Study On Mechanical Properties And Corrosion Resistance Of L245/316L Bimetal Composite Pipe By Heat Treatment

This paper studies the effects of normalizing and solution heat treatment processes on the mechanical properties and corrosion resistance of L245/316L bimetallic composite pipes.Use a thermal expansion phase change instrument to measure the critical temperature of the base tube carbon steel L245,formulate a reasonable normalizing and solution heat treatment plan;use Vickers hardness test,full-scale tensile test,impact test,etc.to complete the mechanical performance research;The research on corrosion performance adopts Fe Cl₃ pitting corrosion test,anti-intergranular corrosion D method,anti-intergranular corrosion E method and electrochemical test;for the study of interfacial bonding strength,interfacial Vickers hardness test and bonding strength test are adopted.The results of the study on the effect of heat treatment on the structure show that the A_C1measured by the thermal expansion phase change method for L245 is 735°C,and the A_C3 is832°C.After normalizing heat treatment,the L245 structure is still F+P,and the grain size of normalizing at 860?for 0.5 h becomes 9.0 from the unheated 8.0.With the normalizing temperature increasing to 900?,normalizing for 0.5 h,920?normalizing The Widmanstatten structure of grade 3.2 B appeared in 0.5 h.After solution heat treatment,When the solution temperature reaches 1180?,the temperature is too high,the grains grow too much,there are martensite and upper bainite structures,and large ferrites appear at the same time.;the grain size of 316L austenitic stainless steel has never been heat treated from 5.0 to 4.0,and is solutionized at 1180?for 1h The grains have a tendency to grow,and more twins are found at the same time.The mechanical properties research results show that the overall Vickers hardness value becomes larger as the normalizing temperature increases,and the hardness value of the L245side increases significantly through solution heat treatment.The tensile test data shows that the tensile strength and yield strength first increase and then decrease with the increase of the normalizing temperature.Normalizing at 860?for 0.5 h is the best;after solution heat treatment,the tensile strength And the yield strength has been greatly improved,and there is no yield plateau in the stress-strain curve after solution heat treatment.The impact test was carried out on the base pipe at 0°C,and the maximum impact toughness of normalizing at 860°C for0.5 h was 80.3 J;after solution treatment,the impact toughness decreased significantly.The comprehensive mechanical properties of normalizing 860?heat preservation for 30 min are the best.The corrosion resistance test of the material after solid solution and normalizing heat treatment was carried out.The study found that:Fe Cl₃ pitting corrosion test 860?normalizing0.5 h corrosion rate is 13.17(g/(m²·h)),which is better than the two groups of solid solution heat treatment Process:The second cycle of the 316L side anti-intergranular corrosion D method is generally faster than the first cycle,and the intergranular corrosion rate after the sensitization treatment is accelerated.The anti-intergranular corrosion D method corrosion performance is ranked from good to bad:1180?solid Solving 1 h>316L side without heat treatment>1130?Solid solution 1 h>1080?Solid 1 h>880?normalizing 0.5 h>860?normalizing 0.5 h>840?normalizing 0.5 h>carbon steel;anti-intergranular corrosion E method There was no intergranular corrosion cracks in 316L without heat treatment and heat treatment,and severe corrosion of carbon steel L245 occurred.Polarization curve test shows that the self-corrosion potential after solution treatment at 1080?is 11.38 m V,and normalizing at 860?for 0.5 h and normalizing at 880?for 0.5 h are inferior to-95.35 m V and-3.02 m V without heat treatment.Through multiple heat treatment tests,the comprehensive mechanical properties of the base pipe after normalizing at 860°C for 0.5 h are better.Although the corrosion resistance of the316L inner coating is reduced,the impact is small.After comprehensive consideration,normalizing at 860°C for 0.5 h can be used as The best heat treatment process for the base tube.