Effect of Carbon Content on V-Bending in High-Strength TRIP-Aided Dual-Phase Steel Sheets with Polygonal Ferrite Matrix

Abstract

Effect of carbon content on V-bending in high-strength TRIP-aided dual-phase (TDP) steel sheets with polygonal ferrite matrix was investigated for automobile applications. V-bending test was performed on a hydraulic testing machine at a processing speed of 1 mm/min, using a rectangular specimen (50 mm in length, 5 mm in width, 1.2 mm in thickness). The main results are as follows.

(1) The (0.1–0.4)C-1.5Si-1.5Mn, mass% TDP steel sheets were able to perform V-bending by strain-induced martensitic transformation of TRIP effect. On the other hand, ferrite-martensite dual-phase (MDP0) steel sheet of 900 MPa grade was not able to perform 90-degree V-bending because of initiation of crack in tension region.

(2) The 0.4C-1.5Si-1.5Mn, mass% TDP4 steel sheet of 1100 MPa grade was able to enable the 90-degree V-bending that considered an amount of springback (Δθ= θ₂−θ₁), in which the θ₁ and the θ₂ are a bending angle on loading and a bending angle after unloading respectively, of more than 2-degree by controlling a displacement of punch bottom dead center.

Phase maps of bcc and fcc in TDP4 steel ((a) microstructure, (b) inner, (c) center, (d) outer). (Online version in color.)