７８０ＭＰａ級Ｄｕａｌ Ｐｈａｓｅ鋼の静的，動的強度特性に及ぼす炭素と珪素の影響

This study investigated the effect of intercritical heat treatment temperature on the tensile properties, work hardening and corrosion resistance of dual phase steel. Ferrite-martensite dual phase steel with different martensite volume fractions were obtained after heat treatment at different intercritical temperatures. Microstructure, mechanical properties of steel were measured and the corrosion resistance was evaluated via polarization test. Tensile strength of the specimens increased by increasing the martensite volume fraction up to 48.2%. Further increase in martensite volume fraction led to decrease in tensile strength. Work hardening behavior analyzing showed that in DP steel with less than 50% martensite volume fraction, the work hardening took place in one stage and by increasing the martensite volume fraction two-stage work hardening behavior was observed in the Holloman analysis. The results of polarization test showed that, the corrosion resistance of dual phase steel is higher than that of plain carbon steel with ferrite-pearlite microstructure.

In the present paper, controlled cooling in different ways was performed using a laboratory hot rolling mill in ultra-high strength hot rolled ferrite-bainite dual phase (DP) steel. The results have shown that the final microstructures of DP steel comprise ferrite, bainite and a small amount of retained austenite and martensite. DP steel has a tensile strength ranging from 1010 to 1130MPa and yet retains considerable total elongation in the range of 14–17%. The addition of Mn and Nb to DP steel leads to the maximum ultimate tensile strength, yield strength and the product of ultimate tensile strength and total elongation due to the formation of retained austenite and granular bainite structure. Laminar flow cooling after hot rolling results in a significant increase in the quantity of ferrite and bainite due to the suppression of pearlite transformation, and as a result, the present steel possesses high strengths and good toughness.

The effects of loading-direction and strain-rate on the mechanical behaviors of human frontal skull bone

Understanding the effects of martensite volume fractions (V m) in dual phase (DP) steel resulting from heat treatment is crucial for designing structures for mechanical impact resistance and optimizing manufacturing processes. DP steel’s material behaviour depends heavily on its microstructure properties. While stress-strain curves for individual phases in DP steels are often determined using empirical models, extensive experimental data is required to establish empirical model constants. This research aims to achieve two main objectives: firstly, to calibrate stress-strain curves for pure ferrite and pure martensite using limited experimental data using micromechanical adaptive iteration algorithm (MAIA). This calibration involves using stress-strain data from DP steels with varying V m during the calibration stage and additional data for verification. Secondly, to conduct a comprehensive sensitivity analysis of MAIA to assess its capabilities and limitations. Microstructure-based finite element (FE) models, simulated with ABAQUS/Standard, are employed to predict stress-strain curves under uniaxial tensile test conditions. The MAIA approach successfully calculated ferrite and martensite stress-strain curves that could predict plastic behaviour of DP steel with different V m, which agreed with experimental work. Key advantages of this approach include avoiding complex 3D microstructure geometries and requiring only two experimentally obtained stress-strain curves with different Vm for material constant calibration, along with another curve for validation. However, the experimental data selected for calibration must have a V m difference between 20%–50% and one of the DP steels must have a low martensite volume fraction. The FE micromechanical model could capture the effect of softening of martensite phase and strengthening of ferrite phase as compared to its bulk properties for DP steel. The effect of V m on strain hardening rate was also successfully captured. This technique comes with obvious shortcomings, such as excluding crystal plasticity behaviour, and change in chemical composition within the individual phase with varying martensite volume fraction.

In order to reduce the rolling force and the roll wear, the lubricants have been used in hot sheet rolling of steel, but the lubrication behavior at the interface between roll and workpiece in hot steel rolling have never been well understood. On the other hand, hot rolling process with high reduction in thickness have been developed to produce the ultra-fine grained steels. The high reduction in hot rolling causes some troubles such as the increase of the rolling force, the occurrence of friction pick up and so on. To solve these problems, the lubrication behavior at the interface between roll and workpiece in hot steel rolling must be quantitatively understood. In this paper, the coefficients of friction were measured by using the newly developed simulation testing machine for hot rolling. The effects of lubricant factors such as the compositions and the viscosity of the base oil and the additive agents on the coefficient of friction were investigated. From these experimental results, the lubrication behavior at the interface between roll and workpiece was investigated and the lubrication mechanism was proposed.

The effect of ferrite grain size and martensite volume fraction on the tensile properties of dual phase steel

Effect of martensite morphology and volume fraction on strain hardening and fracture behavior of martensite–ferrite dual phase steel

In this study, effect of rolling and coiling temperature in thermo mechanical controlled process (TMCP), on the microstructure and mechanical properties of dual phase (DP) steel according to martensite volume fraction (MVF) rate was investigated. By using various finishing mill exit temperature and cooling conditions that is controlled laminar cooling system, the microstructural evolution of coil improves the mechanical properties with lower costs and higher productivities, in comparison to the heat treatment after rolling. The main part of the paper contains the result of tensile, yield and microstructure properties of DP600 steel produced on hot strip rolling plant and run- out table line. The results show that a higher MVF and an increasing cooling rate after the last deformation raised strength of the DP600 steel. The yield strength and ultimate tensile strength increase by decreasing coiling temperature.

