Development of Precipitation Strengthened Steel with Adequate Stretch Flangeability

Abstract

An experimental steel of the composition (in wt.%) 0.04C-0.81Mn-0.38Si-0.15Ti-0.01S-0.013P-0.043Al was hot rolled into 4 mm plates at three different temperatures of 1100, 1000, and 900°C. The yield strengths of these plates were in the range of 434-484 MPa while the ultimate tensile strength varied from 508 to 586 MPa. Elongation values ranged from 13.0 to 17.8%. Hole expansion ratios (k) varied from 23 to 30.7%. In particular, the plate rolled at 1000°C showed a yield strength of 484 MPa, an ultimate tensile strength of 586 MPa, a total elongation of $15%, and a hole expansion ratio of $23%. Transmission electron microscopy showed the presence of fine precipitates of titanium carbosulfide ($10-50 nm). Therefore, maximum precipitation strengthening was obtained in the plate that was hot rolled into a thickness of 4 mm at 1000°C.

On the strengthening mechanisms of a Fe-0.2% C-0.6% Mn-0.2% Mo-1.0% Cr steel intended for pipelines applications.

“…In these micrographs, it was found a contribution to 𝜎 𝑝𝑝𝑡 from 203.93 MPa (HR+WQ+T) to 217.65 MPa (HR+AC). This precipitation strengthening effect has been reported, taken values from 73 MPa (Olivares et al, 2008), 74 MPa (Irvine & Baker, 1984), 94 MPa (Tan et al, 2014), 203 MPa (PW), 217 MPa (PW), 272 MPa (Sarkar & Jha, 2011) and 300 MPa (Misra et al, 2005), depending on processing conditions.…”

“…In addition, Fig. 7 shows the effect of thermomechanical processing and cooling conditions (Carretero-Olalla et al, 2014;Misra et al, 2005;Olivares et al, 2008;Sarkar & Jha, 2011;Takebayashi et al, 2010;Tan et al, 2014;Wang et al, 2006), on the value of 𝜎 𝑑𝑖𝑠 , for several Fe-C plates of steel, with the addition of one or more element, such as Cr, Mn, Mo, Nb, and Ti, where the contribution of dislocation hardening takes values between 155 MPa to 320 MPa. These values are independent of its carbon content and more dependent on the processing route and cooling medium/heat treatment.…”

Processing and Mechanical Properties of Highly Formable Ferritic High Strength Steel Containing Titanium Nanocarbides for Automotive Applications

“…Precipitation coarsening is avoided through the addition of molybdenum and appropriate process design. A homogenous ferritic matrix can ensure high formability [3][4][5][6].…”