Formation of cold characteristics of the thermal input when welding steel with high strength and capacity of 500 ma

1.   DEPENDENCE OF COLD CRACKS FORMATION FROM THE HEAT INPUT WHEN WELDING OF HIGH STRENGTH STEEL WITH YIELD STRENGTH OF 500 MPA

DEPENDENCE OF COLD CRACKS FORMATION FROM
THE HEAT INPUT WHEN WELDING OF HIGH STRENGTH
STEEL WITH YIELD STRENGTH OF 500 MPA
Postgraduate: Alruhaimi Anmar Ghareeb
Supervisor:
Ivanov M.A.

2. Table 1 - Mechanical properties of steel 10G2FBU according to technical regulations 14-101-725-2009.

Grade
10G2FB
U
Ultimate
strength,
MPa, not less
620
Impact strength,
J/cm2, not less
Yield
strength,
MPa, not
less
Elongation,
%, not less
550
24
CET, %,
not less
KCU-60
KCV-20
250
250
0,43
Table 1 - Mechanical properties of steel 10G2FBU according to
technical regulations 14-101-725-2009.

3. Table 2 - Dependence of the cold cracks formation from the welding mode and the cooling rate.

No
1
2
3
4
5
6
7
8
9
10
11
12
Wall
thickness,
mm
Ambient
temperature, C
Heat input, kJ/cm
Vcool, ˚C/sec,
according to
formula [10]
5.8
+20
10.3
14.7
18
5.8
-20
10.3
14.7
5.8
+20
10.3
14.7
36
5.8
-20
10.3
14.7
Designations adopted in the table: + the detected cracks;
Presence of
cracks
98
+
55
39
108
+
61
+
44
98
+
55
39
108
+
61
+
44
- cracks are absent
Table 2 - Dependence of the cold cracks formation from the welding mode
and the cooling rate.

4. Fig. 1 - Photo of cracks on etched plates of samples: a) No. 1; b) No. 5; c) No. 10

a)
b)
c)
Fig. 1 - Photo of cracks on etched plates of samples:
a) No. 1; b) No. 5; c) No. 10

5. Table 2 - Hardness on Vickers, HV10

No
1
2
3
4
5
6
7
8
9
10
11
12
Base
metal
203
196
205
196
199
207
205
217
212
210
207
211
Welding seam
HAZ
288
242
232
287
255
252
278
271
247
329
280
247
left
center
right
250
239
220
266
231
228
236
218
207
261
259
170
268
253
227
301
261
231
285
249
224
305
293
236
255
241
212
273
247
225
253
229
210
258
277
223
Table 2 - Hardness on Vickers, HV10
HAZ
Base metal
296
246
230
289
274
246
291
263
265
310
291
247
206
204
206
231
209
205
205
217
212
220
210
213

6. Fig.2 - Graph of hardness on Vickers of the template of the sample No. 10

Sample10
HV10
350
329
297
294
289
300
275
291
276
250
210
215
264
261
240
258
220
228
194
200
289
306
276
310
305
305
205
Welding Seam
198
206
204
Base Metal
HAZ
150
Base Metal
HAZ
Cracking
Overheating Area
100
50
0
0
2
2
2
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
0,5
2
2
2
length , mm
Fig.2 - Graph of hardness on Vickers of the template of the sample No. 10

7. Summary

Cold cracks in high strength steel 10G2FBU for thicknesses of 18 and 36 mm are not
detected in heat input over 10.3 kJ/cm by welding at the temperature of +20 С, at
the same time when welding at an ambient temperature of –20 С cracks are not
detected when heat input is over 14.7 kJ/cm.
Critical cooling rate in which no cracking appeared is 55 С/s at the temperature of
welding +20 С, as well as 44 С/s at the temperature of welding –20 С for both
thicknesses.
The criterion HVmax < 300 HV is a necessary but insufficient condition for
prevention of cold cracks in steels of the type 10G2FBU. In the conditions of the
experiment, cold cracks in the welding seam are absent at a hardness of no more than
250-260 HV, which is probably due to the presence of diffusive hydrogen, which is
not regulated in the regulations for the supply of this steel grade.