Microstructure And Mechanical Properties Of A New Austenite High Strength Steel

As oil and gas mining depth increases,the temperature and pressure which drilling equipment serves in has improved Constantly,it requires a good match of high strength and toughness as well as mechanical properties,the API standard can not meet the requirements,the demand of oil pipe for high performance is increasing.As one of new high-strength steels,High manganese steel is new high strength steel of austenitic matrix structure,possessing good strength and plasticity,which provides a new direction for high-strength steel used in oilfield.In this paper,it conducts component design of high manganese steel and smelting,received a total of three components of the high-manganese TWIP steel.components are 16%manganese,and the addition of A1 element and Mn element of 16%manganese,the research is about mechanical properties and tissue transformation influenced by cold working deformation,heat treatment,alloying elements,then do a research of mechanical properties micro structural evolution in condition of different amount of deformation,different alloy compositions and different heat treatment.Equipments include stretching machine,impact test machine,SEM,TEM and so on.The research of mechanical properties and tissue influenced by heat treatment shows that with the increase of cold deformation,grain deform in the rolling direction,when the amount of deformation reach 50%,the grain size reduces from 20?m to 5?m,the yield strength increases from 712MPa to 1809MPa,the tensile strength increases from 1283MPa to 1961MPa,elongation reduces from 34.1%down to 6.5%,strength-plasticity reduces from 43771MPa%to 12672MPa%,as the deformation continues to increase,when the grain reaches 1?m or less,the tensile strength can reach up to 2.5GPa;TEM analysis shows in the process of deformation,there are sequentially stacking faults,twins,secondary twins and split interpenetrating grains form a grid structure,and limit the dislocations in the grid,to play a role of strengthening;XRD analysis shows that when the amount of deformation reachs to 30%,there is phase transformation ? from y austenite to ? martensite,when the amount of deformation reaches to 85.9%,the martensitic transformation starts to produce a martensite,and ?phase transition disappears,? is intermediate state between y and a phase.Study of the heat treatment influence on micro structure and mechanical property shows that:heat treatment process leads to carbide precipitation and recrystallization.The photographs of SEM show that,with the increase of heat treatment temperature,a lot of carbide precipitates along the grain boundaries at 650?;recrystallization is occurred at 750?.Stress-strain curves show that the carbide precipitation contributes to higher strength and lower plasticity.When cold drawing happens and providing heat treatment below 550?,its ultimate strength increases from 2.5GPa to 2.8GPa.When heat treatment processes at 650?,elongation reduces abnormally.recrystallization conducive to decreases strength and increase ductility,carbide precipitation and recrystallization are of competing relationship replying on the strength and elongation.When the temperature is at the recrystallization temperature or lower,the precipitation of carbides plays as a main factor;when the temperature reaches the recrystallization temperature,recrystallization plays as a main factor.The research of mechanical properties and tissue influenced by Alloying elements shows,Mn element and A1 element can be able to reduce the strength and increase plasticity,while suppressing deformation-induced ? martensitic transformation,increasing the stability of the austenite matrix.