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The Chemical Elements in Steel

Steel in general is an alloy of carbon and iron, it does contain other elements, some of which are retained from the steel making process, other elements are added to produce specific properties. The more common elements are listed below:-

Carbon ( C ) - Carbon is arguably the most important element in steel, it is essential in steels which have to be hardened by quenching and the degree of carbon controls the hardness and strength of the material.

Manganese ( Mn ) - Its presence has three main effects, it is a mild deoxidant acting as a cleanser taking the sulphur and oxygen out of the melt into the slag. It increases the harden ability and tensile strength but decreases ductility. It combines with sulphur to form globular manganese sulphides, essential in free cutting steels for good machinability .

Silicon ( Si ) - In most commercial steels it is present in a range of 0.05/0.35% and acts as a powerful deoxidiser. It is present in higher contents in Silico-Manganese Spring Steels and Acid and heat resisting steels.

Sulphur (S) - It is normally regarded as an impurity and has an adverse effect on impact properties when a steel is high in sulphur and low in manganese.The welding qualities of steels with high sulphur is poor. Free cutting steels have sulphur added to improve machinability, usually up to a maximum of 0.35%.

Phosphorus (P ) - Although it increases the tensile strength of steel and improves machinability it is usually regarded as an undesirable impurity because of its embrittling effect. Most steels do not exceed 0.05% phosphorus.

Nickel (Ni) - When added to carbon steel in amounts up to 5% it increases the tensile strength, toughness and hardenability without loss of ductility. Often used in combination with other alloying elements, especially chromium and molybdenum. Stainless steels contain between 8% and 14% nickel.

Chromium (Cr) - Increases hardenability and with high carbon improves resistance to abrasion and wear. An essential element in stainless steels and heat resistant steels where contents of up to 30% may be present.

Molybdenum (Mo) - Increases hardenability and reduces the risk of temper brittleness in low alloy steels. It is added to stainless steels to increase their resistance to corrosion and is also used in high speed tool steels.

Vanadium (V) - When used with other alloying elements it restricts grain growth, refines grain size, increases hardenability, and resistance to shock loading. Softening at high temperatures, fatigue stress and wear resistance are improved.

Tungsten (W) - Is used as the main element in high speed tool steels. After heat treatment the steel maintains its hardness at high temperature making it particularly suitable for cutting tools.

Lead (Pb) - The addition of lead in levels of up to 0.30% improves machinability. Providing the distribution is homogenous it has little effect on the physical properties of the steel, and contrary to popular belief, it does not affect weld ability.

Selenium & Tellurium (Se,Te) - These elements are added to certain steels to improve machinability. In free machining stainless steels a selenium content of 0.15/0.25% is typical.
Tellurium levels of 0.03/0.05% are added to leaded free cutting steels to further improve machinability.

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Understanding BS970

Many of our customers insist on using the old EN system when ordering steel. As steel suppliers we understand that some drawings do have the latest BS970 number and the old EN numbers. There is also now in place a new European Standard which in time may replace all the British Standard and EN numbers.

Listed below is how the six digit BS970 system works.

The first three characters are numbers:-


000 - 299
 

Non alloy steel.

000 - 199

 

Carbon and carbon manganese steels, the numbers indicate the average manganese content.

200 - 400

 

Free cutting steels, the second and third numbers indicate the minimum or average sulphur content.

250

 

Silicon manganese spring steels.

300 - 499

 

Stainless, Heat resisting and value steels.

500 - 999

 

Alloy steels

 

The fourth character is either A,H,M or S, this refers to the condition that the material will be supplied in, with the exception of stainless steel where the letter S is used.

A

  

Close limits of chemical composition.

H

  

Hardenability requirements.

M

 

Mechanical property requirements.

 

The fifth and six character in carbon and alloy steels refer to the average carbon content of the steel to be supplied. For example 817M40 is an alloy steel, supplied to mechanical properties with an average carbon content of .40%. If you need any help understanding the new European Grade i.e EN10025, please give our Technical Sales Department a call, they should be able to give you the nearest BS970 or EN equivalent.

Tensile Strengths - Within BS970 you will find certain specifications of material which have a tensile range symbol attached to the grade i.e. BS970 - 817M40T or En24T. Listed below is an explanation of the tensile range symbols and the corresponding strength:-

 

REFERENCE SYMBOL
TENSILE STRENGTH N/mm2
TENSILE STRENGTH Tons/Sq.Inch
P
550 - 700
35 - 45
Q
625 - 775
45 - 50
R
700 - 850
45 - 55
S
775 - 925
50 - 60
T
850 - 1000
55 - 65
U
925 - 1075
60 - 70
V
1000 - 1150
65 - 75
W
1075 - 1225
70 - 80
X
1150 - 1300
75 - 85
Y
1225 - 1375
80 - 90
Z
1550 MIN
100 MIN

 

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The Heat Treatment of Steel

Many changes occur when steel is subjected to heat. There are different heat treatment processes which are listed below:-

Normalising - Heating to a suitable temperature, between 800-900 degrees celsius, according to analysis, holding at temperature followed by cooling in still air. Relieves internal stresses, refines the grain size and improves mechanical properties.

Annealing - Heating and holding at a suitable temperature and cooling slowly in the furnace with the object of softening the steel, improving machinability and cold working properties.

Speroidising - A form of annealing often used for high carbon steels with the object of obtaining the softest state possible to assist machinability.