Crack growth resistance in dual-phase steel was studied. The dual phase steel microstructure was modified through heat treatments to increase the martensite volume fraction from 10% to 40%. The as-received and heat-treated samples were evaluated using a uniaxial tensile test, fatigue crack growth test, and fracture toughness test. Extended Finite Element Method (XFEM) was used to simulate the crack growth in compact tension test specimens. The results showed that an increase in martensite volume fraction is an effective way to increase the fracture resistance under different load conditions, quasistatics and dynamic, increasing the fracture toughness, tensile strength and fatigue resistance of the heat-treated material. Presence of a highest content of martensite results in formation of an important number of secondary cracks during the fatigue crack growth, which slow down the crack propagation. Moreover, martensite generates a crack closure over the crack tip, making the propagation difficult due to the irregularities caused by the crack growth on the martensite. Finally, the computational load-displacement curves are in good agreement with the experimental data.

Interface tensile and fracture behavior of the Ti/Al3Ti Metal-Intermetallic Laminate (MIL) composite under quasi-static and high strain rates

Enhanced mechanical properties of a Fe-Mn-Al-C austenitic low-density steel by increasing hot-rolling reduction

Effects of Zr on the high strain rate superplasticity of 2124 Al

In this research study a low carbon steel with composition of C=0.11 %; Mn=1.30%; Cr=0.45%; Si=0.20%; Al=0.03% and Fe=bal. was cast and used in hot rolled condition. After intercritical annealing at different temperatures for different times, dual phase structures with various volume fraction of martensite were produced. Then the volume fraction of martensite for different samples were measured. Study of the relationship between temperature and time of intercritical annealing and martensite volume fraction showed that a new equation as f γ /f e =1 -exp(-kt) can be used to give variation of martensite volume fraction with temperature and time of annealing. Also it is found that k coefficient changes exponentially with annealing temperature.

In the industrial rolling process of Al sheet, the cold rolling process practically follows immediately to hot rolling process without intermediate annealing. In this case, the hot rolling conditions may have effects on the anisotropy of final annealing sheets.So, we examined, by eare tests, these. effects on the anisotropy of final annealing sheets made of a semi-continuously cast slab (S. C. C. S.) and a book-mold cast slab (B. M. C. S.), both cold rolled in one way and cross way.The results obtained are as follows:(1) The ear values of sheets of S. C. C. S. are not always higher than those of B. M. C. S. but can be made even lower by selecting the proper hot rolling temperature, and are more severely affected by hot rolling temprerature than those of B. M. C. S., in which these effects are almost negligible. (See Fig. 8, 9)(2) Although it has been generally considered that the cross rolling gives lower ear value than one way rolling, it seems to be not always so. (See Fig. 8, 9)(3) In this experiment, both slabs were treated by the same processes after hot rolling, therefore the difference in anisotropies of final sheets made of both slabs should indicate the effects of orientation of cast grains resulted from both casting methodes.(4) The temper of as-hot-rolled plate at 400°C coresponds to I/2 H. When it is annealed, it softens gradually up to 450°C, but in high temperature annealing 600-640°C it rather hardens. (See Fig. 4) Consequently, ears of final annealed sheets become higher at 0-90° directions until the intermediate annealing temperature reaches about 400°C, but when the temperature rises over 400°C, the height of ear becomes lower and then finally the direction changes to 45°. (See Fig. 15)(5) The effects of hot rolling as the antecedents on mechanical properties, can be removed by subsequent intermediate or final annealing, but the effects on ears can never be removed. (See Fig. 13, 14, 15)(6) The pattern appeared on the anodized surface of the sheets made of S. C. C. S. can not be industrially removed by hot or cold rolling and annealing. The only way to cover it is cladding process.

The effect of austenitization and intercritical annealing temperature on mechanical properties and work‐hardening response of high‐formability dual phase (DP) steel with low C and Mn content is studied. Different mechanisms of microstructural development are characterized. At intercritical temperature range, austenite forms in the ferritic matrix, which will transform to martensite during quenching. However, at austenitization temperatures, the material becomes completely austenitic with low hardenability. As a result, during quenching, there will be some ferrite phase in the martensitic matrix of the resultant DP steel. These differences are found to have important effects on the mechanical properties. The yield strength decreases at low martensite fraction due to the disappearance of the yield‐point phenomenon and the presence of martensite‐induced dislocations that move at low stresses. However, the yield strength rapidly increases by the dominance of the martensitic matrix at high martensite fractions. Moreover, the dependence of the ultimate tensile strength on martensite volume fraction is discussed based on the work‐hardening capacity of the DP steels. Finally, the mechanical properties are summarized by consideration of strength‐ductility trade‐off seen for DP steels.