Alloying elements

Keval K. Patil, M.E.-DESIGN, (kevalpatil@gmail.com)

1. Low hardenability.
2. Low corrosion and oxidation resistance.
3. Major loss of hardness on stress-relieving tempering treatment.
4. Poor high temperature properties.
Note- The limitations of carbon steels are overcome by the use of
alloy steels. The presence of alloying elements, not only enhances the
outstanding characteristics of plain carbon steels, but improves some
other properties, or even induces specific properties.
Keval K. Patil, M.E.-DESIGN, (kevalpatil@gmail.com) 2

 The alloying elements not only improve the hardenability, improve
corrosion and oxidation resistance, increase resistance to softening on
tempering, increase high temperature properties, but also increase
resistance to abrasion, and increase strength of the parts that cannot be
subjected to quenching due to physical limitation of parts or the
structure in which it is employed.
 Alloy steels are expensive and may require more elaborate processing,
handling and even heat treatment cycles.
 Every effort should thus, be made to use carbon steels.
 Care should be taken that many inherent properties of plain carbon
steels cannot be improved by adding alloying elements in it.
 Stiffness is one such property which is measured by relationship
between stress and strain within elastic range i.e. by modulus of
elasticity.
 Alloying elements enhance the elastic limit but the modulus of elasticity
is the same of both the plain carbon and the alloy steels.
 The design of the structure can change the stiffness. Judicious and
cautious use of expensive alloying elements has to be made.

Carbon
 As I've already stated, the presence of carbon in iron is necessary to make
steel.
 Carbon is essential to the formation of cementite (as well as other carbides),
and to the formation of pearlite, spheroidite, bainite, and iron-carbon
martensite, with martensite being the hardest of the micro-structures, and the
structure sought after by knifemakers.
 The hardness of steel (or more accurately, the hardenability) is increased by
the addition of more carbon, up to about 0.65 percent.
 Wear resistance can be increased in amounts up to about 1.5 percent. Beyond
this amount, increases of carbon reduce toughness and increase brittleness.
 The steels of interest to knifemakers generally contain between 0.5 and 1.5
percent carbon. They are described as follows:
• Low Carbon: Under 0.4 percent
• Medium Carbon: 0.4 - 0.6 percent
• High Carbon: 0.7 - 1.5 percent
 Carbon is the single most important alloying element in steel.

Manganese
 Manganese slightly increases the strength of ferrite,
and also increases the hardness penetration of steel in
the quench by decreasing the critical quenching speed.
 This also makes the steel more stable in the quench.
 Steels with manganese can be quenched in oil rather
than water, and therefore are less susceptible to
cracking because of a reduction in the shock of
quenching. Manganese is present in most
commercially made steels.

Chromium
 As with manganese, chromium has a tendency to increase hardness
penetration.
 When 5 percent chromium or more is used in conjunction with
manganese, the critical quenching speed is reduced to the point that
the steel becomes air hardening.
 Chromium can also increase the toughness of steel, as well as the
wear resistance.
 Probably one of the most well known effects of chromium on steel is
the tendency to resist staining and corrosion.
 Steels with 14 percent or more chromium are referred to as stainless
steels. A more accurate term would be stain resistant.
 Stainless tool steels will in fact darken and rust, just not as readily as
the nonstainless varieties.
 Steels with chromium also have higher critical temperatures in heat
treatment.

Silicon
 Silicon is used as a deoxidizer in the manufacture of steel.
 It slightly increases the strength of ferrite, and when used
in conjunction with other alloys can help increase the
toughness and hardness penetration of steel.
Nickel
 Nickel increases the strength of ferrite, therefore increasing
the strength of the steel.
 It is used in low alloy steels to increase toughness and
hardenability.
 Nickel also tends to help reduce distortion and cracking
during the quenching phase of heat treatment.

Molybdenum
 Molybdenum increases the hardness penetration of
steel, slows the critical quenching speed, and increases
high temperature tensile strength.
Vanadium
 Vanadium helps control grain growth during heat
treatment.
 By inhibiting grain growth it helps increase the
toughness and strength of the steel.

Tungsten
 Used in small amounts, tungsten combines with the
free carbides in steel during heat treatment, to produce
high wear resistance with little or no loss of toughness.
 High amounts combined with chromium gives steel a
property known as red hardness.
 This means that the steel will not lose its working
hardness at high temperatures.
 An example of this would be tools designed to cut hard
materials at high speeds, where the friction between
the tool and the material would generate high
temperatures.

