## Abstract

A single 0.12 wt.% C alloy has been heat treated to produce dual-phase ferrite-martensite composites of a variety of volume fractions and grain sizes of both phases. Two separate models have been used to describe the 0.2% proof stress of these composites, one based on the topological model of Gurland and the other based on the yield propagation model of Petch. Using the topological model, the 0.2% proof stress in all dual-phase steels could be represented by σ_{0.2%} (MPa) = 280 + 17.4d_{I}^{- 1 2} (1 - g′) + 576g′ where g′ is a parameter related to the volume fractions and contiguities of the two phases and d_{I} is the size of type I grains. This model had some inconsistencies and in particular did not show good extrapolations to either 100% martensite or 100% ferrite. Using the yield propagation model, the 0.2% proof stress could be written as σ_{0.2%} (MPa) = 122 + {16.4 + 432 (V_{II}d_{II})^{ 1 2}}d_{c}^{- 1 2} where d_{c} is an average between the ferrite grain size and the martensite islet size, d_{II} is the size of type II grains and V_{II} is the volume fraction of the secondary phase. This equation showed excellent extrapolation to 100% ferrite but some change in slope was observed towards 75% martensite. The reasons for the inadequacies of representation have been attributed mainly to autotempering in the martensite and to the shortcomings in the measurement of the ferrite and martensite continuities.

Original language | English |
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Pages (from-to) | 229-238 |

Number of pages | 10 |

Journal | Materials Science and Engineering |

Volume | 63 |

Issue number | 2 |

DOIs | |

Publication status | Published - 1984 |

## ASJC Scopus subject areas

- General Engineering