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Abstract

Considering the similarities between structural distribution and deformation behaviour of martensite–ferrite dual phase steels with composite materials reinforced by short, discontinuous fibres, a new expression for the tensile strength of these steels was suggested using shear lag analysis, i.e.

<disp-formula><mml:math><mml:semantics><mml:mrow><mml:msub><mml:mi>σ</mml:mi><mml:mrow><mml:mtext>bDP</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mfrac><mml:mn>1</mml:mn><mml:mi>K</mml:mi></mml:mfrac><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mfrac><mml:mi>β</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:msqrt><mml:mn>3</mml:mn></mml:msqrt></mml:mrow></mml:mfrac><mml:mo>+</mml:mo><mml:mn>0</mml:mn><mml:mo>⋅</mml:mo><mml:mn>65</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:msub><mml:mi>σ</mml:mi><mml:mrow><mml:mtext>bM</mml:mtext></mml:mrow></mml:msub><mml:msub><mml:mi>V</mml:mi><mml:mtext>M</mml:mtext></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mi>σ</mml:mi><mml:mrow><mml:mtext>bF</mml:mtext></mml:mrow></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:msub><mml:mi>V</mml:mi><mml:mtext>M</mml:mtext></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:annotation encoding='MathType-MTEF'></mml:annotation></mml:semantics></mml:math></disp-formula>

where σ_bDP, σ_bM, and σ_bF are the tensile strengths of the steel, the martensite, and the ferrite phases respectively, β is the aspect ratio of martensite islands, K is the strength ratio of martensite to ferrite σ_bM/σ_bF, V _M is the volume fraction of martensite, and (1 – V _M) is the volume fraction of ferrite. The experimentally measured strengths of a variety of dual phase steels are shown to be in good agreement with those calculated using this equation. Problems concerning the load transfer from ferrite to martensite and the degree of utilization of martensite strength are discussed.

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Shear lag analysis of strength of dual phase steels

Abstract

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