METHOD OF INCREASING THE YIELD STRENGTH OF COLD FORMED STEEL SECTIONS

PCT No. PCT/AU95/00378 Sec. 371 Date Dec. 26, 1996 Sec. 102(e) Date Dec. 26, 1996 PCT Filed Jun. 27, 1995 PCT Pub. No. WO96/00305 PCT Pub. Date Jan. 4, 1996Yield strength of a cold rolled steel section is increased and controlled by performing a predetermined amount of strain by way of cold working in an in-line roll forming process followed by a controlled amount of strain aging wherein the temperature of the steel section is elevated to a point below 500 DEG C. and held at an elevated temperature for a time up to 30 seconds. The heating typically takes place by induction heaters (16) and the time aging may be provided in an in-line galvanizing bath (17) before cooling the steel in a quench bath (18). The effect is further enhanced by further cold working and the consequent additional strain in forming rolls (19). For a given steel composition the degree of yield enhancement can be controlled by the temperature and tie parameters and also by the degree of initial roll forming in shaping rolls (10).