ASTM B348 Explained: Titanium and Titanium Alloy Bars and Billets

Executive summary: ASTM B348 is the dominant North American specification for titanium and titanium alloy bars and billets. It defines chemical composition limits, mechanical property minima, testing frequency, and certification requirements for round, square, hexagonal, and rectangular product forms used in machining and forging. The standard covers unalloyed grades 1 through 4 and alloy grades such as Ti-6Al-4V Grade 5 and Ti-6Al-4V ELI Grade 23. Procurement teams should not assume that the base standard alone captures all quality requirements. Supplementary testing for ultrasonic integrity, fracture toughness, or microstructure must be specified in the purchase order, and the mill test report must clearly state the standard edition, grade, heat number, and any agreed supplementary requirements.

What ASTM B348 actually covers

ASTM B348 applies to titanium and titanium alloy bars and billets. Bar is supplied in round, square, hexagonal, and rectangular cross-sections. Billet is supplied as solid sections intended for forging or heavy machining. The standard does not cover sheet, plate, strip, tubing, or pipe — those product forms are governed by ASTM B265, ASTM B338, and ASTM B861 respectively. For a direct comparison between bar and plate material standards, see the ASTM B348 vs ASTM B265 comparison.

The standard classifies material by grade. Unalloyed grades 1, 2, 3, and 4 differ primarily in oxygen and iron content, which controls strength and formability. Grade 1 offers the best formability but the lowest strength. Grade 4 offers the highest strength among the unalloyed grades but reduced cold formability. For a broader overview of how these grades relate, see the titanium grades complete guide.

Alloy grades in ASTM B348 include Ti-6Al-4V Grade 5 and Ti-6Al-4V ELI Grade 23. Grade 5 is the most widely used titanium alloy in aerospace and industrial applications. Grade 23 offers lower oxygen content, improved fracture toughness, and better fatigue performance, making it the preferred choice for medical implants and critical aerospace structures.

Mechanical property requirements and grade selection

ASTM B348 specifies minimum tensile strength, yield strength, and elongation for each grade. The exact limits depend on the product form and condition. Annealed bar in Grade 5 must meet a minimum tensile strength of 895 MPa and a minimum yield strength of 828 MPa, with elongation typically 10 percent. Grade 23 ELI has the same minimum tensile strength as Grade 5 but requires a lower oxygen ceiling, which translates to better ductility and fatigue resistance.

The selection between Grade 5 and Grade 23 is a classic engineering trade-off. Grade 5 costs less and is more widely available in larger diameters. Grade 23 offers superior damage tolerance but commands a material premium and may have longer lead times for large billets. For critical rotating components or implant applications, the additional cost is justified by the improved fatigue and fracture performance. For static structural components where fatigue is not the limiting design factor, Grade 5 is usually the more economical choice.

Testing, certification, and supplementary requirements

ASTM B348 requires chemical analysis and tensile testing for each lot. The lot definition follows ASTM practice and is typically based on a single heat and common processing history. The mill test report must include the chemical composition, tensile properties, and identification of the heat number. Surface condition and dimensional tolerances are also defined in the standard.

However, many aerospace and medical applications require testing beyond the base standard. Common supplementary requirements include ultrasonic testing, fracture toughness testing, and microstructure evaluation. These are not automatically included. If the purchase order only states "ASTM B348 Grade 5," the supplier may deliver material that meets the base standard but lacks the additional inspection data required by the end application.

Procurement teams sometimes assume that ordering to a familiar grade automatically includes all relevant quality checks. That assumption creates receiving-inspection failures and schedule delays. The correct practice is to list each supplementary requirement explicitly in the purchase order and to confirm the certification level, such as EN 10204 Type 3.1, before material release. For more detail on material certification, see the titanium material certification and traceability guide.

When to specify ASTM B348 over AMS specifications

ASTM B348 is a general material specification suitable for commercial, industrial, and many aerospace applications. AMS specifications, such as AMS 4928 for Ti-6Al-4V bar, impose tighter chemistry controls, more restrictive mechanical property ranges, and often require additional testing. Aerospace prime contractors frequently require AMS material for flight-critical components.

One persistent procurement mistake is substituting ASTM B348 material for an AMS requirement to save cost or time. While the chemistry and mechanical properties may appear similar on the surface, the documentation, process controls, and acceptance criteria are not equivalent. Downstream audit failures or customer rejection of the material lot usually erase any initial savings.

Three practical procurement rules for ASTM B348 material

Rule 1: Define the product form and dimensional tolerance in the purchase order. ASTM B348 covers multiple cross-sections and conditions. "Round bar, 25.4 mm diameter, annealed, ASTM B348 Grade 5, EN 10204 Type 3.1" is a complete specification. "ASTM B348 Grade 5 bar" is not. Ambiguity in product form invites quotation variation and delivery discrepancies.

Rule 2: Specify supplementary testing explicitly when the application requires it. Ultrasonic inspection, fracture toughness, and microstructure evaluation are not default requirements. If the component will see cyclic loading, cryogenic temperatures, or critical stress concentrations, list the required test method and acceptance criteria. Do not rely on the supplier to infer the requirement from the application.

Rule 3: Confirm the standard edition and heat treatment condition before order placement. ASTM standards are revised periodically. Older revisions may no longer be acceptable to your customer. The heat treatment condition — typically annealed for most grades — must be stated because mechanical properties depend on it. Requesting a specific revision, such as ASTM B348-22, and confirming annealed condition prevents later disagreements.

Manufacturing pathways from bar to finished component

ASTM B348 bar is the starting point for many manufacturing routes. Round bar is turned on CNC lathes for shafts, pins, fasteners, and valve components. Square and rectangular bar is milled for brackets, housings, and structural fittings. Billet is rough-machined or forged into larger structural forms.

The grain structure of bar stock is oriented along the longitudinal axis. For components with features machined transverse to the bar axis, this orientation can affect fatigue crack initiation and fracture toughness. In critical applications, procurement teams should specify the desired grain orientation or require mechanical testing in the relevant direction. For more on machining cost factors, see the titanium CNC machining cost factors guide.

For organizations sourcing ASTM B348 material for upcoming programs, specifying the grade, product form, condition, supplementary testing, and certification level clearly in the RFQ is the single most effective way to reduce quotation variance and prevent material rejection. Submit your requirements through the RFQ portal for a technical review and firm quotation.