AISI 8630 is a medium-carbon, low-alloy Ni–Cr–Mo steel optimized for forgings and bars where deep hardenability, good toughness and fatigue resistance are required; after proper heat treatment it delivers a balanced combination of strength, wear resistance and impact performance that makes it a preferred choice for oilfield, powertrain and heavy-engineering components.

What is AISI 8630 alloy steel bar?

AISI 8630 (UNS G86300) is a wrought low-alloy steel containing nominally ~0.28–0.33% carbon with deliberate additions of nickel (~0.35–0.75%), chromium (~0.4–0.6%) and molybdenum (~0.15–0.25%). Those alloying additions raise hardenability and toughness relative to plain carbon steels, making 8630 well suited for quenched-and-tempered forgings and heavy shafts where strength through the section and resistance to impact/fatigue are important. The grade is widely stocked as hot-rolled and normalized bars and commonly supplied for parts that require subsequent forging and heat-treating operations.

Key chemical composition

Below is a concise composition table assembled from standard material datasheets and supplier technical notes. Values are typical ranges used by mill and bar suppliers — when specifying, always quote the controlling specification (SAE/AISI, UNS, or AMS) for procurement and inspection.

(Range summary reflects typical mill chemistry used for SAE/AISI 8630 bars; always reference the purchaser’s required spec for acceptance limits.)

Mechanical and physical properties

Mechanical responses vary widely with heat treatment. Below are practical property bands you can expect from commonly available deliveries and after standard quench & temper cycles used in industry.

Typical (hot-rolled / annealed) condition

• Tensile strength: ~480–700 MPa (varies with section and batch).

• Yield strength: ~300–480 MPa (depending on condition).

• Elongation: typically ≥16–22% (in 2" gauge depending on size).

• Brinell hardness (hot-rolled/annealed): ~170–220 HB.

Quenched & tempered condition (common engineering temper ranges)

• Tensile strength: 600–1,200 MPa possible depending on tempering temperature; commonly 620 MPa is cited for typical Q&T shop specs.

• Yield: often 480–900 MPa depending on temper.

• Hardness: usually controlled to a max (e.g., ≤22 HRC) for some oilfield NACE-compliant parts.

Physical

• Density: standard steel ≈ 7,850 kg/m³.

• Thermal conductivity and expansion: similar to other medium-carbon low-alloy steels; consult mill data for precise values for heat-treatment design.

(Values above are representative; specific supply lots and qualification standards determine acceptance limits.)

Common specifications, standards and forms

• Designations: AISI/SAE 8630, UNS G86300. Some suppliers offer “8630 mod” or “8630 H” variants tightened for specific NDT or hardness ranges.

• Forms: Hot-rolled bars, normalized bars, forging stock, round & flat bars, machined forgings.

• Relevant standards & purchasers’ notes: AMS and ASTM cross-references exist for specific product forms; for oilfield / NACE service certain NQT (Net-Quality Type) variants are common.

What is AISI 8630 equivalent to?

There is no single one-to-one across national systems because chemistry and permitted properties shift with spec. Typical cross-references and near-equivalents include variants in SAE/AMS lists and specialist forging grades (e.g., some AMS/ASTM references listed in supplier cross-reference tables). In functional terms, 8630 sits close to other Ni–Cr–Mo low-alloy steels used for heavy forgings; it is often treated as an upgrade over plain Cr-Mo steels where added nickel improves toughness. For specific interchangeability (for procurement or replacement) confirm mechanical and hardenability requirements, not just nominal chemistry.

What is AISI 8630 alloy steel bar used for?

Common end-use sectors and parts:

• Oil & gas: wellhead connectors, hangers, casing connectors and other downhole components where combined fatigue and toughness are required.

• Heavy machinery: shafts, spindles, axles and high-load pins where through-thickness strength and impact resistance are demanded.

• Automotive & powertrain: large gears, crankshafts (in some applications where forging + Q&T is specified).

• Pressure/valve components and general engineering forgings where NACE compliance or specified hardness caps are required.

AISI 8630 vs AISI 4140 — practical differentiation

At a glance, 4140 (Cr-Mo) and 8630 (Ni-Cr-Mo) are neighboring tool-steel/structural alloy families. Chemistry and properties give the checklist:

• Hardenability & toughness: 8630 usually contains nickel which improves low-temperature toughness and hardenability in thicker sections; hence preferred in deep-section forgings where core properties matter. 4140 is widely used and often less costly; it can reach similar strengths but may need different heat-treat schedules for equal toughness at depth.

• Machinability & cost: 4140 typically offers good machinability and is often less expensive than 8630 (nickel adds cost).

• Application choice: choose 8630 when service demands higher through-section toughness and NACE/hardness limits are part of the spec; choose 4140 for many medium-duty parts where cost and availability dominate.

Heat treatment

• Normalization: commonly done after forging to refine grain size.

• Austenitize and quench (oil or controlled quench): then temper to required hardness/toughness. Typical industry practice targets particular HRC ranges (for example ≤22 HRC for specific oilfield NACE acceptance).

