Hot workability of rolled steel depends on many factors, i.e., refining molten steel, heating ingots, condition of the rolling mill, impure elements in material, etc. Especially, in the case of the special-shape steel rolling, such as sash bars for building and rims and side rings for wheels, high level material for hot workability is demanded, because of necessity to make seamless skin and accurate size. The problem of material, principally the influence of impure elements, is one of the most important theme among many factors in workability of steel.
In this report, studies are made on the influences of Cu, Sn, and other factors on the hot workability. Methods to measure the workability are special hot-rolling test, hot-torsion test, hot bending test, hot up-set test, hot rotary-hammering test, sensibility test for over-heating, sulfur-print test, and microstructure test,
In general, the material which shows low workability in these tests, also causes many seams and small cracks on the surface of shaped steel, and is not available for rolling production. The special hot-rolling test and other tests for determining the workability show that either of Cu or Sn as impure elements makes workability of steel lower. Increasing the content of Cu (or Sn), Cu (or Sn) concentrating phenomena re found in the matrix metal just under scale after heating (surface oxidation), through a microscope. Cu (or Sn)-concentrating phase seems to be related to degree of seams and hair cracks on shape steel surface during rolling.