409L/409 Stainless Steel Coil Crystalline Characteristics

(1) The solid and liquid two-phase region of 409L stainless steel is very small, less than 30°C
(2) There is almost no γ phase at high temperatures. Therefore, when the 409L steel begins to crystallize after pouring, the supercooling degree of the liquid phase is largely due to direct contact with the surface of the crystallizer, and at the same time, the surface of the crystallizer promotes non-spontaneous nucleation. Therefore, the nucleation rate of the liquid phase is high and the formation rate is high. Fine equiaxed crystals on the surface.
The formation of fine equiaxed grains on the surface is rapid, and the carbides of titanium are too short to precipitate. After the formation of the fine equiaxed crystal regions, the general steel forms columnar crystals, but the 409L steel does not show columnar crystals.
Due to the narrow temperature range in the liquid-solid two-phase zone, the 409L steel has a small component overcooling zone during crystallization, and the columnar crystals do not easily grow forward. At the same time, after the formation of the fine equiaxed crystal region, titanium and carbon have time to diffuse to form titanium carbide particles after a period of time to promote non-self nucleation.
The above two reasons cause the area to produce equiaxed crystals without columnar crystals. There are no columnar crystal structures on the cross-section, all of which are equiaxed crystals, but of different sizes. In the pouring process, when the temperature of the slab drops to 1100°C if the carbon content is high, part of Cr and C form carbides, and chromium-depleted areas appear around the carbides, and a small amount of Ѵ phase may appear.
At this point, two different phases of the steel appear in the steel, or the delta phase content is 32% to 60% in the blank plastic zone. The carbon content of 409L steel is very low, even if there is a Ѵ phase, the amount is small. Therefore, there is no big impact on performance.
There is almost no α → γ phase transition from high temperature to the low temperature of 409L stainless steel, so the grains are easy to grow up, a coarse ferrite structure appears, and the strength is low. In continuous casting, when the slab is cut upward, the elbow is easy to appear. The phenomenon affects normal production. The main problem in the crystallization of 409L steel is the reduced performance caused by coarse grains.

SS 409 409l Chemical Composition

Grade	C	Si	Mn	S	P	Cr	Ni	Ti
ss 409	≤0.08	≤1.0	≤1.0	≤0.03	≤0.045	10.5～11.7	0.5 Max	6xC – 0.75
ss 409l	≤0.03	≤1.0	≤1.0	≤0.03	≤0.045	10.5～11.7	0.5 Max	6xC – 0.75