Microstructure, Crystallographic Texture, and Stretch‐Flangeability of Hot‐Rolled Multiphase Steel

Abstract

The microstructure, crystallographic texture, strain hardening in the hole edge‐punched and stretch‐flangeability of hot‐rolled multiphase sheet steel is investigated by scanning electron microscopy, electron backscatter diffraction, and microhardness measurements. The results show that the strain hardening in the hole edge‐punched is not the main factor that influences the hole expansion ratio. The bainite fraction, average grain area, and kernel average misorientation distribution mean are microstructure factors that improve the hole expandability and reduce the effect of strain hardening in the hole edge‐punched on the hole expansion ratio. The crystallographic texture affects the hole expandability. The high intensity of {332}<113>α and {111}<112>α components that have higher normal anisotropy (rtrue¯) also reduces the effect of strain hardening at the hole edge‐punched. The cracks propagate through the interfaces following the banded microstructure direction at the hole edge‐punched during the punching process. The gamma distribution analysis of the kernel average misorientation distribution indicates that there are different energy transfer (β parameter) and dislocation densities due to different cooling rates.

Evaluation of Strengthening Mechanisms in Novel Fully Ferritic Advanced High‐Strength Steels

“…Reference [15] used Equation (7), and it was also applied in this study, although the equation does not include the main carbide forming elements (Ti, Mo, V, and Nb). This study also adopted the assumptions concerning the carbon and nitrogen content made in ref.…”

“…[1][2][3][4] The relatively high-volume fraction of martensite and/or bainite, which is often required to achieve a high TS value in the steel, unfortunately tends to have an adverse effect on the stretch flangeability of the dual-phase (DP), multiphase (MP), and low-alloyed, transformation-induced plasticity (TRIP) steels. [6][7][8][9][10][11][12] Excellent strength and flangeability properties can be achieved in the complex-phase (CP) steels and in a steel consisting of tempered martensite and granular bainite; however, that required a strict thermomechanical process control together with a well-balanced steel chemistry. [2,13] Besides the abovementioned steels, the fully ferritic steel grades typically have excellent formability but a relatively low strength; thus, Funakawa et al [14] introduced a method to increase their strength substantially by nanometer-sized interphase precipitates (IP) that were formed during the austenite-to-ferrite phase transformation.…”

Influence of the Replacement of the Actual Plastic Orthotropy with Various Approximations of Normal Anisotropy on Residual Stresses and Strains in a Thin Disk Subjected to External Pressure

“…The radial and circumferential stresses on the right-hand side of Equation (26) should be eliminated using Equations (15) and 16, on the right-hand side of Equation (27) using Equations (18) and (19). The solutions (26) and (27) are valid if the respective yield criterion is not violated in the range a ≤ ρ ≤ 1. This condition is represented as…”

“…The authors of [25] studied the influence of continuous annealing temperature on battery shell steel's mechanical properties. In [26], the normal anisotropy of crystallographic orientations has been calculated to evaluate the effect of crystallographic texture on the stretch-flangeability during the hole expansion test of hot-rolled multiphase steel.…”

Effects of Microstructural Properties on Damage Evolution and Edge Crack Sensitivity of DP1000 Steels

“…The previous research showed that a lower strength differential between the phases, by tempering heat treatment [7] or by adding some alloying elements like Nb [8], could increase the hole expansion ratio (HER). Furthermore, lowering martensite content [9], smaller grain size [10], and more homogeneous microstructure [11] can improve HER. These microstructure changes can vary the damage behavior and mechanism in DP steel as well.…”