Steel K93603
UNS K93603 · ASTM F1684
K93603 is a selenium/sulfur-modified version of Invar 36 in the ASTM F1684 family (also listed as 4J36), formulated for turned and screw-machine low-expansion parts.
Reference datasheet — K93603 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 A condition
K93603 tempers and conditions
K93603 is supplied in 4 conditions, soft to hard. A is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Stress relieved | Post-machining thermal cycling (typ. 830 °C anneal, 315 °C soak, 95 °C hold) used on precision metrology parts to minimize long-term dimensional drift. | 260 | 470 | 34 | 140 HB | 2.1 % IACS |
ADefault Solution annealed | Default stock condition: lowest and most reproducible expansion, best ductility, easiest deep machining of complex parts. | 270 | 480 | 32 | 145 HB | — |
Temper B | Pick when the part needs higher yield and better chip control on automatic screw machines but still moderate ductility. | 480 | 620 | 15 | 17 HRC | — |
Temper C | Highest strength and hardness for wear surfaces, springs and stiff thin sections — accept lower ductility and the largest drift in expansion coefficient. | 700 | 820 | 6 | 26 HRC | — |
What is K93603?
K93603 is a selenium/sulfur-modified version of Invar 36 in the ASTM F1684 family (also listed as 4J36), formulated for turned and screw-machine low-expansion parts. Typical values are 270 MPa yield, 480 MPa tensile, 32 % elongation, 145 HB / 78 HRB, machinability 45 and service to 200 °C, supplied in A, B, C and SR conditions. The free-machining additions cost some expansion consistency; weldability is poor (25) and formability moderate (60), so choose K93050 or standard Invar 36 for welded or deep-drawn parts. K93603 has a density of 8.05 g/cm³ (0.291 lb/in³), heavier than 96% of steel grades. It melts at 1,427°C (2,601 °F). K93603 has a yield strength of 270 MPa (39.2 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 91% of steel grades. Elongation at break is 32% and the elastic modulus is 141 GPa (20.5 Msi).
What is K93603 used for?
- Machined low-expansion fittings
- Precision instrument screws/bushings
- Sealing pins and connector shells
Advantages
- Ductile — tolerates forming and impact — 32%, better than 95% of steel grades
- Good corrosion resistance — 28/100, better than 94% of steel grades
Limitations
- Poor heat conductor — 10.5 W/m·K (6.07 BTU/hr·ft·°F), worse than 100% of steel grades
- Low electrical conductivity — 2.1 % IACS, worse than 99% of steel grades
- Low stiffness — 141 GPa (20.5 Msi), worse than 98% of steel grades
- High embodied carbon — 6 kg CO₂/kg, worse than 98% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
K93603 properties
Typical room-temperature values for K93603-A; bars are the position among steel grades.
Physical3
K93603 has a density of 8.05 g/cm³ (0.291 lb/in³), heavier than 96% of steel grades. It melts at 1,427°C (2,601 °F).
Mechanical15
K93603 has a yield strength of 270 MPa (39.2 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 91% of steel grades. Elongation at break is 32% and the elastic modulus is 141 GPa (20.5 Msi).
Thermal6
K93603 is rated for continuous service to 200°C (392 °F). It conducts heat at 10.5 W/m·K (6.07 BTU/hr·ft·°F), worse than 100% of steel grades. Thermal expansion is 1.7 µm/m·K (0.944 µin/in·°F).
Electrical3
K93603 conducts electricity at 2.1 % IACS, worse than 99% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), better than 94% of steel grades.
Sustainability4
Producing a kilogram of K93603 takes about 80 MJ of energy and emits 6 kg of CO₂ — more than 98% of steel grades. Typical recycled content is 25%.
Manufacturability8
K93603's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (25/100); formability good (60/100).
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. K93603 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with K93603
Is K93603 easy to machine?
Use sharp positive-rake carbide, heavy flood coolant and constant feed; the Se/S inclusions break chips and roughly double tool life versus standard Invar 36, but the alloy still work-hardens and gums if the tool dwells.
Can K93603 be welded?
Avoid fusion welding where possible — selenium/sulfur promote hot cracking and porosity; use mechanical fastening, or vacuum brazing / EB welding with matched Invar filler and low heat input.
Can K93603 be formed, bent or molded?
Anneal-temper stock cold forms and bends readily (min. bend radius ≈ 1t); half- and full-hard tempers need generous radii or intermediate anneals at 830 °C followed by rapid cool.
K93603 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 |
|---|---|---|
| Nicontrols the Invar anomaly; expansion minimum near 36 % | 35 – 36.5 | 36 |
| C | ≤ 0.1 | 0.05 |
| Mn | 0.2 – 0.6 | 0.4 |
| Si | 0.1 – 0.3 | 0.2 |
| Sefree-machining addition (some heats use S instead) | 0.15 – 0.35 | 0.25 |
| Shigher when S is the free-machining agent | ≤ 0.03 | 0.01 |
| P | ≤ 0.03 | 0.01 |
| Cr | ≤ 0.25 | 0.1 |
| Co | ≤ 0.5 | 0.2 |
| Fe | balance |
What surface finishes work on K93603?
Not anodizable; protect with electroless nickel, gold or chrome plate, black oxide or oil — bare surfaces flash-rust in humid shops, and lapped optical seats should be plated before final stabilization.
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 K93603 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- F1684
- Also called
- Free-Cutting Invar
- Similar grades
- 4J36
How much does K93603 cost?
K93603 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.
K93603 — frequently asked
What is K93603 used for?
K93603 is typically used for machined low-expansion fittings, precision instrument screws/bushings and sealing pins and connector shells. In short: free-machining Invar 36; roughly double tool life; avoid fusion welding.
What is the yield strength of K93603?
K93603 has a typical yield strength of 270 MPa (39.2 ksi) and a tensile strength of 480 MPa (69.6 ksi) — weaker than 91% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is K93603 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Use sharp positive-rake carbide, heavy flood coolant and constant feed; the Se/S inclusions break chips and roughly double tool life versus standard Invar 36, but the alloy still work-hardens and gums if the tool dwells.
Can K93603 be welded?
Not readily — weldability is rated poor (25/100). Avoid fusion welding where possible — selenium/sulfur promote hot cracking and porosity; use mechanical fastening, or vacuum brazing / EB welding with matched Invar filler and low heat input.
What surface finishes work on K93603?
Not anodizable; protect with electroless nickel, gold or chrome plate, black oxide or oil — bare surfaces flash-rust in humid shops, and lapped optical seats should be plated before final stabilization.
Can K93603 be formed, bent or molded?
Anneal-temper stock cold forms and bends readily (min. bend radius ≈ 1t); half- and full-hard tempers need generous radii or intermediate anneals at 830 °C followed by rapid cool.
What is the maximum service temperature of K93603?
K93603 is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between K93603-A and K93603-C?
A is the default condition — default stock condition: lowest and most reproducible expansion, best ductility, easiest deep machining of complex parts. C: highest strength and hardness for wear surfaces, springs and stiff thin sections — accept lower ductility and the largest drift in expansion coefficient. Yield strength is 270 MPa in A versus 700 MPa in C.
How much does K93603 cost?
K93603 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 F1684 — Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications — ASTM International (2021)
- GB/T 15009 / YB/T 5241 4J36 (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (controlled-expansion alloys) — ASM International (1990)
- Invar 36 / Free-Cut Invar 36 controlled-expansion alloy datasheets — Carpenter Technology / VDM Metals / Ed Fagan (2022)
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.