Steel grades are classified by carbon content, alloy additions, and intended service — cutting, structural, engineering, or tooling. The three major designation systems used in Australian industry are AS 1442 / AS 1444 (Australian Standards for carbon and alloy steel bars), SAE/AISI (US numbering system, dominant globally), and ISO 683 / EN 10027 (European and international). Most grades map directly across systems: SAE 1045 ≈ AS 1442 K1045 ≈ EN C45.
Common Steel Grades at a Glance
Quick reference covering the grades most frequently encountered in AU industrial supply.
| SAE/AISI | AU Equivalent (AS) | Type | Carbon % | Key Properties | Common Use |
|---|---|---|---|---|---|
| 1018 | AS 1442 K1018 | Low-carbon | 0.15–0.20 | Weldable, easily machined, cold-formable | General fabrication, shafts, mild steel fasteners |
| 1020 | AS 1442 K1020 | Low-carbon | 0.18–0.23 | Structural, good weldability | Structural sections, case-hardened parts |
| 1045 | AS 1442 K1045 | Medium-carbon | 0.43–0.50 | Heat-treatable, higher strength | Shafts, axles, gears, couplings |
| 1144 | — | Free-machining medium-carbon | 0.40–0.48 | Best machinability of carbon steels (S-added) | Threaded studs, machined parts, turned components |
| 4140 | AS 1444 4140 | Chromium-molybdenum alloy | 0.38–0.43 | High strength, tough, heat-treatable | Gears, axles, bolts, hydraulic shafts |
| 4340 | AS 1444 4340 | Nickel-chromium-moly alloy | 0.38–0.43 | Very high strength, excellent toughness | Crankshafts, heavy-duty axles, aircraft parts |
| 8620 | AS 1444 8620 | Case-hardening alloy | 0.18–0.23 | Tough core, hardenable case via carburising | Gears, camshafts, sprockets |
| 1095 | — | High-carbon | 0.90–1.03 | Hardenable, springy, abrasion-resistant | Springs, blades, hand tools, wear parts |
| D2 | — | Cold-work tool steel | 1.40–1.60 | High wear resistance, dimensionally stable | Dies, punches, shear blades, cold-forming |
| A2 | — | Air-hardening tool steel | 0.95–1.05 | Good toughness, air-hardens (minimal distortion) | Punches, knives, gauges, form tools |
| O1 | — | Oil-hardening tool steel | 0.90–1.00 | Good edge retention, oil-quench | Taps, reamers, small dies, woodworking tools |
| M2 | — | High-speed steel (HSS) | 0.85–0.90 | Red hardness to ~600 °C, holds cutting edge | Drill bits, end mills, taps, reamers |
| H13 | — | Hot-work tool steel | 0.32–0.45 | Thermal fatigue resistance, toughness at temperature | Die-casting dies, extrusion tooling, forging dies |
Carbon Steel — Low, Medium and High Carbon Grades
Carbon is the primary hardening element in steel. As carbon content rises, strength and hardenability increase, while weldability and ductility decrease. Australian Standards AS 1442:2007 (reconfirmed 2017) covers hot-rolled carbon steel bars, using the prefix 'K' followed by the SAE/AISI grade number (e.g. K1045).
Low-Carbon Steel (≤0.25% C) — Mild Steel
Low-carbon steels such as 1018 and 1020 are the workhorses of fabrication. They weld readily without preheat in most thicknesses, machine cleanly, and cold-form without cracking. Yield strength sits around 250–350 MPa depending on processing. They cannot be through-hardened to useful hardness but can be surface-hardened by carburising or flame hardening.
| Grade | C % | Mn % | Yield MPa (typ.) | Tensile MPa (typ.) | Elongation % | EN Equiv. |
|---|---|---|---|---|---|---|
| 1018 (AS K1018) | 0.15–0.20 | 0.60–0.90 | 310 | 440 | 25 | C20 / 1.0402 |
| 1020 (AS K1020) | 0.18–0.23 | 0.30–0.60 | 350 | 470 | 22 | C22 / 1.0402 |
| 1030 (AS K1030) | 0.28–0.34 | 0.60–0.90 | 400 | 530 | 20 | C30 / 1.0528 |
Medium-Carbon Steel (0.30–0.60% C)
Medium-carbon grades are the standard choice for shafts, gears, axles, and bolts. They respond well to quench-and-temper heat treatment, achieving tensile strengths of 600–900 MPa in the hardened condition. Weldability is reduced compared to mild steel — preheat is recommended for sections above 12 mm. The SAE 1144 free-machining variant adds sulphur (0.24–0.33%) to dramatically improve machinability at the cost of reduced toughness and weldability.
