CWB level 3 Module 21 practice
questions & Answers(RATED A)
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. - ANSWERTrue
True or false?
Pearlite is a single phase. - ANSWERFalse
What is the resulting structure of a 0.6% carbon steel slowly cooled from 900°C to
room
temperature? - ANSWERAbout 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? - ANSWERInsufficient 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? -
ANSWERNo
Increasing the carbon content:
(a) lowers the martensite start temperature M.
(b) raises the M.
(c) has no effect on M. - ANSWER(a) lowers the martensite start temperature M.
Calculate the ideal critical diameter (hardenability) for a steel with 0.2%C, 0.25%Si, 1
.0%Mn,
, 0.5%Cr, 0.5%Mo, 1.0%Ni (assume an initial grain size of ASTM 8). Use section 2.5.3
and 2.5.4
as a reference. - ANSWER5.0
4. If a thermal stress relief is applied to a welded quenched and tempered steel, the
temperature
should not exceed the:
(a) transformation temperature.
(b) original tempering temperature.
(c) grain coarsening temperature. - ANSWER(b) original tempering temperature.
The effect of increasing the carbon content of a steel on the Charpy transition curve
is to:
(a) lower the transition temperature.
(b) raise the upper shelf.
(c) raise the transition temperature and lower the upper shelf. - ANSWER(c) raise
the transition temperature and lower the upper shelf.
Using Figure 2.34, estimate the fastest 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. - ANSWER30C/s at 540 C
What happens to the carbon trapped in the tetragonal structure when martensite is
tempered? - ANSWERThe carbon is released
Secondary hardening during tempering results from:
(a) retained austenite.
(b) a slow heating rate.
(c) the presence of strong carbide formers. - ANSWER(c) the presence of strong
carbide formers.
What simple heat treatment is widely used to improve the toughness of structural
steels? - ANSWERNormalizing
If plates are deformed more than 5% during fabrication, the simple heat treatment
often
specified to restore ductility is:
(a) a full furnace anneal at 900°C.
(b) normalization.
(c) stress relief, typically at 635°C. - ANSWER(c) stress relief, typically at 635°C.
The main purpose of using a lower finishing temperature during controlled rolling of
steel is to:
(a) limit re-growth of austenite grains.
(b) allow time for precipitates to dissolve.
(c) reduce the force necessary for rolling. - ANSWER(a) limit re-growth of austenite
grains.
questions & Answers(RATED A)
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. - ANSWERTrue
True or false?
Pearlite is a single phase. - ANSWERFalse
What is the resulting structure of a 0.6% carbon steel slowly cooled from 900°C to
room
temperature? - ANSWERAbout 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? - ANSWERInsufficient 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? -
ANSWERNo
Increasing the carbon content:
(a) lowers the martensite start temperature M.
(b) raises the M.
(c) has no effect on M. - ANSWER(a) lowers the martensite start temperature M.
Calculate the ideal critical diameter (hardenability) for a steel with 0.2%C, 0.25%Si, 1
.0%Mn,
, 0.5%Cr, 0.5%Mo, 1.0%Ni (assume an initial grain size of ASTM 8). Use section 2.5.3
and 2.5.4
as a reference. - ANSWER5.0
4. If a thermal stress relief is applied to a welded quenched and tempered steel, the
temperature
should not exceed the:
(a) transformation temperature.
(b) original tempering temperature.
(c) grain coarsening temperature. - ANSWER(b) original tempering temperature.
The effect of increasing the carbon content of a steel on the Charpy transition curve
is to:
(a) lower the transition temperature.
(b) raise the upper shelf.
(c) raise the transition temperature and lower the upper shelf. - ANSWER(c) raise
the transition temperature and lower the upper shelf.
Using Figure 2.34, estimate the fastest 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. - ANSWER30C/s at 540 C
What happens to the carbon trapped in the tetragonal structure when martensite is
tempered? - ANSWERThe carbon is released
Secondary hardening during tempering results from:
(a) retained austenite.
(b) a slow heating rate.
(c) the presence of strong carbide formers. - ANSWER(c) the presence of strong
carbide formers.
What simple heat treatment is widely used to improve the toughness of structural
steels? - ANSWERNormalizing
If plates are deformed more than 5% during fabrication, the simple heat treatment
often
specified to restore ductility is:
(a) a full furnace anneal at 900°C.
(b) normalization.
(c) stress relief, typically at 635°C. - ANSWER(c) stress relief, typically at 635°C.
The main purpose of using a lower finishing temperature during controlled rolling of
steel is to:
(a) limit re-growth of austenite grains.
(b) allow time for precipitates to dissolve.
(c) reduce the force necessary for rolling. - ANSWER(a) limit re-growth of austenite
grains.
