Steel Q550
GB Q550
Q550 is a 550 MPa-class low-alloy structural steel plate from the GB/T high-strength family, supplied thermomechanically rolled (M), quenched and tempered (Q) or normalized, with D, C, E and F impact qualities for low-temperature service.
Reference datasheet — Q550 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the M-D condition
Q550 tempers and conditions
Q550 is supplied in 7 conditions, soft to hard. M-D is the default FabDigit quotes; the values on this page are for it.
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 |
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 |
Supply forms, finishes and certifications
Ways Q550 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
Q-E | Q550QE | Certification |
What is Q550?
Q550 is a 550 MPa-class low-alloy structural steel plate from the GB/T high-strength family, supplied thermomechanically rolled (M), quenched and tempered (Q) or normalized, with D, C, E and F impact qualities for low-temperature service. Engineers use it to cut section weight in welded machinery structures; typical plate values are 590 MPa yield, 730 MPa tensile, 18 % elongation and about 225 HB. Elongation and cold bendability are lower than Q355 or Q460, hot forming above ~600 °C destroys the delivered TMCP or Q&T condition, and the steel has no atmospheric corrosion resistance. Q690 is the next step up when more strength is needed. Q550 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). Q550 has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 76% of steel grades. Elongation at break is 18% and the elastic modulus is 210 GPa (30.5 Msi).
What is Q550 used for?
- excavator booms
- heavy equipment frames
- cranes
Advantages
- High strength — 590 MPa (85.6 ksi), better than 76% 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 properties
Typical room-temperature values for Q550-M-D; bars are the position among steel grades.
Physical3
Q550 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 has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 76% of steel grades. Elongation at break is 18% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
Q550 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 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 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's machinability is fair (45/100, worse than 65% of steel grades); weldability very good (72/100); formability fair (52/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. Q550 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Q550
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
How much does Q550 cost?
Q550 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Q550 — frequently asked
What is Q550 used for?
Q550 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?
Q550 has a typical yield strength of 590 MPa (85.6 ksi) and a tensile strength of 730 MPa (106 ksi) — stronger than 76% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is Q550 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 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?
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 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?
Q550 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.
How much does Q550 cost?
Q550 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.