| Grade | C % | Mn % | Notes | EN Equiv. |
|---|---|---|---|---|
| 1040 (AS K1040) | 0.37–0.44 | 0.60–0.90 | General engineering, heat-treatable | C40 / 1.0511 |
| 1045 (AS K1045) | 0.43–0.50 | 0.60–0.90 | Most common shaft grade in AU supply | C45 / 1.0503 |
| 1060 (AS K1060) | 0.55–0.65 | 0.60–0.90 | Springs, rail clips, higher hardness | C60 / 1.0601 |
| 1144 | 0.40–0.48 | 1.35–1.65 | S 0.24–0.33% — free-machining; not for welding | — |
High-Carbon Steel (>0.60% C)
High-carbon grades harden to HRC 58–65 when quenched, making them suitable for springs, cutting edges, and wear surfaces. They are brittle compared to lower-carbon grades and require care during welding and machining. Grade 1095 is the standard high-carbon spring steel available in bar form; AS 1442 K1095 is the Australian equivalent.
| Grade | C % | Hardness (HRC, hardened) | EN Equiv. | Typical Use |
|---|---|---|---|---|
| 1075 | 0.70–0.80 | 55–60 | C75 / 1.0605 | Springs, blades |
| 1095 (AS K1095) | 0.90–1.03 | 62–65 | C101 / 1.1274 | Springs, knives, hand tools, saw blades |
Alloy Steel — When Carbon Steel Isn't Enough
Alloy steels add deliberate quantities of chromium, molybdenum, nickel, or vanadium to improve hardenability, strength, toughness, or a combination of these. Australian Standards AS 1444:2007 (reconfirmed 2017) covers hot-rolled alloy steel bars. The SAE 4xxx and 8xxx series are the most commonly stocked grades in AU industrial supply.
SAE 4140 — Chromium-Molybdenum (the workhorse alloy steel)
SAE 4140 (AS 1444 grade 4140 / EN 42CrMo4 / 1.7225) is the most widely used alloy steel in Australian industrial supply. It combines good hardenability with excellent strength-to-toughness balance. In the quenched-and-tempered (Q&T) condition at 315 °C temper, tensile strength is approximately 1,000 MPa. At 650 °C temper, it is around 655 MPa — trading strength for toughness. Carbon equivalent (CE) = approximately 0.75, so preheat to 150–260 °C is required for welding.
| Element | C | Mn | Cr | Mo | Si |
|---|---|---|---|---|---|
| Composition % | 0.38–0.43 | 0.75–1.00 | 0.80–1.10 | 0.15–0.25 | 0.15–0.35 |
Typical applications: hydraulic shafts, gears, bolts and studs (Grade 8.8 and above), automotive axles, crankshafts, mining equipment components.
SAE 4340 — Nickel-Chromium-Molybdenum (highest-strength common alloy steel)
SAE 4340 (AS 1444 grade 4340 / EN 36CrNiMo4 / 1.6511) delivers the highest strength of the commonly stocked alloy steels. The nickel addition (1.65–2.00%) dramatically improves toughness at high strength levels, preventing brittle fracture. It achieves tensile strengths of 980–1,470 MPa in Q&T condition. CE ≈ 0.90 — preheat above 230 °C is required.
| Element | C | Mn | Ni | Cr | Mo |
|---|---|---|---|---|---|
| Composition % | 0.38–0.43 | 0.60–0.80 | 1.65–2.00 | 0.70–0.90 | 0.20–0.30 |
Typical applications: crankshafts, aircraft landing gear, heavy-duty transmission shafts, highly loaded fasteners (Grade 10.9 / 12.9), motorsport components.
