Analysis Of Microstructure And Properties After Flame Straightening Of High Speed Train Bogie Frame

In recent years, the rapid development of Chinese high-speed rail industry and a growing number of foreign orders all reflect the growing maturity of Chinese high-speed rail technology. Bogie technology is one of the most important technologies in high speed railway, the straightening of the bogie frame after welding will do an important effect on the safety. In order to guarantee the excellent mechanical properties of the bogie frame base metal, the mechanical correction method is adopted in the production in foreign countries. Machine rectification is time-consuming, inflexible and inefficient, while flame correction has advantages of flexibility and efficiency. The purpose of this paper is to explore whether flame straightening will have a bad effect on mechanical properties of the bogie frame base metal, whether it can be applied in the practical production, and whether it will bring security hazards to the operation of high-speed rail vehicles.In this paper, S355J2 W weathering steel was researched. Through the thermal simulation test, heating temperatures were set at 650 ℃, 700 ℃, 750 ℃ and 800 ℃ to simulate flame straightening with water cooling. By carrying out a series of mechanical properties test, this paper systematically analyzed the microstructure, hardness of the material, intensity, plasticity, bending properties and impact toughness of specimens in different thermal simulation temperatures and also compared with the original base material. This paper systematically and thoroughly studied the sensitivity and feasibility of the steel under flame straightening processing parameters.In the impact test, when temperatures of thermal simulation were set at 750 ℃and800 ℃, some granular bainite generated and distributed along proeutectoid ferrite grain boundaries. This seriously deteriorated the impact toughness of the marerial and brought great potential safety hazards for the material during use. The specimens were all brittle fracture at each temperatures in the impact test. The impact absorbing energy of specimens were only 31.67 J and 50.88 J at 20 ℃, and the impact absorbing energy of specimens were only 13.78 J and 25.39 J at-40 ℃. This can not meet requirements of excellent impact toughness for the bogie frame, and at the same time cannot guarantee the normal operation of high-speed trains.In the tensile test, when temperatures of thermal simulation were set at 650 ℃and700 ℃, layered fracture occurred in the center of specimens’ cross section. When the temperature of thermal simulation was set at 650 ℃, layered fracture occurred at both1/4 ends of the specimen cross section. And when the temperature of thermal simulation was set at 700 ℃, layered fracture occurred completely in the center of the plate layer of the specimen, running through the entire specimen tested, which was primarily due to the growth of banded pearlite and distribution of(Mn、Fe)S and Si O2 type inclusions and particles in the center of the metal. It must bring potential safety hazards in practical use.In view of the actual application status of bogie, impact toughness is one of the most important safety performance indicators. It was obtained by analyzing of the microstructure and mechanical properties of S355J2 W weathering steel that flame straightening temperature should be strictly controlled under 700 ℃ in the actual production.It must cause the deterioration of the impact toughness if temperature is above the range.