PSI - Issue 72

Nedeljko Vukojević et al. / Procedia Structural Integrity 72 (2025) 157 –163

162

Table 1. Comparison of mechanical tests results before and after plastic forming (p=20bar, S=1,5)

Materials

M1(S235JR+N)

M2(P460NL1)

Diameter / thickness, mm

Ø1500/Ø 3000#6 Ø1500/Ø 3000#15 Ø1500/Ø 3000#6 Ø1500/Ø 3000#15

Treatment ISF Yield strength Tensile strength

before after

before after

before after

before after

ReH (MPa) Rm (MPa)

344 534/577 340 465 597/631 475

612/568 407 614/623 531 763/636 637/609 593 682/720 670 780/754

Contraction Elongation

Δ (%) A (%) KV (J)

51,6 38,5/30,5 52,6 25/32 43,6 21,5/30 50,3 22,5/29,5 27,3 9,75/8,75 34,0 10,7/11 20,8 9,5/17,5 31,6 11,7/18,5

Impact energy

53

45/36

87

103/70 35

15/30 48

41/42

Hardness

(HV)

171 194/217 158 277 186/131 193

214/220 232 278/271 247 313/301 181/169 294 234/245 366 134/102

Residual stress

Ϭ res (MPa)

Fracture toughness KJIC (MPa·m1/2) -

51,8

45,5 -

-

60,1

-

52,2

Table 2. Comparison of dish ends thicknesses depending on diameter and yield strength Yield stress, MPa

Dish end  1250 thickness, mm Dish end  2500 thickness, mm

Certif. BM

Ser.I HAZ

Ser. II HAZ

Ser.II HAZ MPa

Certif. BM

Ser. I HAZ Plate

Ser. II HAZ

Certif. BM

Ser. I HAZ Plate

Ser. II HAZ  3000

Samples

MPa MPa MPa

Plate

 1500 Plate

Material/t, mm Plate Plate

 1500

 3000 s

s

s

s

s

s

S235#6mm 345 344 543 S235#15mm 330 340 612 P460#6mm 469 407 614 P460#15mm 466 531 763

577 568 623 636

4,0 4,1 3,2 3,2

4,0 4,1 3,6 3,0

2,9 2,7 2,7 2,4

7,0 7,3 5,4 5,5

7,0 7,1 6,1 4,9

4,6 4,7 4,3 4,3

Results show, the smallest wall thicknesses are required for Series II (after plastic deformation). Also, from the comparative result of the required wall thickness of the base material (BM) and the welded joint (Series I), it is clear that the HAZ is not a weak point because it has very good strength properties. 5. Conclusion Based on the performed mechanical testing and calculations, the following conclusions can be made:  The tensile properties are above the standard prescribed values for the analyzed materials.  The hardness of Series II is higher compared to Series I.  Poor impact properties at room temperature, which correspond to brittle material behavior, as indicated by the fracture characteristics of the material. Values of total impact energy measured in the HAZ by Series II are below those measured in the base material and Series I.  Effect of plastic deformation is positive in terms of reducing the level of residual stresses. The diameter of the base plate does not affect the level of residual stress reduction, while the thickness and mechanical properties of the material have a significant impact on the reduction effect in specific combinations.  Thinner sheets give better fracture toughness results for the same material. HAZ made of steel P460 has higher values of fracture toughness and therefore greater resistance to cracks than HAZ steel S235.  The calculation results illustrated that a smaller dish end wall thickness of the Series II is required in HAZ than in the case of the basic material or HAZ Series I. Better mechanical properties can be obtained by the correct and high-quality production of the welded joints, as well as by incremental sheet forming. HAZ is not a weak point in terms of designed strength.