SAE 8620 — Nickel-Chromium-Molybdenum Case-Hardening Grade
SAE 8620 (AS 1444 grade 8620 / EN 20NiCrMo2 / 1.6523) is the standard case-hardening alloy steel. Its low carbon content (0.18–0.23%) ensures a tough, ductile core after carburising. The case, enriched to approximately 0.8% carbon during carburising, hardens to HRC 58–62 on quenching, producing a wear-resistant surface over a tough core — the ideal combination for gears, camshafts, and sprockets.
Tool Steel — D, A, O, M and H Series
Tool steels are high-alloy steels designed for cutting, forming, and measuring tools. They are classified by their primary alloying and hardening method per the AISI tool steel classification system, which is the globally dominant reference used in Australian tooling supply. Sutton Tools manufactures a range of HSS cutting tools in M-series grades — see the Sutton Tools collection and the carbide vs HSS guide for selection guidance.
D-Series — Cold-Work High-Chromium (Maximum Wear Resistance)
D-series tool steels contain 11–13% chromium and 1.4–2.3% carbon, giving them near-stainless corrosion resistance and outstanding wear resistance. They are used where long die life is more important than maximum impact toughness. They air-harden or oil-harden with minimal distortion.
| Grade | C % | Cr % | Mo % | V % | HRC (hardened) | EN Equiv. |
|---|---|---|---|---|---|---|
| D2 | 1.40–1.60 | 11.00–13.00 | 0.70–1.20 | 1.00 max | 58–62 | X153CrMoV12 / 1.2379 |
| D3 | 2.00–2.35 | 11.00–13.50 | — | 1.00 max | 60–64 | X210Cr12 / 1.2080 |
A-Series — Air-Hardening Medium-Alloy (Balanced Wear and Toughness)
A-series grades air-harden from austenitising temperature — no quench bath is needed. This produces minimal distortion, making them preferred for close-tolerance punches, gauges, and form tools. A2 is the most widely used grade.
| Grade | C % | Cr % | Mo % | HRC (hardened) | EN Equiv. |
|---|---|---|---|---|---|
| A2 | 0.95–1.05 | 4.75–5.50 | 1.00–1.30 | 58–62 | X100CrMoV5 / 1.2363 |
O-Series — Oil-Hardening (Good All-Round Tool Steel)
O1 is the classic general-purpose tool steel — the choice for taps, reamers, woodworking tools, and small dies where close dimensional tolerance is required after hardening. It is oil-quenched and gives a good combination of edge-holding and toughness at a lower cost than D or A grades.
| Grade | C % | Mn % | Cr % | W % | HRC (hardened) | EN Equiv. |
|---|---|---|---|---|---|---|
| O1 | 0.90–1.00 | 1.00–1.40 | 0.40–0.60 | 0.40–0.60 | 57–62 | 100MnCrW4 / 1.2510 |
M-Series — High-Speed Steel (Cutting Tools)
M-series high-speed steels (HSS) maintain their hardness at cutting temperatures up to approximately 600 °C — the key advantage over carbon tool steels. They are the standard material for drill bits, end mills, taps, reamers, and milling cutters in general engineering. M2 is the baseline grade; M35 and M42 add cobalt for improved performance on hard or abrasive materials such as stainless steel and titanium.
| Grade | C % | W % | Mo % | Cr % | V % | Co % | HRC | EN Equiv. |
|---|---|---|---|---|---|---|---|---|
| M2 | 0.85–0.90 | 5.50–6.75 | 4.50–5.50 | 3.75–4.50 | 1.75–2.20 | — | 62–65 | HS6-5-2C / 1.3343 |
| M35 | 0.82–0.88 | 5.50–6.75 | 4.50–5.50 | 3.75–4.50 | 1.75–2.20 | 4.50–5.50 | 64–67 | HS6-5-2-5 / 1.3243 |
| M42 | 1.05–1.15 | 1.15–1.85 | 9.00–10.00 | 3.50–4.25 | 0.95–1.35 | 7.75–8.75 | 66–70 | HS2-9-1-8 / 1.3247 |
Selection guide: Use M2 for general-purpose drilling, tapping, and milling of carbon and low-alloy steels. Upgrade to M35 for stainless steel, heat-resistant alloys, and hard plastics. Use M42 for the most demanding applications — titanium, Inconel, hardened steels above HRC 40, and where tool life is the primary concern.
