A514 Quenched & Tempered Steel — 100 ksi Yield High-Strength Plate

ASTM A514 is a family of quenched and tempered alloy steel plates with a minimum yield strength of 100 ksi (690 MPa) across all grades and thicknesses up to 2.5 inches. It is the highest-strength structural steel plate commonly available in North America, used where maximum strength-to-weight ratio is required: military vehicles, long-span bridge girders, crane booms, offshore structures, and heavy-lift equipment.

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A514 Mechanical Properties

The yield-to-tensile ratio of A514 is considerably higher than that of A572-50 (0.77) or A992 (0.77). A high Fy/Fu ratio means less reserve capacity between first yield and fracture — an important consideration for seismic design and plastic design applications, where ductility demands are high.

The Quench and Temper Process

A514 achieves its extraordinary strength through heat treatment, not through carbon content alone. The process has two critical steps:

Quenching (Step 1): The steel plate is heated above its austenitizing temperature (approximately 1,650 degrees F / 900 degrees C), held to ensure complete transformation to austenite, then rapidly cooled by water spray or immersion. This produces a hard but brittle martensitic microstructure with high dislocation density. The cooling rate must be fast enough to avoid the nose of the time-temperature-transformation (TTT) curve — typically faster than 50 degrees F (28 degrees C) per second through the critical 1,100–900 degrees F range.

Tempering (Step 2): The quenched plate is reheated to 1,000–1,300 degrees F (540–700 degrees C), held for a specified time (typically 30–60 minutes per inch of thickness), then air cooled. This allows some carbon to diffuse out of the supersaturated martensite lattice, precipitating fine carbides that restore ductility and notch toughness without sacrificing too much strength. The tempering temperature is the primary control knob: higher temperature = more ductility but lower yield strength.

The result is a microstructure of tempered martensite — an extremely fine-grained structure that provides 100 ksi yield strength while retaining 18% elongation and usable weldability.

A514 Grade Designations and Thickness Availability

A514 covers multiple grades (A through T), each with a slightly different chemical composition optimized for specific thickness ranges and applications. The mechanical properties are identical across all grades — only the alloy chemistry differs.

Thickness effect on strength: For plates thicker than 2.5 inches, the tensile strength reduces to 100–120 ksi (from 110–130 ksi for thinner plates). Grades E, P, and Q are engineered for the thickest sections, with alloy chemistries that provide sufficient hardenability to achieve martensitic transformation through the full thickness.

Boron (B) in A514: Nearly all grades contain 0.0005–0.005% boron as a microalloying addition. Boron is an extraordinarily potent hardenability agent — at just 5–50 parts per million, it significantly delays ferrite and pearlite formation during quenching, allowing the material to form martensite even at slower cooling rates. This is how A514 achieves 100 ksi yield in 6-inch-thick plates without requiring impractical water quenching rates.

Welding A514 — Preheat, Interpass, and Post-Weld Requirements

Welding A514 is demanding but entirely achievable with proper procedures. The two governing principles are:

1. Avoid hydrogen cracking (cold cracking): High-strength martensitic steels are susceptible to hydrogen embrittlement in the heat-affected zone (HAZ). Use low-hydrogen electrodes (H4 or H8), control preheat, and manage cooling rate.
2. Do not over-temper the HAZ: A514's strength comes from the tempering treatment. If a weld pass heats adjacent material above the original tempering temperature, strength can be locally reduced by 10–25 ksi. Control interpass temperature and limit heat input.

Preheat Requirements

Preheat is mandatory for A514. The required temperature depends on thickness, carbon equivalent, and hydrogen level:

Preheat must extend at least 3 inches beyond the weld zone in all directions. Temperature measurement should use temperature-indicating crayons (Tempilstik) or contact thermocouples — infrared guns are unreliable on bare steel surfaces.

Maximum Interpass Temperature

Do not exceed 400 degrees F interpass temperature. Higher temperatures risk over-tempering the HAZ. If interpass temperature rises above 400 degrees F, stop welding and allow to cool to 300 degrees F before resuming.

Filler Metal Selection

Filler metal must match or slightly under-match the base metal strength:

• SMAW (stick): E11018-M or E12018-M (low-hydrogen, -M suffix for military/structural)
• FCAW: E110T5-K4 or E111T1-K4 (gas-shielded flux core)
• GMAW (MIG): ER110S-1 or ER120S-1 solid wire
• SAW: F11A4-EM2-M2 with appropriate flux

Using filler metals significantly weaker than 100 ksi (e.g., standard 70-ksi electrodes) creates an under-matched weld that yields before the base metal, concentrating plastic strain in the weld. This is acceptable for some non-critical applications but requires engineering review.

Post-Weld Heat Treatment (PWHT)

Stress-relief heat treatment for A514 is rarely performed because the required temperature (1,000–1,100 degrees F) would over-temper the base metal, reducing yield strength from 100 ksi to approximately 70–85 ksi. If PWHT is required by code (e.g., pressure vessel applications), specify the minimum time and temperature consistent with the applicable code and accept the strength reduction in design calculations.

A514 vs A913 — Which 100-ksi Steel to Specify?

