Temperature Measurement Deviation during Annealing of Multiphase Steels

Abstract

A pyrometric analysis of the temperature of continuous annealed strip material is an essential component of industrial production. However, despite calibration, the development of composition-dependent oxides during annealing prevents an accurate pyrometric measurement of actual strip temperature. An Al-based and a Si-based transformation induced plasticity (TRIP)-assisted steel were pyrometrically analyzed during annealing under a reducing atmosphere (5 pct H 2 and 95 pct Ar). Oxide development on both steels led to a deviation between pyrometer readings and simultaneous thermocouple measurements. The developing oxides influenced the pyrometer readings to different extents because of unique emissivities and different growth kinetics.

The Causes and Effects of Preannealed Radiative Property Variations Across Full‐Hard Advanced High‐Strength Steel Coils

“…Various studies have examined how evolving radiative properties may lead to pyrometry errors, with a particular focus on surface oxides during annealing. Thiessen et al [ 10 ] observed variations between thermocouple and pyrometric temperature measurements of transformation‐induced plasticity (TRIP) steel samples when annealed in a reducing atmosphere of 95% Ar and 5% H 2 ; these differences were attributed to emissivity changes caused by the formation of surface oxides during annealing. Somveille et al [ 9 ] also showed how oxidation of DP DP‐780 and 980 steels during annealing may influence emissivity and pyrometric temperature measurements.…”

Development of a multivariate spectral emissivity model for an advanced high strength steel alloy through factorial design-of-experiments

“…Many methods have been developed to mitigate pyrometer errors caused by uncertain spectral emissivity [2][3][4][5][6][7]. Whenever possible, pyrometers are aimed at the notch formed between the steel strip and the roll to exploit the blackbody cavity effect [2].…”

“…Unfortunately, this method is sensitive to misalignment and any temperature difference between the strip and the roll; moreover, many key points in steel production do not facilitate this type of measurement. Dual-and multi-spectral measurements are also often used to mitigate the impact of uncertain radiative properties [3][4][5][6][7]. In two-color pyrometry (a version of dual-spectral pyrometry), the ratio of the spectral emissivity at the two detection wavelengths is assumed to be constant and known.…”

“…In the case where the radiative properties are taken to be independent of wavelength, i.e. the greybody assumption, this ratio is unity [5]. While the ratio method is resilient to partially-filled field-of-views and atmospheric attenuation if both detection wavelengths are equally attenuated, it does not address the fact that the spectral emissivity ratio varies with the evolving surface state of the strip.…”

Automatic detection of material phase transitions from spectroscopic data

“…It might be within the semiconductor industry [6] or for materials that readily oxidize in an oxygen containing atmosphere [3], [7]. The motivation for the development of the ECSP temperature measurement method was the inability to predict the emissivity changes for a Ti6Al4V-specimen subjected to thermal processing [3].…”