Steel A48 Class 20-SR (Stress relieved)
Heat-treated state
ASTM A48 Class 20 · EN EN-GJL-150, GG15 · JIS FC150 · GB HT150
Choose for machine tool bases, housings and any casting that must stay dimensionally stable after machining; strength and matrix essentially unchanged.
Values for the SR condition
Other A48 Class 20 tempers and conditions
A48 Class 20 is listed in 8 conditions; see the grade overview at A48 Class 20.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Use when maximum softness/machinability is needed or to remove chill and carbides in thin sections; costs some tensile strength. | 90 | 135 | 0.8 | 125 HB | 2.3 % IACS |
Class 20C | For heavy-section castings where slow cooling coarsens graphite; hardness and strength trend to the low end. | 90 | 145 | 0.5 | 140 HB | 2.3 % IACS |
Class 20S | Used when the test bar size/geometry is negotiated to represent an unusual casting section. | 96 | 150 | 0.5 | 155 HB | 2.2 % IACS |
SRThis page Stress relieved | Choose for machine tool bases, housings and any casting that must stay dimensionally stable after machining; strength and matrix essentially unchanged. | 98 | 150 | 0.5 | 150 HB | 2.2 % IACS |
Class 20B | Most common A48 test-bar size; matches general-purpose 15–25 mm wall castings. | 98 | 152 | 0.5 | 156 HB | 2.2 % IACS |
Full hard | For wear faces (ways, liners, guides) — only marginally effective on Class 20 because the low-pearlite matrix limits attainable case hardness. | 100 | 152 | 0.3 | 45 HRC | 2.2 % IACS |
Class 20A | A48 test-bar designation for thin-wall castings; same 138 MPa minimum but finer graphite and slightly higher hardness. | 101 | 155 | 0.5 | 165 HB | 2.1 % IACS |
FDefault As fabricated | Standard supply condition for Class 20 castings — pick unless dimensional stability or hardness control demands a heat treatment. | — | 152 | 0.5 | 156 HB | 53 W/m·K |
What is A48 Class 20-SR?
A48 Class 20-SR is A48 Class 20 heat treated to SR — choose for machine tool bases, housings and any casting that must stay dimensionally stable after machining; strength and matrix essentially unchanged. A48 Class 20-SR has a tensile strength of 150 MPa (21.8 ksi), weaker than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 80 GPa (11.6 Msi). A48 Class 20-SR has a density of 7.1 g/cm³ (0.257 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F). F is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.6 kg CO₂/kg, better than 100% of steel grades
- Conducts heat well — 54 W/m·K (31.2 BTU/hr·ft·°F), better than 99% of steel grades
- Easy to machine — 92/100, better than 99% of steel grades
Limitations
- Low stiffness — 80 GPa (11.6 Msi), worse than 100% of steel grades
- Limited ductility — 0.5%, worse than 100% of steel grades
- Low fracture toughness — 12 MPa·√m (10.9 ksi·√in), worse than 100% of steel grades
- Hard to polish — 30/100, worse than 100% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
A48 Class 20-SR properties
Typical room-temperature values for A48 Class 20-SR; 21 are specific to this condition. Other listed values are A48 Class 20 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A48 Class 20-SR has a density of 7.1 g/cm³ (0.257 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F).
Mechanical13
A48 Class 20-SR has a tensile strength of 150 MPa (21.8 ksi), weaker than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 80 GPa (11.6 Msi).
Thermal6
A48 Class 20-SR is rated for continuous service to 350°C (662 °F). It conducts heat at 54 W/m·K (31.2 BTU/hr·ft·°F), better than 99% of steel grades. Thermal expansion is 11.4 µm/m·K (6.33 µin/in·°F).
Electrical3
A48 Class 20-SR conducts electricity at 2.2 % IACS, worse than 98% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of A48 Class 20-SR takes about 17 MJ of energy and emits 1.6 kg of CO₂ — less than 100% of steel grades. Typical recycled content is 85%.
Manufacturability7
A48 Class 20-SR's machinability is excellent (92/100, better than 99% of steel grades); weldability poor (30/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A48 Class 20-SR
Is A48 Class 20 easy to machine?
Among the easiest ferrous materials to cut — dry machining with carbide or ceramic, high speeds, short abrasive chips; watch out for hard chill at thin edges and for abrasive sand skin on the first pass.
Can A48 Class 20 be welded?
Poor weldability: preheat 300–400 °C, use ENi-CI/ENiFe-CI electrodes or braze-weld, peen and cool slowly to avoid a hard martensitic HAZ and cracking; repair welding only.
Can A48 Class 20 be formed, bent or molded?
No cold forming; produced by green sand or shell moulding — high fluidity and near-zero shrinkage make thin, complex sections easy, keep wall ≥4–5 mm to avoid chill.
What surface finishes work on A48 Class 20?
Shot blast then prime/paint or enamel for corrosion protection; graphite flakes prevent a true mirror polish, and electroplating requires careful pre-cleaning to strip surface graphite.
A48 Class 20 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 |
|---|---|---|
| Ctotal carbon; CE ≈ 4.3–4.6, chemistry not specified by ASTM A48 — typical foundry practice | 3.2 – 3.6 | 3.45 |
| Si | 2 – 2.8 | 2.4 |
| Mn | 0.4 – 0.8 | 0.6 |
| Phigher P improves fluidity, lowers toughness | ≤ 0.3 | 0.15 |
| S | ≤ 0.15 | 0.1 |
| Fe | balance | — |
A48 Class 20-SR — frequently asked
What is A48 Class 20-SR used for?
A48 Class 20-SR is typically used for machine bases, housings, brackets and counterweights. In short: easiest ferrous material to machine; best vibration damping; lowest-strength gray iron.
What is the tensile strength of A48 Class 20-SR?
A48 Class 20-SR has a typical tensile strength of 150 MPa (21.8 ksi) — weaker than 100% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is A48 Class 20-SR easy to machine?
Yes — machinability is rated excellent (92/100, better than 99% of steel grades). Among the easiest ferrous materials to cut — dry machining with carbide or ceramic, high speeds, short abrasive chips; watch out for hard chill at thin edges and for abrasive sand skin on the first pass.
Can A48 Class 20-SR be welded?
Not readily — weldability is rated poor (30/100). Poor weldability: preheat 300–400 °C, use ENi-CI/ENiFe-CI electrodes or braze-weld, peen and cool slowly to avoid a hard martensitic HAZ and cracking; repair welding only.
What surface finishes work on A48 Class 20-SR?
Shot blast then prime/paint or enamel for corrosion protection; graphite flakes prevent a true mirror polish, and electroplating requires careful pre-cleaning to strip surface graphite.
Can A48 Class 20-SR be formed, bent or molded?
No cold forming; produced by green sand or shell moulding — high fluidity and near-zero shrinkage make thin, complex sections easy, keep wall ≥4–5 mm to avoid chill.
What is the maximum service temperature of A48 Class 20-SR?
A48 Class 20-SR is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A48 Class 20-F and A48 Class 20 20A?
F is the default condition — standard supply condition for Class 20 castings — pick unless dimensional stability or hardness control demands a heat treatment. 20A: a48 test-bar designation for thin-wall castings; same 138 MPa minimum but finer graphite and slightly higher hardness.
Sources
- ASTM A48/A48M — Standard Specification for Gray Iron Castings — ASTM International (2022)
- GB/T 9439 (HT150) — SAC (2010)
- EN 1561 Founding — Grey cast irons (EN-GJL-150) — CEN (2011)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (Gray Iron) — ASM International (1990)
- ASM Handbook Vol.15 — Casting — ASM International (2008)
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.