Advanced rail transit mainly includes high-speed railways, heavy-haul railways, urban subways and intercity rail transit. The main directions for the development of advanced rail transit are high-speed, high-efficiency, safety, comfort (low noise, low vibration), longevity, energy saving and emission reduction, and greening. The requirements for steel are high strength and high toughness, wear resistance, rust resistance, high temperature resistance, and excellent manufacturing process, and stainless steel can play an important role in many of the above requirements. The advantages of stainless steel and its products applied to rolling stock are very obvious.

However, stainless steel is not immune to corrosion. Because there is a purification film on the surface of stainless steel, it is not easy to chemically react with certain media and be corroded under normal circumstances. But it is not that it will not be corroded in any environment and under any conditions. The corrosion types of stainless steel mainly include three types: intergranular corrosion, stress corrosion and pitting corrosion.

1. Improper storage, transportation and lifting

The mixed storage of stainless steel materials and other materials, and the improper packaging materials used for storage will easily pollute the surface of stainless steel and cause chemical corrosion.

2. Raw material blanking and molding

Stainless steel raw materials are generally rolled, and need to be flattened, slitting, cutting, bending and other methods before they can be processed into parts required for subway metro bodies. However, if the surface of the stainless steel is not clean, in the above-mentioned processing process, due to cutting, clamping, heating, grinding tool extrusion, cold work hardening, etc., the structure of the stainless steel will undergo uneven changes, and the purification film on the surface will be destroyed, causing electric shock. chemical corrosion.

3. Poorly designed structure

In the actual production process, many unreasonable design structures will also cause corrosion of the stainless steel metro body. For example, the semi-enclosed welding structure in a narrow space is easy to corrode, because it is not easy to polish and clean the weld seam after the welding operation of stainless steel parts, and the welding slag is not easy to remove, and the adhesion of rust-prone substances and corrosive media form electrochemical corrosion.

The unreasonable design structure leads to poor drainage, and finally the stainless steel netro body structure is wet with water, resulting in chemical and electrochemical corrosion.

4. Improper tool selection and process execution

In the actual operation process, the selection of some tools and improper process execution will also lead to corrosion. For example, incomplete removal of the passivation paste during passivation of the weld will lead to chemical corrosion. The wrong tool is selected when cleaning slag and splash after welding, resulting in incomplete cleaning or damage to the base metal. Improper oxidation color grinding destroys the surface oxide layer or the adhesion of rust-prone substances, all of which will lead to electrochemical corrosion. The periphery of the weld seam needs to be sealed with glue, and the soapy water used when repairing the surface of the glue also causes corrosion of the stainless steel metro body.