The document discusses different classifications of steel based on carbon content and other alloying elements. It describes plain carbon steels, low alloy steels, and high alloy steels. Within these classifications it discusses ranges of carbon content and how that affects properties like hardness, strength and weldability. It also describes different types of stainless steel (austenitic, ferritic, martensitic) and how alloying elements like chromium and nickel are used to achieve desired properties in stainless steels.

2. Arshed Mehmood 08-ME-05
Usman Hafeez 08-ME-10
Asad Munir 08-ME-14
Ali Adnan 08-ME-16

4. Steel can be classified according to,
 American’s Standard
 % age of Carbon content

6. The Society of Automotive Engineers
(SAE) has established standards for
specific analysis of steels. In the 10XX
series, the first digit indicates a plain
carbon steel. The second digit indicates
a modification in the alloys. 10XX means
that it is a plain carbon steel where the
second digit (zero ) indicates that there
is no modification in the alloys. The last
two digits denote the carbon content in
points. For example SAE 1040 is a
carbon steel where 40 points represent
0.40 % Carbon content. Alloy steels are
indicated by 2XXX, 3XXX, 4XXX, etc..

7. 10XX
Plane Carbon Modification
Carbon Contents
Steel in the Alloys
In the Points

11. SAE - AISI
Number
Classification
1XXX Carbon steels
Low carbon steels: 0 to 0.25 % C
Medium carbon steels: 0.25 to 0.55 % C
High carbon steels: Above 0.55 % Carbon
2XXX Nickel steels
5 % Nickel increases the tensile strength without
reducing ductility.
8 to 12 % Nickel increases the resistance to low
temperature impact
15 to 25 % Nickel (along with Al, Cu and Co)
develop high magnetic properties. (Alnicometals)
25 to 35 % Nickel create resistance to corrosion at
elevated temperatures.

12. NICKEL-CHROMIUM STEELS
3XXX
THESE STEELS ARE TOUGH AND DUCTILE AND EXHIBIT HIGH WEAR
RESISTANCE, hardenability and high resistance to
corrosion.
MOLYBDENUM STEELS
4XXX Molybdenum is a strong carbide former. It has a strong
effect on hardenability and high temperature hardness.
Molybdenum also increases the tensile strength of low
carbon steels.

15. Generally, carbon is the most
important commercial steel alloy. Increasing
carbon content increases hardness and
strength and improves hardenability. But
carbon also increases brittleness and reduces
weldability because of its tendency to form
martensite.
This means carbon content can be both
a blessing and a curse when it comes to
commercial steel.

16. Most commercial steels are classified into
one of three groups:
 Plain carbon steels
 Low-alloy steels
 High-alloy steels

17. These steels usually are iron with less
than 1 percent carbon, plus small amounts of
manganese, phosphorus, sulfur, and silicon.
The weldability and other characteristics
of these steels are primarily a product of
carbon content, although the alloying and
residual elements do have a minor influence.

18.  Low
 Medium
 High
 Very high

20. Low-carbon steels called mild steels, low-
carbon steels have less than 0.30 percent
carbon and are the most commonly used
grades. They machine and weld nicely and are
more ductile than higher-carbon steels.
Medium-carbon steels have from 0.30 to
0.45 percent carbon. Increased carbon means
increased hardness and tensile strength,
decreased ductility, and more difficult
machining.

21. High Plane Carbon Steel With 0.45 to
0.75 percent carbon, these steels can
be challenging to weld. Preheating,
postheating (to control cooling rate),
and sometimes even heating during
welding become necessary to produce
acceptable welds and to control the
mechanical properties of the steel
after welding.

22. With up to 1.50 percent carbon
content, very high-carbon steels are
used for hard steel products such as
metal cutting tools and truck springs.
Like high-carbon steels, they require
heat treating before, during, and after
welding to maintain their mechanical
properties.

24. When these steels are designed
for welded applications, their carbon
content is usually below 0.25 percent
and often below 0.15 percent. Typical
alloys include nickel, chromium,
molybdenum, manganese, and silicon,
which add strength at room
temperatures and increase low-
temperature notch toughness.

25. These alloys can, in the right
combination, improve corrosion
resistance and influence the steel's
response to heat treatment. But the
alloys added can also negatively
influence crack susceptibility, so it's a
good idea to use low-hydrogen
welding processes with them.
Preheating might also prove
necessary. This can be determined by
using the carbon equivalent formula,
which we'll cover in a later issue.

26. For the most part, we're talking
about stainless steel here, the most
important commercial high-alloy
steel. Stainless steels are at least 12
percent chromium and many have
high nickel contents.

27.  Austenitic
 Ferritic
 Martensitic

28. Austenitic stainless steels offer
excellent weldability, but austenite
isn't stable at room temperature.
Consequently, specific alloys
must be added to stabilize austenite.
The most important austenite
stabilizer is nickel, and others include
carbon, manganese, and nitrogen.

29. Ferritic
Ferritic stainless steels have 12 to 27
percent chromium with small amounts of
austenite-forming alloys.
Martensitic
Martensitic stainless steels make up the
cutlery grades. They have the least
amount of chromium, offer high
hardenability, and require both pre- and
postheating when welding to prevent
cracking in the heat-affected zone (HAZ).