H-Series — Hot-Work Tool Steel
H-series grades are designed for tooling that contacts hot metal — die-casting dies, extrusion tooling, and forging dies. They must resist thermal fatigue (repeated heating and quenching by molten metal or hot workpiece) while maintaining hardness at working temperatures. H13 is the dominant grade globally and in Australian supply.
| Grade | C % | Cr % | Mo % | V % | HRC (hardened) | EN Equiv. |
|---|---|---|---|---|---|---|
| H13 | 0.32–0.45 | 4.75–5.50 | 1.10–1.75 | 0.80–1.20 | 44–50 | X40CrMoV5-1 / 1.2344 |
Stainless Steel — Where It Fits
Stainless steels are a distinct family — they contain ≥10.5% chromium, which forms a passive oxide layer conferring corrosion resistance. The most common grades in Australian fastener and industrial supply are the 300-series austenitic grades (304 and 316) and 400-series martensitic grades. For a full treatment of stainless grades, composition, corrosion behaviour, and marine suitability, see the stainless steel fasteners guide. Stainless grades use a different designation system — ISO 3506 for fasteners, ASTM A276 and AS/NZS 1554.6 for bar and structural use.
AS, SAE/AISI, ISO and EN Designation Systems Explained
Three primary designation systems are in use in Australian industry. Understanding their structure makes cross-referencing straightforward.
Australian Standards (AS 1442 / AS 1444)
Standards Australia adopted the SAE/AISI numbering system for most carbon and alloy steel grades, prefixed with 'K' for carbon steels (AS 1442) and using the SAE number directly for alloy steels (AS 1444). This makes cross-referencing between AU and US specifications straightforward in most cases.
- AS 1442:2007 (R2017) — hot-rolled carbon steel bars. Grades K1018 through K1095.
- AS 1444:2007 (R2017) — hot-rolled alloy steel bars. Grades 4130, 4140, 4340, 8620, etc.
- AS/NZS 3678:2016 — structural steel plate, floorplate, and slabs. Grades 250, 350, 400, 450.
- AS/NZS 3679.1:2016 — structural steel hot-rolled bars and sections. Grades 300, 350.
SAE/AISI Numbering (US — globally dominant)
The SAE/AISI four-digit system encodes steel composition directly. For carbon steels (SAE J403:2024), the first two digits indicate the steel series; the last two digits indicate nominal carbon content in hundredths of a percent. For alloy steels (SAE J404:2009), the first digit indicates the primary alloy series and the second indicates a subgroup within that series.
| SAE Series | Primary Alloy | Example |
|---|---|---|
| 10xx | Plain carbon | 1045 = 0.45% C, no alloy |
| 11xx | Free-machining (S-added) | 1144 = resulfurised |
| 41xx | Chromium-molybdenum | 4140 = Cr-Mo alloy |
| 43xx | Nickel-chromium-molybdenum | 4340 = Ni-Cr-Mo |
| 86xx | Nickel-chromium-molybdenum (low Ni) | 8620 = case-hardening Ni-Cr-Mo |
ISO and EN Designation Systems
ISO 683 series covers engineering steels for heat treatment, covering carbon and alloy grades under ISO 683-1:2016 (non-alloy), ISO 683-2:2016 (alloy), ISO 683-3:2022 (case-hardening), and ISO 683-6:2023 (bright products). EN 10027-1:2016 provides the European symbolic designation system, encoding steel type, composition, and subgroups in alphanumeric codes.
