Temper embrittlement

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Abstract:
This report contains an important phenomena in steels called “temper
embrittlement”, causes of embrittlement, it’s effects on steels, different types of
embrittlement and their remedies. This report also contains microstructures of carbon steel
tempered at different temperatures.
Objective:
To Study the effect of Temper Embrittlement in Steel
Material and Equipment:
 Steel samples
 Heating furnace
 Quenching medium (Oil)
 Rockwell Hardness Testing machine
Introduction:
Temper embrittlement (TE) is commonly observed phenomena in certain
alloy steels. It has been observed that certain type of steels, either on cooling slowly or on
holding for prolonged periods within a specific tempering temperature range (400-660°C)
show a marked decrease in the toughness values. This phenomena is called “temper
embrittlement”.
The reason for this reduced toughness is the precipitation or segregation of
certain elements mainly P,Sb,Sn,As,Cr,Mn along the grain boundaries during slow cooling.
This effect is widely observed in alloy steels as compared to carbon steels. The degree of
embrittlement depends upon the cooling rate from embrittlement range. Higher the cooling
rate, lesser the embrittlement. An interesting feature of this embrittlement is that most of
the mechanical properties tensile strength, yield strength etc. are not affected significantly.

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Fig 1. Effect of cooling rate on toughness
Types of Temper Embrittlement:
1. Blue Brittleness:
Also called tempered martensite embrittlement (TME) is an
irreversible phenomenon that occurs in the range of approximately 250–400°C (480°F–750°F).
Both intergranular and transgranular fracture modes may be observed in tempered
martensite embrittlement. The combination of the segregation of impurities such as
phosphorus to the austenitic grain boundaries during austenitizing and the formation of
cementite at prior austenitic grain boundaries during tempering are responsible for the
intergranular fracture mode of tempered martensite embrittlement. The transgranular
fracture mode is caused by the formation of cementite between parallel martensitic lathes
during tempering.
2. Temper Embrittlement:
Temper embrittlement (TE) is a reversible phenomenon
occurring when steels are heated and slow cooled through the temperature range of 375–
575°C (705°F –1070°F). This is due to the segregation of impurity elements (P, Sn, As, Sb) to

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prior austenite grain boundaries. This causes decohesion of the boundaries, resulting in the
tendency for low-energy intergranular fracture under certain loading conditions.
Remedies for Temper Embrittlement:
 Heating steel above the embrittlement range followed by rapid cooling.
 Avoid presence of stray elements (P,Sn,As,Sb)
 Add embrittlement suppressing elements (Mo,Ti,Zr)
 Reduce Ni,Mn,Cr and Si which increases embrittlement
Procedure:
 First of all, we austenitized all the steel samples at 875°C for 45 min
 After austenitizing, all samples were quenched in an oil bath
 After that, all 4 samples were tempered at 150,250,350,450°C respectively for 30 min
and after cooling their hardness were measured
 After that, their microstructures were observed
Observations and Calculations:
Specimen Tempering temperature
(°C)
HRc
1 150 55
2 250 48.5
3 350 49.1
4 450 44

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Fig 1. Graph representing relationship b/w tempering temperature and hardness
Microstructures:
 Sample 1:
Tempering temperature = 150°C
Magnification = 400x
0
10
20
30
40
50
60
0 100 200 300 400 500
HRc
Tempering Temperautre (°C)
Tempering Temperature Vs Hardness
50 µm

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 Sample 2:
Tempering Temperature = 250°C
Magnification = 400x
 Sample 3:
Tempering Temperature = 350°C
Magnification = 400x
50 µm
50 µm

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 Sample 4:
Tempering Temperature = 450°C
Magnification = 400x
References:
 ASM Handbook Volume 4
 “Introduction to Physical Metallurgy” by Sydney H. Avner
 “Heat Treatment Principles And Techniques” by T.V Rajan, C.P Sharma and Ashok
Sharma
50 µm