Difference between 304 and 316 Stainless Steel

What is the difference between 304 and 316 stainless steel?

Stainless Steels are alloys that contain additions of chromium. Classified into four main classes, grades 304 and 316 falls under authentic class. Since they belong to the austenitic class of stainless steel, their basic chemical makeup remains nearly similar, concerning the elements used to alloy the. However, it is the specificity of their chemistry that separates the two grades from one and the other. Both alloys contain chromium and nickel. But the percentage of these elements vary. For instance, the content in chromium in grade 304 stainless steel is 18% chromium and 8% nickel, which is why the alloy may also be referred to as 18/8 stainless steel. On the other hand, alloy 316, which may also be referred to as marine grade contains about 16% chromium in its alloy.

With regards to the chemical composition of the alloy, what separates the two is the addition of molybdenum in the alloy of the stainless steel grade 316. While grade 304 has trace quantities of molybdenum, this particular element exists in a higher percentage ( 2% to 3%) in alloy 316. Molybdenum, when added to a higher degree is known to improve the corrosion resistance properties of an austenitic stainless steel alloy. Which explains why molybdenum-bearing austenitic alloys such as grade 316, tend to have significant levels of corrosion resistance properties. Due to the specificity of the chemistry in the alloys, each metal adopts mechanical properties to varying degrees. For example, the tensile and yield strength of grade 304 is lower than that of alloy 316. Moreover, grade 316 has high creep strength, which means the alloy could be used at temperatures higher than grade 304. Although the properties of stainless steel alloy 316 are at a significantly higher level, the addition of molybdenum in its alloy increases the price as well. While comparing the price of both metals, grade 304 would cost lesser simply, because of the absence of molybdenum in its alloy.

304 vs 316 stainless steel machinability

In general, austenitic stainless steels tend to have difficult machining behavior. In particular stainless steels that belong to the 300 series have the tendency to work harden. Hence, specialized tools must be used to machine these alloys. In comparison to grade 304, stainless steel 316 is more prone to work hardening, and so, it requires special machining tools with cutting rates that differ from grade 304. The chemical composition of these austenitic alloys makes them difficult to machine.

304 316 stainless steel magnetic properties

The crystalline structure for both alloy 316 as well as 304 is austenite. This face centered cubic microstructure is a result of gamma-phase iron, which is otherwise known as austenite. Being a solid solution of iron, these alloys tend to be nonmagnetic. However, if they are cold worked, these austenitic alloys tend to become magnetic. This being said, it is important to note that due to the alloy being magnetic, the corrosion resistance of these alloys will decrease.

How to check ss 304 and 316?

Like most stainless steel alloys, it is virtually impossible to separate alloys 316 and 304, just by visual examination. The difference between these two alloys could be told apart by the use of an MTR, or what is referred to as a material test report or even as a mill test report. This test report essentially confirms the chemical composition of the alloy. Aside from confirming the elemental chemistry of any given alloy, the material test report also acts as a certificate for the physical properties of the alloy.

Different markings on 304 and 316 products to recognize

Pipes Tubes
ASTM A312 TP304 SA 213 TP304
ASTM A312 TP304L SA 213 TP304L
ASTM A312 TP316 SA 213 TP316
ASTM A312 TP316L SA 213 TP316L
ASTM A312 TP321 SA 213 TP321

Why SS 304 is Food Grade Stainless Steel?

Because its resistant to wear & tear and has heat resistance which is safe for cooking.

SS 304 chemical composition

AISI 304 304N 304LN
Ni 8 – 11 8 – 11 8 – 11
Fe Balance
Cr 18 – 20 18 – 20 18 – 20
C 0.08 max 0.08 max 0.035 max
Si 0.75 max 0.75 max 0.75 max
Mn 2 max 2 max 2 max
P 0.040 max 0.040 max 0.040 max
S 0.030 max 0.030 max 0.030 max
N 0.10 – 0.16 0.10 – 0.16

304 stainless steel mechanical properties

Stainless Steel Gr. 304
Rockwell B (HR B) max. 92
Brinell (HB) max. 201
Tensile Strength min. (MPa) 515
Yield Strength 0.2% Proof min. (MPa) 205
Elongation min. (% in 50mm) 40
Hardness -

304 stainless steel equivalent grades and standard

AISI/ SUS UNS EN JIS AFNOR BS WERKSTOFF NR. GOST SS
Grade USA EUROPE JAPAN RUSSIAN BRITISH GERMAN RUSSIAN SWEDISH
SS 304 S30400 X5CrNi18-10 SUS 304 Z7CN18‐09 304S31 1.4301 08Х18Н10 2332

316 stainless steel yield strength and mechanical properties

SUS 316 Yield Strength 0.2% Proof minimum (MPa) 205
Tensile Strength minimum (MPa) 515 Elongation minimum (% in 50mm) 40
Hardness: Rockwell B (HR B) maximum 95 Brinell (HB) maximum 217

316 stainless steel chemical composition

ASTM A312 C Mn Si P S Cr Mo Ni N
316 min. - - - - - 16.0 2.0 10.0 -
max. 0.08 2.0 0.75 0.045 0.03 18.0 3.0 14.0 0.10

SS 316 equivalent material

GRADE SS 316 JAPAN JIS SUS 316
USA UNS S31600 RUSSIAN AFNOR Z7CND17‐11‐02
GERMAN WERKSTOFF NR. 1.4401 / 1.4436 BRITISH BS 316S31 / 316S33
RUSSIAN GOST - SWEDISH SS 2347
EUROPE EN X5CrNiMo17-12-2 / X3CrNiMo17-13-3    

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