Grade Cross-Reference Table
| SAE/AISI | AU (AS) | EN Symbolic | EN Numeric | Notes |
|---|---|---|---|---|
| 1018 | AS 1442 K1018 | C20 | 1.0402 | Low-carbon, general fabrication |
| 1045 | AS 1442 K1045 | C45 | 1.0503 | Medium-carbon shaft grade |
| 1095 | AS 1442 K1095 | C101 / Ck101 | 1.1274 | High-carbon spring and blade steel |
| 4140 | AS 1444 4140 | 42CrMo4 | 1.7225 | Cr-Mo alloy, most common alloy steel in AU |
| 4340 | AS 1444 4340 | 36CrNiMo4 | 1.6511 | Ni-Cr-Mo, highest-strength common alloy |
| 8620 | AS 1444 8620 | 20NiCrMo2 | 1.6523 | Case-hardening alloy |
| D2 | — | X153CrMoV12 | 1.2379 | Cold-work tool steel |
| A2 | — | X100CrMoV5 | 1.2363 | Air-hardening tool steel |
| M2 | — | HS6-5-2C | 1.3343 | Standard HSS cutting tool grade |
| H13 | — | X40CrMoV5-1 | 1.2344 | Hot-work die steel |
Mechanical Properties Reference
Properties shown are for annealed or normalised bar unless otherwise noted. Heat-treated values vary significantly with section size and tempering temperature — always verify against the relevant material certificate or datasheet for the actual supply condition.
| Grade | Condition | Yield MPa | Tensile MPa | Elongation % | Hardness |
|---|---|---|---|---|---|
| 1018 | Hot-rolled | 310 | 440 | 25 | 126 HB |
| 1045 | Normalised | 405 | 585 | 20 | 170 HB |
| 1045 | Q&T (315 °C) | 655 | 827 | 16 | 241 HB |
| 1095 | Hardened & tempered | — | — | — | 62–65 HRC |
| 4140 | Normalised | 655 | 1,020 | 18 | 302 HB |
| 4140 | Q&T (315 °C) | 1,000 | 1,090 | 14 | 311 HB |
| 4140 | Q&T (650 °C) | 655 | 758 | 20 | 217 HB |
| 4340 | Q&T (315 °C) | 1,230 | 1,470 | 10 | 440 HB |
| 4340 | Q&T (600 °C) | 862 | 980 | 18 | 287 HB |
| D2 | Hardened (oil) | — | — | — | 58–62 HRC |
| A2 | Hardened (air) | — | — | — | 58–62 HRC |
| M2 | Hardened | — | — | — | 62–65 HRC |
| H13 | Hardened & tempered | — | — | — | 44–50 HRC |
For density values for use in weight calculations, see the material density chart. For hardness conversion between HRC, HB, and HV scales, see the hardness testing guide.
Selecting Steel Grade by Application
Grade selection follows a logical sequence: define the service requirements, then narrow to the grade that meets them at lowest cost and complexity.
| Requirement | Start here | Upgrade to | Notes |
|---|---|---|---|
| General fabrication, low stress | 1018 / 1020 | — | Weld freely, no preheat, cheapest option |
| Shaft, key and gear (moderate load) | 1045 | 4140 Q&T | 1045 normalised covers most shafts; 4140 for higher load |
| Heavy-duty shaft, crankshaft, landing gear | 4140 Q&T | 4340 Q&T | 4340 where failure is catastrophic |
| Case-hardened gear or camshaft | 8620 | 4320 | Carburise then quench; tough core + hard case |
| Spring, blade, saw | 1095 | 5160 | 5160 (Cr-bearing) for automotive leaf springs |
| Cold-work die (long run) | D2 | — | Maximum wear resistance; air or oil harden |
| Punch or form tool (close tolerance) | A2 | — | Air-harden; minimal distortion |
| Tap, reamer, small die | O1 | A2 | O1 for general; A2 where distortion is critical |
| Drill, end mill, tap (cutting tools) | M2 HSS | M35 / M42 HSS-Co | M35 for stainless; M42 for titanium and hard alloys |
| Die-casting die, extrusion tooling | H13 | — | Thermal fatigue resistance essential |
| Corrosive environment | 304 stainless | 316 stainless | See stainless grades guide; different designation system |
Carbon Equivalent — Weldability Check
The International Institute of Welding (IIW) carbon equivalent formula assesses weld cracking risk for alloy steels:
CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
As a practical guide: CE below 0.40 — weldable without preheat in most conditions; CE 0.40–0.60 — preheat recommended (100–250 °C depending on section and heat input); CE above 0.60 — preheat essential, low-hydrogen electrodes required, post-weld heat treatment often needed.
