Explanation of stainless steel electric heating tube grade material:
200 Series - Chromium-Nickel-Manganese Austenitic Stainless Steel 300 Series - Chromium-Nickel Austenitic Stainless Steel
Model 301—Good ductility for forming products. It can also be hardened by mechanical processing. Good weldability. Wear resistance and fatigue strength are better than 304 stainless steel.
Model 302—Corrosion resistance is the same as 304, because the carbon content is relatively high and the strength is better.
Model 303—It is easier to cut than 304 by adding a small amount of sulfur and phosphorus.
Model 304—Universal model; ie 18/8 stainless steel. The GB grade is 0Cr18Ni9.
Model 309 - Better temperature resistance than 304.
Model 316—After 304, the second most widely used steel grade is used primarily in the food industry and surgical equipment, adding molybdenum to give it a special structure that resists corrosion. It is also used as "ship steel" because it has better resistance to chloride corrosion than 304. SS316 is commonly used in nuclear fuel recovery units. 18/10 grade stainless steel also generally meets this application level. 
Model 321—Besides the addition of titanium reduces the risk of weld rust in the material, the performance is similar to 304.
400 Series - Ferritic and Martensitic Stainless Steel
Model 408—Good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.
Model 409—The cheapest model (British and American), usually used as a car exhaust pipe, is a ferritic stainless steel (chrome steel).
Model 410—Martensite (high-strength chrome steel) with good wear resistance and poor corrosion resistance.
Model 416—Addition of sulfur improves the processing properties of the material.
Model 420—“cutting grade” martensitic steel, similar to the earliest stainless steel of Brinell high chromium steel. Also used for surgical knives, it can be done very brightly.
Model 430 - Ferritic stainless steel, for decoration, for example for automotive accessories. Good formability, but poor temperature resistance and corrosion resistance.
Model 440—High-strength cutting tool steel with slightly higher carbon content. After proper heat treatment, it can obtain higher yield strength and hardness of 58HRC, which is among the hardest stainless steel. The most common application example is the "razor blade." There are three commonly used models: 440A, 440B, 440C, and 440F (easy processing type).
500 Series - heat resistant chrome alloy steel.
600 Series - Martensitic precipitation hardened stainless steel.
Model 630—The most commonly used type of precipitation hardened stainless steel, also commonly referred to as 17-4; 17% Cr, 4% Ni.