409L stainless steel characteristics and applications

Among the 400 series stainless steel, the application range of 409L stainless steel coil is second only to 430 stainless steel. It has good corrosion resistance, heat resistance, low temperature resistance and good mechanical properties. It is mostly used to manufacture automobile exhaust system components. It well meets the requirements for lightweight and long life of exhaust system components, and can also effectively reduce exhaust gas emissions.
The cost of 409L is relatively low, the flexibility is relatively good, the yield rate is high, and it is easy to replace. It is a great recyclable and environmentally friendly material.
The crystallization characteristics of 409L stainless steel are as follows.
The solid-liquid two-phase zone of 409L stainless steel during crystallization is very small, lower than 30°C. There is essentially no gamma phase at high temperatures. Therefore, when 409L stainless steel begins to crystallize after pouring, the liquid phase is supercooled due to direct contact with the surface of the crystallizer. At the same time, the surface of the crystallizer promotes non-spontaneous nucleation, so the nucleation rate of the liquid phase is relatively high, resulting in Surface fine equiaxed crystals. The formation speed of the fine equiaxed grain area on the surface is very rapid. At this time, the titanium carbide has no time to precipitate due to the short time. After the fine equiaxed grain zone is generated, ordinary steel forms columnar crystals, but 409L stainless steel does not appear columnar crystals.
Because the temperature range of the liquid-solid two-phase zone of 409L stainless steel is narrow, the supercooling zone of the composition during crystallization is small, and the columnar crystals are not easy to grow forward. At the same time, after a period of time has passed after the formation of the fine equiaxed crystal region, titanium and carbon have time to diffuse, forming titanium carbide particles and promoting non-spontaneous nucleation. The above two reasons cause equiaxed crystals to be generated in this region instead of columnar crystals. There is no columnar crystal structure on the cross section, all are equiaxed crystals, but the sizes are different. During the pouring process, when the temperature of the steel billet drops to 1100°C, if the carbon content is high, part of Cr and C will form carbides, causing a chromium-depleted area to appear around the carbides, and a small amount of δ phase may appear. At this time, two phases with different properties appear in the steel, or the δ phase content is between 32% and 60%, which is the plastic zone of the billet. The carbon content of 409L steel is very low, and even if delta phase appears, the amount is very small. Therefore, there will be no big impact on performance.
409L stainless steel has almost no α → γ phase transformation from high temperature to low temperature, so the grains are easy to grow, a coarse ferrite structure appears, and the strength is low. In continuous casting, when the slab is cut and moved upward, elbows are prone to occur. phenomenon, affecting normal production. The main problem when crystallizing 409L steel is the performance reduction caused by coarse grains.