Steel A48 Class 30-SR (Stress relieved)
Heat-treated state
ASTM A48 Class 30 · EN EN-GJL-200, GG20 · JIS FC200 · GB HT200
Sub-critical stress relief for machine tool bases and precision housings to stabilise dimensions before final machining.
Values for the SR condition
Other A48 Class 30 tempers and conditions
A48 Class 30 is listed in 14 conditions; see the grade overview at A48 Class 30.
- CLASS20
- FERRITIZE-ANN
- CLASS25
- SR
- CLASS30
- FLAME-HARD
- CLASS225
- CLASS35
- CLASS40
- CLASS45
- CLASS325
- CLASS50
- CLASS55
- CLASS60
Compare all 14 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
as-cast, 20 ksi / 150 MPa minimum tensile | Softest, most machinable and most damping grade — pick for thin uncritical covers, weights and counterweights where strength is irrelevant. | 115 | 152 | 0.6 | 156 HB | 55 W/m·K |
Ferritizing annealed (~760–900 °C, softened for machining) | Full ferritizing anneal used when maximum machinability and minimum hardness are needed and strength can be sacrificed. | 120 | 180 | 0.8 | 150 HB | 2.4 % IACS |
as-cast, 25 ksi / 175 MPa minimum tensile | Light-duty castings needing a little more strength than Class 20 while keeping easy machining and high damping. | 130 | 179 | 0.6 | 174 HB | 52 W/m·K |
SRThis page Stress relieved | Sub-critical stress relief for machine tool bases and precision housings to stabilise dimensions before final machining. | 148 | 215 | 0.5 | 183 HB | 2.2 % IACS |
CLASS30Default as-cast, 30 ksi / 200 MPa minimum tensile | The workhorse general-engineering gray iron: best balance of strength, machinability, damping and cost for housings, bases and pump bodies. | 150 | 214 | 0.6 | 210 HB | 50 W/m·K |
Flame/induction surface hardened (~50 HRC case) | Localised hardening of pearlitic gray iron ways, cams and liner bores for wear resistance with a tough machinable core. | 150 | 220 | 0.3 | 50 HRC | 2 % IACS |
Metric Class 225 | Metric-only intermediate class between 200 and 250 MPa, used when a drawing is written to SI tensile minima. | 165 | 235 | 0.6 | 205 HB | 49 W/m·K |
as-cast, 35 ksi / 250 MPa minimum tensile | Higher-strength pearlitic gray iron for pressure-tight bodies, gearboxes, cylinder blocks and machine slides. | 180 | 252 | 0.5 | 212 HB | 48 W/m·K |
as-cast, 40 ksi / 275 MPa minimum tensile | Common continuous-cast bar and heavy-duty casting grade — good wear surfaces, still readily machinable. | 200 | 293 | 0.5 | 21 HRC | 46 W/m·K |
as-cast, 45 ksi / 300 MPa minimum tensile | High-strength alloyed/inoculated gray iron for loaded machine structures, dies and hydraulic bodies. | 220 | 327 | 0.5 | 24 HRC | 44 W/m·K |
Metric Class 325 | Metric-only class between 300 and 350 MPa for SI-specified high-strength gray iron castings. | 235 | 340 | 0.5 | 25 HRC | 43 W/m·K |
as-cast, 50 ksi / 350 MPa minimum tensile | Alloyed pearlitic gray iron for diesel cylinder blocks/heads, heavy machine tool structures and wear parts. | 250 | 362 | 0.4 | 26 HRC | 42 W/m·K |
as-cast, 55 ksi / 375 MPa minimum tensile | Near-maximum-strength flake iron, only achievable with alloying and controlled section size; specify when ductile iron cannot be used. | 270 | 396 | 0.4 | 29 HRC | 40 W/m·K |
as-cast, 60 ksi / 400 MPa minimum tensile | Highest ASTM A48 class — hard, stiff, alloyed gray iron for high-load, high-wear castings; hardest to machine and most section-sensitive. | 290 | 431 | 0.4 | 32 HRC | 38 W/m·K |
What is A48 Class 30-SR?
A48 Class 30-SR is A48 Class 30 heat treated to SR — sub-critical stress relief for machine tool bases and precision housings to stabilise dimensions before final machining. A48 Class 30-SR has a yield strength of 148 MPa (21.5 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 100 GPa (14.5 Msi). A48 Class 30-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). CLASS30 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
- Easy to machine — 87/100, better than 99% of steel grades
Limitations
- Low strength — 148 MPa (21.5 ksi), worse than 100% of steel grades
- Low stiffness — 100 GPa (14.5 Msi), worse than 100% of steel grades
- Limited ductility — 0.5%, worse than 100% of steel grades
- Low fracture toughness — 15 MPa·√m (13.7 ksi·√in), worse than 100% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
A48 Class 30-SR properties
Typical room-temperature values for A48 Class 30-SR; 21 are specific to this condition. Other listed values are A48 Class 30 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A48 Class 30-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).
