CWB Level 3 Module 21 Practice Questions And 100%
Correct Answers
The maximum solubility of carbon in a iron is:
(a) 2% .
(b) 0.002%.
(c) 0.02%.
(d) There is no solubility. - Answer (c) 0.02%.
True or false?
When a steel is heated into the austenite region, all carbon and most other compounds
dissolve
to form a single phase. - Answer True
True or false?
Pearlite is a single phase. - Answer False
What is the resulting structure of a 0.6% carbon steel slowly cooled from 900°C to room
temperature? - Answer About 25% proeutectoid ferrite and 75% pearlite
Most fine grain steels retain their fine grains: (
(a) up to the melting temperature.
(b) up to the grain coarsening temperature, but above that behave as coarse grain steel.
C
(c) only up to the transformation temperature. - Answer (b)
, Why is martensite produced rather than pearlite when a
steel is rapidly quenched from, 900°C? - Answer Insufficient time for carbon to diffuse to
form carbides
The hardness of martensite depends mainly on the:
(a) alloy content.
(b) rate of cooling.
(c) carbon content.
(d) size of the part. - Answer (c)
Can bainite normally be produced in continuous cooling of a plain carbon steel? -
Answer No
Increasing the carbon content:
(a) lowers the martensite start temperature M.
(b) raises the M.
(c) does not affect M. - Solution (a) decreases the martensite start temperature M.
Calculate the ideal critical diameter (hardenability) for a steel containing 0.2%C,
0.25%Si, 1
.0%Mn,
0.5%Cr, 0.5%Mo, 1.0%Ni (assuming an initial grain size of ASTM 8). Use section 2.5.3
and 2.5.4
as a guide. - Solution 5.0
Using Figure 2.34, estimate the quickest rate a weld could cool without the HAZ
becoming
harder than 350 HV for a
Steel of 0.2%C, 0.18%Si, t2%Mn, 0.35%Cr. - Answer 30C/s at 540 C
Correct Answers
The maximum solubility of carbon in a iron is:
(a) 2% .
(b) 0.002%.
(c) 0.02%.
(d) There is no solubility. - Answer (c) 0.02%.
True or false?
When a steel is heated into the austenite region, all carbon and most other compounds
dissolve
to form a single phase. - Answer True
True or false?
Pearlite is a single phase. - Answer False
What is the resulting structure of a 0.6% carbon steel slowly cooled from 900°C to room
temperature? - Answer About 25% proeutectoid ferrite and 75% pearlite
Most fine grain steels retain their fine grains: (
(a) up to the melting temperature.
(b) up to the grain coarsening temperature, but above that behave as coarse grain steel.
C
(c) only up to the transformation temperature. - Answer (b)
, Why is martensite produced rather than pearlite when a
steel is rapidly quenched from, 900°C? - Answer Insufficient time for carbon to diffuse to
form carbides
The hardness of martensite depends mainly on the:
(a) alloy content.
(b) rate of cooling.
(c) carbon content.
(d) size of the part. - Answer (c)
Can bainite normally be produced in continuous cooling of a plain carbon steel? -
Answer No
Increasing the carbon content:
(a) lowers the martensite start temperature M.
(b) raises the M.
(c) does not affect M. - Solution (a) decreases the martensite start temperature M.
Calculate the ideal critical diameter (hardenability) for a steel containing 0.2%C,
0.25%Si, 1
.0%Mn,
0.5%Cr, 0.5%Mo, 1.0%Ni (assuming an initial grain size of ASTM 8). Use section 2.5.3
and 2.5.4
as a guide. - Solution 5.0
Using Figure 2.34, estimate the quickest rate a weld could cool without the HAZ
becoming
harder than 350 HV for a
Steel of 0.2%C, 0.18%Si, t2%Mn, 0.35%Cr. - Answer 30C/s at 540 C
