What are the composition, properties and uses of high speed steel ? State its various types.

What are the composition, properties and uses of high speed steel ? State its various types.

Ans. As the name indicates, high speed steel is used for high speed cutting

tools. These steels can be divided into two groups depending upon the principal

alloying element. The first group is called tungsten high speed steels and is

designated by T-series. Steels of this group contain high amount of tungsten

with addition of chromium, vanadium and cobalt. The second group of high

speed steels is called molybdenum steels. In addition to molybdenum, they

also contain tungsten, chromium, vanadium and cobalt. This group is designated

by M-series.

Composition -The composition of high speed steels is as follows –

 

S.No. Type %C %CR %W %Mo %V %Co
(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

T1

T2

T3

T4

M1

M2

M6

M34

0.70

0.85

0.75

0.80

0.80

0.85-1.00

0.80

0.85

4.00

4.00

4.00

4.00

4.00

4.00

4.00

4.00

18.00

18.00

18.00

18.00

1.50

6.00

4.00

2.00

8.00

5.00

5.00

8.00

1.00

2.00

1.00

2.00

1.00

2.00

1.50

2.00

5.00

8.00

12.00

8.00

 

Properties– Various properties of high speed steels are given as follows-

(i) The main characteristic of high speed steel is that it maintains

high hardness at temperature up to 550°C.

(ii) They possess high wear resistance.

(iii) It is hard steel and cannot be machined by ordinary methods.

(iv) It allows the tool to cut the metal at high speed.

 

Uses– The uses of high speed steel include-

(i) Hand tools, such as chisels, punches, hammers etc.

(ii) Machine tools for cutting metals.

(iii) Shears for cutting materials.

(iv) Dies for deep drawing, extrusion, forging etc.

(v) For the manufacturing of drills, milling cutters, hobs, broaches,

saws, reamer etc.

Types- High speed steels can be of following types-

(i) 184-1 High Speed Steel- This steel, contains about 18%

tungsten, 4% chromium and I% vanadium. It is one of the best all purpose

tool steels. It is widely used for drills, lathe, planner and shaper tools, milling

cutters, reamers, broaches, threading dies, punches, etc.

(ii) Molybdenum High Speed Steel– This steel contains abouf6%

tungsten, 6% molybdenum, 4% chromium and 2% vanadium. It is better and

cheaper than other types of steels. It has excellent toughness and cutting

ability and particularly used for drilling and tapping operations.

(iii) Super High Speed Steel– This steel contains 20% W, 4% Cr,

2% V and 12% Co. Due to high cobalt content, it is also called cobalt high

speed steel. Cobalt increases its cutting efficiency especially at high

temperatures. Due to its high cost, this steel is used for heavy cutting operations

which impose high pressure and temperatures on the tool.

(iv) Vanadium High Speed Steel This steel contains more than

I% V. It has better abrasive resistance than 18-4-1 steel. It is generally used

for machining difficult to machine materials.

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