Mechanical15
A48 Class 30-SR has a yield strength of 148 MPa (21.5 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 100 GPa (14.5 Msi).
Thermal6
A48 Class 30-SR is rated for continuous service to 350°C (662 °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 µm/m·K (6.11 µin/in·°F).
Electrical3
A48 Class 30-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 30-SR takes about 18 MJ of energy and emits 1.6 kg of CO₂ — less than 100% of steel grades. Typical recycled content is 90%.
Manufacturability8
A48 Class 30-SR's machinability is excellent (87/100, 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 30-SR
Is A48 Class 30 easy to machine?
Excellent dry machining with carbide or ceramic tools — flake graphite breaks chips and lubricates; watch abrasive casting skin, chilled edges and free graphite dust extraction.
Can A48 Class 30 be welded?
Poor weldability: preheat 200–320 °C, use NiFe/Ni electrodes or braze-weld, peen and slow-cool to avoid martensite and cracking — repair only, not structural joining.
Can A48 Class 30 be formed, bent or molded?
Sand/shell/lost-foam casting only; near-zero cold formability, so plan generous fillets, uniform sections ≥5 mm and consider CE and inoculation for section size.
What surface finishes work on A48 Class 30?
Shot-blast then paint, phosphate-and-oil or E-coat; can be black-oxided, hard-chromed or electroless-nickel plated, but graphite flakes limit high-gloss polishing and can cause plating pinholes.
A48 Class 30 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 specifies no chemistry — tensile strength governs | 3.1 – 3.6 | 3.3 |
| Sitypical foundry practice for Class 30 | 1.8 – 2.4 | 2.1 |
| Mn | 0.5 – 0.9 | 0.7 |
| P | ≤ 0.15 | 0.08 |
| S | ≤ 0.15 | 0.09 |
| Croptional, raises strength/pearlite content | ≤ 0.35 | 0.1 |
| Cuoptional strengthener from scrap charge | ≤ 0.5 | — |
| Fe | balance | — |
A48 Class 30-SR — frequently asked
What is A48 Class 30-SR used for?
A48 Class 30-SR is typically used for machine tool bases, pipe fittings, housings, counterweights and manifolds. In short: best-machining cast iron; high vibration damping; lowest-cost iron casting.
What is the yield strength of A48 Class 30-SR?
A48 Class 30-SR has a typical yield strength of 148 MPa (21.5 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 100% of steel grades. Strength varies by condition: see the 14 listed tempers.
Is A48 Class 30-SR easy to machine?
Yes — machinability is rated excellent (87/100, better than 99% of steel grades). Excellent dry machining with carbide or ceramic tools — flake graphite breaks chips and lubricates; watch abrasive casting skin, chilled edges and free graphite dust extraction.
Can A48 Class 30-SR be welded?
Not readily — weldability is rated poor (30/100). Poor weldability: preheat 200–320 °C, use NiFe/Ni electrodes or braze-weld, peen and slow-cool to avoid martensite and cracking — repair only, not structural joining.
What surface finishes work on A48 Class 30-SR?
Shot-blast then paint, phosphate-and-oil or E-coat; can be black-oxided, hard-chromed or electroless-nickel plated, but graphite flakes limit high-gloss polishing and can cause plating pinholes.
Can A48 Class 30-SR be formed, bent or molded?
Sand/shell/lost-foam casting only; near-zero cold formability, so plan generous fillets, uniform sections ≥5 mm and consider CE and inoculation for section size.
What is the maximum service temperature of A48 Class 30-SR?
A48 Class 30-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 30 CLASS30 and A48 Class 30 CLASS60?
CLASS30 is the default condition — the workhorse general-engineering gray iron: best balance of strength, machinability, damping and cost for housings, bases and pump bodies. CLASS60: highest ASTM A48 class — hard, stiff, alloyed gray iron for high-load, high-wear castings; hardest to machine and most section-sensitive. Yield strength is 150 MPa in CLASS30 versus 290 MPa in CLASS60.
Sources
- ASTM A48/A48M — Standard Specification for Gray Iron Castings — ASTM International (2022)
- EN 1561 — Founding: Grey cast irons (EN-GJL-200) — CEN (2011)
- GB/T 9439 — (HT200) — SAC (2010)
- JIS G 5501 — Grey iron castings (FC200) — JISC (1995)
- 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)
- Machinery's Handbook, machinability ratings for cast irons — Industrial Press (2020)
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.