System helps produce dual-phase steel strip

A special version of a fibre optic infrared temperature measurement system helps produce dual-phase ferrite/martensite steel straight from the hot strip mill for the automotive industry.

Land Instruments International has developed a special version of its M3 Fibroptic infrared temperature measurement system to help steelmakers produce dual-phase ferrite/martensite steel straight from the hot strip mill.

Steel of this type is increasingly favoured by car manufacturers for passenger protection components such as side impact beams, because of its ability to absorb crash impacts more effectively at lower cost and with less mass than conventional HSLA steels.

The difficulty for the steelmaker is that the necessary dual-phase microstructure can be achieved at the hot rolling stage only if the strip is coiled at less than 250 deg C.

More usual temperatures of around 450 deg C yield a tri-phase structure that has to be subjected to a costly heat treatment process to produce the required dual-phase material.

Assurance that coiling temperatures are consistently below 250 deg C can be provided by Lands M3, which is the only Fibroptic non-contact thermometer on the market designed specifically for temperatures in this range.

For this application, the M3 is supplied as a complete ruggedised Under Strip Thermometer System (USTS) suitable for fitting beneath the roller table, where it avoids the excessive scale, ambient light and cooling water sprays in the overhead position that can cause temperature measurement problems.

Configured to suit the layout of the mill on which it is installed, the system is normally protected by a cooling jacket and an air purge to keep the optic head lens clean.

In some cases measurement redundancy is provided by using two M3 thermometers focused on the same target spot from slightly different positions.

The M3 is capable of measuring targets as small as 5mm at a distance of 100mm and in a response time of 100ms.

It is accurate to within +/-3 deg C at 75 deg C under recommended conditions and has three focus variants (100mm, 250mm and 500mm), three standard light guide lengths (1m, 2m, and 3.5m), and an industry-standard 4 to 20mA linear output.

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