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
|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
|Ni||8 – 11||8 – 11||8 – 11|
|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|
304 stainless steel equivalent grades and standard
|AISI/ SUS||UNS||EN||JIS||AFNOR||BS||WERKSTOFF NR.||GOST||SS|
|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
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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