S550Q and S690Q are both high-strength, quenched and tempered (Q) structural steels under EN 10025-6 standard, which is a European norm. The primary difference is their minimum yield strength: S550Q has a minimum yield strength of 550 MPa, while S690Q offers a higher minimum yield strength of 690 MPa, making S690Q stronger and suitable for heavier loads, with S690Q having higher tensile strength and generally better toughness properties.
Chemical Composition
|
S550QChemical Composition |
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|
Grade |
The Element Max (%) |
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|
C |
Si |
Mn |
P |
S |
N |
B |
Cr |
|
|
S550 Q |
0.20 |
0.80 |
1.70 |
0.020-0.025 |
0.010-0.015 |
0.015 |
0.005 |
1.50 |
|
Cu |
Mo |
Nb |
Ni |
Ti |
V |
Zr |
|
|
|
0.50 |
0.70 |
0.06 |
2.0 |
0.05 |
0.12 |
0.15 |
|
|
|
S690QChemical Composition |
| Grade | C % | Si % | Mn % | P % | S % | N % | B % | Cr % |
| S690Q | 0.200 | 0.800 | 1.700 | 0.025 | 0.015 | 0.015 | 0.005 | 1.500 |
| Cu % | Mo % | Nb % | Ni % | Ti % | V % | Zr % | ||
| 0.500 | 0.700 | 0.060 | 2.000 | 0.050 | 0.120 | 0.150 |
Mechanical Property
|
Grade |
S550QMechanical Property |
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|
Thickness |
Yield |
Tensile |
Elongation |
Min Impact Energy
|
||
|
S550 Q |
mm |
Min Mpa |
Mpa |
Min % |
-20 |
30J |
|
3<t≦50 |
550 |
640-820 |
16 |
-20 |
30J |
|
|
50<t≦100 |
530 |
640-820 |
16 |
-20 |
30J |
|
|
100<t≦150 |
490 |
590-770 |
16 |
-20 |
30J |
|
| Grade | Thickness | Min Yield | Tensile | Elongation | Min Impact Energy | |
| S690Q | 8mm-50mm | Min 690Mpa | 770-940Mpa | 14% | -20 | Min 30J |
| 51mm-100mm | Min 650Mpa | 760-930Mpa | 14% | -20 | Min 30J | |
| 101mm-150mm | Min 630Mpa | 710-900Mpa | 14% | -20 | Min 30J |
Key Differences
Yield Strength:
S550Q: Minimum yield strength of 550 MPa.
S690Q: Minimum yield strength of 690 MPa.
Tensile Strength: S690Q has significantly higher tensile strength (e.g., 770-940 MPa) compared to S550Q, indicating superior load-bearing capacity.
Applications:
S550Q: Used in demanding structural applications where high strength is needed, but perhaps less extreme than S690Q.
S690Q: Ideal for heavy-duty structures like cranes, heavy machinery, bridges, and offshore applications due to its superior strength-to-weight ratio.
Impact Toughness: Both are available in different toughness grades (e.g., Q for standard toughness, QL for lower temperatures), but S690Q generally provides higher inherent toughness for extreme conditions.
