AISI 4330V is the nickel-chrome-molybdenum steel behind most of the high-strength downhole tooling in service today — drill collars, jar bodies, heavy-weight drill pipe, tool joints and pressure-control components. This data sheet pulls the chemistry, the three strength classes, the AMS 6411 limits, the heat treatment window and the 4330V / 4330V Mod comparison into one page, so a specification can be checked without reconciling five separate tables.
Key takeaways
- 4330V is supplied in three minimum-yield classes: 135 ksi, 150 ksi and 155 ksi, each with its own hardness and Charpy requirement.
- Vanadium at 0.05–0.10% is what separates 4330V from plain 4330: it refines grain size and lifts impact toughness at the same strength.
- 4330V Mod widens the chemistry window and is the grade that satisfies AMS 6411 / AMS 6427 aerospace callouts after VAR or ESR remelting.
- Large sections must be normalised before austenitising; skipping that step is the usual cause of scattered impact results in bars over 10 in.
4330V Data Sheet: The Numbers in One Table
| Designation | AISI 4330V / UNS G43306 (4330V Mod per AMS 6411) |
| Class | Low-alloy Ni-Cr-Mo-V steel, quenched and tempered |
| Product standards | ASTM A26, ASTM A646, API 7-1 (drill stem elements) |
| Aerospace standards | AMS 6411, AMS 6427, BMS 7-122, BMS 7-27, FMS 1012, EMS 96242 |
| Delivery condition | Quenched and tempered, stress relieved on request |
| Typical hardness | 30–36 HRC (135 ksi) / 34–40 HRC (150 and 155 ksi) |
| Density | 7.84 g/cm³ (0.283 lb/in³) |
| Specific heat | 0.16 cal/g·°C (0.16 Btu/lb·°F) |
| Typical forms | Forged round bar, hollow bar, bored bar, near-net forgings |
Chemical Composition of 4330V and 4330V Mod
The 4330V range is deliberately tight on phosphorus and sulphur. Both are treated as residuals to be suppressed, not alloying elements: above roughly 0.015% P the temper embrittlement risk at 150–155 ksi rises sharply, and sulphur above 0.010% drops transverse toughness in large sections.
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | V |
|---|---|---|---|---|---|---|---|---|---|
| 4330V | 0.30–0.34 | 0.75–1.00 | 0.15–0.35 | ≤ 0.025 | ≤ 0.010 | 0.75–1.00 | 0.40–0.50 | 1.65–2.00 | 0.05–0.10 |
| 4330V Mod | 0.28–0.34 | 0.60–1.00 | 0.10–0.40 | ≤ 0.015 | ≤ 0.010 | 0.60–1.10 | 0.35–0.65 | 1.65–3.10 | 0.05–0.15 |
Values in weight percent. Single values are maximum unless a range is shown.
What each element is doing
- Carbon (0.30–0.34%) — carries the strength. Below 0.28% the 155 ksi class becomes difficult to reach without over-alloying; above 0.35% toughness and weldability fall away.
- Nickel (1.65–2.00%) — the toughness element. It lowers the ductile-to-brittle transition and is the main reason 4330V keeps Charpy values that a 4140 of the same strength cannot.
- Chromium (0.75–1.00%) — hardenability and modest corrosion resistance; forms the carbides that survive tempering.
- Molybdenum (0.40–0.50%) — suppresses temper embrittlement and keeps strength at temperature, which matters for downhole service where the tool sits at 120–175 °C.
- Vanadium (0.05–0.10%) — grain refinement and secondary hardening during tempering. This is the addition that lets 4330V hold impact toughness at 150–155 ksi.
- Manganese and silicon — deoxidation and hardenability; silicon also contributes solid-solution strengthening.
Mechanical Properties by Strength Class
4330V is not a single set of properties. It is a family of three minimum-yield classes, and the class has to be stated in the purchase order — “4330V” alone leaves the supplier to choose.
| Property (minimum) | 135 ksi class | 150 ksi class | 155 ksi class |
|---|---|---|---|
| 0.2% proof stress (ksi) | 135 | 150 | 155 |
| Tensile strength (ksi) | 145 | 160 | 165 |
| Elongation (%) | 14 | 14 | 14 |
| Reduction of area (%) | 50 | 45 | 45 |
| Hardness (HRC) | 30–36 | 34–40 | 34–40 |
| Hardness (HBW) | 286–341 | 319–371 | 319–371 |
| Charpy V-notch at 23 °C (J) | 65 | 54 | 54 |
| Charpy V-notch at −20 °C (J) | — | 32 | 27 |
| Charpy V-notch at −40 °C (J) | 50 | — | — |
Test location matters as much as the value. For bar from 1 to 10 in the specimen is taken at mid-radius; from 10 to 12.5 in it is taken 1 in below the surface. A certificate that reports mid-radius results for a 12 in bar is not testing the region that governs.
Actual production data at 155 ksi
The table below is a production test record for a 4330V 155 ksi heat supplied by SHUNFU — the reference point when comparing a quotation against a data sheet minimum.
