2019 Volume 105 Issue 11 Pages 1070-1079
The hot stretch reducing process of steel tubes has been attracting attention as an effective means to achieve both high strength and excellent formability by developing the {011}<100> texture reducing in austenite and ferrite (α/γ) two-phase region. However, it has been known that, in the case of control-rolled steel plate, the textures developed by the hot rolling in the α/γ region closely relate with the brittle fracture.
In this study, the quantitative relationship between textures and toughness of the steel tubes reduced in the α/γ region was investigated. The increase of the DBTT (Ductile Brittle Transition Temperature) due to the stretch reducing in the α/γ region is observed only when the carbon content is below 0.06%. In contrast, the increase of DBTT is negligible small due to grain refinement when the carbon content is in the range from 0.12% to 0.18%. The increase of the DBTT in the low carbon steel tubes is attributed to the increment of coarse and brittle grains with high orientation factor for brittle fracture cos2θ by the stretch reducing in the α/γ region. Accordingly, the DBTT shows a strong dependence on both the area fraction of the brittle crystal grains Af (cos2θ≧0.9) and maximum grain size rather than average grain size.
