Study On The High Temperature Performance Of 3Cr25Ni20 Heat Resistant Steel For Automobile Exhaust Manifold

Compared with ferritic ductile cast iron and high silicon molybdenum ductile cast iron,3Cr25Ni20 austenitic heat resistant steel has higher high temperature strength.The exhaust manifold manufactured has better oxidation resistance,high thermal creep resistance,dimensional stability and corrosion resistance,which can effectively guarantee the service life.3Cr25Ni20 austenitic heat resistant stainless steel meets the requirements of automobile exhaust manifold in performance and economy.In this paper,3Cr25Ni20 heat resistant steel was taken as the research object,its high temperature strength,high temperature oxidation resistance and high temperature creep behavior were experimentally studied to explore the material's high temperature performance change mechanism at different temperatures.The research results can provide an important basis for the application of heat resistant steel in the manufacture of automobile exhaust manifold.Compared with different annealing process temperatures,the internal microstructure of the samples was observed by MDJ-DM optical metallograph and Zeiss-Supra40scanning electron microscope,and the appropriate annealing temperature was determined by combining the hardness values measured by HR-150A Rockwell hardness tester.The tensile strength of annealed 3Cr25Ni20 heat-resistant steel and as-cast steel was tested by WDW-200 tensile testing machine and WDW-100G high-temperature tensile testing machine at normal temperature and high temperature.The casting and the heat-resistant steel after heat treatment were put into the SX-G07122 energy-saving box furnace to simulate the real working environment,and the high-temperature oxidation comparison was carried out.The TP-214 electronic balance was used for weighing.Finally,the oxidation rate was calculated.The main research results and contents are as follows:1.After high temperature annealing at different temperatures,it was found that with the increase of annealing temperature,the hardness of 3Cr25Ni20 austenitic heat resistant steel decreased.Combined with the observation of metallographic structure,the appropriate processing temperature with good cutting performance was 1140?.2.After annealing at 1140?,the tensile strength of 3Cr25Ni20 austenitic heat-resistant steel was 539.8 MPa,and the toughness w improved.The tensile strength of the test steel in the solution state was 507.5 MPa,and the yield strength of the test steel in the cast state was 477.6 MPa.The yield strength of the test steel after the solution heat treatment was 457.7MPa,and the maximum total elongation is increased from 9.96%in the cast state to 11.29%.At high temperature,the tensile strength decreases at 1000?and the tensile strength increased with the increased of ambient temperature.3.The high-temperature oxidation kinetic curve of heat-resistant steel 3Cr25Ni20Si at800 and 900°C followed a linear to parabolic transformation law.The transformation time was 10 h.At 1000°C,the oxidation resistance of heat-resistant steel decreased,and the oxidation rate achieved 0.77 mg/cm~2 after 50 h oxidation.4.The fracture of heat-resistant steel showed good high-temperature plasticity and ductile fracture after creeping.As the stress increased,the fracture dimples became deeper.At 650°C and 700°C,the stress indices were 8.6 and 6,respectively.After high temperature creeping at 700?,the precipitated phases increased significantly and the network structure became larger.5.By using Pro CAST to optimize the structural design and process design of castings,and use one mold with two parts.