1. Ievads
ASTM A36 is the standard specification for a low-carbon structural steel widely used for plates, formas, bars and welded components in building and general structural applications.
It is valued for predictable, ductile mechanical properties, excellent weldability and broad availability in many product forms.
A36 oglekļa tērauds is not a high-strength alloy — its appeal lies in economy, robust toughness at ambient temperatures, un izgatavošanas vieglums.
Designers must account for its relatively modest yield strength, basic corrosion behavior (unprotected mild steel will rust) and limited hardenability when deciding whether A36 is the right material for a component or structure.
2. What is ASTM A36 Carbon Steel?
ASTM A36 is the most common specification for a low-carbon, structural steel grade used in general construction and fabrication.
It is a hot-rolled, mild steel designed to provide predictable, ductile mechanical behaviour, easy weldability and wide availability in plates, formas, bars and other mill products used for building frames, tilti, machinery bases and general structural fabrication.
Why the name matters
The designation “A36” comes from the ASTM specification under which the material is standardized (ASTM A36/A36M).
The number “36” refers to the nominal minimum yield strength in ksi (36 ksi ≈ 250 MPA) that the material must meet in its as-rolled condition.
That single metric is one reason A36 is often treated as the default structural steel in many regions and industries.
Common product forms:
- Hot-rolled plates (thicknesses from a few millimetres to 150+ mm)
- Structural shapes (Es, H, C, U sections), angles and channels
- Stieņi: ap, square and flat (for machining and forging blanks)
- Rolled coils and sheet (limited thickness range)
3. Chemical composition of ASTM A36 Carbon Steel
| Elements | Parasti diapazons (wt.%) — indicative |
| Ogleklis (C) | ≤ ~0.25–0.29 (ar zemu oglekļa saturu) |
| Mangāns (Nojaukšanās) | ~0.60–1.20 |
| Fosfors (Pūtīt) | ≤ 0.04 (maksimums) |
| Sērs (S) | ≤ 0.05 (maksimums) |
| Silīcijs (Un) | ≤ 0.40 - 0.50 (izsekot) |
| Varš, Iekšā, Krekls, Noplūde | residual or low ppm levels |
4. Mechanical Properties of ASTM A36 Carbon Steel
Values shown are representative for hot-rolled, as-rolled ASTM A36. Actual properties depend on section thickness, rolling practice and heat chemistry.
| Īpašums | Tipisks / Minimum value | Piezīmes |
| Minimum yield strength (RP0.2) | 36 ksi (≈ 250 MPA) | Basis of the A36 designation; use as minimum yield for preliminary structural design unless MTR shows higher value. |
| Stiepes izturība (Rm) | 58 - 80 ksi (≈ 400 - 550 MPA) | Range varies with product form and thickness; confirm exact value on MTR. |
| Pagarināšana | ≥ 20% (iekšā 2 iekšā / 50 MM mērītāja garums) | Indicates good ductility; elongation decreases with increasing thickness. |
| Elastības modulis (E) | ≈ 200 GPA (29,000 ksi) | Standard structural steel value used for stiffness and deflection calculations. |
Shear modulus (Gan) |
≈ 79 GPA (11,500 ksi) | Used for torsion and shear deformation calculations. |
| Poisson’s ratio (n) | ≈ 0.28 | Typical value for low-carbon structural steels. |
| Brinela cietība (HBW) | ~120 – 160 HBW | Indicative range for as-rolled condition; correlates with tensile strength. |
| Charpy impact toughness | Not specified by ASTM A36 | Impact toughness is not mandatory; specify CVN testing if low-temperature or fracture-critical service is expected. |
5. Fizisks & Thermal Properties of ASTM A36 Carbon Steel
Numbers given are representative tipisks values at or near room temperature unless noted otherwise — actual values depend on chemistry, rolling/homogenization history and temperature.