Copper
 The addition of copper in amounts of 0.2 to 0.5 percent
primarily improves steels resistance to atmospheric
corrosion.
 It should be noted that with respect to knife steels, copper
has a detrimental effect to surface quality and to hot-
working behavior due to migration into the grain
boundaries of the steel.
Boron
 Boron can significantly increase the hardenability of steel
without loss of ductility.
 Its effectiveness is most noticeable at lower carbon levels.
 The addition of boron is usually in very small amounts
ranging from 0.0005 to 0.003 percent.

Titanium
 This element, when used in conjunction
with Boron, increases the effectiveness of
the Boron in the hardenability of steel.

 As per name tool steels are used for
manufacturing different tools.
 For manufacturing different tools different
properties are required such as hardness,
resistance to abrasion, wear and deformation and
ability to hold a cutting edge at high temperatures.
 Tool steels include large number of alloy
elements.
 Some major alloying elements are tungsten,
chromium, vanadium molybdenum, etc.

Water Hardening tool steel
 Water hardening tool steel is usually plane carbon steel but some
time alloy elements are used for achieving better properties.
 It is cheap as compare to other tool steel and hence largely used.
 It is goes from water quenched process for hardening.
Shock Resisting tool steel
 As per name, shock resistance tool steels are designed to resist shock
at low and high temperature.
 They contain chromium, tungsten, manganese, silicon, molybdenum
as alloy elements or as group of alloying like chromium-tungsten,
silicon-manganese, etc.
 It shows properties like abrasion resistance and hardenability.

Cold work tool steel
 Cold work tool steels are use for cutting and forming
materials at low temperature.
 It possesses high hardenability and resistance to wear.
 They go from oil quenching and air hardening as per
requirement of properties.
 Cold work tool steels are again classified in three
types as follow
1. Oil Hardening tool steel
2. Medium alloy air hardening tool steel
3. High carbon, high chromium tool steel

Hot Work tool steel
 Hot work tool steels are used for forming
materials at high temperature.
 They are again classified in three types and these
are as follow.
1. Chromium base tool steel
2. Tungsten base tool steel
3. Molybdenum base tool steel

High speed tool steel
 High speed tool steel maintain their hardness at
high temperature and hence it is use in cutting
tools like drills, milling cutters, tool bits, gear
cutters, etc.
 This is again classified in two types according to
alloy elements and these are as follow.
1. Tungsten base tool steel
2. Molybdenum base tool steel

Special purpose tool steel
 These types of steel are manufacture for achieve
some properties as per requirement.
 For some properties like increased in wear
resistance, high hardness, to hold sharp cutting
edge, etc.
 According to alloy elements they are further
divided in two types and these are as follow.
1. Low alloy tool steel
2. Carbon Tungsten tool steel

 Stainless steel contains chromium, molybdenum, and
nickel alloying elements in steel, which make it highly
corrosion resistance.
 They do not corrode in most of the environmental
condition.
 Due to this, they are known as stainless steel.
 They are highly corrosion resistance due to this
stainless steel are largely used.
 Stainless steel identify by three numerical numbers
like 304, 310, 440, etc.
 Stainless steels are classified in four types and these
are as follow.

Austenitic stainless steels
 Austenitic stainless steel contains chromium, nickel and
manganese.
 They are non magnetic.
 Austenitic stainless steel has high strength in high
temperature, resist to scaling and better corrosion
resistance than other types of stainless steel.
 Austenitic steels are not hardenable by heat treatment.
Ferritic stainless steels
 Ferritic stainless steel is straight chromium stainless steel.
 It consist 14 to 27 percent chromium approximately.
 This can be hot worked or cold worked and it is magnetic.

Martensitic stainless steels
 Martensitic stainless steels found in high or low-carbon
steels, contain 11 to 18 percent chromium.
 Martensitic stainless steel usually tempered and hardened.
 Tempered steel shows good hardness and high toughness.
Duplex stainless steels or austenitic-ferritic stainless steels
 Duplex stainless steels consist two phases that are
austenite and ferrite in metallurgical structure and hence it
is also known as austenitic-ferritic stainless steels.
 It shows High resistance to stress corrosion cracking and
high yield stress than austenitics.

Alloying elements

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