Study On Microstructure And Properties Of E Class Cast Steel Repair Welding Joints

China’s railway locomotive vehicle manufacturing, production of cast steel occupies an important position, which is more than85%of the casting production approximately. Bolster, side frame and coupling are three key components of rolling stock. E class cast steel (ZG25MnCrNiMo) is commonly used in railway vehicle manufacturing.All the casting defects in steel casting production and invalidation in process need with the aid of the method of repair welding for the integrity of the casting and performance. The quality of Repair welding, not only affect the subsequent processing procedure and the influence on the using of performance, but also the occurrence of malignant accidents. Therefore, analyse the cast steel weldability has great practical significance.In this paper, We use SMAW welding E class high-strength low-alloy cast steel welding joint which are commonly used on the freight train couples with J857T and J707electrode, then the mechanical properties and microstructure analysis of the corresponding joint were studied through tensile, bend, impact and hardness examination as well as the anti-crack performance tests of E class high-strength low-alloy cast steel, and provide the basis for the actual production of the cast steel welding.The results showed that:The weld preheating is very necessary for the E class high-strength low-alloy cast steel which has higher hardenability. When welding the quenched and tempered state E class cast steel with J857T electrode and with J707electrode, pre-heating temperature should be≥150℃and≥100℃.Whether with the J857T electrode and J707electrode, the tensile strength and yield strength of welded joints are The base is quite, its welded joint tensile properties. Whether with the J857T electrode and J707electrode welded joints are broken in the base metal of E class low-alloy steel. Its welded joint bending performance excellent. The welding joint impact energy is greater than the parent metal with the J857T electrode and J707electrode. Its welded joint impact resistance excellent at room temperature and-40℃.Both the microstructures in the parent metal is tempered sorbite wih J857T electrode and J707electrode. The microstructure in the weld metal contains acicular ferrite、pearlite and a small amount of bainite. The microstructure in the fusion zone of welding joint contains blocky proeutectoid ferrite, acicular ferrite, pearlite and granular bainite.And there are a small amount of martensite in the fusion zone with J857T electrode. The microstructure in the normalized zone contains ferrite and an amount of blocky pearlite which are uniform grain size small organizations. When we used the J857T electrode and J707electrode to weld E class high-strength low-alloy cast steel.The hardness of welding joint are similar between the weld metal and the parent metal which is250HV～280HV. The hardness of fusion zone is288HV～340HV. There is softing phenomenon in HAZ, which is slight.