Alloy steel — Hydraulic Couplings Supplier — CNC Machining Parts Manufacturer

Low alloy steel

Low alloy steels are usually used to achieve better hardenability, which in turn improves its other mechanical properties. They are also used to increase corrosion resistance in certain environmental conditions.

With medium to high carbon levels, low alloy steel is difficult to weld. Lowering the carbon content to the range of 0.10% to 0.30%, along with some reduction in alloying elements, increases the weldability and formability of the steel while maintaining its strength. Such a metal is classed as a high-strength low-alloy steel.

Some common low alloy steels are:

D6AC

300M

256A

Principal low alloy steels

SAE designation

Composition

13xx

Mn 1.75%

40xx

Mo 0.20% or 0.25% or 0.25% Mo 0.042% S

41xx

Cr 0.50% or 0.80% or 0.95%, Mo 0.12% or 0.20% or 0.25% or 0.30%

43xx

Ni 1.82%, Cr 0.50% to 0.80%, Mo 0.25%

44xx

Mo 0.40% or 0.52%

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% or 0.40% or 0.50% or 0.65%

50xxx

Cr 0.50%, C 1.00% min

50Bxx

Cr 0.28% or 0.50%

51xx

Cr 0.80% or 0.87% or 0.92% or 1.00% or 1.05%

51xxx

Cr 1.02%, C 1.00% min

51Bxx

Cr 0.80%

52xxx

Cr 1.45%, C 1.00% min

61xx

Cr 0.60% or 0.80% or 0.95%, V 0.10% or 0.15% min

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 0.82% or 0.85%, Cr 0.00% or 0.65%

94Bxx

Ni 0.45%, Cr 0.40%, Mo 0.12% Material science

Alloying elements are added to achieve certain properties in the material. As a guideline, alloying elements are added in lower percentages (less than 5%) to increase strength or hardenability, or in larger percentages (over 5%) to achieve special properties, such as corrosion resistance or extreme temperature stability.

Manganese, silicon, or aluminium are added during the steelmaking process to remove dissolved oxygen from the melt. Manganese, silicon, nickel, and copper are added to increase strength by forming solid solutions in ferrite. Chromium, vanadium, molybdenum, and tungsten increase strength by forming second-phase carbides. Nickel and copper improve corrosion resistance in small quantities. Molybdenum helps to resist embrittlement. Zirconium, cerium, and calcium increase toughness by controlling the shape of inclusions. Manganese sulfide, lead, bismuth, selenium, and tellurium increase machinability.

The alloying elements tend to either form compounds or carbides. Nickel is very soluble in ferrite, therefore it forms compounds, usually Ni3Al. Aluminium dissolves in the ferrite and forms the compounds Al2O3 and AlN. Silicon is also very soluble and usually forms the compound SiO2MxOy. Manganese mostly dissolves in ferrite forming the compounds MnS, MnOSiO2, but will also form carbides in the form of (Fe,Mn)3C. Chromium forms partitions between the ferrite and carbide phases in steel, forming (Fe,Cr3)C, Cr7C3, and Cr23C6. The type of carbide that chromium forms depends on the amount of carbon and other types of alloying elements present. Tungsten and molybdenum form carbides if there is enough carbon and an absence of stronger carbide forming elements (i.e. titanium niobium), they form the carbides Mo2C and W2C, respectively. Vanadium, titanium, and niobium are strong carbide forming elements, forming the carbides V3C3, TiC, and NiC, respectively.

Alloying elements also have an effect on the eutectoid temperature of the steel. Manganese and nickel lower the eutectoid temperature and are known as austenite stabilizing elements. With enough of these elements the austenitic structure may be obtained at room temperature. Carbide forming elements raise the eutectoid temperature; these elements are known as ferrite stabilizing elements.

Principal effects of major alloying elements for steel

Element

Percentage

Primary function

Aluminium

0.951.30

Alloying element in nitriding steels

Bismuth

-

Improves machinability

Boron

0.0010.003

Powerful hardenability agent

Chromium

0.52

Increases hardenability

418

Corrosion resistance

Copper

0.10.4

Corrosion resistance

Lead

-

Improves machinability

Manganese

0.250.40

Combines with sulfur to prevent brittleness

>1

Increases hardenability by lowering transformation points and causing transformations to be sluggish

Molybdenum

0.25

Stable carbides; inhibits grain growth

Nickel

25

Toughener

1220

Corrosion resistance

Silicon

0.20.7

Increases strength

2

Spring steels

Higher percentages

Improves magnetic properties

Sulfur

0.080.15

Free-machining properties

Titanium

-

Fixes carbon in inert particles; reduces martensitic hardness in chromium steels

Tungsten

-

Hardness at high temperatures

Vanadium

0.15

Stable carbides; increases strength while retaining ductility; promotes fine grain structure See also

HSLA steel

Microalloyed steel

SAE steel grades

Reynolds 531 References Notes

^ Smith, p. 393.

^ a b Degarmo, p. 112.

^ Classification of Carbon and Low-Alloy Steel, http://www.key-to-steel.com/Articles/Art62.htm, retrieved 2008-09-25 .

^ Smith, p. 394.

^ Degarmo, p. 113.

^ Smith, pp. 394-395.

^ Smith, pp. 395-396

^ Degarmo, p. 114. Bibliography

Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4 .

Groover, M. P., 2007, p. 105-106, Fundamentals of Modern Manufacturing: Materials, Processes and Systems, 3rd ed, John Wiley Sons, Inc., Hoboken, NJ, ISBN 978-0-471-74485-6.

Smith, William F.; Hashemi, Javad (2001), Foundations of Material Science and Engineering (4th ed.), McGraw-Hill, p. 394, ISBN 0-07-295358-6  Categories: Steels