Module 3 - Benjamin-Mills

SS2.5
Which is the right steel
for the job?
(Optional extension)
This activity illustrates how the properties and
eventual use of a steel relate to its composition.
Introduction
An army tank and a kitchen sink are each made from steel. The different uses
demand quite different properties from the metal, however. One of the major
factors leading to different properties is the composition of the steel.
What you do
Use the Information Sheet (Some elements and their effects on the properties
of steel) to match the eight steel uses (A–H) to the specifications numbered 1–8
in Table 1.
The first one has been done for you to show you the idea: the steel with
specification number 1 would be suitable for use D, the CO 2
cylinder for a fizzydrinks
maker. The steel must be capable of being moulded into shape without
developing cracks, but must be strong enough to hold the gas safely at high
pressure. So a medium-carbon steel is used with aluminium and manganese
added for toughness and good moulding properties. Low sulphur, phosphorus
and nitrogen reduce its tendency to crack.
Now match the most suitable composition to each of the remaining steel
applications. Briefly explain the reasons for your answers.
Steel uses
A A paper clip (mild steel which can be drawn to form a wire)
B Stainless steel for severe marine environments, such as in living quarters on
oil rigs
C Stainless steel for a surgeon’s knife
D Sodastream CO 2
cylinder
E A high-speed drill tip
F An off-shore gas pipe
G A finely-machined spindle for a galvanometer
H A ring spanner
Steel specification 1 2 3 4 5 6 7 8
C 0.350 0.110 0.100 0.750 0.025 0.043 0.500 0.070
Si 0.200 0.350 0.400 0.400 0.350 0.042 0.300 0.005
Mn 1.400 0.650 1.500 0.400 1.700 0.252 1.000 1.300
P 0.018 0.030 0.009 0.350 0.040 0.013 0.035 0.060
S 0.003 0.010 0.001 0.350 0.007 0.014 0.035 0.350
Cr 0.20 12.50 0.03 4.00 17.20 0.02 1.00 0.03
V 0.15 0.15 0.15 1.20 0.20 0.15 0.15 0.15
Mo 0.002 0.30 0.002