Steel Q550 M-C
Certified grade
GB Q550
M-C = q550MC
Lowest-cost quality class of the TMCP plate; use only for indoor or mild-climate structures.
Values for the M-C condition
Other Q550 tempers and conditions
Q550 is listed in 7 conditions; see the grade overview at Q550.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Normalized | Legacy normalized supply for sections and older drawings; strength falls off faster with thickness than TMCP or Q&T. | 575 | 700 | 17 | 18 HRC | 7.8 % IACS |
M-CThis page Q550MC | Lowest-cost quality class of the TMCP plate; use only for indoor or mild-climate structures. | 585 | 730 | 18 | 20 HRC | 7.5 % IACS |
M-DDefault Q550MD | The standard stocked plate condition: TMCP-rolled, low carbon equivalent, good weldability, guaranteed 34 J at -20 °C. | 590 | 730 | 18 | 20 HRC | 7.5 % IACS |
Q550ME | Cold-region grade for cranes, mining equipment and bridges exposed to -40 °C service. | 595 | 730 | 19 | 21 HRC | 7.5 % IACS |
Q550MF | Extra-low-temperature quality class (special order) for polar/high-altitude equipment. | 600 | 735 | 19 | 21 HRC | 7.4 % IACS |
Q550QD | Q&T route (GB/T 16270) for thick plate (>40–100 mm) where TMCP cannot hold 550 MPa through-thickness. | 600 | 700 | 18 | 20 HRC | — |
Q550QF | Special-order Q&T plate with the deepest low-temperature toughness guarantee. | 610 | 705 | 18 | 19 HRC | 7.2 % IACS |
What is Q550 M-C?
Q550 M-C is Q550 in a M-C certified grade — lowest-cost quality class of the TMCP plate; use only for indoor or mild-climate structures. Q550 M-C has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 75% of steel grades. Elongation at break is 18% and the elastic modulus is 210 GPa (30.5 Msi). Q550 M-C has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). M-D is the default condition FabDigit quotes; M-C is available on request or by drawing note.
Advantages
- High strength — 585 MPa (84.8 ksi), better than 75% of steel grades
- Readily welded — 72/100, better than 75% of steel grades
Limitations
- Hard to polish — 45/100, worse than 84% of steel grades
Q550 M-C properties
Typical room-temperature values for Q550 M-C; 24 are specific to this condition. Other listed values are Q550 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Q550 M-C has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical17
Q550 M-C has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 75% of steel grades. Elongation at break is 18% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
Q550 M-C is rated for continuous service to 350°C (662 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Q550 M-C conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of Q550 M-C takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 25%.
Manufacturability5
Q550 M-C's machinability is fair (45/100, worse than 65% of steel grades); weldability very good (72/100); formability fair (52/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Q550 M-C
Is Q550 easy to machine?
Machines like a 220 HB low-alloy steel — use coated carbide, rigid setups and moderate speeds (~90–130 m/min turning); expect ~50 % of 1212 tool life and springy, stringy chips.
Can Q550 be welded?
Good weldability at CEV ≤0.65 — use low-hydrogen consumables (E/ER 69-class), control heat input to ~1.0–2.5 kJ/mm to avoid HAZ softening, and preheat 80–150 °C for plate over ~25 mm.
Can Q550 be formed, bent or molded?
Cold bend with radius ≥2–3 t transverse to the rolling direction; hot forming above ~600 °C destroys the TMCP/Q&T strength unless the plate is re-heat-treated.
What surface finishes work on Q550?
No inherent corrosion resistance: blast to Sa 2.5 and apply zinc-rich epoxy primer, hot-dip galvanize (watch for hydrogen and distortion in high-strength plate) or metallize.
Q550 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C≤0.18 % for TMCP (M) delivery; ≤0.20 % for Q&T (Q) plate | ≤ 0.18 | 0.1 |
| Si | ≤ 0.6 | 0.3 |
| Mn | ≤ 2 | 1.6 |
| P≤0.025 for E, ≤0.020 for F quality | ≤ 0.03 | 0.02 |
| S≤0.020 for E, ≤0.010 for F quality | ≤ 0.03 | 0.01 |
| Nbmicro-alloy | ≤ 0.11 | 0.05 |
| Vmicro-alloy | ≤ 0.12 | 0.05 |
| Timicro-alloy / N fixing | ≤ 0.2 | 0.02 |
| Crhardenability, higher in Q&T plate | ≤ 1 | 0.3 |
| Nitoughness | ≤ 0.8 | 0.3 |
| Cu | ≤ 0.8 | 0.2 |
| Mo | ≤ 0.3 | 0.2 |
| BQ&T grades only | ≤ 0 | 0 |
| N | ≤ 0.02 | 0.01 |
| Alacid-soluble Als ≥0.015 % | ≥ 0.02 | 0.03 |
| Fe | balance | — |
Q550 M-C — frequently asked
What is Q550 M-C used for?
Q550 M-C is typically used for excavator booms, heavy equipment frames and cranes. In short: weight-saving 550 MPa-class plate; step above Q460 strength; TMCP or Q&T supply.
What is the yield strength of Q550 M-C?
Q550 M-C has a typical yield strength of 585 MPa (84.8 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 75% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is Q550 M-C easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machines like a 220 HB low-alloy steel — use coated carbide, rigid setups and moderate speeds (~90–130 m/min turning); expect ~50 % of 1212 tool life and springy, stringy chips.
Can Q550 M-C be welded?
Yes — weldability is rated very good (72/100). Good weldability at CEV ≤0.65 — use low-hydrogen consumables (E/ER 69-class), control heat input to ~1.0–2.5 kJ/mm to avoid HAZ softening, and preheat 80–150 °C for plate over ~25 mm.
What surface finishes work on Q550 M-C?
No inherent corrosion resistance: blast to Sa 2.5 and apply zinc-rich epoxy primer, hot-dip galvanize (watch for hydrogen and distortion in high-strength plate) or metallize.
Can Q550 M-C be formed, bent or molded?
Cold bend with radius ≥2–3 t transverse to the rolling direction; hot forming above ~600 °C destroys the TMCP/Q&T strength unless the plate is re-heat-treated.
What is the maximum service temperature of Q550 M-C?
Q550 M-C is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Q550 M-D and Q550 Q-F?
M-D is the default condition — the standard stocked plate condition: TMCP-rolled, low carbon equivalent, good weldability, guaranteed 34 J at -20 °C. Q-F: special-order Q&T plate with the deepest low-temperature toughness guarantee. Yield strength is 590 MPa in M-D versus 610 MPa in Q-F.
Sources
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.13B: Corrosion — Materials — ASM International (2005)
- High-strength structural plate datasheets (Baosteel / Ansteel / Nanjing Iron & Steel) — Chinese mills (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.