Differences Between 304, 304H, 321, 321H, 316, 316L, 317, 317L, 347, 347H, and 310S Stainless steel

Stainless steel is a popular Material used in various industries due to its Corrosion resistance, durability, and aesthetic appeal. Among the different types of stainless steel available, 304, 304H, 321, 321H, 316, 316L, 317, 317L, 347, 347H, and 310S are some of the most commonly used grades. While they may seem similar at first glance, each grade has its own unique properties and applications.

Chemical Composition, Mass Fraction (%)
Grade		C		Mn		Mo		Cr		Ni	Cu	P	S	Si
	Type	min	max	min	max	min	max	min	max	max	max	max	max	max
1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
H40	—	—	—	—	—	—	—	—	—	—	—	—	0.03	—
J55	—	—	—	—	—	—	—	—	—	—	—	—	0.03	—
K55	—	—	—	—	—	—	—	—	—	—	—	—	0.03	—
N80	1	—	—	—	—	—	—	—	—	—	—	0.03	0.03	—
N80	Q	—	—	—	—	—	—	—	—	—	—	0.03	0.03	—
R95	—	—	0.45 c	—	1.9	—	—	—	—	—	—	0.03	0.03	0.45
L80	1	—	0.43 a	—	1.9	—	—	—	—	0.25	0.35	0.03	0.03	0.45
L80	9Cr	—	0.15	0.3	0.6	0.9	1.1	8	10	0.5	0.25	0.02	0.03	1
L80	13Cr	0.15	0.22	0.25	1	—	—	12	14	0.5	0.25	0.02	0.03	1
C90	1	—	0.35	—	1.2	0.25 b	0.85	—	1.5	0.99	—	0.02	0.03	—
T95	1	—	0.35	—	1.2	0.25 b	0.85	0.4	1.5	0.99	—	0.02	0.03	—
C110	—	—	0.35	—	1.2	0.25	1	0.4	1.5	0.99	—	0.02	0.03	—
P110	e	—	—	—	—	—	—	—	—	—	—	0.030 e	0.030 e	—
Q125	1	—	0.35		1.35	—	0.85	—	1.5	0.99	—	0.02	0.01	—
NOTE Elements shown shall be reported in product analysis.
a The carbon content for L80 may be increased up to 0.50 % maximum if the product is Oil-quenched or polymer-quenched.
b The molybdenum content for Grade C90 Type 1 has no minimum tolerance if the Wall thickness is less than 17.78 mm.
c The carbon content for R95 may be increased up to 0.55 % maximum if the product is oil-quenched.
d The molybdenum content for T95 Type 1 may be decreased to 0.15 % minimum if the wall thickness is less than 17.78 mm.
e For EW Grade P110, the phosphorus content shall be 0.020 % maximum and the sulfur content 0.010 % maximum.

Let’s start with 304 and 304H stainless steel. Both grades are austenitic stainless steels, but 304H has a higher carbon content, which makes it suitable for high-temperature applications. 304 stainless steel is commonly used in kitchen appliances, food processing equipment, and architectural applications, while 304H is preferred for pressure vessels, heat exchangers, and other high-temperature environments. Moving on to 321 and 321H stainless steel, these grades are stabilized with titanium to prevent carbide precipitation during Welding. This makes them ideal for applications where high temperatures are involved, such as in the aerospace and automotive industries. 321H stainless steel has a higher carbon content than 321, making it more suitable for elevated temperature applications.

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Chemical Composition	C	Mn	P≤	S≤	Si≤
	0.06-0.18	0.27-0.63	0.035	0.035	0.25

Moving on to 317 and 317L stainless steel, these grades are similar to 316 and 316L but with higher molybdenum content for improved corrosion resistance in chloride environments. 317 stainless steel is commonly used in pulp and paper processing, chemical processing, and pharmaceutical industries, while 317L is preferred for welding applications due to its low carbon content. Next, we have 347 and 347H stainless steel. These grades are stabilized with niobium to prevent intergranular corrosion after welding. 347 stainless steel is commonly used in high-temperature applications such as in the aerospace and power generation industries, while 347H is preferred for applications where higher strength and creep resistance are required. Lastly, we have 310S stainless steel, which is a high-temperature grade with excellent oxidation resistance. 310S stainless steel is commonly used in heat treatment furnaces, kilns, and other high-temperature applications where thermal cycling is involved. In conclusion, while 304, 304H, 321, 321H, 316, 316L, 317, 317L, 347, 347H, and 310S stainless steel may seem similar at first glance, each grade has its own unique properties and applications. It is important to consider the specific requirements of your application when selecting the appropriate grade of stainless steel to ensure optimal performance and longevity.