Non-destructive measurement of microstructure and tensile strength in varying thickness commercial DP steel strip using an EM sensor

Consideration of Magnetic Measurements for Characterisation of Ferrite–Martensite Commercial Dual-Phase (DP) Steel and Basis for Optimisation of the Operating Magnetic Field for Open Loop Deployable Sensors

“…The correlation coefficients for the best-fit equation are R 2 HV = 0.8753 and R 2 UTS = 0.8601 for hardness and tensile strength, respectively. From Figure 2, it can be observed that, whilst the different grades group into data clusters, there is much more scatter for the DP800 steel grades than the other samples, which has been described elsewhere [8], and there is potential for overlap in the ferrite fraction between the grades, indicating that a fraction of ferrite alone is not a good indicator to characterise the grade or mechanical properties in the DP steel samples. The decrease in tensile strength/hardness of dual phase steel (DP) with increasing ferritic fraction is well known and broadly discussed [21].…”

“…From Figure 4, much more scatter for the DP800 grades than the other steels is again observed. This is believed to be due to the magnetic properties also being influenced by the ferrite grain size as the grain boundaries act as effective pinning points to magnetic domain movement and there is more variation in the ferrite grain size for the DP800 steels (66% difference) compared to the DP600 steels (50% difference) and the DP1000 steels (28% difference); see Table 1 [8,10]. Figure 5 shows a clear link between tensile strength (UTS) and coercivity for the commercial DP steel samples; this also agrees with reports in the literature, and literature data [12] are included to show the general trends.…”

“…It can be seen from Figure 8 that there is an increase in the initial permeability value as the ferrite fraction increases; hence, the initial permeability value of these samples shows an increasing order of DP1000 < DP800 < DP600. The correlation coefficients for the best-fit line, R 2 µ i = 0.8602, is low as the effect of grain size on permeability is not taken into account, which has been described elsewhere [8,29]. In summary, higher permeability values can be observed in the DP600HR4 mm with a larger ferrite grain size (10 µm) than the other DP600 samples (ferrite grain size of 6-7 µm), and lower permeability values are observed in the DP800 samples with the smaller ferrite grain size (3 µm) compared to the ferrite grain size of 5-6 µm for the rest of DP800 samples.…”

“…In recent years, the use of magnetic methods for nondestructive evaluation/ characterisation of steels has increased rapidly [4][5][6][7][8]. For ferromagnetic materials, the interaction between lattice imperfections and Bloch walls is reasonably well explained [9], and characteristic magnetic flux density (B)-magnetic field strength (H) curves are detected.…”

Local magnetic flux density measurements for temperature control of transient and non-homogeneous processing of steels

“…The electromagnetic properties of steel are directly related to microstructure. In isothermal conditions, electromagnetic measurements are used to study phase fraction 29–31 , hardness 32–34 , stress-states 35–37 , mechanical properties 38 , and surface treatments 39–41 . However, the temperature dependence of the electromagnetic properties 42,43 can be further exploited to characterize and monitor the steels during transient thermal and thermomechanical processing 44–46 with non-homogeneous conditions.…”