Technical Data

Metallurgical Terms

Grain Size Measurement.

An etched section is compared with  standard charts, or the number of grains intersected by a line of standard length is counted, as in the Snyder and Graff method. The result is often reported as an arbitrary number. In the ASTM system the grain size number N is given by the formula: number of grains per sq. in. at x 100 = 2^N-I. Grain size may also be measured by comparing the fracture surface with the standard specimens as in the Shepherd test. Usually the grain size refers to the austenite grains which formed in the preceding austenizing treatments.

Graphitizing.

An annealing process applied to certain iron based alloys, such  as cast iron, or to some steels with high carbon and silicon contents, by which the combined carbon is wholly or in part transformed to graphitic or free carbon.

Gravity Die Casting.

(See Die Casting).

Grey Iron.

(See Cast Iron).

Grinding Cracks.

Cracks caused by incorrect grinding, producing local heating and rapid cooling. They generally occur in the grinding of hardened material such as high carbon or case hardened steels, and appear in the form of a network.

Growth.

(a) The swelling and weakening experienced by cast iron on repeated heatings in oxidizing atmospheres.

(b) In powder metallurgy, the increase in  dimensions of a compact which may occur during sintering, although normally the tendency is for the compact to shrink.