{"id":3531,"date":"2026-09-16T10:57:17","date_gmt":"2026-09-16T07:57:17","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-440c\/"},"modified":"2026-09-25T16:29:56","modified_gmt":"2026-09-25T13:29:56","slug":"aisi-440c","status":"publish","type":"page","link":"https:\/\/www.defencemetal.com\/index.php\/en\/aisi-440c\/","title":{"rendered":"AISI 440C \/ (1.4125) \/ AMS 5618 \/ AMS 5630"},"content":{"rendered":"

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AISI 440C \/ (1.4125) \/ UNS S44004 \/ AMS 5618 \/ AMS 5630<\/h1>\n
DEFENCE METAL<\/span><\/p>\n
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AISI 440C<\/div>\n
UNS S44004 \u00b7 W.Nr. 1.4125 \u00b7 X105CrMo17. This is a MARTENSITIC stainless steel: it transforms to martensite on austenitising and quenching and is then TEMPERED. It does NOT precipitation harden; there is NO H900 \/ H1025 type ageing step. It is the HIGHEST CARBON grade of the family and of the standard stainless steels: C 0.95-1.20%. That is about eight times the carbon ceiling of 410 (0.15%) and it is the single reason the grade reaches 58-62 HRC. EN 10088-3 for 1.4125: C 0.95-1.20% – Si 1.00% max – Mn 1.00% max – P 0.040% max – S 0.030% max – Cr 16.0-18.0% – Mo 0.40-0.80%. ASTM A276 \/ the Carpenter type analysis: C 0.95-1.20% – Cr 16.00-18.00% – Mn 1.00% max – Si 1.00% max – Mo 0.75% max – P 0.04% max – S 0.03% max. THE DECISIVE DIFFERENCE BETWEEN EN AND ASTM IS THE MOLYBDENUM: EN 10088-3 specifies a FLOOR for molybdenum (0.40% minimum), while ASTM gives only a CEILING (0.75% maximum) and sets no floor. An order placed as ‘UNS S44004’ or ‘ASTM A276 440C’ alone can be met with a heat containing next to no molybdenum.<\/div>\n
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Not to be confused with<\/div>\n

AISI 420<\/a><\/div>\n<\/div>\n

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For what<\/div>\n
Bought where wear resistance and high hardness come first, the environment is mild and the part is not welded: rolling element bearing races and balls (AMS 5880 is a bearing specification outright), valve seats and balls, nozzles, industrial knives and cutters, surgical instruments, knife edges,\u2026<\/div>\n<\/div>\n
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Forms<\/div>\n
Round bar, flat bar, plate. Supplied annealed, hardened or semi-finished. All forms are supplied to order.<\/div>\n<\/div>\n
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Standards<\/div>\n
AMS (all three verified, plain S44004): 5630 (bars, wire, forgings and forging stock) \u00b7 5618 (bars, wire and forgings; with a CONSUMABLE ELECTRODE VACUUM MELTED requirement) \u00b7 5880 (bars, wire, forgings and forging stock; for BEARING APPLICATIONS). ASTM: A276 \/ SA-276 (bars and shapes). EN: 1.4125 \u00b7 EN 10088-3 (bars, wire, sections; +A condition). Welding procedure: ASME Section IX P-No 6 (although this grade is not welded in practice).
THE THREE AMS NUMBERS ARE NOT THE SAME THING: AMS 5630 is general bar, wire and forging; AMS 5618 calls for the SAME chemistry but specifies the MELTING ROUTE (consumable electrode vacuum melted), so AMS 5630 material IS NOT ACCEPTED against AMS 5618;<\/span><\/div>\n<\/div>\n
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Advantage<\/div>\n
IT REACHES THE HIGHEST HARDNESS OF ANY STANDARD STAINLESS STEEL. In numbers: the as-quenched hardness is 59-62 HRC (Lucefin 60 HRC, INTOCO 60-62 HRC, SB Specialty Metals 59 HRC);<\/div>\n<\/div>\n
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Welding<\/div>\n
IT IS NOT WELDED IN PRACTICE. Carpenter states that ‘because of its high-hardness capability, this steel is seldom welded’. Where it cannot be avoided, three sources give the same cycle: a PREHEAT of about 260 \u00b0C (500 \u00b0F), maintained throughout; Rolled Alloys requires welding with high heat inputs;<\/div>\n<\/div>\n
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Limits<\/div>\n
1) FORBIDDEN TEMPERING BAND: 425-593 \u00b0C. Carpenter requires that the grade not be tempered ABOVE 427 \u00b0C (800 \u00b0F) where maximum corrosion resistance is wanted; Abrams writes that 425-565 \u00b0C reduces impact strength and corrosion resistance;<\/div>\n<\/div>\n
REQUEST A QUOTE<\/a>All stainless 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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