Steel Mild Steel-SR (Stress relieved)
Heat-treated state
Use to stabilise dimensions of welded or heavily machined mild-steel assemblies with minimal loss of strength.
Values for the SR condition
Other Mild Steel tempers and conditions
Mild Steel is listed in 7 conditions; see the grade overview at Mild Steel.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Use when maximum ductility for severe forming, deep drawing or spinning is needed, or to relieve prior cold work. | 210 | 340 | 38 | 100 HB | — |
Cold rolled | Pick for thin sheet needing a clean bright surface, tight thickness tolerance and good deep-draw/bend behaviour. | 240 | 350 | 32 | 110 HB | — |
HRDefault Hot rolled | Default, cheapest form for structural plate, sections and hot-rolled bar where mill scale and loose tolerances are acceptable. | 250 | 400 | 24 | 120 HB | — |
Normalized | Choose for uniform fine-grain structure and consistent toughness in thicker plate, forgings and weldments. | 260 | 420 | 28 | 125 HB | — |
SRThis page Stress relieved | Use to stabilise dimensions of welded or heavily machined mild-steel assemblies with minimal loss of strength. | 280 | 400 | 24 | 120 HB | 10.8 % IACS |
Cold drawn | Best pick for machined shafts and fixture parts: bright surface, tight diameter tolerance and ~40 % higher yield than hot-rolled. | 370 | 440 | 15 | 130 HB | — |
Carburized & quenched | Pick when a mild-steel part needs a wear-resistant surface (gears, pins, bushings) while keeping a tough low-carbon core. | 380 | 550 | 12 | 60 HRC | 10 % IACS |
What is Mild Steel-SR?
Mild Steel-SR is Mild Steel heat treated to SR — use to stabilise dimensions of welded or heavily machined mild-steel assemblies with minimal loss of strength. Mild Steel-SR has a yield strength of 280 MPa (40.6 ksi) and a tensile strength of 400 MPa (58 ksi) — weaker than 90% of steel grades. Elongation at break is 24% and the elastic modulus is 200 GPa (29 Msi). Mild Steel-SR 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; SR is available on request or by drawing note.
Advantages
- Readily welded — 95/100, better than 97% of steel grades
- High electrical conductivity — 10.8 % IACS, better than 94% of steel grades
- Forms and bends easily — 80/100, better than 93% of steel grades
- Conducts heat well — 51 W/m·K (29.5 BTU/hr·ft·°F), better than 92% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
Limitations
- Low strength — 280 MPa (40.6 ksi), worse than 90% of steel grades
Mild Steel-SR properties
Typical room-temperature values for Mild Steel-SR; 22 are specific to this condition. Other listed values are Mild Steel reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Mild Steel-SR 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-SR has a yield strength of 280 MPa (40.6 ksi) and a tensile strength of 400 MPa (58 ksi) — weaker than 90% of steel grades. Elongation at break is 24% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
Mild Steel-SR 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-SR conducts electricity at 10.8 % IACS, better than 94% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of Mild Steel-SR 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-SR's machinability is good (62/100, better than 89% of steel grades); weldability excellent (95/100); formability very good (80/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Mild Steel-SR
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-SR — frequently asked
What is Mild Steel-SR used for?
Mild Steel-SR 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-SR?
Mild Steel-SR has a typical yield strength of 280 MPa (40.6 ksi) and a tensile strength of 400 MPa (58 ksi) — weaker than 90% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is Mild Steel-SR easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% 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-SR be welded?
Yes — weldability is rated excellent (95/100). 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-SR?
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-SR 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-SR?
Mild Steel-SR 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-SR?
Yes — Mild Steel-SR 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.