• Post-heat control & testing: hardness mapping, PMI/chemistry verification and NDT (UT/MPI) for critical components. For components used in sour service check NACE/AMPP MR0175 requirements and tempered hardness limits.

Machining, welding and fabrication notes

• Machining: in annealed state 8630 machines reasonably well (shop guides often list machinability percentages). Carbide tooling and reduced depths when processing quenched & tempered stock.

• Welding: preheat and controlled interpass temperature are standard practice to avoid cracking; post-weld heat treatment (PWHT) may be required depending on thickness and service.

• Inspection readiness: chemical analysis certificates (mill test cert), hardness maps and traceable heat numbers are typical buyer requirements.

Sizes & weight — round bar quick table and how to calculate mass per meter

Formula (round bar):
mass (kg/m) = (π/4) × (d² mm) × ρ / 1,000,000
with ρ ≈ 7,850 kg/m³ → simplified numeric factor: mass(kg/m) ≈ 0.006168 × d² (d in mm).

Common diameters — mass per metre

(Use the formula to compute any other diameter; round to project precision.) — calculated using standard steel density.

2025 Market snapshot — USA, Europe, China

Important framing: alloy bar prices do not trade on a public exchange like iron ore or hot-rolled coil; they reflect mill & service-center offers, order quantity, required chemistry, sectional size, and finish. What follows is a procurement snapshot and indicative price ranges (ex-works or mill/stock) for alloy round/forging bar forms in mid-2025 market conditions, based on recent industry price indexes and distributor listings. Use these as a starting point — request formal quotations for firm pricing.

How to interpret: these broad bands align to prevailing base-steel price levels (hot-rolled and long-product indexes) plus an alloy / fabrication premium. For small orders or special chemistries (NQT, low-S, low-P) add premium. For very large steady orders you can negotiate mill pricing and stock commitments.

(Sources: pan-industry price trackers and recent market commentary for long products; consult Mill/service center quotes for firm prices.)

FAQs

1. Q. Can 8630 be substituted for 4140?
   A. Sometimes; technically similar in many properties but nickel in 8630 gives better toughness and hardenability in thick sections — verify heat-treatment and hardness acceptance before swapping.

2. Q. Is 8630 suitable for sour service?
   A. Certain 8630 variants (e.g., NQT with hardness limits) can meet NACE/AMPP MR0175 requirements when properly heat treated — specify NACE compliance up front.

3. Q. Typical hardness after Q&T?
   A. Shop practice varies; many components are tempered to values between ~18–28 HRC depending on required toughness. Always specify both hardness limits and Charpy/impact requirements if critical.

4. Q. Can 8630 be induction hardened?
   A. Yes for surface-hardening applications, but final process must be qualified to ensure required case depth and core toughness.

5. Q. Welding recommendations?
   A. Preheat and controlled interpass temps; filler metal choice and PWHT depend on section and service. Consult welding procedure specification (WPS).

6. Q. What inspection certificates are typical?
   A. Mill test certificate (chemical & mechanical), heat number traceability, NDT reports (MPI/UT) for critical parts and hardness maps.

7. Q. Are forging stocks offered in “8630 mod” or special variants?
   A. Yes, many mills supply modified chemistries or heat-treatment-controlled variants to meet oilfield NQT specs.

8. Q. How does 8630 perform at low temperatures?
   A. Nickel content improves low-temperature toughness compared with plain Cr-Mo steels; specify required impact energy at the required temperature to engineer correctly.

9. Q. Lead time for stocked bar orders?
   A. Typical stock orders (standard diameters) can ship in days–weeks from a service center; custom forgings or large diameters may take longer. See MWAlloys section below for our typical lead times.

10. Q. Any special corrosion resistance?
    A. 8630 is not a corrosion-resistant stainless; for corrosive environments apply coatings or select corrosion-resistant alloys.

Why choose MWAlloys for AISI 8630 supply

As an experienced mill & stock supplier, MWAlloys offers:

• Factory direct pricing: 100% mill/plant origin pricing for standard stocked sizes — lower landed cost compared with multi-tier distributors.

• Stock & fast dispatch: common diameters held in China warehouse for rapid export; average stock lead times: 2–10 business days for stocked round bar shipments (confirm per size).

• Quality assurance: full mill test certificates (chemical, mechanical), traceable heat numbers, PMI on request and NDT for critical orders.

• Customization: forging, normalization, quench & temper to buyer temper ranges, and NACE-qualified variants available.

• Global supply: export experience to USA, EU and MENA markets with export packing and documentation.

(If you have a Bill of Materials or target delivery window, MWAlloys can produce a detailed offer showing ex-works pricing, MOQ, and delivery.)

Practical procurement checklist (what to include in RFQ)

• Material designation and exact spec (e.g., SAE/AISI 8630, UNS G86300, or AMS reference).

• Required chemistry tolerances and any low-P/S controls.

• Requested form & surface finish (hot-rolled, normalized, forged).

• Required heat treatment (state on delivery).

• Hardness and Charpy/impact requirements (temperatures).

• NDT requirements (UT, MPI), PMI and MTC expectations.

• Quantity, required delivery term (EXW/FCA/CIF), and target lead time.