| Īpašums | Tipiska vērtība (pārstāvis) | Praktiska piezīme |
| Blīvums | ≈ 7.85 g · cm⁻³ (7850 kg·m⁻³) | Use for mass, inertia and structural weight calculations. |
| Siltumvadītspēja, kandids | ≈ 50–60 W·m⁻¹·K⁻¹ (≈54 W·m⁻¹·K⁻¹ commonly quoted at 20–25 °C) | Conductivity falls with rising temperature; important for heat-flow, cooling and quench design. |
| Īpatnējā siltuma jauda, cp | ≈ 460–500 J·kg⁻¹·K⁻¹ (izmantot ≈ 470 J·kg⁻¹·K⁻¹ as a practical value at 20–25 °C) | cp increases with temperature; governs energy required to heat/cool sections. |
| Termiskā difūzija, α = k/(ρ·cp) | ≈ 1.4–1.6 × 10⁻⁵ m²·s⁻¹ (using k = 54, ρ = 7850, cp = 470 → α ≈ 1.46×10⁻⁵) | Controls how fast temperature changes penetrate the material (transient thermal response). |
| Coefficient of linear thermal expansion, αL | ≈ 11.7–12.5 × 10⁻⁶ K⁻¹ (tipisks: 12×10⁻⁶ K⁻¹) | Use for thermal growth calculations and joint clearances. |
Kušanas diapazons (apm.) |
Solidus ≈ 1425 ° C; Liquidus ≈ 1540 ° C | Melt/solidus ranges vary slightly with composition. Not used for normal structural design. |
| Emissivity (surface-dependent) | 0.1 - 0.95 (typical oxidized steel ≈ 0.7–0,9; bright polish ≈ 0.05–0,2) | Use for radiative heat-transfer models; always pick emissivity consistent with surface finish and oxidation state. |
| Elektriskā pretestība (ciets) | ≈ 0.10 - 0.20 μω · m (≈ 1.0–2.0 ×10⁻⁷ Ω·m) | Varies with chemistry and temperature; affects electrical heating and eddy-current losses. |
| Magnetic behaviour | Feromagnētisks below Curie point (~770 °C for iron) | Magnetic properties influence NDT (MPI) and induction heating behavior. |
6. Fabrication behavior: veidošanās, machining and cold work
Veidošanās (cold & karsts):
- A36 hot-rolled products form well by bending, rolling and simple drawing.
- Auksta formēšana (saliekšana, apzīmogošana) is practical within design limits — ensure bend radii and reduction limits match material thickness and temper to avoid cracking.
Typical minimum bend radii are recommended in forming tables and depend on thickness and mill condition.
Apstrāde:
- A36 machines easily with conventional carbon and carbide tooling. Machinability is comparable to other mild steels; standard speeds and feeds apply.
Heavy chip loads, deep interrupted cuts and poor coolant can work-harden surfaces and reduce tool life.
Cold work effects:
- Cold bending or drawing increases yield locally by strain hardening; subsequent stress-relief anneal is possible if ductility must be restored.
7. Metināšana un pievienošanās
Metināmība: Lielisks. Low carbon content and limited alloying make A36 readily weldable with all common fusion and solid-state techniques (Smirdēt, Gtaw, GMAW/MIG, Fcaw).
Filler metal selection:
- Common consumables: mild steel filler rods/wires (Piem., ER70S series for GMAW, E7018 or E7016 for SMAW) matched for strength and ductility.
Choose consumables that deliver ductile, crack-resistant weld metal.
Preheat and interpass:
- For typical plate thicknesses (<25 mm) and benign environments, no preheat is usually required. For thicker sections, restrained joints, or cold ambient conditions, modest preheat (Piem., 50–150 °F / 10-65 °C) reduces hydrogen cracking risk and residual stresses.
Interpass temperature controls are essential for multi-pass welds.
Pēc termiņa (Phwht):
- Not required for most A36 welded assemblies. PWHT may be used to reduce residual stress or when weld procedure qualification demands it (pressure or fatigue critical components), but A36 lacks hardenability;
PWHT generally involves stress-relief annealing (Piem., ~600–650 °C) rather than hardening.
8. Termiskā apstrāde: capabilities and limits for A36
ASTM A36 is not a heat-treatable alloy in the sense of quench & temper hardening (low carbon and lack of alloying impede martensitic transformation).