Stress Relieving - Frequently carried out after rough machining or cold work to remove stresses. It is usually carried out at a temperature range of 600-650 degrees celsius.

Hardening - Heating to a temperature slightly above the critical range, soaking for sufficient time at that temperature followed by quenching in a suitable medium such as water, oil, or air.

Tempering - Carried out immediately after hardening to relieve stresses remove brittleness and reduce hardness to the required range. Usually carried out between 150 - 650 degrees celsius. Cool in still air or quench.

Nitriding - A process for producing a very hard case by the absorption of nitrogen into the surface of the steel. Depending on the specification hardness figures up to 1100 VPN can be attained.

Carburising - The diffusion of carbon into the surface of a steel that is low in carbon by heating in a solid, liquid, or gaseous medium, containing carbon at a temperature around 900 degrees celsius.

Induction Hardening - A surface hardening process where a component is heated by high frequency induction followed by immediate quenching. The surface hardness will depend on the carbon content of the steel. For ideal results this is usually in the range 0.40%-0.45%C.

FINISHED SIZES

 

WHAT SIZE DO I NEED FOR MY FINISHED MACHINE SIZE

Hot Rolled Dia mm

Required Finished Size in mm

Hot Rolled dia mm

Required Finished Size in mm

20

18.91

70

66.53

21

19.87

71

67.49

22

20.83

72

68.45

23

21.79

73

69.41

24

22.75

74

70.37

25

23.71

75

71.33

26

24.67

76

71.71

27

25.54

80

75.55

28

26.50

85

80.35

29

27.46

90

85.15

30

28.42

95

89.76

31

29.38

100

94.56

32

30.34

105

99.36

33

31.30

110

104.16

34

32.26

115

108.96

35

33.22

120

113.76

36

34.18

125

118.08

37

35.14

130

122.88

38

36.10

135

127.68

39

36.96

140

132.48

40

37.92

145

137.28

41

38.88

150

142.08

42

39.84

155

146.88

43

40.80

160

151.68

44

41.76

165

156.00

45

42.72

170

160.80

46

43.68

175

165.60

47

44.64

180

170.40

48

45.60

185

175.20

49

46.56

190

180.00

50

47.52

195

184.80

51

48.48

200

189.60

52

49.34

205

193.92

53

50.30

210

198.72

54

51.26

215

203.52

55

52.22

220

208.32

56

53.18

230

217.92

57

54.14

240

227.52

58

55.10

250

237.12

59

56.06

255

241.92

60

57.02

260

246.72

61

57.98

270

256.32

62

58.99

280

265.92

63

59.90

290

275.52

64

60.86

300

285.12

65

61.73

305

289.92

66

62.69

320

304.32

67

63.65

330

313.92

68

64.61

350

333.12

69

65.57

360

346.50

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Tolerances for Bright Drawn, Turned & Ground Bars

All tolerances are quoted a minus limits

  Tolerance in Millimetres
(sizes in metric) dia		   Tolerance in Thousandths of an Inch
 (sizes in imperial) dia
  h 11
turned
bar		 h10
drawn
bar		 h 9
ground
bar		     h 11
turned
bar		 h 10
drawn
bar		 h 9
ground
bar
1 to 3 .060 .040 .025   1/16" - 1/8" .0024 .0016 .0010
3 to 6 .075 .048 .030   1/8" - 1/4" .0029 .0019 .0012
6 to 10 .090 .058 .036   1/4" - 3/8" .0035 .0023 .0014
10 to 18 .110 .070 .043   3/8" - 3/4" .0043 .0028 .0017
18 to 30 .130 .084 .052   3/4" - 13/16" .0051 .0033 .0020
30 to 50 .160 .100 .062   13/16" - 2" .0063 .0039 .0025
50 to 80 .190 .120 .074   2" - 31/8" .0074 .0047 .0029
80 to 120 .220 .140 .087   31/8" - 43/4" .0086 .0055 .0034
120 to 180 .250 .160 .100   43/4" - 7" .0098 .0063 .0039

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Conversion Factors

To Convert Multiply by   To Convert Multiply by
Centimetres to Inches 0.3937   Kilograms to tons 0.0009842
Cubic centimetres to cubic inches 0.06103   Kilos per sq mm to tons per sq in 0.635
Cubic feet to cubic metres 0.02832   Metres to feet 3.281
Cubic inches to cubic centimetres 16.39   Miles to Kilometres 1.609
Cubic inches to litres 0.01639   Millimetres to inches 0.0394
Cubic metres to cubic feet 35.32   N/mm2 to tons f/in2 0.06475
Cubic metres to cubic yards 1.308   Pounds to kilograms 0.4536
Cubic yards to cubic metres 0.7645   Pounds per foot to kilos per metre 1.488
Feet to metres 0.3048   Square centimetres to sq. inches 0.1550
Foot pounds to kilogram metre 0.1382   Square feet to sq. metres 0.09290
Gallons to litres 4.536   Square inches to sq. centimetres 6.452
Gallons to cubic feet 0.1606   Square metres to sq. feet 10.76
Grains to grams 0.06480   Temperature conversion:-
°C =
°F =
5/9 (°F - 32)
(9/5 x °C) + 32
Grams to lbs 0.002205   Inches to centimetres 2.540
Inches to millimetres 25.40   Tons per sq. in. to kilos per sq. mm 1.575
Kilogram metres to foot pounds 7.233 Tons per f/in2 to N/mm2 15.444
Kilograms to lbs 2.205 Tons to kilograms 1016.0

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