Patent ID: 6171412
Filing Date: 2001-01-09
Classification: C21D,C22C

Abstract:
Bake-hardenable sheet steel with good anti-aging property, which has a chemical composition comprising, in terms of % by weight, not larger than 0.005% of C, not larger than 1.0% of Si, not larger than 3.0% of Mn, not larger than 0.15% of P, not larger than 0.05% of S, from 0.01 to 0.20% of Al, not larger than 0.01% of N, and from 0.01 to 0.2% of Ti, with a balance of Fe and inevitable impurities, and has a degree of bake hardenability (BH) of not smaller than 30 MPa, and which is characterized in that the value A defined below is not smaller than 0.4 and that the value AI.sub.QUENCH defined below is not smaller than 30 MPa:A=(AI.sub.QUENCH -AI)/AI.sub.QUENCHwherein;AI.sub.QUENCH indicates the aging index (MPa) of the sheet steel having been heated at 500.degree. C. for 40 seconds and then quenched in water,AI indicates the aging index (MPa) of the sheet steel, and the ""aging index"" indicates the increase in the yield stress (MPa) of the sheet steel, which is pre-treated to have a tensile pre-strain of 7.5% and then heated at 100.degree. C. for 30 minutes, and this is the difference between the yield stress of the heat-treated sheet steel and that of the non-treated one.