Typical thermal treatments:
- Rūdīšana / Normalizēšana: possible to refine grain and restore ductility after heavy cold work or welding. Annealing temperatures typically ~ 700–900 °C depending on thickness and desired effect.
- Stresa mazināšanas rūdīšana: zema temperatūra (~ 550–650 ° C) to reduce residual weld stresses.
- Dzēst & rūdījums: not effective for significant strength increase because of low carbon/hardenability; quenching yields limited hardening and substantial distortion.
Dizaina nozīme: do not rely on heat treatment to raise yield strength; choose a higher-strength steel if greater allowable stresses are needed.
9. Corrosion behaviour and surface protection strategies
Intrinsic corrosion: A36 is unalloyed carbon steel and will corrode (form iron oxide) when exposed to moisture and oxygen. Rate depends on environment (mitrums, salts, pollutants).
Aizsardzības stratēģijas:
- Paint systems: gruntējums + virsmas (epoksīda, poliuretāns) are economical for atmospheric protection.
Surface prep (abrasive blast to Sa 2½, SSPC SP10) improves adhesion and longevity. - Cinkojošs: karstā cinkošana (HDG) gives sacrificial protection; commonly used for exterior structural members, fasteners and components exposed to weather.
- Katodiskā aizsardzība: used for submerged or buried structures (pārklājumi + upurēšanas anodi).
- Corrosion allowances: specify thickness allowances and inspection schedules in aggressive environments.
Uzturēšana: periodic inspection and touch-up are critical for long service life—coating failure allows localized corrosion and pitting.
10. Typical Applications of ASTM A36 Steel
A36 is the default choice where economy, availability and fabrication simplicity are priorities. Tipiskas lietojumprogrammas ietver:
- Building structures: sijas, kolonnas, plates and bracing
- Tilti (non-high-strength components), walkways, platforms
- General fabrication: rāmji, atbalsts, trailers
- Machinery bases, apvalki, non-pressure components
- Fittings and welded assemblies where ductility and weldability are essential
11. Priekšrocības & Limitations of ASTM A36 Carbon Steel
Galvenās priekšrocības
- Rentabilitāte: Lowest cost among structural steels (30-40% cheaper than HSLA steels like A572 Gr.50, 70-80% cheaper than stainless steel 304).
- Superior weldability: Eliminates preheating for thin sections, reducing manufacturing time and cost.
- Excellent processability: Easy to form, mašīna, and forge, suitable for both simple and complex components.
- Broad availability: Global supply chain, with diverse product forms (šķīvji, stieņi, formas, BIGNIEKUMI) and sizes.
- Līdzsvarots spēks: Meets most structural requirements (statiskas kravas, low dynamic loads) without over-engineering.
Galvenie ierobežojumi
- Poor corrosion resistance: Requires surface protection for outdoor or corrosive environments; not suitable for marine/chemical applications without coating.
- Limited low-temperature toughness: Unmodified A36 is brittle below 0°C, not recommended for cryogenic applications (Piem., Arctic structures).
- Neapmierināms: Cannot be significantly strengthened via heat treatment (max tensile strength ~550 MPa); insufficient for high-stress components.
- Lower fatigue resistance: Not ideal for high-cycle dynamic loads (Piem., automobiļu motora detaļas) – use HSLA or alloy steels instead.
