ASTM A302 Grade D Steel Plate Properties, Composition, Applications and Supplier Guide

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ASTM A302 Grade D steel plate is a manganese-molybdenum-nickel (Mn-Mo-Ni) alloy steel plate manufactured for welded boilers and pressure vessels operating under moderate to elevated temperature. As the highest-alloy member of the ASTM A302 family (Grades A, B, C and D), Grade D adds 0.70–1.00% nickel to the Mn-Mo base, delivering an excellent balance of tensile strength, elevated-temperature stability and notch toughness. The grade is also specified under ASME code construction as SA302 Grade D, making it a common material choice for boiler drums, reactors, heat exchangers and large storage spheres in the oil, gas, chemical and power generation industries.
In this guide, we cover the chemical composition, mechanical properties, heat treatment, fabrication characteristics and typical applications of A302 Grade D steel plate, along with practical advice for buyers specifying this grade.

What Is ASTM A302 Grade D?
ASTM A302/A302M is the standard specification for pressure vessel plates, alloy steel, manganese-molybdenum and manganese-molybdenum-nickel. The four grades share the same manganese and molybdenum bands; what distinguishes each grade is its nickel content:

Grade A – Mn-Mo base, no specified nickel

Grade B – Mn-Mo base, no specified nickel, minimum yield 345 MPa

Grade C – Mn-Mo-Ni with 0.40–0.70% Ni (heat analysis)

Grade D – Mn-Mo-Ni with 0.70–1.00% Ni (heat analysis), the highest-nickel A302 grade

The nickel addition does not primarily raise room-temperature strength — Grades B, C and D share identical tensile requirements. Instead, nickel in Grade D improves fracture toughness and helps the plate meet demanding drawing and code requirements for thick-section vessels. Note that a Grade C heat cannot be re-certified as Grade D; the nickel band must fall within the Grade D limits.
ASTM A302 Grade D is produced as killed steel, supplied to pressure vessel quality (PVQ) requirements under ASTM A20, and is normally supplied in the normalized condition, with normalizing plus tempering for thicker sections.

Chemical Composition of ASTM A302 Grade D:
The following table shows the heat (ladle) analysis requirements per ASTM A302/A302M:

Element	Requirement (Heat Analysis)
Carbon (C)	≤ 0.20% (t ≤ 25 mm); ≤ 0.23% (25–50 mm); ≤ 0.25% (t > 50 mm)
Manganese (Mn)	1.15 – 1.50%
Silicon (Si)	0.15 – 0.40%
Molybdenum (Mo)	0.45 – 0.60%
Nickel (Ni)	0.70 – 1.00%
Phosphorus (P)	≤ 0.025%
Sulfur (S)	≤ 0.025%

Product analysis tolerances (when required by ASTM A20) allow, for example, Mn 1.07–1.62%, Mo 0.41–0.64% and Ni 0.67–1.03%. Carbon equivalent (CE) limits and tighter residual element restrictions can be added as supplementary requirements when specified.

Mechanical Properties of A302 Grade D:

Property	Requirement
Tensile strength	550 – 690 MPa (80 – 100 ksi)
Yield strength, min	345 MPa (50 ksi)
Elongation in 200 mm (8 in.), min	17%
Elongation in 50 mm (2 in.), min	20%
Density	7.85 g/cm³
Typical hardness (as treated)	160 – 200 HB

Test specimens are prepared under ASTM A20. Where a simulated post-weld heat treatment (PWHT) is specified, coupons are heat-treated through the vessel cycle before testing. Charpy V-notch impact testing at service temperature (e.g. −20 °C, −40 °C or lower) is frequently specified as a supplementary requirement for critical vessels.
Heat Treatment of ASTM A302 Grade D:
The standard heat treatment is normalizing — typically in the 890–950 °C range followed by air cooling — with tempering at approximately 590–650 °C applied to develop uniform properties across the section and reduce internal stress. Plates above roughly 50 mm are generally required to be supplied normalized to guarantee through-thickness consistency.

Fabrication: Cutting, Forming and Welding A302 Grade D

Cutting

A302 Grade D plates can be cut by flame cutting, plasma cutting or mechanical shearing. Because of the alloy content and thick sections typical of this grade, preheating the cut line to roughly 80–150 °C is recommended to avoid cold cracking at the cut edge, and slow cooling after heavy flame cutting helps preserve edge quality. For precision profiles — nozzle openings, manways, shell dishes — CNC flame or plasma cutting with a controlled heat input is standard practice.

