S690QL vs S700MC
Their yield strengths are nearly equal (690 vs 700 MPa); yet they are produced by two fundamentally different methods. S690QL stands out in thick sections and at low temperature through quenching + tempering (Q+T); S700MC excels in thin sheet, bending and series production through thermomechanical rolling (TMCP).
The Key Difference: Production Method
S690QL and S700MC, as can be seen from the numbers in their names (690 and 700 MPa), have almost the same minimum yield strength. This is why the question "which is stronger?" is misleading; both are high-strength steels. The real difference lies in how the strength is achieved and the character this gives the material.
S690QL is produced to EN 10025-6 by quenching and tempering (Q+T) heat treatment. This method provides high strength and low-temperature toughness even in thick sections; it is typically supplied as thick plate of 8–120 mm.
S700MC, on the other hand, is produced to EN 10149-2 by thermomechanical controlled rolling (TMCP), forming a micro-alloyed (Nb, Ti, V) fine grain structure. Its low carbon content gives it superior cold formability and easy weldability; however, by the nature of the process it is limited to thinner sections (generally ~1.5–12 mm).
Overview: Q+T and TMCP
The two production methods determine almost every property of the steel.
S690QL — Quenching + Tempering (Q+T)
The plate is first heated to austenitizing temperature (~900 °C), then rapidly cooled with water (quench) to obtain a hard martensitic structure. In the final step, toughness is restored through tempering. This method provides high strength and −40 °C impact toughness even in thick sections. EN 10025-6 · 8–120 mm.
S700MC — Thermomechanical Rolling (TMCP)
The steel is rolled within controlled temperature ranges and cooled in a controlled manner. The very fine grain structure formed with micro-alloy elements (Nb, Ti, V) provides strength, while the low carbon content brings superior cold formability and easy welding with a low CEV. EN 10149-2 · generally ~1.5–12 mm.
S690QL vs S700MC — Detailed Table
A side-by-side comparison of the standard, mechanical and fabrication properties of the two grades.
| Property | S690QL | S700MC |
|---|---|---|
| Standard | EN 10025-6 | EN 10149-2 |
| Min. Yield Strength (ReH) | ≥ 690 MPa | ≥ 700 MPa |
| Tensile Strength (Rm) | 770–940 MPa | 750–950 MPa |
| Production Method | Quenching + tempering (Q+T) | Thermomechanical rolling (TMCP) |
| Thickness Range | 8 – 120 mm (thick plate) | ~1.5 – 12 mm (generally thin sheet) |
| Elongation at Break (A) | ≥ 14 % | ≥ 10 % (typically 12–17 %) |
| Impact Toughness (Charpy V) | −40 °C, ≥ 30 J | −20 °C, ≥ 40 J |
| Cold Formability | Limited — min. inner radius 3–4 × t | Superior — min. inner radius 1.5–2 × t |
| Weldability (CEV) | Careful — CEV ~0.65, preheating required | Easy — CEV 0.35–0.41, mostly no preheating |
| Hardness (typical) | 235–280 HBW | 200–250 HBW |
| Microstructure | Martensitic / bainitic (tempered) | Fine-grained ferritic-bainitic |
| Typical Use | Crane boom, bridge, heavy chassis, ship, pressure vessel | Trailer/semi-trailer, automotive chassis, profile, agricultural machinery |
Note: Values are based on EN 10025-6 and EN 10149-2 standards and on typical/reference data; actual values may vary with thickness, manufacturer and melt analysis. Mechanical guarantees may decrease stepwise especially as thickness increases.
Which One Should I Choose?
Two clear scenarios: your section thickness and fabrication method determine the choice.
Choose S690QL
- If you need a thick section (above 12 mm, up to 120 mm)
- Structural / load-bearing construction, bridges, heavy chassis
- Crane boom, telescopic arm, lifting equipment
- Low-temperature application (−40 °C toughness guarantee)
- Shipbuilding, offshore and pressure vessel shells
- Thick load-bearing plate under high static load
Choose S700MC
- Thin sheet application (approximately below 12 mm)
- Parts requiring heavy bending and complex geometry
- Cold forming, profile rolling
- Trailer/semi-trailer, truck superstructure, trailer chassis
- Automotive body/chassis, agricultural machinery parts
- Series production and lightweight structural designs
Chemical & Mechanical Quick Note
The fundamental chemical differences that define the character of the two grades.
The strength strategy of the two steels is different. S690QL gets its strength from high carbon and alloying elements (Cr, Ni, Mo) + heat treatment; while S700MC gets it from the fine grain structure achieved with low carbon + micro-alloying (Nb, Ti, V). This is why the carbon equivalent (CEV) of S700MC is markedly lower and its weldability is better.
| Element | S690QL (max. %) | S700MC (max. %) |
|---|---|---|
| Carbon (C) | 0.20 | 0.12 |
| Silicon (Si) | 0.80 | 0.60 |
| Manganese (Mn) | 1.70 | 2.10 |
| Chromium (Cr) | 1.50 | — |
| Nickel (Ni) | 2.00 | — |
| Molybdenum (Mo) | 0.70 | — |
| Niobium (Nb) | 0.06 | 0.09 |
| Titanium (Ti) | 0.05 | 0.22 |
| Vanadium (V) | 0.12 | 0.20 |
| Carbon Equivalent (CEV) | typical ~0.65 | 0.35 – 0.41 |
Note: Values are based on the permitted maximums of EN 10025-6 / EN 10149-2 and on typical manufacturer data. In S700MC, Cr, Ni, Mo are not mandatory; strength is provided mainly by micro-alloying + TMCP. For exact values, the product inspection certificate (EN 10204 3.1) should be consulted.
S690QL vs S700MC — Frequently Asked Questions
Which is stronger, S690QL or S700MC?
Their yield strengths are almost equal: S690QL ≥ 690 MPa, S700MC ≥ 700 MPa. The 10 MPa difference is not decisive in practice. The real difference is hidden in thickness:
- S690QL retains its high strength in thick sections (120 mm and above).
- S700MC, on the other hand, is generally produced in thin sheet below roughly 12 mm.
So the answer to "which is stronger" depends on the section: in thick sections S690QL, in thin sheet S700MC is the more correct practical choice.
Which should be preferred for thin sheet?
For thin sheet (approximately below 12 mm), S700MC is preferred. Thermomechanical rolling provides economical production, a smooth surface and superior formability in thin sections. S690QL is typically suitable for thick plate of 8 mm and above; in very thin sections it loses the Q+T advantage and is generally not available in stock in this range either.
Which is more suitable for bending?
For bending and cold forming, S700MC is markedly superior:
- S700MC: min. inner bending radius ≈ 1.5–2 × t, suitable for complex geometry.
- S690QL: min. inner bending radius ≈ 3–4 × t, more limited.
Thanks to its low carbon content and fine grain structure, S700MC can be bent at smaller radii without cracking. For heavily bent, profile-type parts, S700MC is recommended.
Are both weldable?
Yes, both are weldable; the difference is in the degree of difficulty:
- S700MC: Thanks to its low CEV (0.35–0.41) it mostly requires no preheating and welds easily. The only caution: excessive heat input must be avoided, otherwise the mechanical properties gained with TMCP may decrease.
- S690QL: Due to its higher CEV (~0.65) it requires 100–200 °C preheating depending on thickness, low-hydrogen (H5) electrodes and a max. ~250 °C interpass temperature.
When the two materials are welded together, the procedure of S690QL, which has the higher CEV, is taken as the basis.
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