12. Standard Compliance & International Equivalents
ASTM A36 is globally recognized, with equivalent standards in major industrial regions, ensuring cross-border compatibility:
| Reģions | Equivalent Standard | Pakāpes apzīmējums | Galvenās atšķirības |
| Eiropa | Iekšā 10025-2:2004 | S235JR | Lower yield strength (235 MPA vs. 250 MPa for A36 ≤19 mm); similar ductility and weldability. |
| Ķīna | GB/T 700-2006 | Q235B | Peļņas izturība 235 MPA; phosphorus/sulfur limits stricter (≤0.045% vs. A36’s 0.040% Pūtīt, 0.050% S). |
| Japāna | JIS G3101:2015 | SS400 | No specified yield strength (stiepts 400-510 MPA); equivalent for structural applications. |
| Indija | Ir 2062:2011 | E250A | Peļņas izturība 250 MPA; compatible with A36 in construction and machinery. |
13. Comparative analysis — A36 vs. higher-strength structural steels
| Aspekts | A36 (bāzes līnija) | A572 Gr 50 (HSLA) | A992 (konstrukcijas formas) | A514 (Ņurds&T high-strength plate) |
| Metallurgical class | Low-carbon mild steel (hot-rolled) | Lielas izturības, zema sakausējuma (HSLA) | Structural HSLA with controlled chemistry for shapes | Apslāpēts & rūdīts, high-strength alloyed plate |
| Typical minimum yield | 36 ksi (≈250 MPa) | 50 ksi (≈345 MPa) | 50 ksi (≈345 MPa) | 100 ksi (≈690 MPa) |
| Typical tensile range | 58–80 ksi (≈400–550 MPa) | 60–80 ksi (≈415–550 MPa) | 60–80 ksi (≈415–550 MPa) | ~110–140 ksi (≈760–965 MPa) (mainās atkarībā no pakāpes) |
| Pagarināšana | ≥ ~20% (depends on thickness) | ~18–22% (sadaļa atkarīga) | ~18–22% | Lower — often ~10–18% (section and heat dependent) |
| Metināmība (shop) | Lielisks; common consumables | Ļoti labs; similar practice to A36 | Ļoti labs; specified for building columns/beams | More demanding — welding must be controlled; preheat/interpass and qualified WPS often required |
Heat treatment capability |
Not heat-treatable for strength | Not intended for quench/temper; strengthened by chemistry/thermomechanical processing | Not heat-treatable for strengthening | Heat-treated (Ņurds&T) — strength obtained via quench & rūdījums |
| Izturība / low-temperature behavior | Good for general service; specify CVN if required | Improved toughness over A36 (depending on spec) | Good — specified chemistry for structural sections and controlled toughness | Can have good toughness if specified, but requires control; risk of brittle behaviour if not properly supplied/treated |
| Formīgums & auksts darbs | Good forming characteristics | Labi, but greater springback; less ductile than A36 | Good for gross forming of shapes | Limited — formability poor compared with A36/A572; cold forming not recommended for full-strength use |
Useable plate/shape thickness ranges |
Plašs, standard mill stock | Plašs; commonly available in plate and shapes | Primarily wide-flange shapes and beams | Typically heavy plate (biezākas sekcijas) for high-stress components |
| Tipiskas lietojumprogrammas | General structural frames, iekavas, non-critical members | Tilti, building members, structural sections where higher allowable stress reduces weight | Wide-flange beams/columns in buildings — industry standard for structural shapes | High-strength machine frames, excavation equipment, highly stressed structural members |
| Relatīvās materiālu izmaksas | Zems (most economical) | Mērens | Mērens (similar to A572) | Augsts (premium for high strength and Q&T processing) |
| Design tradeoffs | Zemas izmaksas, simple fabrication but heavier sections | Weight saving, higher allowable stress, modest extra fabrication control | Optimized for building steelwork (section tolerances, flange geometry) | Major weight reduction possible but requires careful welding/fabrication and NDE |
14. Dzīves cikls, maintenance and recyclability
Service life: With standard paint systems and maintenance, A36 structural components commonly last decades in moderate atmospheres. Corrosive or marine environments require higher maintenance or galvanizing.
Remonts & uzturēšana: Weld repair is straightforward. Structural inspections, corrosion monitoring and timely recoating extend life.
Pārstrāde: Steel is highly recyclable (one of the most recycled engineering materials). A36 scrap is readily consumed in electric arc furnaces (Eafs) or integrated mills; specifying recycled content is feasible.
15. Secinājums
ASTM A36 mild/low carbon steel remains a cornerstone material for general structural steelwork because it combines economy, predictable ductile properties and straightforward fabrication.
It is the right choice when loads and environmental conditions match its design envelope and when fabrication simplicity and cost are dominant drivers.
Tomēr, when higher allowable stresses, larger spans, svara samazināšana, improved low-temperature toughness or superior corrosion resistance are required, engineers should evaluate higher-strength structural steels, HSLA alloys, weathering steels or corrosion-resistant alloys as appropriate.
