{"id":3559,"date":"2026-09-16T11:00:08","date_gmt":"2026-09-16T08:00:08","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/en\/300m\/"},"modified":"2026-09-25T16:30:55","modified_gmt":"2026-09-25T13:30:55","slug":"300m","status":"publish","type":"page","link":"https:\/\/www.defencemetal.com\/index.php\/en\/300m\/","title":{"rendered":"300M"},"content":{"rendered":"

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300M \/ AMS 6257 \/ AMS 6417<\/h1>\n
DEFENCE METAL<\/span><\/p>\n
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300M<\/div>\n
UNS K44220 \u00b7 300M \u00b7 4340M \u00b7 E4340 Mod \u00b7 SAE 434M \u00b7 BS S155. NO VERIFIED W.Nr.\/EN NUMBER EXISTS; order against UNS K44220 and an AMS number. 300M is the SILICON- AND VANADIUM-MODIFIED derivative of AISI 4340: the Cr-Ni-Mo skeleton of 4340 is kept, silicon is RAISED from the 0.15-0.35% band to 1.45-1.80%, 0.05-0.10% vanadium is added and molybdenum is raised from 0.20-0.30% to 0.30-0.50%. THE COMPOSITION DEPENDS ON THE AMS NUMBER and the difference is IN THE CARBON: AMS 6417 C 0.38-0.43% \u00b7 AMS 6419 C 0.40-0.45% \u00b7 AMS 6257 C 0.40-0.44%. The other elements are the same in all three per the SAE title records: nominal 1.6Si \u2013 0.82Cr \u2013 1.8Ni \u2013 0.40Mo \u2013 0.08V. In aircraft quality the phosphorus and sulphur ceilings are tight (SSA and Lork: P 0.010% max, S 0.008% max) and ALL THREE AMS NUMBERS CARRY A CONSUMABLE ELECTRODE VACUUM REMELTED (VAR) REQUIREMENT. IT IS A MARTENSITIC QUENCH-AND-TEMPER STEEL: it hardens by austenitising, oil quenching and DOUBLE TEMPERING. It does NOT precipitation harden; there is no H900 \/ H1025 type aging step. IT IS NOT STAINLESS.<\/div>\n
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Not to be confused with<\/div>\n

AISI 4340<\/a>AerMet 100<\/a><\/div>\n<\/div>\n

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For what<\/div>\n
Bought for primary structural parts that must reach 1860-1930 MPa tensile strength in thick section, where weight is critical and failure loses the aircraft. The dominant application is AIRCRAFT LANDING GEAR: shock strut outer cylinders, inner pistons, axles, pins and attachment lugs.<\/div>\n<\/div>\n
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Forms<\/div>\n
Round bar \u00b7 flat bar \u00b7 plate \u00b7 sheet \u00b7 tube \u00b7 forging. All forms are supplied to order. The AMS coverage extends ONLY to bars, forgings, forging stock and MECHANICAL tubing; no verified AMS number covers plate, sheet or strip in this alloy (see the standards map).<\/div>\n<\/div>\n
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Standards<\/div>\n
AMS (all three verified, and all three carry a CONSUMABLE ELECTRODE VACUUM REMELTED requirement): AMS 6417<\/b> \u2014 ‘Steel, Bars, Forgings, and Tubing, 1.6Si – 0.82Cr – 1.8Ni – 0.40Mo – 0.08V (0.38 – 0.43C), Consumable Electrode Vacuum Remelted’; scope bars, forgings, mechanical tubing and forging stock; current revision K-2021. \u00b7 AMS 6419<\/b> \u2014 the same title with a CARBON BAND of 0.40-0.45%; current revision K-2021. \u00b7 AMS 6257<\/b> \u2014 ‘Steel Bars, Forgings, Forging Stock, and Mechanical Tubing 1.6Si – 0.82Cr – 1.8Ni – 0.40Mo – 0.08V (0.40 – 0.44C) Consumable Electrode Vacuum Remelted NORMALIZED AND TEMPERED’; current revision G-2022. This number is a DELIVERY CONDITION specification: the material is supplied normalized and tempered. Military specifications it replaced (per SSA): AMS 6417<\/b> \u2190 MIL-S-83135 \u00b7 AMS 6257<\/b> \u2190 MIL-S-8844 Rev D Class 3. Other military and OEM specifications: MIL-S-8844 Class 3 \u00b7 BMS 7-26 Class 1 (Boeing) \u00b7 DMS 1935 \u00b7 CE-0896 \u00b7 GM-1012 \u00b7 LC-05-1190 \u00b7 BS S155. ASTM: no ASTM number belonging to this alloy could be CONFIRMED across four independent sources, so none is given.
AMS 6417 AND AMS 6419 ARE 300M, NOT PLAIN 4340. This is the most common confusion on the 4340 side. Both SAE title records define the alloy as ‘1.6Si – 0.82Cr – 1.8Ni – 0.40Mo – 0.08V’; plain 4340 carries 0.15-0.35% silicon and no vanadium.<\/span><\/div>\n<\/div>\n
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Advantage<\/div>\n
Its single most important practical advantage is the TEMPERING RESISTANCE that silicon brings, and it has two concrete consequences. FIRST, THE STRENGTH CEILING: the AMS 6417 floor is 1862 MPa tensile \/ 1517 MPa yield and the AMS 6419 floor is 1931 MPa tensile \/ 1586 MPa yield;<\/div>\n<\/div>\n
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Welding<\/div>\n
IT IS WELDABLE, BUT WELDING IS USUALLY AVOIDED ON AIRCRAFT PARTS. Supreme Steels states plainly: ‘Welding is possible with preheat and post-weld heat treatment’, ‘improper welding reduces toughness and strength’, and for critical components ‘shops often avoid welding and use forged or machined\u2026<\/div>\n<\/div>\n
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Limits<\/div>\n
1) IT IS NOT STAINLESS. Chromium is 0.70-0.95% and no passive film forms. Dynamic Metals states that 300M requires protective measures in corrosive environments and that its stress corrosion cracking resistance is poor. PROTECTION by plating, cadmium or its alternatives, or paint IS MANDATORY.<\/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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