Patent ID: 8747577
Filing Date: 2014-06-10
Classification: C21D,C22C,C23C,Y10T

Abstract:
1. A hot rolled steel sheet for spot welding comprising by mass %, C: over 0.030 to less than 0.10%, Si: 0.54 to 0.65%, Mn: 1.7 to 2.49%, P: 0.001 to 0.02%, S: 0.0001 to 0.006%, Al: 0.060% or less, N: 0.0001 to 0.0070%, Ti: 0.01 to 0.055%, Nb: 0.012 to 0.055%, Mo: 0.07 to 0.55%, B: 0.0005 to 0.0040%, and simultaneously satisfying having a balance comprised of iron and unavoidable impurities, having a microstructure composed of lower bainite or bainitic ferrite as a main phase which constitutes over 85% of the area of the microstructure, having a yield ratio of 0.68 to less than 0.92, a TS×(El) having a minimum value of CTS (cross-tensile strength) of 0.8 or more among 10 values of CTS obtained by welding 10 test pieces by a welding current of (CE+1.5) kA, where CE is welding current immediately before expulsion and surface flash, and wherein the minimum value of CTS among 10 values obtained by welding 10 test pieces by a welding current of CE is defined as “1”, and having an X-ray intensity ratio of a {110} plane parallel to the sheet surface at ⅛ the thickness of the steel sheet of 1.0 or more.