Metallurgical and Materials Transactions A

, Volume 36, Issue 4, pp 989–997 | Cite as

Modeling the ductile-brittle transition behavior in thermomechanically controlled rolled steels

  • S. J. Wu
  • C. L. Davis
  • A. Shterenlikht
  • I. C. Howard
Article

Abstract

The Charpy impact transition temperature (ITT) is well modeled for hot-rolled or normalized steels having uniform grain size using empirical equations. However, the ITT of nonhomogeneous steel microstructures, such as duplex (mixed fine and coarse) grain sizes, and the scatter in experimental Charpy energy values, observed in the transition region, are not accurately modeled. This article describes research on the microstructure-fracture property relationship and the prediction of the ITT using a cellular automata finite element (CAFE) model in thermomechanically controlled rolled (TMCR) Nb-microalloyed steels. The ferrite grain size distributions for two TMCR steel plates were analyzed and used for the prediction of the local fracture stress (σ F ) values based upon the Griffith model. It was found that the coarse grain size distribution could be used to predict the range of σ F values observed. The CAFE model was used to predict the ITT using the predicted σ F distribution for a TMCR steel. Results showed that the CAFE model realistically predicted the Charpy ITT; in particular, it was able to reproduce the scatter in values in the transition region. Within the model, the percentage of brittle failure and the upper shelf ductile energy were predicted well. However, the lower shelf brittle energy was overestimated due to computational limitations in the commercial FE software used with the current CAFE model.

Keywords

Ferrite Material Transaction Grain Size Distribution Maximum Principal Stress Ductile Damage 

Nomenclature

cB, cD

strain concentration coefficients for the ductile and the brittle CA arrays

D

parameter of the Rousselier’s model

d

grain size

f0

initial void volume fraction in the Rousselier’s model

H

hardening term in the Rousselier’s model

E

Young’s modulus

m

Weibull modulus

mi

Weibull modulus of the FE i

m*

the mean Weibull modulus across all FEs in the plastic zone

P

probability of cleavage

Papp

applied load

PGY

general yield load

ti

time at increment i

Vi

volume of ith FE

V0

characteristic volume of material

Y1

integrity of a FE

Y2

percentage of brittle phase per FE

Ym(B), Ym(D)

state of cell m in the brittle or the ductile CA array

β

damage variable of the Rousselier’s model

βF

critical value of the damage variable

γp

effective surface energy

ɛpeq

equivalent plastic strain

v

Poisson’s ratio

ϑ1

orientation angle of cell 1

ϑF

grain misorientation threshold

ρ

dimensionless density

σ1

parameter of the Rousselier’s model

σF

local fracture stress

σeq

Von Mises equivalent stress

σI

the maximum principal stress

σm

mean stress

σu

reference stress

σw

Weibull stress

σY

yield stress

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Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 2005

Authors and Affiliations

  • S. J. Wu
    • 1
  • C. L. Davis
    • 2
  • A. Shterenlikht
    • 3
  • I. C. Howard
    • 4
  1. 1.School of Materials Science and EngineeringBeijing University of Aeronautics and AstronauticsBeijingP.R. China
  2. 2.the Department of Metallurgy and MaterialsThe University of BirminghamBirminghamUnited Kingdom
  3. 3.Mechanical Science CentreUniversity of ManchesterManchesterUnited Kingdom
  4. 4.the Department of Mechanical EngineeringThe University of SheffieldSheffieldUnited Kingdom

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