PROPERTIES OF STEEL
Steels are known by certain tests. Early tests were more or less crude, and depended upon the ability of the workman to judge the "grain" exhibited by a freshly broken piece of steel. The cold-bend test was also very useful—a small bar was bent flat upon itself, and the stretched fibers examined for any sign of break. Harder stiff steels were supported at the ends and the amount of central load they would support before fracture, or the amount of permanent set they would acquire at a given load noted. Files were also used to test the hardness of very hard steel.
These tests are still used to a considerable extent, especially in works where the progress of an operation can be kept under close watch in this way, the product being periodically examined by more precise methods. The chief furnace-man, or "melter," in a steel plant, judges the course of the refining process by casting small test ingots from time to time, breaking them and examining the fracture. Cutlery manufacturers use the bend test to judge the temper of blades. File testing of case-hardened parts is very common.
However there is need of standardized methods which depend less upon the individual skill of the operator, and which will yield results comparable to others made by different men at different places and on different steels. Hence has grown up the art of testing materials.