Forming

Cold bending and rolling are carried out at room temperature or with low preheat; a minimum bending radius of about 1.5 × plate thickness is a common starting point for shell courses. Hot forming, when required, should be followed by re-normalizing to restore mechanical properties.

Welding

The grade is readily weldable with standard low-alloy procedures:

Processes: SMAW, GTAW, SAW and GMAW with matching low-alloy, low-hydrogen consumables (e.g. E7018-type electrodes or equivalent SAW wires)

Preheat: typically 100–150 °C depending on thickness and restraint

PWHT: stress-relief tempering in the 595–650 °C range where required by the fabrication code

Weld procedures should be qualified per ASME Section IX for code vessels, and interpass temperature and hydrogen control deserve particular attention on thick sections.

Typical Applications of ASTM A302 Grade D Steel Plate:

Because it combines high tensile strength with elevated-temperature stability and good toughness, A302 Grade D is specified for:

Boiler drums in thermal power plants

Reactors, heat exchangers and separators in petrochemical and refining service, including hydrogenation units

Spherical storage tanks and liquefied gas vessels

High-pressure vessels in chemical processing

Hydropower and nuclear plant structural pressure components

The grade is suited to continuous service at moderate to elevated temperature (commonly referenced up to about 410 °C, with allowable stresses governed by the applicable design code).

A302 Grade D vs Grade B and Grade C: Which Should You Order?

Grade	Alloy system	Ni (heat analysis)	Yield min	Tensile
A302 Gr. B	Mn-Mo	Not specified	345 MPa	550–690 MPa
A302 Gr. C	Mn-Mo-Ni	0.40–0.70%	345 MPa	550–690 MPa
A302 Gr. D	Mn-Mo-Ni	0.70–1.00%	345 MPa	550–690 MPa

Practical rule: order Grade D when the drawing explicitly names A302 Gr D or requires 0.70–1.00% nickel; if 0.40–0.70% Ni is sufficient, Grade C is the correct (and typically more economical) band; if no nickel is required, Grade B delivers the same strength at lower alloy cost.

Buying Guide: What to Specify When Ordering A302 Grade D

To avoid re-work and certification disputes, include these points in your enquiry or purchase order:

Dimensions – thickness range (commonly 6–150 mm; heavier by enquiry), width and length

Delivery condition – normalized, or normalized + tempered

Certification – EN 10204 3.1 or 3.2 / third-party inspection (TUV, SGS, BV, etc.)

Supplementary tests – Charpy impact at service temperature, ultrasonic examination (e.g. ASTM A578 level), simulated PWHT mechanical testing

Marking and traceability – heat number, plate number and stamping requirements per A20

Frequently Asked Questions

What is the difference between A302 Grade D and SA302 Grade D?

They are the same steel. SA-302 Grade D is the ASME Boiler and Pressure Vessel Code designation that adopts the ASTM A302/A302M requirements; vessels built to ASME code use the SA prefix.

What is the yield strength of ASTM A302 Grade D?

The specified minimum yield strength is 345 MPa (50 ksi), with a tensile strength range of 550–690 MPa (80–100 ksi). Actual mill test values are typically higher than the minimum.

What is A302 Grade D used for?

It is used mainly for welded boilers and pressure vessels — boiler drums, reactors, heat exchangers, separators, spherical tanks and LPG vessels — in power generation, refining, chemical and gas industries.

Is ASTM A302 Grade D suitable for low-temperature service?

The nickel addition improves toughness relative to Grade B, and Charpy impact requirements at low temperatures can be specified as supplementary requirements. For dedicated cryogenic service, however, nickel-alloy grades such as ASTM A203 or A553 are normally more appropriate.

Can A302 Grade D plates be flame cut?

Yes. Flame, plasma and mechanical cutting are all suitable, with preheat of about 80–150 °C recommended for thicker sections to prevent edge cracking.

Conclusion

ASTM A302 Grade D steel plate remains a reliable, code-recognized choice for thick-wall welded pressure equipment that needs 550–690 MPa tensile strength together with dependable toughness at elevated temperature. Understanding its composition bands — especially the 0.70–1.00% nickel requirement — and its normalizing/PWHT behavior helps buyers order the right grade the first time and helps fabricators plan cutting, forming and welding procedures that pass code inspection without surprises.