Gauge plate, also known as flat stock, is supplied in the form of flat plate and square/rectangular sections. It was originally made for toolmakers for making tools, jigs and fixtures.
It key properties are that it is supplied with 2 surfaces, in the cases of plates or 4 surfaces, in the case of other shapes, are ground and where appropriate the dimension are very accurate.
It is made from a steel alloy. This is formulated so that the metal is easy to machine in its untreated state but can be heated treated to harden it and it is dimensionally stable when heat treated.
Several manufacturers make it and the formulation is not exactly the same though it is very similar
C 0.9 W 0.6 Mn 1.2 V 0.15 Cr 0.5
Saxon Steels Ltd
C 0.85-1.05 W 0.4-0.6 Mn 1.0-1.4 V 0.15-0.3 Cr 0.4-0.6 Si 0.15-0.4
Heat treatment – hardening
Preheat to 500ºC, raise to 790º-815º, according to size ie long enough for the temperature to be uniform but no longer, quench in oil.
Heat treatment – annealing
temper for 1 hour. Hardness will then depend upon tempering temperature
150C Rockwell C 63-64
Gauge plate and silver steel
Gauge plate is very similar in its properties to silver steel though its composition is very different. But, whereas gauge plate is available in flat shapes but not rounds on the other hand silver steel is only available in round shapes.