4330V Mod VAR to AMS 6411
The aerospace version of the grade is remelted — vacuum arc remelted (VAR) as standard, with electro-slag remelting (ESR) permitted when the end user specifies it. Remelting is not a quality gesture; it is what brings hydrogen, oxygen and inclusion content down to the levels the fatigue and fracture-toughness requirements assume.
| Cross-section area | Tensile strength | 0.2% yield | Avg. reduction of area | Individual minimum |
|---|---|---|---|---|
| Up to 144 in² incl. | 220 ksi | 185 ksi | 35% | 30% |
| Over 144 to 225 in² incl. | 220 ksi | 185 ksi | 30% | 25% |
| Over 225 in² | 220 ksi | 185 ksi | 25% | 20% |
Inspection and microstructure requirements
- Each bar 100% ultrasonically tested to ASTM A388, acceptance to API 6A PSL 3 / PSL 4.
- Above a rolled size of 10.25 in, the central 20% of the bar is excluded from ultrasonic coverage.
- Grain size ASTM 5 or finer.
- Minimum reduction ratio 4:1 from ingot or bloom to finished bar.
Heat Treatment Window
| Step | Temperature | Practice |
|---|---|---|
| Normalise | 871–927 °C (1600–1700 °F) | Air cool; required for large sections |
| Austenitise | 843–871 °C (1550–1600 °F) | 15 min per inch of thickness, oil quench |
| Temper | 260–593 °C (500–1100 °F) | Selected by strength class |
| Temper for 220–240 ksi UTS | 260–371 °C (500–700 °F) | AMS 6411 condition |
Furnaces are surveyed and calibrated to AMS 2750. Material is austenitised and liquid quenched, then tempered to the selected strength variant, and supplied stress-free or stress-relieved.
Forging, Machining and Welding
Forging
Forge between 1066 and 1232 °C (1950–2250 °F). Because of the high hardening capability, preheat the tooling and either furnace-cool or cool in ash or lime after forging. Air cooling a large 4330V section is how cracking starts.
Machining
Normalise and temper at a maximum of 677 °C before rough machining. The steel can be machined at full strength, but then needs a stress relief at approximately 204 °C afterwards to avoid distortion when the bore is opened up.
Welding
Weldability is good relative to the strength level, provided preheat and post-weld heat treatment are applied. Resistance flash welding is the common production route for tool joints.
4330V vs 4330V Mod: Which One to Specify
The two grades share a base composition; the “Mod” designation widens the windows and tightens the residuals, which is what allows a mill to guarantee the higher strength classes in large sections and to meet the aerospace callouts.
| Aspect | 4330V | 4330V Mod |
|---|---|---|
| Governing standards | ASTM A26, ASTM A646, API 7-1 | AMS 6411 / 6427, OEM specs |
| Melting route | EAF + ladle refining + vacuum degassing | Plus VAR or ESR remelt |
| Phosphorus limit | ≤ 0.025% | ≤ 0.015% |
| Nickel range | 1.65–2.00% | 1.65–3.10% |
| Typical use | Drill collars, jars, HWDP, tool joints | Aerospace landing gear, high-stress shafts |
Three Specification Mistakes That Cost Bars
- Calling out “4330V” without a strength class. The three classes carry different tempering temperatures and different acceptance values. Without a class the mill will supply whichever is convenient, and the MTR may not match the drawing.
- Ignoring the test location. Mid-radius values on a 12 in bar are not representative of the surface region that carries bending stress. Specify the sampling position alongside the property.
- Skipping normalising on large sections. Direct austenitise-and-quench from the forging heat leaves a mixed grain structure, and the Charpy scatter shows up only after the bar is already cut.
For a comparison against the neighbouring downhole grades, see 4130 vs 4140 vs 4145H Mod. If hardness consistency across a bar section is the concern, the method in four-quadrant hardness testing is the practical check.
Frequently Asked Questions
Is 4330V the same as 4330?
No. 4330 is the base Ni-Cr-Mo grade; 4330V adds 0.05–0.10% vanadium for grain refinement and secondary hardening, which raises achievable strength and impact toughness. A 4330 bar will generally not meet the 155 ksi class with acceptable Charpy values.
What does the “V Mod” in 4330V Mod mean?
It marks a composition-adjusted variant with wider alloy ranges and tighter phosphorus, produced to aerospace specifications such as AMS 6411 and normally remelted by VAR or ESR. It is the grade used where fracture toughness and cleanliness are specified, not just strength.
Can 4330V be welded in the field?
Only with preheat, a controlled interpass temperature and post-weld heat treatment. Without PWHT the weld and heat-affected zone sit at a hardness that is prone to hydrogen cracking under load.
What size range is available in hollow bar?
Hollow bar is typically produced in outside diameters from roughly 4 to 24 in with bore sizes selected to leave a wall thick enough to machine the final component. See the 4330V forged Q&T hollow bar range for the current size list.
Does 4330V resist hydrogen embrittlement?
It can be processed for sour service, but resistance is a function of hardness, cleanliness and stress level rather than the grade name. For H₂S-bearing wells the maximum hardness usually has to come down below the standard 150–155 ksi class.
Available Forms and Supply
SHUNFU METAL supplies 4330V and 4330V Mod as forged and rolled alloy steel bar in the 135, 150 and 155 ksi classes, and as quenched and tempered hollow bar for drill collar and jar bodies. Every heat is supplied with an MTR traceable to heat number, ultrasonic report to ASTM A388, and grain size and reduction ratio records.
Related grades we hold or roll to order: 4145H Mod for drill collars and stabilisers, and 4130 hollow bar for lower-strength, higher-toughness tooling.
Need 4330V to a specific class? Send the strength class, section size, test location and any OEM specification, and we will confirm chemistry, heat treatment route and lead time. Request a quotation.
