Steel Mild Steel · heat-treated state
Steel Mild Steel CARB
Properties of the CARB condition, compared with the other Mild Steel tempers.
Pick when a mild-steel part needs a wear-resistant surface (gears, pins, bushings) while keeping a tough low-carbon core.
What is Mild Steel CARB?
Mild Steel CARB is Mild Steel heat treated to CARB — pick when a mild-steel part needs a wear-resistant surface (gears, pins, bushings) while keeping a tough low-carbon core. Mild Steel CARB has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 67% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi). Mild Steel CARB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,495°C (2,723 °F). HR is the default condition FabDigit quotes; CARB is available on request or by drawing note.
Advantages
- High electrical conductivity — 10.8 % IACS, better than 94% of steel grades
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
Limitations
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited formability — 10/100, worse than 94% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
Mild Steel CARB properties
Typical room-temperature values for Mild Steel CARB — 9 properties are specific to this condition; the rest are grade-level values shared by every Mild Steel temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
Mild Steel CARB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,495°C (2,723 °F).
Mechanical16
Mild Steel CARB has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 67% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
Mild Steel CARB is rated for continuous service to 400°C (752 °F). It conducts heat at 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
Mild Steel CARB conducts electricity at 10.8 % IACS, better than 94% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 87% of steel grades.
Sustainability4
Producing a kilogram of Mild Steel CARB takes about 25 MJ of energy and emits 2.1 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
Mild Steel CARB's machinability is poor (15/100, worse than 98% of steel grades); weldability poor (30/100); formability not recommended (10/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Mild Steel tempers and conditions
Mild Steel is also supplied in 7 other conditions. The full side-by-side table is on the Mild Steel overview.
- HRDefaultDefault, cheapest form for structural plate, sections and hot-rolled bar where mill scale and loose tolerances are acceptable.250 MPa yield · 120 HB
- CARBPick when a mild-steel part needs a wear-resistant surface (gears, pins, bushings) while keeping a tough low-carbon core.380 MPa yield · 60 HRC
- CDBest pick for machined shafts and fixture parts: bright surface, tight diameter tolerance and ~40 % higher yield than hot-rolled.370 MPa yield · 130 HB
- NChoose for uniform fine-grain structure and consistent toughness in thicker plate, forgings and weldments.260 MPa yield · 125 HB
- HDGChoose for outdoor or damp service where painting is impractical; zinc coating gives sacrificial protection for decades.250 MPa yield
- CRPick for thin sheet needing a clean bright surface, tight thickness tolerance and good deep-draw/bend behaviour.240 MPa yield · 110 HB
- ANNUse when maximum ductility for severe forming, deep drawing or spinning is needed, or to relieve prior cold work.210 MPa yield · 100 HB
Working with Mild Steel CARB
Is Mild Steel easy to machine?
Easy but gummy in the annealed/hot-rolled state — use positive-rake tools, moderate speeds and flood coolant; cold-drawn bar chips and finishes noticeably better.
Can Mild Steel be welded?
Excellent by SMAW/GMAW/FCAW/TIG/resistance with no preheat below ~25 mm (CE typically <0.35); use E7018/ER70S-6 filler and remove mill scale, galvanizing or oil first.
Can Mild Steel be formed, bent or molded?
Very good cold formability — bends to 1t–2t radii, deep-draws in Al-killed CR sheet; hot forge 1050–1250 °C, allow springback and grain-direction effects.
What surface finishes work on Mild Steel?
Not anodizable; protect with zinc plating, hot-dip galvanizing, phosphate + paint/powder coat, black oxide or oil, since bare surfaces flash-rust within hours in humid air.
Mild Steel 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≤0.26 % for A36 plate; 0.14–0.22 % for Q235/1018 | 0.05 – 0.25 | 0.18 |
| Mn | 0.25 – 1.2 | 0.6 |
| Si≤0.05 % in Al-killed CR sheet | 0 – 0.4 | 0.2 |
| P | ≤ 0.05 | 0.02 |
| S | ≤ 0.05 | 0.03 |
| Curesidual; 0.20 % min if copper-bearing specified | ≤ 0.35 | 0.1 |
| Fe | balance | — |
Mild Steel CARB — frequently asked
What is Mild Steel CARB used for?
Mild Steel CARB is typically used for welded frames and weldments, machine brackets and mounting plates, sheet metal enclosures and chassis, structural beams, base plates and gussets, laser-cut and formed panels and ducting and guarding. In short: workhorse mild-steel plate.
What is the yield strength of Mild Steel CARB?
Mild Steel CARB has a typical yield strength of 380 MPa (55.1 ksi) and a tensile strength of 550 MPa (79.8 ksi) — weaker than 67% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is Mild Steel CARB easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Easy but gummy in the annealed/hot-rolled state — use positive-rake tools, moderate speeds and flood coolant; cold-drawn bar chips and finishes noticeably better.
Can Mild Steel CARB be welded?
Not readily — weldability is rated poor (30/100). Excellent by SMAW/GMAW/FCAW/TIG/resistance with no preheat below ~25 mm (CE typically <0.35); use E7018/ER70S-6 filler and remove mill scale, galvanizing or oil first.
What surface finishes work on Mild Steel CARB?
Not anodizable; protect with zinc plating, hot-dip galvanizing, phosphate + paint/powder coat, black oxide or oil, since bare surfaces flash-rust within hours in humid air.
Can Mild Steel CARB be formed, bent or molded?
Very good cold formability — bends to 1t–2t radii, deep-draws in Al-killed CR sheet; hot forge 1050–1250 °C, allow springback and grain-direction effects.
What is the maximum service temperature of Mild Steel CARB?
Mild Steel CARB is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Mild Steel-HR and Mild Steel CARB?
HR is the default condition — default, cheapest form for structural plate, sections and hot-rolled bar where mill scale and loose tolerances are acceptable. CARB: pick when a mild-steel part needs a wear-resistant surface (gears, pins, bushings) while keeping a tough low-carbon core. Yield strength is 250 MPa in HR versus 380 MPa in CARB.
Can FabDigit make parts in Mild Steel CARB?
Yes — Mild Steel CARB is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A36/A36M — Carbon Structural Steel — ASTM International (2019)
- GB/T 700 — (Q195–Q275) — SAC (2006)
- EN 10025-2 — Non-alloy structural steels (S235JR) — CEN (2019)
- ASTM A1008/A1008M — Cold-Rolled Carbon Steel Sheet — ASTM International (2021)
- ASTM A108 / A29 — Cold-Finished and Hot-Wrought Carbon Steel Bars — ASTM International (2018)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- worldsteel LCI data for steel products — World Steel Association (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.