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5 Chemical composition
5.1 Ladle analysis
The chemical composition of the steels dealt with in this standard shall be as specified in table 2. Small departures from these specifications are permissible if they do not impair the performance of the steel.
5.2 Product analysis
When a product analysis is carried out on finished tubes, the permitted deviations given in table 3 shall apply to the ladle analysis specified in table 2.
Table 2: Chemical composition of steel grades shown on ladle analysis
|
Steel grade
|
Chemical composition, as a percentage by mass
|
|
Symbol
|
Material number
|
С
max.
|
Si
max.
|
Mn
max.
|
P
max.
|
S
max.
|
Al
|
|
RSt 34-2
|
1.0034
|
0,15
|
0,30
|
0,60
|
0,025
|
0,025
|
1)
|
|
RSt 37-2
|
1.0038
|
0,17
|
0,30
|
0,70
|
0,025
|
0,025
|
1)
|
|
St 44-2
|
1.0044
|
0,21
|
0,30
|
1,10
|
0,025
|
0,025
|
1)
|
|
St 52-3
|
1.0570
|
0,22
|
0,35
|
1,60
|
0,025
|
0,025
|
=>0.020
|
The following alloying elements may be added:
Nb: <= 0,03 %; Ti: <= 0,03 %; V: <= 0,05%; Nb + Ti + V: <= 0,05 %.
1) This steel grade may be killed by aluminium only (aluminium content 0,020% or more). |
Table 3: Permitted deviations of the product analysis from the specified ladle analysis
|
Element
|
Permitted deviations from the specified limits of the ladle analysis, as a percentage by mass
|
|
C
|
+0.02
|
|
Si
|
+0.03
|
|
Mn
|
+0.06
|
|
P
|
+0.005
|
|
S
|
+0.005
|
|
Nb
|
+0.01
|
|
Ti
|
+0.01
|
|
V
|
+0.01
|
6 Final supply conditions
Tubes are to be supplied in one of the final supply conditions specified in table 4.
Table 4: Final supply conditions
|
Designation
|
Symbol
|
Description
|
| Welded and sized |
BKM
|
Tubes do not undergo heat treatment following welding and sizing and thus have a rather high resistance to deformation. |
| Annealed |
GBK
|
Sizing is followed by annealing in a controlled atmosphere. |
| Normalized |
NBK
|
Sizing is followed by annealing above the upper transformation point in a controlled atmosphere. |
7 Mechanical properties
7.1 The mechanical properties are a function of the final supply condition (cf. table 4) and shall comply with table 4.
7.2 When tested as described in subclauses 10.2.2.2 and 10.2.2.3 tubes shall show no cracks.
7.3 In the case of steel grades and/or final supply conditions other than those specified in tables 2 and 4, the required mechanical properties shall be subject to agreement. Such tubes shall be supplied in quality grade C.
7.4 On the basis of their chemical composition and the way they have been processed, the steels listed in table 2 are to be regarded as weldable. It should, however, be noted that, due to subsequent welding, the mechanical properties of tubes in the BKM condition are modified in the area of the tube which has been subjected to heat.
Table 5: Mechanical properties of tubes at ambient temperature
|
Final supply condition
|
Welded and sized (BKM)1)
|
Annealed (GBK)1)
|
|
Steel grade
|
|
Material designation
|
Material number
|
Minimum tensile strength, Rm, in N/mm2 |
Minimum elongation at fracture, A5, as a percentage |
Minimum tensile strength, Rm, in N/mm2 |
Minimum elongation at fracture, A5, as a percentage |
|
RSt 34-2
|
1.0034
|
330
|
8
|
300
|
28
|
|
RSt 37-2
|
1.0038
|
390
|
7
|
315
|
25
|
|
St 44-2
|
1.0044
|
440
|
6
|
390
|
21
|
|
St 52-3
|
1.0570
|
540
|
5
|
490
|
22
|
|
Final supply condition
|
Normalized (NBK)
|
|
Steel grade
|
|
Material designation
|
Material number
|
Tensile strength, Rm, in N/mm2 |
Tensile strength, ReH2), in N/mm2 |
Minimum elongation at fracture, A5, as a percentage |
|
RSt 34-2
|
1.0034
|
310 to 410
|
205
|
28
|
|
RSt 37-2
|
1.0038
|
340 to 470
|
235
|
25
|
|
St 44-2
|
1.0044
|
410 to 540
|
255
|
21
|
|
St 52-3
|
1.0570
|
490 to 630
|
355
|
22
|
1) The yield strength for the annealed (GBK) condition shall be equal to at least 50 % of the tensile strength. Depending on the extent of deformation, the yield strength of tubes delivered in the (BKM) condition may come close to reaching the tensile strength. Calculations should be based on a minimum value of 70 % of the tensile strength.
2) For tubes with an outside diameter up to 30 mm and a wall thickness up to 3 mm, the minimum yield strength may be 10 N/mm2 lower. |