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Split Ends and Cracking Problem During Hot Rolling of Continuously Cast Steel Billets

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Abstract

The paper presents a detailed analysis of split end and cracking problems that occurred during hot rolling of thermomechanically treated (TMT) grade steel bars. The major analytical tool was a multiscan computer-controlled ultrasonic image analysis system for analysis of the defects observed on transverse cut slices of the billets under investigation. The possible reasons for billet cracking during hot rolling such as a low Mn/S ratio, high casting speed, high degree of superheat, and high inclusion content in steel were analyzed. Additionally in the process parameters such as low roll diameter, high friction, and low reduction ratio were also analyzed. The cracking appeared to be associated with large surface/internal defects, axial porosity, off-centered cavities/porosities, off-centered cracks, and inclusion bands. The analysis results suggested methods to prevent such defects in continuously cast steel billets and to reduce/eliminate split end problems. The casting parameters should include: (a) Mn/S ratio >35, (b) degree of superheat <60 °C, and (c) casting speed: <3.0 m/min, where roll radius and initial thickness of the workpiece should be optimized.

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Abbreviations

h f, h o :

Strip thickness

J*:

Total power per unit width

j*:

Total relative power

\( j_{\Upgamma }^{ * } \) :

Relative shear power

\( k \) :

Yield stress in shear

\( \bar{k} \) :

Mean value of yield stress

l d :

Length of the projection of the arc of contact

\( m \) :

Constant friction factor

R a :

Distance (see Fig. 1)

R o :

Roll radius

\( R_{\Upgamma } \) :

Discontinuity surface radius

{v}:

Velocity vector

v f, v o :

Velocity of workpiece

v r :

Roll surface velocity

X a, Y a :

x, y coordinate of point A

Y a :

Yield stress

αc :

Contact angle

ε:

Relative reduction

εi :

Effective strain rate

εv :

Volumetric strain rate

σv :

Vertical component of stress

ξb, ξf :

Back and front relative stress

\( \Upphi_{1}, \Upphi_{2} \) :

Angles, (see Fig. 1)

ω, ωo :

Zone II and roll rotational velocity

i :

Serial, i = 1, 2, 3

opt:

Optimal

se, sf:

Split ends, sound flow

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Acknowledgment

The authors are thankful to the management of Tata Steel for giving permission to publish this work.

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Authors and Affiliations

  1. R&D and SS Division, Tata Steel Ltd., Jamshedpur , Jharkhand, India

    J. C. Pandey & Manish Raj

  2. Merchant Mill, Tata Steel Ltd., Jamshedpur , Jharkhand, India

    P. N. Choubey

Authors
  1. J. C. Pandey
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  2. Manish Raj
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  3. P. N. Choubey
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Correspondence to J. C. Pandey.

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Pandey, J.C., Raj, M. & Choubey, P.N. Split Ends and Cracking Problem During Hot Rolling of Continuously Cast Steel Billets. J Fail. Anal. and Preven. 9, 88–96 (2009). https://doi.org/10.1007/s11668-008-9194-x

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  • DOI: https://doi.org/10.1007/s11668-008-9194-x

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