For grade 4140, CE ≈ 0.75. For grade 4340, CE ≈ 0.90. Both require careful welding procedure and should only be welded in the pre-hardened or annealed condition where possible. For fastener grade identification and material specifications, see the bolt grade chart. AIMS stocks steel bar stock and raw materials — browse the raw materials collection for available grades and sections.
People Also Ask — Steel Grades
Q: What is the difference between mild steel and high tensile steel?
Mild steel (typically SAE 1018 or 1020, ≤0.25% carbon) is soft, weldable, and easy to fabricate, but has low yield strength (around 250–275 MPa). High tensile steel — such as SAE 4140 or grade AS/NZS 3678 Grade 350 — uses alloy additions or higher carbon content to reach yield strengths of 350 MPa and above, making it suited to structural members, bolts, and shafts that carry significant load.
Q: What does SAE 1045 mean?
SAE 1045 is a medium-carbon steel designation under the SAE/AISI system. The first two digits '10' indicate a plain carbon steel with no significant alloying. The last two digits '45' indicate a nominal carbon content of 0.45% (actual range 0.43–0.50%). It is equivalent to AS 1442 grade K1045 and European EN C45 (1.0503).
Q: What is the strongest grade of steel?
In common industrial supply, SAE 4340 (nickel-chromium-molybdenum) is one of the strongest engineering steels, achieving tensile strengths above 1,000 MPa in the heat-treated condition. M42 cobalt HSS reaches HRC 68–70 in hardness. For most AU industrial applications, 4140 or 4340 in the Q&T condition covers the practical upper range.
Q: What steel grade is used for shafts?
SAE 1045 is the most common shaft material for general engineering. SAE 4140 is used where higher strength or impact toughness is required. SAE 4340 is selected for high-load shafts such as crankshafts. In Australian supply, 1045 and 4140 are both readily available as round bar to AS 1442 and AS 1444 respectively.
Q: What is the difference between AS 1442 and AS 1444?
AS 1442:2007 (R2017) covers hot-rolled bars in unalloyed (plain carbon) steels — grades K1018, K1045, K1095, etc. AS 1444:2007 (R2017) covers hot-rolled bars in alloy steels — grades 4140, 4340, 8620, etc. — which contain deliberate additions of chromium, molybdenum, nickel, or vanadium.
Q: AISI 4140 vs 4340 — which is stronger?
SAE 4340 is stronger. 4140 (Cr-Mo) achieves tensile strength of 655–1,000 MPa in Q&T condition. 4340 (Ni-Cr-Mo) achieves 980–1,470 MPa with higher impact toughness. For most shaft and gear applications, 4140 is the cost-effective choice; 4340 is for maximum-strength applications such as crankshafts and aerospace components.
Q: Can mild steel be heat-treated?
Mild steel (≤0.25% carbon) has insufficient carbon for useful through-hardening. It can be surface-hardened by carburising or nitriding. For through-hardening, a minimum of around 0.30–0.35% carbon is needed; medium-carbon grades such as 1045 or alloy steels such as 4140 are the standard choices.
Q: What is tool steel?
Tool steel is a category of high-alloy, high-carbon steel engineered for cutting, forming, and shaping other materials. Tool steels are characterised by high hardness (HRC 58–70), excellent wear resistance, and the ability to hold a cutting edge. They are classified into D-series (cold-work), A-series (air-hardening), O-series (oil-hardening), M-series (high-speed), and H-series (hot-work).
Q: What does D2 stand for in tool steel?
D2 is a cold-work tool steel in the AISI D-series. The 'D' denotes high-chromium cold-work die steel. D2 contains approximately 1.5% carbon and 12% chromium, giving exceptional wear resistance and dimensional stability during hardening to HRC 58–62. European equivalent: X153CrMoV12 (EN 1.2379).
Q: What is HSS made of?
High-speed steel (HSS) is an M-series tool steel containing tungsten, molybdenum, chromium, vanadium, and in cobalt grades, cobalt. The most common grade is M2 (0.85–0.90% C, 6% W, 5% Mo, 4% Cr, 2% V). M35 adds 5% cobalt; M42 contains up to 8% cobalt and reaches HRC 70 — suited to hard materials such as stainless steel and titanium alloys.