Research On Torsion Bar Material With Excellence Cold-resistance Performance For Rrailwaay Applicationn

The high speed EMU,running in extreme cold area,required the materials with an excellence cold-resistance performance.The torsion bar was one of the important parts of EMU to ensure running safety,and thus the low temperature performance played a key role on the materials of torsion bar.Usually,the mechanical property of steel material was determined by the heat treatment and material composition,and the low temperature impact performance was another important material design basis for the use in the low temperature condition.In this thesis,by optimizing the heat treatment process and chemical composition,the materials which meet the application requirement of torsion bar in the lower temperature was researched.The mechanical properties,the impact performance in different temperature and the metallographic analysis were analyzed.Moreover,the finished products of torsion bar with good cold-resistance performance were developed.The main contents were as follows: 1.The low temperature performance of 42 CrMo and 52CrMoV4,which meet the application requirement of anti-rolling bar in the current normal condition,weretested,and the ductile-to-brittle transition temperature was deduced.The ductile-to-brittle transition temperature of 42 CrMo material was about-50 ℃,within the scope of use risk;while that of 52CrMoV4 was about-80 ℃,to be safe use in the cold condition;2.The influence of heat treatment process of the torsion arm material 42 CrMo on the mechanical properties under room temperature and the impact toughness under low temperature was researched.The 42 CrMo was the quenched and tempered steel and had a good bainite formation ability.The optical heat treatment process was quenching(860 ℃)for 150 min and high tempering(600 ℃)for 180 min,and the quenching cooling way was water cooling.3.The new chemical composition 42 CrMo A for the long-term use of torsion arm in the cold condition with-50 ℃ was researched bycollaborated with a steel mill.The 42 CrMoA was designed on the basis of the original material 42 CrMo,which increased the content of alloy elements Cr,Mn,Mo,and reduced the content of harmful elements Cu,P,S.The final optical composition contents were: Cr: 1.00 ~ 1.20%;Mo: 0.19 ~ 0.25%;Mn: 0.60 ~ 0.90%;Cu was not more than 0.30%;P was not more than 0.015%;S was not more than 0.015%.Furthermore,the improved material 42 CrMo A is heat treated by the optimized heat treatment process,and then was carried out the corresponding low temperature performance test.The results showed that,the material mechanical properties and low temperature impact work were increased significantly,and the ductile-to-brittle transition temperature was about-80 ℃which was much lower than the train operation requirements;4.The finished products of torsion axis and torsion arm were made by the optimized chemical composition and heat treated process,and the stiffness,elastic and fatigue performance of torsion bar in the specific low temperature,were tested.The results showed that,the finished products of torsion axis and torsion arm had no defects and cracks,and the whole performance was satisfied the requirement of stands.The two kinds of new products meet the train running environment under-50 ℃.