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Sunday, March 13, 2011

Steel Numbering Sytem

A steel numbering system is used to identify the many types of steel. A steel’s numerical name usually consists of four numbers or digits. The first two digits refer to the alloy content. The last two digits (or three digits, in the case of a five- digits number) refer to the percentage of carbon in the steel. See Figure 1 below.


Figure 1: A steel’s name usually consists of four digits. It supplies information about the alloy content and percentage





 The steel numbering system is shown in Table 1 below . In 5147 steel, for example, the “51” identifies chromium as a key alloying element. In 2517 steel, the “25” indicates that there is an unusual amount of nickel in this steel. In 4718 steel, the “47” indicates that the amount of chromium, nickel and molybdenum in the steel is higher than average. In 1040 steel, the “10” means that the steel has very little alloy content except carbon. As shown by these examples, the first two numbers always give an indication of the alloy content in the steel.

Table 1:  AISI/SAE Steel Numbering System

Type
Steel Numerical Name
Key element
Carbon steels
10XX
Plain carbon, Mn 1.00% max
11XX
Resulfurized free machining
12XX
Resulfurized/rephosphorized free machining
15XX
Plain carbon, Mn 1.00-1.65%
Manganese steel
13XX
Mn 1.75%
Nickel steels
23XX
Ni 3.50%
25XX
Ni 5.00%
Nickel-chromium steels
31XX
Ni 1.25%, Cr .65-.80%
32XX
Ni 1.75%, Cr 1.07%
33XX
Ni 3.50%, Cr 1.50-1.57%
34XX
Ni 3.00%, Cr .77%
Molybdenum steels
40XX
Mo .20-.25%
44XX
Mo .40-.52%
Chromium-molybdenum steels
41XX
Cr .50-.95%, Mo .12-.30%
Nickel-chromium-molybdenum steels
43XX
Ni 1.82%, Cr .50-.80%, Mo .25%
47XX
Ni 1.05%, Cr .45%, Mo .20-.35%
Nickel-molybdenum steels
46XX
Ni .85-1.82%, Mo .20-.25%
48XX
Ni 3.50%, Mo .25%


Chromium steels
50XX
Cr .27-.65%
51XX
Cr .80-1.05%
50XXX
Cr .50%, C 1.00% min
51XXX
Cr 1.02%, C 1.00% min
52XXX
Cr 1.45%, C 1.00% min
Chromium-vanadium steels
61XX
Cr .60-.95%, V .10-.15%
Tungsten-chromium steels
72XX
W 1.75%, Cr .75%
Nickel-chromium-molybdenum steels
81XX
Ni .30%, Cr .40%, Mo .12%
86XX
Ni .55%, Cr .50%, Mo .20%
87XX
Ni .55%, Cr .50%, Mo .25%
88XX
Ni .55%, Cr .50%, Mo .35%
Silicon-manganese steels
92XX
Si 1.40-2.00%, Mn .65-.85%, Cr 0-.65%
Nickel-chromium-molybdenum steels
93XX
Ni 3.25%, Cr 1.20%, Mo .12%
94XX
Ni .45%, Cr .40%, Mo .12%
97XX
Ni .55%, Cr .20%, Mo .20%
98XX
Ni 1.00%, Cr .80%, Mo .25%

The last two digits (or three digits) of a numerical name for steel indicate the percentage of carbon in the steel. A two digit number represents hundredths of a percent. In 1040 steel, for example the “40” means there is 0.40% carbon in the steel. In the 1018 steel, the “18” indicates the the steel has only 0.18% carbon, thus it is a low steel. There is approximately 0.60% carbon in 8660 steel 0.60% carbon in 8660 steel which would make it medium-carbon steel.

When the carbon content of the steel is 1% or more, three digits are needed to describe the carbon content. For example 50100 steel contains 1.00%. See Table 2.

Table 2: Examples of steel names and carbon content
Indentification No.
Carbon Content
1040
0.40%
1018
0.18%
8660
0.60%
50100
1.00%

A steel numerical name provides much information about the alloy content of the steel. Indirectly, the number tells you about the quality, strength and corrosion resistance of the steel. For example 8622 steel has 0.22% carbon, 0.20% molybdenum, 0.50% chromium and 0.55% nickel. Molybdenum makes this steel strong at high temperatures. Chromium improves its corrosion resistance, while nickel improves the steel’s toughness.

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