The Effect Of Annealing Treatments And Pre-strains On Mechanical Properties And Corrosion Properties Of TWIP Steels Used In Expandable Tubular

As oil drilling turning to ocean deep and deep underground,the purpose of enhancing drilling efficiency and reducing cost has become increasingly urgent.The expandable tubular technology is using expandable device to make tube that down the well plasticity deformation.In terms of mechanical properties,the deformation twins in TWIP steel result in uniform deformation and high strength.Thus,TWIP steel is an ideal material for expandable tube.Annealing treatment and pre-strain treatment lead to microstructure change,and cause a change of mechanical properties as well as corrosion properties.The main work and conclusions of study are summarized as below:(1)TWIP steel maintains the austenite structure after annealing treatment with different temperature,and annealing twin density increasing with annealing temperature increasing.The yield strength and tensile strength decrease slightly with increasing annealing temperature,but the elongation is increasing obviously.The TWIP steel has a high impact absorbing energy and a low hardness,and they both reduced as annealing temperature increasing.Annealed TWIP steel showed no stress corrosion crack(SCC)occurred.The fracture mechanism of SSRT is ductile fracture.Electrochemical experiments showed that corrosion resistance properties are better than before.(2)The deformation twin density increased with increasing pre-strains and the cross deformation twins were observed.The yield strength and tensile strength increase with increasing pre-strains,and the elongation is at a high value.The hardness increased after pre-strains,and the impact behavior is also good.Pre-strained steel showed no SCC occurred,and the fracture mechanism of SSRT is ductile fracture.It can be inferred that corrosion resistance properties declined with pre-strain increasing from electrochemical experiments.The experiment results showed that the mechanical properties and corrosion resistance properties are better than hot-rolled steel,and it can be used at expandable tube.The steel with good properties can provide necessary material basis for extending expandable tubular technology.