Effect of Heating and Deformation on Properties of Highly Deformable Pipe Metal During Cold Bend Manufacture

Аннотация

The change in mechanical properties and shape parameters is studied for pipe with high deformation capacity (HDC) 1420 × 21.7 mm in size of strength class K60 during cold bend manufacture with a reduction in bend radius. Features are demonstrated of steel structure of HDC pipes providing ageing resistance and improved deformation capacity, including presence of MA component and polygonal ferrite in a bainitic matrix. The use of HDC pipes will make it possible to prepare bent sections with a radius reduced to R ≈ 20D_o without corrugation formation and with geometric parameters within the framework of specifications for “standard” bends. Thermal action during application of an anticorrosion coating (200–250°C) leads to an increase in strength, especially σ_y(Rt_0.5) and the ratio σ_y(Rt_0.5)/σ_u in the longitudinal direction and reduction in ductility (δ₅ and δ_u). However, after HDC pipe heating sufficient deformation capacity is obtained for bends. Features are determined for the change in mechanical properties and tensile curves for steel in zones subjected to tension (TZ) and compression (CZ) during pipe bending with residual plastic deformation up to ~3%. For TZ and CZ metal, there is a different direction of the change in σ_y and σ_y/σ_u in the longitudinal direction, and also a reduction in ductility indices (δ₅ and δ_u) in transverse and longitudinal directions. The production limitations revealed during pipe bending arising due to the danger of jamming of a mandrel in a pipe during bending are revealed.