Steel K93603-SR (Stress relieved)
Heat-treated state
UNS K93603 · ASTM F1684
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.
Values for the SR condition
Other K93603 tempers and conditions
K93603 is listed in 4 conditions; see the grade overview at K93603.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SRThis page 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-SR?
K93603-SR is K93603 heat treated to SR — 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. K93603-SR has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 34% and the elastic modulus is 141 GPa (20.5 Msi). K93603-SR 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). A is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Ductile — tolerates forming and impact — 34%, better than 97% 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-SR properties
Typical room-temperature values for K93603-SR; 23 are specific to this condition. Other listed values are K93603 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
K93603-SR 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-SR has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 34% and the elastic modulus is 141 GPa (20.5 Msi).
Thermal6
K93603-SR 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 1.6 µm/m·K (0.889 µin/in·°F).
Electrical3
K93603-SR 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-SR 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-SR's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (25/100); formability good (58/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with K93603-SR
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.
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.
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 | — |
K93603-SR — frequently asked
What is K93603-SR used for?
K93603-SR 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-SR?
K93603-SR has a typical yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is K93603-SR 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-SR 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-SR?
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-SR 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-SR?
K93603-SR 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.