Investigation And Analysis Of TCS Type Stainless Steel: Property And Microstructure In Heat Affected Zone And Alloying Method

TCS stainless steel is a new kind of ferritic stainless steel used in railway vehicle. It is similar to the 3Crl2 type materials. Currently, thousands of wagons which were made of TCS steel are running on the way, with distinct benefit. TCS steel has been one of the most important materials used for railway vehicle in the future. However, there are still some problems to deal with, such as selecting the type of the steel, welding process, and body designing.Analytic methods including optical microscope metallography analysis, Charpy impact test, SEM fracture analysis were applied to study the property and microstructure of the HAZ of TCS type steel. In order to control the growth of the ferritic grain of the materials, the welding process was studied and the alloying method was analyzed. The research results established a technical basis to optimize the material and make suitable welding process.The main results are as follows:1. When the heat input increases of welding, the ferritic grain becomes coarsering and the width of the coarse grained HAZ (CGHAZ) comes wider. As a result, the impact toughness of the HAZ decreases.2. When the heat input at the same level, the microstructure and impact toughness of the HAZ of three kinds of steel were tested, including grain size, width, content of martensite and impact toughness. The result suggest that N4003 is the favorite one, and TCS-B is better than TCS-T.3. The essential method to control the growth of the ferritic grain of the CGHAZ is to decrease the heat input. This study found that increasing the weld pass or using pulse MAG can enhance the toughness of the HAZ, when the heat input was decreased appropriately. In addition to this, increasing the groove angle is a effective method to improve the impact toughness of the HAZ.4. The existing of a certain amount of austenite in high temperature zone is necessary to inhibit the growth of the ferritic grain. The result suggested that decreasing the ferrite element and increasing the austenitize element can elevate the amount of austenite in high temperature zone. On cooling, material which has amount of austenite will transform to martensite, resulting in a tough fine-grained structure. Then the impact toughness of the HAZ improved.