{"id":3537,"date":"2026-09-16T10:57:39","date_gmt":"2026-09-16T07:57:39","guid":{"rendered":"https:\/\/www.defencemetal.com\/index.php\/en\/kovar\/"},"modified":"2026-09-25T16:28:05","modified_gmt":"2026-09-25T13:28:05","slug":"kovar","status":"publish","type":"page","link":"https:\/\/www.defencemetal.com\/index.php\/en\/kovar\/","title":{"rendered":"Kovar \/ (1.3981) \/ ASTM F15"},"content":{"rendered":"

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Kovar \/ (1.3981) \/ UNS K94610 \/ ASTM F15<\/h1>\n
DEFENCE METAL<\/span><\/p>\n
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Kovar<\/div>\n
UNS K94610 \u00b7 W.Nr. 1.3981 \u00b7 DIN 17745 \u00b7 FeNi29Co17 \u00b7 ~53% Fe \u2013 29% Ni \u2013 17% Co. Minor elements: C 0.02-0.04% max \u00b7 Mn 0.30-0.50% max \u00b7 Si 0.20% max \u00b7 Cr 0.20% max \u00b7 Cu 0.20% max \u00b7 Mo 0.20% max \u00b7 Al, Mg, Zr, Ti 0.10% max each \u00b7 P and S 0.02% max. It is an iron-nickel-cobalt controlled-expansion alloy. ASTM F15 requires the iron, nickel and cobalt contents to be ADJUSTED by the manufacturer so that the alloy meets the expansion coefficient requirement; the figures given for those three elements are nominal. Other producer names: NILO alloy K, Alloy K, Rodar, Pernifer 2918.<\/div>\n
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Not to be confused with<\/div>\n

Invar 36<\/a><\/div>\n<\/div>\n

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For what<\/div>\n
Its real job is the HERMETIC GLASS-TO-METAL SEAL. It is NOT PRECIPITATION HARDENABLE and cannot be hardened by heat treatment; its distinguishing property is not mechanical strength but THE SHAPE OF ITS THERMAL EXPANSION CURVE.<\/div>\n<\/div>\n
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Forms<\/div>\n
Round bar \u00b7 flat bar \u00b7 plate \u00b7 sheet \u00b7 strip \u00b7 tube \u00b7 wire \u00b7 forging. All forms are supplied to order.<\/div>\n<\/div>\n
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Standards<\/div>\n
AMS 7726<\/b> \u2014 wire; SAE title ‘Iron-Nickel-Cobalt Alloy, Wire 53Fe – 29Ni – 17Co Low Expansion, Glass Sealing, Annealed’. \u00b7 AMS 7727<\/b> \u2014 bars and forgings; SAE title ‘Iron-Nickel-Cobalt Alloy, Bars and Forgings 53Fe – 29Ni – 17Co Low Expansion, Glass Sealing’. \u00b7 AMS 7728<\/b> \u2014 sheet, strip and plate; SAE title ‘Iron-Nickel-Cobalt Alloy, Sheet, Strip, and Plate, 53Fe – 29Ni – 17Co, Low Expansion Glass Sealing, Annealed’. \u00b7 AMS-I-23011 \/ MIL-I-23011 Class 1 (‘Iron-Nickel Alloys for Sealing to Glasses and Ceramic’). \u00b7 ASTM F15 \u2014 iron-nickel-cobalt sealing alloy; it covered wire, rod, bar, strip, sheet and tubing and was WITHDRAWN IN 2024 WITH NO REPLACEMENT. The last valid edition is F15-04(2022). \u00b7 DIN 17745.
SPECIFICATION GAP: with the withdrawal of ASTM F15 in 2024, the only specification family left in force is AMS 7726\/7727\/7728. Those three numbers cover WIRE, BAR AND FORGINGS, and SHEET, STRIP AND PLATE; TUBING appears in none of them.<\/span><\/div>\n<\/div>\n
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Advantage<\/div>\n
The expansion CURVE is flat between 20 and 450 \u00b0C and follows the curve of borosilicate glass across that band. For NILO alloy K, Special Metals gives mean coefficients referenced to 20 \u00b0C of 20-100 \u00b0C: 6.0 \u00b7 20-200 \u00b0C: 5.5 \u00b7 20-250 \u00b0C: 5.3 \u00b7 20-300 \u00b0C: 5.1 \u00b7 20-400 \u00b0C: 4.9 \u00b7 20-500 \u00b0C: 6.2 x\u2026<\/div>\n<\/div>\n
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Welding<\/div>\n
In glass-to-metal seal parts Kovar is joined by brazing and resistance welding rather than by fusion welding; where fusion welding is used, GTAW is chosen and the heat input is limited.<\/div>\n<\/div>\n
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Limits<\/div>\n
ABOVE 450 \u00b0C THE EXPANSION CURVE BREAKS DOWN. The inflection point is 450 \u00b0C; above it the coefficient rises sharply (the 20-500 \u00b0C mean is 6.2, the 600-700 \u00b0C value 7.8 and the 800-900 \u00b0C value 10.3 x 10-6\/\u00b0C). The match with the glass ends and the seal is left under stress. The Curie temperature is 435 \u00b0C;<\/div>\n<\/div>\n
REQUEST A QUOTE<\/a>All nickel alloys →<\/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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