SHEET STEEL FOR MANUFACTURE OF PRESS-HARDENED PARTS, PRESS-HARDENED PART CHARACTERIZED BY COMBINATION OF HIGH STRENGTH AND DUCTILITY IN EVENT OF ACCIDENT, AND METHODS FOR THEIR MANUFACTURE

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to the field of metallurgy, namely to the production of press-hardened parts used as structural elements in motor vehicles to implement the functions of preventing the penetration or absorption of energy in a collision. The steel part is made of steel having a composition containing, weight percentage: 0.15 ≤ C ≤ 0.22, 3.5 ≤ Mn < 4.2, 0.001 ≤ Si ≤ 1.5, 0.020 ≤ Al ≤ 0.9, 0.001 ≤ Cr ≤ 1, 0.001 ≤ Mo ≤ 0.3, 0.001 ≤ Ti ≤ 0.040, 0.0003 ≤ B ≤ 0.004, 0.001 ≤ Nb ≤ 0.060, 0.001 ≤ N ≤ 0.009, 0.0005 ≤ S ≤ 0.003, 0.001 ≤ P ≤ 0,020, if necessary 0.0001 ≤ Ca ≤ 0.003, the rest is iron and inevitable impurities. The microstructure of the part in the main piece, which is at least 95% of the volume, when expressed in fractions of the surface, consists of at least 50% of the carbon-redistributed martensite, no more than 30% of ferrite, at least 2% of residual austenite, no more than 5% of fresh martensite and cementite, the surface density of its particles having a size of more than 60 nm is less than 10^7/mm². Residual austenite is characterized by an average C content of at least 0.5%. ;EFFECT: manufactured parts have high mechanical strength, high impact resistance, good corrosion resistance and dimensional accuracy with a significant reduction in weight. ;20 cl, 1 dwg, 6 tbl