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AISI numbers question


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Today at work someone asked if i knew what the AISI designation meant for steel. So i started explaining that each number had a meaning and was showing him what they were. I used a coupe examples then got to carbon content. I noticed that 15N20 steel was listed as having .75% carbon. From what i have been taught is the last 2 numbers is carbon content like 1095 has .95%, why is it not 15N75? 

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15N20 is not an AISI/SAE designation. Rather, that is the name of the steel given to it by the manufacturer Bohler-Uddeholm; I think the "N20" refers to its 2.0% nickel content.

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  • 3 weeks later...

15N20 etc are not specific designations by one company but are the designations used in many of the European countries. 17CrNiMo6 is another example, but there are hundreds, just like in the SAE system. Many times there are equivalents from one system to another and sometimes not. Each system make sense in its own way, but they are all different. Japan has a different system as does China. There is also something called the Unified Number System. In that system, most of the familar SAE designations are prefixed by the letter G and given a couple of extra digits at the end. For example, 1095 is G1095x.  In this system Tool steels all start with T, stainless with S, copper with C, titanium and other refractory metals with R. Each system has strengths and weaknesses. I like the SAE system because that is what I learned first and am most familiar with, but I"m sure someone from Europe would say the same about their system.

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Thank you for illustrating why I just nod my head when someone starts talking about steel designations, Patrick. I've never been able to keep any but the most basic straight so I look them up if I need something special. 

Frosty The Lucky.

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SAE (Society of Automotive Engineers) Steels


xx denotes carbon levels in hundredths of a percent.


10xx Carbon; Mn <1.0

11xx Resulfurized

12xx Resulfurized and rephosphorized

13xx Mn 1.75

15xx Mn 1.0–1.65

23xx Ni 3.5

25xx Ni 5.0

31xx Ni 1.25; Cr 0.65, or 0.80

32xx Ni 1.75; Cr 1.07

33xx Ni 3.50; Cr 1.50, or 1.57

34xx Ni 3.00; Cr 0.77

40xx Mo 0.2%, 0.25, or Mo 0.25

41xx Mo 0.4%, or 0.52

43xx Ni 1.82; Cr 0.50–0.80; Mo 0.25

46xx Ni 0.85, or 1.82; Mo 0.20, or 0.25

47xx Ni 1.05; Cr 0.45; Mo 0.20, or 0.35

48xx Ni 3.50; Mo 0.25

50xx Cr 0.27, 0.40, 0.50, or 0.65

51xx Cr 0.80, 0.87, 0.92, 1.00, or 1.05

52xxx Cr 1.45; C 1.0

53xx Cr 1.80; C 1.0

61xx Cr 0.60, 0.80, 0.95; V 0.10, or 0.15.

72xx W 1.75; Cr 0.75

81xx Ni 0.30; Cr 0.40; Mo 0.12

86xx Ni 0.55; Cr 0.50; Mo 0.20

87xx Ni 0.55; Cr 0.50; Mo 0.25

88xx Ni 0.55; Cr 0.50; Mo 0.35

92xx Si 1.40, or 2.00; Mn 0.65 or 0.85; Cr 0.65

93xx Ni 3.25; Cr 1.20; Mo 0.12

94xx Ni 0.45; Cr 0.40; Mo 0.12

97xx Ni 0.55; Cr 0.20; Mo 0.20

98xx Ni 1.00; Cr 0.80; Mo 0.2



ANSI (American National Standards Institute) Low Alloy Steels


Low-alloy steels are a category of ferrous materials that exhibit mechanical properties better than plain carbon steels as the result of alloying elements such as Ni, Cr, W, V, and Mo. Alloy contents of the low alloy category can range from about 2% up to 10%.



AISI (American Iron and Steel Insitiute)Steel codes


A Air hardening alloys

D Die steel alloys

F Tungsten alloys

H Hot work alloys

L Low alloy

M Molybdenum alloys

O Oil hardening alloys

P Mold steel alloys

S Shock resistant steels

W Water hardening steels

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