. 11–12, Nov.–Dec., 2012). The authors are at the Prometey Central Research Institute of Structural Materials.

“A concept of structure formation (and consequently properties) for thick rolled sheet was developed as applied to equipment of reversing hot-rolling mills with different properties”

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SLIDE 32
  • Usually very easy to

use

  • Continues to lack

generalization

  • However, it is

possibly a type of model suitable for

  • n-site industry

multipass rolling

Plate mill: an expert practical system

Possible strong and weak points

Charles Hatchett Seminar 32

Comparison of calculated results for ferrite grain size with experimental data (steel X80, dγ = 17 μm, cooling rate 1°C/sec).

  • V. V. Orlov and E. I. Khlusova , SIMULATION OF THROUGH PRODUCTION PROCESSES FOR MANUFACTURING THICK-WALLED PLATE IN HOT ROLLING

REVERSING MILLS, Metallurgist, Vol. 56, Nos. 11–12, March, 2013 (Russian Original Nos. 11–12, Nov.–Dec., 2012). The authors are at the Prometey Central Research Institute of Structural Materials.

Empirical models

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SLIDE 33
  • Easy to use
  • Lack of

generalization

  • Might be useful for
  • n-site modelling of

multipass rolling

Plate mill: an expert practical system

Summary

Empirical models

Charles Hatchett Seminar 33

Physically based model

  • Enhances

understanding

  • Difficulty with some

variables

  • Might be not practical

for on-site multipass rolling modelling

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SLIDE 34

Conclusions

  • First steps were taken to develop a simple,

reliable, applicable on-site model.

  • Results from plate 16-mm thick plate have

been used to validate the model. The suggested optimized schedule showed potential to improve mechanical properties of the plate.

  • The proposed model seems suitable to be

used as an on-site tool.

Charles Hatchett Seminar Plate mill: an expert practical system 34