Research On The Preparation Of DT300 High-Strength Steel By Powder Metallurgy

DT300,the self-developed steel in domestic,has the properties of high strength,high toughness and low alloy,which has tensile strength of 1800 MPa and fracture toughness more than 100 MPa·m1/2.In order to achieve the purpose of machining,the hardness of steel needs to be reduced in the factory.However,DT300 steel is used for the thin-walled and precision parts in the military field,which need to ensure the strength and reduce the weight.The traditional machining is difficult to meet the quality and efficiency of machining.With the increase of alloying elements,the casting defects such as segregation and shrinkage porosity is difficult to eliminate all of these limits the popularization and application of DT300.Powder metallurgy technology that has the characteristics of low energy consumption,high material utilization and low cost can realize the net formed.Thus,it can significantly reduce the difficulty of machining.Due to the fine and uniform organization of alloy powder,it has become an important method for new material development.The cold isostatic pressing(CIP)+ prepared by vacuum sintering(CIP)and prepared by hot isostatic pressing(HIP)has been studied by density analysis,metallographic analysis,fracture analysis,XRD analysis and SEM analysis method in this paper.The powder preparation has two methods,which is element mixed method and vacuum atomization.During the process of vacuum atomization,three kinds of spherical powder that obtains 106μm,48μm and 25μm can be achieved by sieving.Six different sintering temperature which can be obtained by CIP rules are compared through preparing the four kinds of powders.Two kinds of sintering temperature need to be made comparative analysis with the method of HIP.The two kinds of best samples achieved by two types of manufacturing process need also be made comparative analysis with 920℃×1h oil quenching and 300℃×2h heat treatment.The results can be obtained: Using CIP method,The density of 25μm powder is 94.8% after sintering which the temperature is 1250℃.Besides,The density of 48μm powder is 87.3% after sintering which the temperature is 1300℃.The density of 25μm powder and 48μm powder are 99.3% and 99.7% respectively after sintering which the condition is 1160℃+100MPa using HIP method.DT300 with 25μm powder prepared by hot isostatic pressing after heat treatment,the value of tensile strength,impact toughness,hardness and fracture toughness is 1870 Mpa,108 J·cm-2,66 HRC,and 114 MPa·m1/2 respectively.Meanwhile,DT300 with 48μm powder prepared by hot isostatic pressing after heat treatment,the value of tensile strength,impact toughness,hardness and fracture toughness is 1850 Mpa,104 J·cm-2,65 HRC,and 110 MPa·m1/2 respectively.The structure of fine lath martensite can be achieved through heat treatment.The performance of CIP method is the same as the casting method.The results of HIP method are improved by 20% compared with the casting method.Considering the objective factors of organizational performance,operation feasibility and economic,In summary,the vacuum atomization process of 48μm powder is the best preparation process,which adopts the HIP method after 1160℃ + 100 MPa sintering.The preparation process that is convenient and feasible has practical application value.