| With the continuous development of railway rolling stock towards high speed,heavy load and low cost,the steel used for railway rolling stock also requires higher strength and atmospheric corrosion resistance.09CuPTiRe and 09CuPCrNi grades of weathering steel has gradually failed to meet the requirements of the strength of railway vehicles.With the designation of the main technology of heavy-duty and accelerated railway,it is increasingly important to develop high strength weather-resistant structural steels.Atmospheric corrosion resistance is one of the most important properties of weathering steels.As the most commonly used evaluation method of corrosion resistance of weathering steel at present,weathering index is not in good agreement with corrosion rate,so it needs to be improved.In this paper,through reasonable composition design and rolling process,high strength weather resistant H-beam steel is developed.By studying the influence of grain size,microstructure content and tempering on atmospheric corrosion resistance,the internal relationship between these factors and corrosion resistance is established,which can be used to predict the corrosion resistance of weathering steel and provide reference for the development of weathering steel.Specific research contents and results are as follows:(1)Based on low C,low P,low S,Cu,Cr,Ni and Nb,V microalloying,450 MPa weather-resistant H-beam for railway was designed.The rolling work of simulating flange deformation of H-beam was carried out.The results show that the experimental steels at different finishing temperatures are composed of ferrite and bainite.When the finishing rolling temperature is higher,the strength of the experimental steel is higher,but the impact toughness at low temperature is worse.When the finishing rolling temperature is low,the strength of the experimental steel is lower,but the low temperature impact toughness is better.Quantitative calculation of different strengthening mechanisms shows that with the decrease of finishing rolling temperature,the strengthening amount of fine grain and precipitation increases,while the strengthening amount of bainite second phase decreases.According to the comprehensive analysis of experimental results,the final rolling temperature of the experimental steel is 800 ℃-830 ℃,and the experimental steel has a good combination of strength and toughness,which meets the use requirements.(2)The corrosion performance of experimental steel in industrial atmospheric environment was studied by periodic infiltration accelerated corrosion experiment,the corrosion rate of 72 h corrosion was calculated,and the morphology,phase and element distribution of rust layer were observed.After accelerated corrosion for 72 h,compared with the control steel Q345B,the relative corrosion rate of the experimental steel in atmospheric environment is 54.1%,which meets the requirements of TB/T1979-2014 standard.The corrosion products of Q345B and experimental steel are composed of αFeOOH and γ-FeOOH and a small amount of Fe3O4.The must layer of the contrast steel Q345B is loose and has poor protection for the matrix.The experimental steel has fewer voids and cracks in the rust layer and is tightly combined with the matrix.The enrichment of Cr and Cu is observed in the rust layer of the experimental steel.The addition of corrosion-resistant elements improves the structure and density of the rust layer,thus improving the atmospheric corrosion resistance of the experimental steel.(3)The influence of grain size on corrosion resistance of weathering steel was explored by periodic wetting accelerated corrosion test and electrochemical test.The results showed that the corrosion rate increased with the increase of grain size of experimental steel.The rust layer of experimental steel with smaller grain size is enriched with more corrosion-resistant elements,and the rust layer is denser.The rust layer has better protection for the substrate and better corrosion resistance.(4)The influence of microstructure types on the corrosion resistance of weathering steel was investigated by cyclic infiltration accelerated corrosion test and electrochemical test.The results showed that martensite microstructure had the best corrosion resistance,followed by bainite,and F+B microstructure had the worst corrosion resistance.From the electrochemical corrosion experiment,it can be seen that there is a potential difference between different structures,and many micro-battery pairs will be formed on the surface of steel,which accelerates the corrosion process and has poor corrosion resistance,while the single-phase structure is relatively uniform,thus the corrosion resistance is relatively good.(5)The effects of hot rolling and tempering processes on the corrosion resistance of weathering steel were studied by periodic wetting accelerated corrosion test and electrochemical test.The results showed that the corrosion rate of tempered steel at 500℃was the lowest,followed by hot rolled experimental steel and tempered steel at 700℃ was the highest.The increase of corrosion resistance of 500℃ tempered experimental steel is due to the decrease of dislocation density in crystal,while the poor corrosion resistance of 700℃ tempered experimental steel is mainly due to the increase of average grain size of ferrite.The decrease of dislocation density is beneficial to improve the self-corrosion potential of experimental steel and reduce the electrochemical corrosion tendency of experimental steel.Compared with dislocation density,corrosion resistance is more sensitive to grain size.(6)Based on the research on the influence law of alloy composition,grain size and microstructure type on the corrosion resistance of weathering steel,the influence law model of alloy composition,the evaluation method of the corrosion resistance of weathering steel was studied,and microstructure content and grain size on the corrosion resistance was established.The relationship between element content and corrosion rate is exponential,and the relationship between microstructure type and grain size and corrosion rate is quadratic function model.By comprehensively considering grain size,microstructure content and alloying elements,an evaluation method for corrosion resistance of weathering steel is established,which can quantitatively predict the relative corrosion rate of steel with good prediction effect. |