Both A514 and A913 Grade 70 provide approximately 100 ksi yield strength (note: A913-70 has Fy=70 ksi / 483 MPa; A913-65 has Fy=65 ksi / 450 MPa). For truly equivalent strength to A514, consider A913-70 (70 ksi) plus material overstrength. However, the product form determines which specification applies:

Use A514 when you need high-strength plates for built-up girders, crane booms, pressure vessels, or military equipment. Use A913 when you need high-strength rolled W-shapes for building columns.

Applications of A514 Steel

Bridge Construction

Long-span steel bridges use A514 for girders and box sections where the strength-to-weight ratio reduces the overall steel tonnage. For a 600-foot span, replacing A572-50 with A514 in the bottom flange of girders reduces the flange area by approximately 50%, which reduces fabrication and erection costs. The I-35W Saint Anthony Falls Bridge (Minneapolis) used A514 in critical tension members. However, most US highway bridges use A709 HPS 70W (70 ksi weathering) rather than A514, because the cost premium of 100-ksi steel is rarely justified by weight savings alone for standard spans.

Military and Defense

A514 is specified under MIL-DTL-46100 (formerly MIL-A-46100) for armor plate and structural components of military vehicles. Grades H, K, and M are the most common military designations. The combination of high hardness (up to 293 HBW), high strength, and good weldability makes A514 suitable for blast-resistant structural frames where weight must be minimized for transportability.

Crane and Heavy Equipment

Mobile crane booms, excavator arms, and heavy-lift spreader bars use A514 because every pound saved in the structure translates to additional lifting capacity. A514 Grade C is specifically designed for maximum thickness in crane and earthmoving applications. The 100 ksi yield allows lattice boom chords to be fabricated from thin-walled tubes rather than solid bars, reducing self-weight by 40–60% compared to A572-50 designs.

Pressure Vessels

A514 Grades E, Q, and R are qualified under ASME Boiler and Pressure Vessel Code Section VIII for pressure-retaining components. The high strength allows thinner vessel walls, which is critical for transportable pressure vessels (tube trailers, cryogenic tanks) where weight directly determines payload capacity.

AISC 360 Design Values for A514

AISC 360-22 Specification does not provide separate design values for 100-ksi steel in the main text, because the standard tables are calibrated to 50-ksi steel. For member design with A514, use the general provisions of Chapters D through K with the actual Fy=100 ksi and Fu=110 ksi values.

Compression member design (Chapter E) for A514 requires special attention. The column buckling curve in AISC 360 is calibrated to 50-ksi steels. For 100-ksi steel, the inelastic buckling range (Fe vs Fy relationship) changes because the critical slenderness parameter lambda_c = (KL / pi r) * sqrt(Fy / E) shifts. Columns with intermediate slenderness ratios (KL/r between 40 and 80) will not develop the full 100 ksi due to inelastic buckling — the effective critical stress Fcr must be calculated explicitly using Equation E3-2 or E3-3, not taken from tables developed for 50-ksi steel.

Frequently Asked Questions

What is the difference between A514 and T-1 steel?

T-1 is a trademark of ArcelorMittal (formerly Bethlehem Steel) for a specific grade of 100-ksi quenched and tempered plate. ASTM A514 is the industry standard specification that covers T-1 and equivalent products from all manufacturers. T-1 corresponds most closely to A514 Grade B, with similar chemistry and the same mechanical properties. In specifications, always reference ASTM A514 rather than the trademark to allow competitive bidding.

Can A514 be substituted for A36 or A572-50?

A514 can be substituted where higher strength is beneficial, but not in reverse — you cannot substitute A36 for A514. However, direct substitution of A514 for lower-strength steel requires a complete redesign: deflection limits (which depend on stiffness E, not strength Fy) may govern, connection designs must be checked for the higher transferred forces, and weld metal must be upgraded. The cost premium (50–100%) means substitution is only justified where weight savings produce measurable fabrication, transportation, or erection savings.

Does A514 require post-weld heat treatment?

No. Post-weld heat treatment is generally not recommended for A514 because the PWHT temperature range (1,000–1,100 degrees F) overlaps the original tempering temperature. PWHT will reduce the strength of the HAZ by over-tempering. If PWHT is required by a governing code, the strength reduction must be accounted for in design — typically Fy reduces to 85–95 ksi and Fu reduces to 100–115 ksi.

What electrodes do I need for welding A514?

Use E11018-M or E12018-M low-hydrogen stick electrodes, or equivalent strength filler metals for other processes (E110T5-K4 FCAW, ER110S-1 GMAW). Do not use standard E7018 electrodes — the 70-ksi weld metal will yield before the 100-ksi base metal, concentrating plastic strain in the weld. All electrodes must be stored in a rod oven at 250–300 degrees F to maintain the H4 low-hydrogen classification.

How does A514 compare to A913 high-strength steel?

A514 is a plate product with 100 ksi minimum yield. A913 is a W-shape product available in grades up to 70 ksi yield (Grade 70, which typically runs 75–80 ksi actual yield). For a true 100-ksi W-shape, there is no direct A913 equivalent. A913-70 is the closest at 70 ksi minimum yield. A514 plates can be fabricated into built-up sections with 100 ksi properties, but this adds fabrication cost. For standard rolled beams and columns, use A913 (up to 70 ksi); for plate girders and built-up members, use A514 (100 ksi).