Steel A48 Class 40-SR (Stress relieved)
Heat-treated state
ASTM A48 Class 40 · EN EN-GJL-250, GG25 · JIS FC250 · GB HT250
Choose for dimensionally critical machined parts (machine bases, valve bodies) to remove casting residual stress with almost no loss of strength.
Values for the SR condition
Other A48 Class 40 tempers and conditions
A48 Class 40 is listed in 6 conditions; see the grade overview at A48 Class 40.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Use when maximum machinability is needed and the strength drop from decomposing pearlite is acceptable. | 165 | 230 | 0.9 | 165 HB | 2.4 % IACS |
Class 40C | Heavy-section castings; slower cooling coarsens graphite so strength and hardness fall to the class minimum. | 213 | 278 | 0.7 | 17 HRC | 2.3 % IACS |
SRThis page Stress relieved | Choose for dimensionally critical machined parts (machine bases, valve bodies) to remove casting residual stress with almost no loss of strength. | 220 | 285 | 0.6 | 230 HB | 2.2 % IACS |
ACDefault Spheroidize annealed | Standard commercial supply condition for sand castings of medium wall thickness. | 225 | 293 | 0.6 | 235 HB | — |
Full hard | Pick for wear surfaces — ways, cam faces, cylinder bores — where a hard martensitic skin over an unchanged gray-iron core is wanted. | 230 | 293 | 0.4 | 50 HRC | 2 % IACS |
Class 40A | Thin-section castings where faster cooling gives finer graphite and higher strength/hardness. | 240 | 310 | 0.5 | 23 HRC | 2.1 % IACS |
What is A48 Class 40-SR?
A48 Class 40-SR is A48 Class 40 heat treated to SR — choose for dimensionally critical machined parts (machine bases, valve bodies) to remove casting residual stress with almost no loss of strength. A48 Class 40-SR has a yield strength of 220 MPa (31.9 ksi) and a tensile strength of 285 MPa (41.3 ksi) — weaker than 98% of steel grades. Elongation at break is 0.6% and the elastic modulus is 125 GPa (18.1 Msi). A48 Class 40-SR has a density of 7.15 g/cm³ (0.258 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F). AC is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.7 kg CO₂/kg, better than 99% of steel grades
- Easy to machine — 68/100, better than 95% of steel grades
Limitations
- Low stiffness — 125 GPa (18.1 Msi), worse than 99% of steel grades
- Limited ductility — 0.6%, worse than 99% of steel grades
- Low fracture toughness — 16 MPa·√m (14.6 ksi·√in), worse than 99% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
- Hard to polish — 35/100, worse than 99% of steel grades
A48 Class 40-SR properties
Typical room-temperature values for A48 Class 40-SR; 21 are specific to this condition. Other listed values are A48 Class 40 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A48 Class 40-SR has a density of 7.15 g/cm³ (0.258 lb/in³), lighter than 99% of steel grades. It melts at 1,150°C (2,102 °F).
Mechanical14
A48 Class 40-SR has a yield strength of 220 MPa (31.9 ksi) and a tensile strength of 285 MPa (41.3 ksi) — weaker than 98% of steel grades. Elongation at break is 0.6% and the elastic modulus is 125 GPa (18.1 Msi).
Thermal6
A48 Class 40-SR is rated for continuous service to 400°C (752 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
A48 Class 40-SR conducts electricity at 2.2 % IACS, worse than 98% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of A48 Class 40-SR takes about 18 MJ of energy and emits 1.7 kg of CO₂ — less than 100% of steel grades. Typical recycled content is 90%.
Manufacturability8
A48 Class 40-SR's machinability is good (68/100, better than 95% of steel grades); weldability poor (25/100); 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 40-SR
Is A48 Class 40 easy to machine?
Machines easily and gives short broken chips — run dry or with air blast, use carbide (K10/K20) or CBN at high speed; expect abrasive wear from casting skin and hard edges, so break through the skin on the first cut.
Can A48 Class 40 be welded?
Poor weldability: repair only, using nickel or NiFe electrodes with 300–500 °C preheat, short stringer beads with peening, and slow cool to avoid white-iron/crack-prone HAZ.
Can A48 Class 40 be formed, bent or molded?
Not formable — shape is fixed in the mould; excellent green-sand/shell fluidity, low shrinkage (~1%) and good feeding, but control section transitions and cooling rate to keep hardness and strength uniform.
What surface finishes work on A48 Class 40?
Shot-blast then prime/paint or phosphate for corrosion protection; can be flame/induction hardened or nitrided for wear; not anodizable and graphite flakes limit polished or chrome-plated finishes.
A48 Class 40 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; ASTM A48 does not fix composition — typical foundry practice for Class 40 / HT250 | 2.9 – 3.4 | 3.2 |
| Si | 1.6 – 2.3 | 1.9 |
| Mnpearlite stabilizer | 0.6 – 1 | 0.8 |
| P | ≤ 0.15 | 0.08 |
| S | ≤ 0.12 | 0.08 |
| Croptional, to raise strength/hardness in heavy sections | 0 – 0.35 | 0.2 |
| Cuoptional pearlite promoter | 0 – 0.6 | 0.2 |
| Fe | balance | — |
A48 Class 40-SR — frequently asked
What is A48 Class 40-SR used for?
A48 Class 40-SR is typically used for cylinder blocks, gearbox housings, brake drums and machine frames. In short: higher-strength gray iron class; excellent vibration damping; free-machining ferrous casting.
What is the yield strength of A48 Class 40-SR?
A48 Class 40-SR has a typical yield strength of 220 MPa (31.9 ksi) and a tensile strength of 285 MPa (41.3 ksi) — weaker than 98% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is A48 Class 40-SR easy to machine?
Reasonably — machinability is rated good (68/100, better than 95% of steel grades). Machines easily and gives short broken chips — run dry or with air blast, use carbide (K10/K20) or CBN at high speed; expect abrasive wear from casting skin and hard edges, so break through the skin on the first cut.
Can A48 Class 40-SR be welded?
Not readily — weldability is rated poor (25/100). Poor weldability: repair only, using nickel or NiFe electrodes with 300–500 °C preheat, short stringer beads with peening, and slow cool to avoid white-iron/crack-prone HAZ.
What surface finishes work on A48 Class 40-SR?
Shot-blast then prime/paint or phosphate for corrosion protection; can be flame/induction hardened or nitrided for wear; not anodizable and graphite flakes limit polished or chrome-plated finishes.
Can A48 Class 40-SR be formed, bent or molded?
Not formable — shape is fixed in the mould; excellent green-sand/shell fluidity, low shrinkage (~1%) and good feeding, but control section transitions and cooling rate to keep hardness and strength uniform.
What is the maximum service temperature of A48 Class 40-SR?
A48 Class 40-SR is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A48 Class 40-AC and A48 Class 40-ANN?
AC is the default condition — standard commercial supply condition for sand castings of medium wall thickness. ANN: use when maximum machinability is needed and the strength drop from decomposing pearlite is acceptable. Yield strength is 225 MPa in AC versus 165 MPa in ANN.
Sources
- ASTM A48/A48M — Standard Specification for Gray Iron Castings — ASTM International (2022)
- GB/T 9439 (HT250) — SAC (2010)
- EN 1561 Founding — Grey cast irons (EN-GJL-250) — CEN (2011)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.15 — Casting — ASM International (2008)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- Continuous cast gray iron bar stock datasheets (Class 40 grade) — bar-stock producers (2023)
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.