{"id":3551,"date":"2026-09-16T10:59:03","date_gmt":"2026-09-16T07:59:03","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-8740\/"},"modified":"2026-09-25T21:14:36","modified_gmt":"2026-09-25T18:14:36","slug":"aisi-8740","status":"publish","type":"page","link":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-8740\/","title":{"rendered":"AISI 8740 \/ AMS 6322 \/ AMS 6325"},"content":{"rendered":"

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AISI 8740 \/ AMS 6322 \/ AMS 6325<\/h1>\n
DEFENCE METAL<\/span><\/p>\n
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AISI 8740<\/div>\n
UNS G87400 (hardenability-band grade 8740H = H87400) \u00b7 W.Nr. 1.6546 \/ 40NiCrMo2-2 (cross-reference tables give DIN name 40NiCrMo22, UNI 40NiCrMo2, JIS SNCM240 – FOUND IN THREE SOURCES, the band could not be verified element by element) \u00b7 SAE J404 \/ ASTM A29 band: C 0.38-0.43% – Mn 0.75-1.00% – Si 0.15-0.35% – Ni 0.40-0.70% – Cr 0.40-0.60% – Mo 0.20-0.30% – P 0.035% max – S 0.040% max – balance Fe. The AMS 6322 chemistry gives the same band with tighter impurity limits: P 0.025% max, S 0.025% max, Cu 0.35% max. The nominal form used in the AMS titles is 0.50Cr – 0.55Ni – 0.25Mo (0.38-0.43C). IT IS A QUENCH-AND-TEMPER STEEL – NOT A CARBURIZING STEEL. Its carbon is 0.38-0.43%, which is too high for carburizing. 8620, which looks as if it belongs to the same 87xx family, carries 0.18-0.23% carbon and is a carburizing steel; THE TWO ARE NOT INTERCHANGEABLE. 8740 works on the same logic as 4140 and 4340: austenitize, oil quench, temper. IT IS NOT STAINLESS. IT DOES NOT PRECIPITATION HARDEN; there is no H900 \/ H1025 \/ H1150 type ageing step.<\/p>\n
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Not to be confused with<\/div>\n

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

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For what<\/div>\n
Bought for medium-to-high strength fasteners and machine parts used hardened and tempered: aircraft engine bolts and aerospace fasteners, axles, drill tool joints, drill and reamer bodies, piston rods, heavy-duty shafts.<\/div>\n<\/div>\n
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Forms<\/div>\n
Round bar \u00b7 flat bar \u00b7 plate \u00b7 sheet \u00b7 tube \u00b7 forgings \u00b7 fasteners. All forms are supplied to order.<\/div>\n<\/div>\n
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Standards<\/div>\n
AMS (verified, 0.50Cr – 0.55Ni – 0.25Mo, C 0.38-0.43% chemistry): 6322 (BARS, FORGINGS, RINGS AND STOCK FOR FORGING OR FLASH WELDED RINGS; AIRCRAFT QUALITY; latest revision S\/2023) \u00b7 6323 (MECHANICAL TUBING; latest revision M\/2017) \u00b7 6325 (BARS AND FORGINGS; HEAT TREATED, 105 ksi \/ 724 MPa TENSILE STRENGTH) \u00b7 6327 (BARS AND FORGINGS; HEAT TREATED, 125 ksi \/ 862 MPa TENSILE STRENGTH) \u00b7 6358 (SHEET, STRIP AND PLATE; AIRCRAFT QUALITY). Cleanliness: AMS 2301<\/b> \u00b7 AMS 2304<\/b>. Heat treatment procedure: AMS 2759<\/b>\/1 (Heat Treatment of Carbon and Low-Alloy Steel Parts). ASTM: A29 \/ A29M (general requirements) \u00b7 A322 (alloy steel bars, standard grades) \u00b7 A331 (cold-finished bars) \u00b7 A519 (seamless mechanical tubing) \u00b7 A711 (stock for forgings) \u00b7 A752 (alloy steel wire rod) \u00b7 A320 \/ A320M Grade L7C (low-temperature bolting). SAE: J404 (chemistry) \u00b7 J1268 (hardenability bands for H grades) \u00b7 J1397. Military: MIL-S-6049 \/ AMS-S-6049 (8740 bars and reforging stock, aircraft quality – superseded by AMS-6322, AMS-6325 and AMS-6327) \u00b7 MIL-B-6812 (aircraft bolts). EN and others: W.Nr. 1.6546 \/ 40NiCrMo2-2 \u00b7 UNI 40NiCrMo2 \u00b7 JIS SNCM240 (three sources, band not verified).
AMS 6322, 6325 AND 6327 ARE NOT INTERCHANGEABLE. All three share one chemistry; THE DIFFERENCE IS THE DELIVERY CONDITION AND THE TARGET STRENGTH.<\/span><\/div>\n<\/div>\n
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Advantage<\/div>\n
That one material can be tied BY SPECIFICATION to three separate strength targets. AMS 6325 supplies it heat treated to 105 ksi (724 MPa) tensile, AMS 6327 heat treated to 125 ksi (862 MPa) tensile, while AMS 6322 covers the aircraft-quality delivery condition.<\/div>\n<\/div>\n
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Welding<\/div>\n
WELDABLE, BUT PREHEAT IS REQUIRED. Its carbon is 0.38-0.43%, the same band as 4140, and without preheat the heat-affected zone turns into hard, brittle martensite.<\/div>\n<\/div>\n
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Limits<\/div>\n
1) IT IS NOT STAINLESS. Chromium is 0.40-0.60% and no passive layer forms. Without plating, phosphating, oil or paint it rusts in damp conditions; it is not suitable for marine or chloride-bearing environments.
\n2) IT IS NOT A CARBURIZING STEEL AND IS NOT CARBURIZED.<\/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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