Heat treatment process and diameter expansion performance of expandable tubular steels

The expandable tubular tested steels after heat treatment three important indices,work hardening index(n),thick anisotropy index(r) and properties after prestrain,thus allowing for their diameter expansion performance evaluation.The results show that the lnσ-lne curve of tested steels complies with linear relationship of Hollomond formula.The results also show that heat treatment can improve the n value of tested steels,so that uniform deformation property before necking has been improved.After heat treatment,the r value of tested steels are more than 1,hard to occur the localized necking,the expandable tubular is very favorable.The yield strength has a severely increase,while the tensile strength has a slight change when prestrain value is 12%.The tested steels have superior deformation property and reaching the strength level of general oil well casing after prestrain.Based on overall consideration,the chemical compositions and the heat treatment process of expandable tubular steels are determined.