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.
|