{"id":3529,"date":"2026-09-16T10:51:31","date_gmt":"2026-09-16T07:51:31","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-4140\/"},"modified":"2026-09-25T16:30:32","modified_gmt":"2026-09-25T13:30:32","slug":"aisi-4140","status":"publish","type":"page","link":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-4140\/","title":{"rendered":"AISI 4140"},"content":{"rendered":"

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AISI 4140 \/ UNS G41400 \/ AMS 6349 \/ AMS 6382<\/h1>\n
DEFENCE METAL<\/span><\/p>\n
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AISI 4140<\/div>\n
UNS G41400 (aircraft quality E4140 = G41406) \u00b7 W.Nr. 1.7225 \u00b7 EN 42CrMo4 (free-machining variant 42CrMoS4 = 1.7227) \u00b7 ASTM A29 \/ SAE J404 band: C 0.38-0.43% – Mn 0.75-1.00% – Si 0.15-0.35% – Cr 0.80-1.10% – Mo 0.15-0.25% – P 0.035% max – S 0.040% max – balance Fe. NICKEL IS NOT A SPECIFIED ELEMENT; in 4140 nickel is a residual. The EN 10083-3 42CrMo4 band is NOT THE SAME: C 0.38-0.45% – Si 0.40% max – Mn 0.60-0.90% – Cr 0.90-1.20% – Mo 0.15-0.30% – P 0.025% max – S 0.035% max. The two bands do not fully overlap on chromium (ASTM floor 0.80%, EN floor 0.90%; ASTM ceiling 1.10%, EN ceiling 1.20%) and are offset on manganese. Material certified to 42CrMo4 is therefore not automatically acceptable against a 4140 order; acceptance depends on the heat analysis meeting both bands. THIS IS A MARTENSITIC QUENCHED-AND-TEMPERED STEEL: it transforms to martensite on austenitising and oil quenching, and is then TEMPERED. IT IS NOT STAINLESS. It does NOT precipitation harden; there is NO H900 \/ H1025 \/ H1150 type ageing step.<\/div>\n
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Not to be confused with<\/div>\n

AISI 4340<\/a>H11<\/a><\/div>\n<\/div>\n

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For what<\/div>\n
Bought for machine and structural parts that are hardened by heat treatment and need medium-to-high strength together with toughness: shafts and spindles, gears, pins and bushings, hydraulic cylinder rods, die holders and plates, drilling and earth-moving components, and secondary structure and\u2026<\/div>\n<\/div>\n
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Forms<\/div>\n
Round bar, flat bar, plate, sheet, pipe\/tube, forging. All forms are supplied to order.<\/div>\n<\/div>\n
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Standards<\/div>\n
AMS (verified, plain 4140 chemistry 0.95Cr – 0.20Mo – C 0.38-0.43%): 6382 (bars, forgings, rings and stock for forging or flash welded rings; AIRCRAFT QUALITY; ANNEALED) \u00b7 6349 (BARS only; NORMALIZED) \u00b7 6529 (BARS only; SPECIAL AIRCRAFT-QUALITY CLEANLINESS; NORMALIZED) \u00b7 6381 (MECHANICAL TUBING; first issued 1942, current revision K\/2022) \u00b7 6395 (SHEET, STRIP, PLATE) \u00b7 6452 (WELDING WIRE; vacuum melted; environment-controlled packaging) \u00b7 6390 (mechanical tubing – listed in the SAE catalogue with 4140 chemistry, but its current status could not be verified; see the standards note). ASTM: A29 \/ A29M (general requirements for hot-wrought alloy steel bars) \u00b7 A322 (alloy steel bars, standard grades) \u00b7 A331 (cold-finished bars) \u00b7 A519 (seamless mechanical tubing) \u00b7 A513 (ERW mechanical tubing) \u00b7 A506 (hot-rolled sheet and strip) \u00b7 A711 (stock for forgings) \u00b7 A646 (premium quality blooms and billets for aerospace forgings) \u00b7 A752 (wire rod) \u00b7 A829 (alloy structural steel plate) \u00b7 A193 B7 and B7M with A194 2H \/ 2HM (bolting and nuts) \u00b7 A320 L7 and L7M (low-temperature bolting). EN \/ ISO: EN 10083-3 42CrMo4 (1.7225) and 42CrMoS4 (1.7227) \u00b7 ISO 683-2. SAE: J404 \u00b7 J412 \u00b7 J1397.
THE AMS NUMBERS ARE NOT INTERCHANGEABLE. All six carry the same chemical band (0.95Cr – 0.20Mo – C 0.38-0.43%), but they differ in PRODUCT FORM, DELIVERY CONDITION and CLEANLINESS LEVEL: 6382 is ANNEALED bar, forging and ring material and carries the\u2026<\/span><\/div>\n<\/div>\n
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Advantage<\/div>\n
Its single most important practical advantage is that the same material is the base of both a structural quench-and-temper table and a bolting specification, and both guarantee numbers.<\/div>\n<\/div>\n
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Welding<\/div>\n
IT IS WELDABLE, BUT PREHEAT IS MANDATORY, and the delivery condition of the material governs the welding decision. PREHEAT: citing the Procedure Handbook of Arc Welding, Welding Answers gives 205-260 \u00b0C (400-500 \u00b0F) up to 13 mm (\u00bd in) and 316-371 \u00b0C (600-700 \u00b0F) for 13-50 mm (\u00bd-2 in);<\/div>\n<\/div>\n
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Limits<\/div>\n
1) IT IS NOT STAINLESS. Chromium is 0.80-1.10% and no passive layer forms. Without oil, paint, phosphating, plating or another protective measure it rusts in damp air; it is not suitable for marine or chloride-bearing environments.
\n2) CHOICE OF TEMPERING BAND: the 250-450 \u00b0C band is not used for structural quench and temper.<\/div>\n<\/div>\n
REQUEST A QUOTE<\/a>All alloy steels →<\/a>TECHNICAL DETAILS ↓<\/span><\/div>\n
Compiled from manufacturer data sheets \u00b7 confirm against the current specification before ordering<\/div>\n<\/div>\n<\/div>\n

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