The Production Technology And Practice Of 30MnCrMo Seamless Steel Pipes Used For Coupling Material

With the increasing exploitation of domestic oil and natural gas and the expansion of the depth and scale of various drilling platforms,the demand for seamless steel pipes and matching couplings is gradually increasing.How to use domestic resources to improve the quality of domestic seamless steel pipes,technology added value,and improve market competitiveness are all factors that cannot be ignored.As one of the main manufacturers of seamless steel pipes in China,Baotou Iron & Steel Co.,Ltd.often uses seamless steel 25 CrMnMo steel as the coupling material for 80-110 steel grade seamless pipes.However,the hardenability of the currently used 25 CrMnMo steel is not very good,and it does not reach the hardness corresponding to 90% martensite.As a result,failure modes often occur,such as: tripping,threaded joint failure,gluing,breaking,deformation,wear and corrosion.Therefore,under the premise of ensuring the quality,the cost is reduced,and at the same time,the strength,plasticity,hardness and inclusion level of the material can meet the requirements of the user.Moreover,the material must not only meet the conventional needs,but also ensure high hardenability.In order to improve the hardenability of steel,it is possible to add elements that improve the hardenability,such as the commonly used C element and Mn element,and further improve the hardenability by multi-component compounding,that is,relative to 25 CrMnMo.It is proposed to reduce the cost of chromium and molybdenum by means of carbon and manganese,and to reduce the cost while ensuring that the hardness of the new trial coupling is 90% martensite,and the heat treatment process is used to meet the relevant performance design requirements.The steel grade is30 MnCrMo.Through the test of the hardenability of the experimental steel 30 MnCrMo and the comparative steel 25 CrMnMo,it was found that the hardenability of the 30 MnCrMo experimental steel was significantly better than that of the 25 CrMnMo comparative steel.At the same time,the heat treatment process of 30 MnCrMo was explored.It was found that the tempering temperature of30 MnCrMo steel increased by 80 °C,the yield strength decreased by about 240 MPa,the tensile strength decreased by about 180 MPa,the elongation rate was not improved,and the 0°C impact toughness was improved by about 50 J.The strength of 25 CrMnMo is obviously reduced,which is mainly caused by the decrease of Mo content.It is well known that Mo improves the tempering resistance of materials.880 °C quenching,heat preservation for 60 minutes,tempering at 610-630 °C,holding for 90 minutes,tensile properties and impact work meet the technical requirements of P110 steel grade indicators,tempering at 670 °C,mechanical properties test results meet API 5CT to N80 Q Steel grade technical requirements,tempering at 690 °C,meeting the technical requirements of L80-1 mechanical properties.Finally,30 MnCrMo economical coupling material was trial produced,and it was tested to meet the design requirements.