| The transportation of coal mines in China mainly relies on railway freight.The main railway freight vehicles are gondola.The railway coal transport gondola works in open-air conditions and its operating environment is very complicated.Under the effects of rain,snow,wind,frost and various complex mixed corrosive media,the freight car body and other components are prone to corrosion.The typical environment is the acidic medium corrosive environment formed at the bottom of coal trucks,which caused strong sulfuric acid corrosion to the bottom of gondola cars.At present,steel Q450NQR1 for railway wagons has high strength and good weather resistance,but it does not have sulfuric acid corrosion resistance and cannot effectively resist sulfuric acid corrosion.In order to prolong the service life of railway freight cars,this paper adopted sulfuric acid corrosion resistance element antimony(Sb),through reasonable chemical composition and rolling process design,developed a new sulfuric acid corrosion resistant steel S450AW for high-strength railway freight cars.The main research works and conclusions are as follows:(1)The steel S450AW is based on low-carbon,low-phosphorus.and low-sulfur,Antimony element was added to improve the sulfuric acid corrosion resistance.Chromium,nickel and copper elements were added to ensure the weather resistance.Niobium and titanium microalloy elements were added to ensure the mechanical properties of the steel plate.Three different components of the S450AW were designed.(2)phase evolution instrument was used to study the microstructure evolution of the austenite during the cooling process,and the continuous cooling transformation(CCT)curve of the austenite of the experimental steel was drawn.The results showed that under deformation conditions,when the cooling rate of S450AW steel is 0.1 to 2 ℃/s,the obtained structure is ferrite and pearlite,when the cooling rate is 2 to 10℃/s,the obtained structure is ferrite and Bainite;when the cooling rate is 10 to 40℃/s3，the structure obtained is mainly bainite.As the cooling rate increases,the transformation structure transitions from ferrite and pearlite to ferrite and bainite,and finally changed to bainite.(3)By controlling the structure and properties of the experimental steel,the best composition and process parameters of S450AW were determined.The results showed that the best composition of S450AW steel was 0.1%Sb Nb-Ti system.The best rolling process was that the final rolling temperature was 860～880℃,the steel was cooled after rolling and the final temperature was 640～660℃/s.The microstructure was ferrite and pearlite,the yield strength reached 460 MPa,the tensile strength was 625 MPa,and the impact result at-40℃was 152 J.The performance satisfied the requirements of railway freight steel standards.(4)The corrosion behavior of S450AW in the industrial atmosphere was simulated by using the periodic infiltration corrosion method.The research showed that after 72 hours of accelerated corrosion,the corrosion rate of 0.06%Sb steel is 2.64 g/(m2·h),compared to the corrosion rate of steel Q345B at 4.98 g/(m2·h),and the corrosion of S450AW relative to Q345B The rate was 53.5%,which met the requirements of the standard(relative corrosion rate≤55%).The corrosion products of S450AW and Q345B are γ-FeOOH,α-FeOOH,and Fe3O4.The percentage of α-FeOOH in the corrosion products of S450AW is as high as 58%.With the addition of corrosion-resistant elements,the morphology of the corrosion products changed from needle floc to pellets.The corrosion-resistant elements Cr,Cu,Ni,and Sb are enriched in the rust layer,making the corrosion products fine in size,dense in structure,and excellent in atmospheric corrosion resistance.(5)The corrosion behavior of S450AW experimental steel in a mixed environment of sulfuric acid(H2SO4+NaCl)was studied by uniform all-immersion corrosion method.The research showed that the corrosion rate of 0.06%Sb S450AW experimental steel after 24h corrosion was 1.23 g/(m2·h).The corrosion rate of 0.1%Sb S450AW experimental steel in the environment of 10%H2SO4+ 3.5%NaCl solution for 24 hours was 0.575 g/(m2·h),and the corrosion rate of Q345B was 4.435 g/(m2·h).The experimental steel met the requirements of corrosion rate ≤0.8 g/(m2·h),and the corrosion rate was only 13%relative to Q345B.Increasing the content of Sb element has greatly improved the sulfuric acid corrosion resistance of S450AW.With the increase of corrosion time from 24 hour to 48 hour,the annual corrosion rate of 0.1%Sb S450AW decreased from 0.637 mm/a to 0.571 mm/a.As the sulfuric acid concentration increased from 10%to 20%,the annual corrosion rate of the 0.06%SbS450AW experimental steel decreased from 1.235 mm/a to 1.031 mm/a,the Cu content in the corrosion products increased by 2 times,and the Sb element increased by 5 times,the corrosion resistance of S450AW in sulfuric acid mixed solution was improved.(6)The industrial trial production of S450AW acid resistant steel was carried out on a 2250 hot continuous rolling production line of a domestic steel plant,and its microstructure,mechanical properties and corrosion properties were studied.The research showed that the industrial microstructure of S450AW acid-resistant steel consists of ferrite and pearlite,which had excellent mechanical properties and met the standard requirements.The relative Q345B corrosion rate in the industrial atmosphere was 53.5%,and the weight loss rate in the sulfuric acid mixed environment was 0.541 g/(m2·h).At present,the industrialized mass production of S450AW has been achieved.(7)The effects of three different welding heat inputs on 11,13 and 15 kJ/cm on the microstructure,mechanical properties and resistance to sulfuric acid corrosion of the welded joint were studied.The best welding heat input was 11 kJ/cm,and the performance indexes of the welded joint met the requirements.The structure of the weld zone was mainly ferrite,and the structure of the heat affected zone was bainite.The yield strength and tensile strength after welding were close to the base metal,the elongation and low-temperature toughness were lower than the base metal,and the sulfuric acid corrosion resistance rate was 0.535 g/(m2·h),which met the standard requirements. |
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