| name | steel-lookup |
| description | Steel designation lookup — AISI/SAE system, ASTM designations, heat treatment conditions, mechanical properties, hardness-strength conversions, international equivalents. |
| metadata | {"priority":6,"promptSignals":{"phrases":["steel grade","AISI","4340","1018","4140","heat treatment","steel designation","hardness","Rockwell","Brinell"],"minScore":3}} |
Steel Lookup — Complete Skill
AISI/SAE Designation System
Format: XXXX
First two digits = alloy class
Last two digits = nominal carbon content × 100
| Series | Alloy | Notes |
|---|
| 10XX | Plain carbon | 1018, 1045, 1095 |
| 11XX | Free machining (S added) | 1117, 1144 |
| 12XX | Free machining (S+P) | 1215 |
| 13XX | Mn 1.75% | 1340, 1345 |
| 40XX | Mo 0.25% | 4012, 4023 |
| 41XX | Cr-Mo | 4130, 4140, 4150 |
| 43XX | Ni-Cr-Mo | 4340 |
| 44XX | Mo 0.53% | — |
| 46XX | Ni-Mo | 4620, 4640 |
| 47XX | Ni-Cr-Mo | 4720 |
| 51XX | Cr 1.0% | 5120, 5140, 5160 |
| 52100 | Cr 1.5% (bearing) | 52100 |
| 61XX | Cr-V | 6150 |
| 86XX | Ni-Cr-Mo (low) | 8620, 8640 |
| 87XX | Ni-Cr-Mo (higher) | 8720, 8740 |
| 92XX | Si-Mn (spring) | 9255, 9260 |
Letter prefix: B = Bessemer; E = Electric furnace (cleaner, aircraft grade E4340)
Suffix H: hardenability guaranteed (4340H)
Properties by Grade
Low Carbon (1018, A36, 1020)
AISI 1018: C=0.18%, annealed: Sy=220 MPa, Sut=340 MPa, HB=130, good weldability, case-hardenable
AISI 1020: C=0.20%, HR: Sy=210 MPa, Sut=380 MPa; CD: Sy=390 MPa, Sut=470 MPa
ASTM A36: structural; Fy=250 MPa (36 ksi), Fu=400-550 MPa (58-80 ksi), excellent weld
Medium Carbon (1045, 1060)
AISI 1045: C=0.45%, N&T 425°C: Sy=635 MPa, Sut=720 MPa, HB=207
AISI 1060: C=0.60%, Q&T 315°C: Sy=770 MPa, Sut=960 MPa, HB=280 (spring range)
High Carbon (1095, 52100)
AISI 1095: C=0.95%, Q&T: Sy=830 MPa, Sut=1010 MPa; springs, saw blades
AISI 52100: C=1.00%, Cr=1.45%; bearing steel: Sy=1670 MPa, Sut=1930 MPa (Q&T 150°C), HRC 62-64 (surface hardened)
Alloy Steels
AISI 4130: Cr-Mo; annealed: Sy=435 MPa, Sut=560 MPa; Q&T 400°C: Sy=1000 MPa, Sut=1080 MPa; aircraft structure
AISI 4140: Cr-Mo (0.40C); Q&T 315°C: Sy=1100 MPa, Sut=1170 MPa, HB=340; general purpose alloy
AISI 4340 (E4340): Ni-Cr-Mo; Q&T 315°C: Sy=1380 MPa, Sut=1480 MPa, HB=430; best combination of strength+toughness
AISI 4150: Q&T 315°C: Sy=1330 MPa, Sut=1450 MPa; heavy-section shafts
AISI 8620: Ni-Cr-Mo (case hardening grade); case: 58-63 HRC, core: 25-35 HRC; gears, cams
AISI 6150: Cr-V; Q&T: Sy=1170 MPa, Sut=1310 MPa; springs, axles, high fatigue
Structural Steels (ASTM)
| Grade | F_y [MPa] | F_u [MPa] | Notes |
|---|
| A36 | 250 | 400-550 | Most common structural |
| A572 Gr50 | 345 | 450 | HSLA, general structural |
| A992 | 345-450 | 450 | W-shapes (web/flange ratio limits) |
| A514 | 690 | 760-895 | Quenched & tempered plate, bridges |
| A709 Gr 50W | 345 | 485 | Weathering steel, bridges |
Heat Treatment Conditions
| Condition | Abbrev. | Description |
|---|
| Annealed | A | Slow cool from austenitize → soft, ductile |
| Normalized | N | Air cool from austenitize → slightly harder than annealed |
| Quenched & Tempered | Q&T | Water/oil quench + temper → high strength |
| Spheroidize anneal | SA | Carbides globular → best machinability for high-C |
| Stress relieved | SR | Low T anneal → residual stress reduction |
| Case hardened | CH | Carburize/nitrize + quench → hard case, ductile core |
Tempering temperature vs. hardness (4140):
150°C temper: HRC 54, Sut ≈ 1930 MPa (high strength, brittle)
315°C temper: HRC 48, Sut ≈ 1170 MPa
425°C temper: HRC 40, Sut ≈ 970 MPa
540°C temper: HRC 30, Sut ≈ 760 MPa (tough)
Hardness-Strength Conversions (Approx., Carbon/Alloy Steels)
Sut ≈ 3.45 × HB [MPa] (for HB < 400)
Sut ≈ 0.5 × HV [MPa] (Vickers, approximate)
Sy ≈ 0.55-0.65 × Sut (typical ratio for Q&T alloy steels)
| HRC | HB (approx) | Sut [MPa] |
|---|
| 20 | 227 | 784 |
| 30 | 286 | 987 |
| 40 | 370 | 1278 |
| 50 | 481 | 1660 |
| 60 | 639 | 2210 |
Rockwell to Brinell: ASTM E140 conversion tables (preferred over formula)
Stainless Steel (AISI Series 300/400)
| Grade | Type | Sy [MPa] | Sut [MPa] | Notes |
|---|
| 304 | Austenitic | 205 | 515 | Most common, weldable |
| 316 | Austenitic+Mo | 205 | 515 | Better corrosion (Cl⁻) |
| 410 | Martensitic | 310 | 517 | Hardenable, moderate corr. |
| 430 | Ferritic | 205 | 450 | Magnetic, moderate |
| 17-4 PH | PH | 1100-1170 | 1170-1310 | Precipitation hardened, aerospace |
International Equivalents (Approx.)
| AISI/SAE | DIN (Germany) | JIS (Japan) | BS (UK) |
|---|
| 1018 | C15 | S15C | 080M15 |
| 1045 | C45 | S45C | 080M46 |
| 4140 | 42CrMo4 | SCM440 | 708M40 |
| 4340 | 36CrNiMo4 | SNCM439 | 816M40 |
| 8620 | 20NiCrMo2 | SNCM220 | 805M20 |
Output
Provide: full grade designation, heat treatment condition, Sy [MPa], Sut [MPa], HB/HRC, weldability rating, application recommendation.
