Steel 4J29
GB 4J29 · UNS K94610
4J29 is the precision-alloy designation for the Kovar-type Fe-29Ni-17Co sealing alloy (UNS K94610), whose expansion curve follows borosilicate hard glass and alumina ceramic.
Reference datasheet — 4J29 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the M condition
4J29 tempers and conditions
4J29 is supplied in 5 conditions, soft to hard. M is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Wet-hydrogen decarburised / degassed sealing grade | Pick when the part will be glass-sealed: wet-H₂ treatment removes carbon and hydrogen so the seal does not gas or blister. | 320 | 500 | 33 | 140 HB | 3.5 % IACS |
MDefault Thermomechanically controlled processed | Standard stocked condition for stamping, deep drawing, machining of seal parts and lead frames. | 345 | 520 | 30 | 150 HB | — |
Stress relieved | For machined or drawn parts needing dimensional stability and a repeatable expansion curve without full softening. | 450 | 600 | 18 | 11 HRC | 3.5 % IACS |
Half hard | Use for springy leads, pins and strip that must keep flatness and stiffness without full-hard brittleness. | 500 | 630 | 12 | 15 HRC | 3.4 % IACS |
Hard | Highest strength and best turning/screw-machining behaviour; must be re-annealed before glass sealing. | 720 | 820 | 5 | 28 HRC | 3.3 % IACS |
What is 4J29?
4J29 is the precision-alloy designation for the Kovar-type Fe-29Ni-17Co sealing alloy (UNS K94610), whose expansion curve follows borosilicate hard glass and alumina ceramic. It is specified for hermetic seals in electron tubes and semiconductor packages and is supplied as strip, foil, bar and wire in annealed (M, M-H2), half-hard (Y2), hard (Y) and stress-relieved conditions. Typical values are 345 MPa yield, 520 MPa tensile, 30 % elongation, 150 HB (80 HRB) and service to 450 °C. Machinability is low (35) and the alloy rusts unless plated; where only a soft-glass or lead-frame match is needed, Alloy 42 is cheaper and easier to form. 4J29 has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 99% of steel grades. It melts at 1,440°C (2,624 °F). 4J29 has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 75% of steel grades. Elongation at break is 30% and the elastic modulus is 138 GPa (20 Msi).
What is 4J29 used for?
- vacuum tube envelopes
- hermetic electronic packages
- glass-metal feedthroughs
Advantages
- Ductile — tolerates forming and impact — 30%, better than 93% of steel grades
- Forms and bends easily — 80/100, better than 93% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
- Readily welded — 75/100, better than 76% of steel grades
Limitations
- Low stiffness — 138 GPa (20 Msi), worse than 99% of steel grades
- High embodied carbon — 7.5 kg CO₂/kg, worse than 99% of steel grades
- Poor heat conductor — 17 W/m·K (9.82 BTU/hr·ft·°F), worse than 98% of steel grades
- Low electrical conductivity — 3.5 % IACS, worse than 86% of steel grades
- Difficult to machine — 35/100, worse than 84% of steel grades
4J29 properties
Typical room-temperature values for 4J29-M; bars are the position among steel grades.
Physical3
4J29 has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 99% of steel grades. It melts at 1,440°C (2,624 °F).
Mechanical14
4J29 has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 75% of steel grades. Elongation at break is 30% and the elastic modulus is 138 GPa (20 Msi).
Thermal6
4J29 is rated for continuous service to 450°C (842 °F). It conducts heat at 17 W/m·K (9.82 BTU/hr·ft·°F), worse than 98% of steel grades. Thermal expansion is 5.5 µm/m·K (3.06 µin/in·°F).
Electrical3
4J29 conducts electricity at 3.5 % IACS, worse than 86% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (25/100), better than 92% of steel grades.
Sustainability4
Producing a kilogram of 4J29 takes about 105 MJ of energy and emits 7.5 kg of CO₂ — more than 99% of steel grades. Typical recycled content is 20%.
Manufacturability7
4J29's machinability is fair (35/100, worse than 84% of steel grades); weldability very good (75/100); formability very good (80/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 4J29 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 4J29
Is 4J29 easy to machine?
Gummy and work-hardening like austenitic stainless: use sharp positive-rake carbide, rigid setup, heavy constant feed, low speed (~25–40 m/min) and flood coolant; avoid dwelling.
Can 4J29 be welded?
Readily resistance, laser, electron-beam and TIG welded to itself and to Ni-Fe alloys; keep heat input low and avoid carbon/oxygen pickup so the seal remains gas-tight — filler is usually autogenous.
Can 4J29 be formed, bent or molded?
Excellent deep drawing and stamping in the annealed condition; interstage anneal at 850–950 °C in dry H₂ or vacuum after ~50 % reduction.
4J29 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Ni | 28.5 – 29.5 | 29 |
| Co | 16.8 – 17.8 | 17.3 |
| Mn | 0.2 – 0.6 | 0.4 |
| Si | ≤ 0.3 | 0.15 |
| Ckept low for gas-free glass seals | ≤ 0.03 | 0.02 |
| P | ≤ 0.02 | |
| S | ≤ 0.02 | |
| Cu | ≤ 0.2 | |
| Crmax; kept low to avoid tenacious Cr oxide that spoils sealing | ≤ 0.2 | |
| Al | ≤ 0.1 | |
| Mg | ≤ 0.1 | |
| Febalance ≈53 % | balance |
What surface finishes work on 4J29?
Oxidise in wet hydrogen (or air) before glass sealing to form the adherent Fe/Ni/Co oxide; after sealing, electroplate or electroless nickel then gold for solderability and corrosion protection — never anodized.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 4J29 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K94610
How much does 4J29 cost?
4J29 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
4J29 — frequently asked
What is 4J29 used for?
4J29 is typically used for vacuum tube envelopes, hermetic electronic packages and glass-metal feedthroughs. In short: kovar-type sealing alloy; matches borosilicate glass; service to 450 °C.
What is the yield strength of 4J29?
4J29 has a typical yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 75% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is 4J29 easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of steel grades). Gummy and work-hardening like austenitic stainless: use sharp positive-rake carbide, rigid setup, heavy constant feed, low speed (~25–40 m/min) and flood coolant; avoid dwelling.
Can 4J29 be welded?
Yes — weldability is rated very good (75/100). Readily resistance, laser, electron-beam and TIG welded to itself and to Ni-Fe alloys; keep heat input low and avoid carbon/oxygen pickup so the seal remains gas-tight — filler is usually autogenous.
What surface finishes work on 4J29?
Oxidise in wet hydrogen (or air) before glass sealing to form the adherent Fe/Ni/Co oxide; after sealing, electroplate or electroless nickel then gold for solderability and corrosion protection — never anodized.
Can 4J29 be formed, bent or molded?
Excellent deep drawing and stamping in the annealed condition; interstage anneal at 850–950 °C in dry H₂ or vacuum after ~50 % reduction.
What is the maximum service temperature of 4J29?
4J29 is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4J29-M and 4J29-Y?
M is the default condition — standard stocked condition for stamping, deep drawing, machining of seal parts and lead frames. Y: highest strength and best turning/screw-machining behaviour; must be re-annealed before glass sealing. Yield strength is 345 MPa in M versus 720 MPa in Y.
How much does 4J29 cost?
4J29 is a high-cost steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM F15 — Iron-Nickel-Cobalt Sealing Alloy — ASTM (2018)
- Kovar Alloy technical data (Fe-29Ni-17Co) — CRS/Ed Fagan/Nickel-alloy producers (2020)
- ASM Handbook Vol. 2 — Properties of Controlled-Expansion Alloys — ASM International (1990)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.