On the Tensile Deformation Behaviour of Two-Phase Iron Alloys

Abstract

Synopsis:Tensile deformation behaviour of two-phase iron alloys with ductile second phase is studied and tried to be understood by the difference in strain between the harder phase and the softer phase. The alloys used are classified into the three groups; Fe-Cr-Ni alloys, Fe-Ni-C alloys and Fe-C alloys composed of austenite and ferrite, austenite and martensite, and ferrite and martensite respectively with various volume fractions. The mean effective grain size of each alloy is adjusted to be nearly same by heat treatment .The main results obtained are as follows:(1) The tensile deformation behaviour of a two-phase alloy is dependent on the C-value (=0.2% proof stress of the harder phase/0.2% proof stress of the softer phase), volume fraction and shape of the harder phase. This is because the degree of strain-inequality m (m =e2/e1:e1 is the mean strain of the softer phase and e2 is that of the harder phase) is affected by these factors.(2) The flow stress of a two-phase alloy with small C-value (smaller than about 3) is estimated by the strain-equal model (m=1).(3) The m-value of a two-phase alloy with nearly spherical second phase decreases with an increase in C-value and its tensile deformation behaviour approaches to the stress-equal model (m=0).In this case, the m-value is decreased with decreasing the volume fraction of the harder phase. When the volume fraction of the harder phase becomes close to unity, the deformation of the softer phase is strongly restricted by the around harder phase, so that the tensile deformation behaviour of a two-phase alloy approaches to the strain-equal model, independent on C-value.(4) The m-value is slightly affected by the overall strain of a two-phase alloy. It is small at small strain and increases with an increase in strain.(5) The tensile deformation behaviour of a two-phase alloy with long fiberous or disc second phase whose largest axis is parallel to the tensile direction is nearly shown by the strain-equal model even if Cvalue is large.

Design of novel high strength bainitic steels: Part 1

“…19 Sometimes composites of the above two models have also been considered. 20,21 However, these models are not based on a detailed consideration of solid mechanics.…”

Quantification of Large Deformation with Punching in Dual Phase Steel and Change of its Microstructure –Part I: Proposal of the Quantification Technique of the Punching Damage of the Dual Phase Steel

“…Tatsuo YOKOI, 1) * Hiroshi SHUTO, 1) Ken-ichi IKEDA, 2) Nobuo NAKADA, 3) Toshihiro TSUCHIYAMA, 4) Takahito OHMURA, 5) Yoji MINE 6) and Kazuki TAKASHIMA 6) steel sheets comprising car body members or application of light-gauge and high-strength steel sheets is demanded as a solution to achieving the two contradictory objectives of lower fuel economy and higher crashworthiness. 1) However, increasing the strength of steel sheets is generally known to decrease their formability.…”

“…2) Since the late 1970s, research has been conducted on dual-phase (DP) steel with a microstructure composed of soft ferrite and hard martensite as sheet steel that can be strengthened while limiting the degradation of formability to the extent possible. [3][4][5][6][7] These research efforts have culminated in the development of high-strength DP steel sheets with a low yield ratio, high work hardening rate, room-temperature non-aging property, high bake hardenability, 8,9) and excellent fatigue properties. 10) After the mid-1990s when the Japan New Car Assessment Program (JNCAP) was initiated to evaluate the crashworthiness of cars, these high-strength sheet steels rapidly replaced mild steels as materials for frame structural members to ensure crashworthiness.…”

Simulation-based method for hierarchal material design to improve ductile crack growth resistance of structural component

“…The rule of mixture could be approximately applied when the strength mismatch of matrix phase and second phase is not so high (Tomota et al 1975). Figure 11a shows the equivalent stressσ -equivalent plastic strainε p curves for the ferrite and pearlite phases and that for the two-phase steel.…”