Question 1

What is AISI 4330V / 4330 MOD steel used for?

Accepted Answer

AISI 4330V (also called 4330 MOD or 4330 Modified, per AMS 6411) is a high-performance NiCrMoV alloy steel specified for the most demanding oil & gas downhole drilling and aerospace structural applications. Primary applications include: high-performance drill collars for deepwater, extended reach, and HPHT BHA assemblies per API Spec 7-1 Class 2; MWD/LWD and rotary steerable system (RSS) tool housing mandrels; downhole motor (PDM) mandrels and power section housings; shock sub and drilling jar mandrels for high-energy BHA configurations; aerospace structural forgings and landing gear components per AMS 6411; subsea wellhead equipment bodies; and high-performance pressure vessel closures. It is specified over 4145H when API 7-1 Class 2 toughness requirements cannot be met by 4145H, particularly in deepwater, HPHT, and high-cycle fatigue applications.

Question 2

What is the difference between 4330V and 4145H for drill collar applications?

Accepted Answer

Both 4145H and 4330V are used for API Spec 7-1 BHA components, but they address different performance levels. 4145H is the standard Class 1 (120 ksi YS min) and Class 2 (150 ksi YS min) material. 4330V is specified for Class 2 when the toughness requirements of the application cannot be met by 4145H at Class 2 strength. The key differences are: (1) Toughness - 4330V provides significantly better Charpy impact energy at Class 2 strength levels due to vanadium grain refinement, elevated silicon (resists temper embrittlement), and high nickel (1.65-2.00%). (2) Fatigue resistance - the finer grain structure from vanadium gives better fatigue crack initiation resistance. (3) Cost - 4330V is more expensive and has more limited availability than 4145H. For standard UAE and GCC onshore drilling with API 7-1 Class 1 requirements, 4145H is the correct and more economical choice. For demanding deepwater, extended reach, or HPHT Class 2 applications, specify 4330V.

Question 3

What does AMS 6411 specify for 4330V?

Accepted Answer

AMS 6411 (SAE Aerospace Material Specification) governs the chemistry, cleanliness, and testing requirements for 4330V bar, forgings, and tubing. Key requirements: carbon 0.28-0.34%, silicon 1.45-1.80% (elevated - distinguishing feature), nickel 1.65-2.00%, chromium 0.75-1.00%, molybdenum 0.35-0.50%, vanadium 0.05-0.10% (defining addition). Phosphorus and sulphur are each limited to 0.010% maximum - much tighter than ASTM A29 standard - reflecting the aerospace quality requirement. The specification also references AMS 2300 (premium aircraft quality - ultrasonic and magnetic particle inspection) and AMS 2301 (aircraft quality) for cleanliness levels. When specifying AMS 6411 material, always state the required cleanliness level at order stage.

Question 4

What is API 7-1 Class 2 and how does it differ from Class 1?

Accepted Answer

API Spec 7-1 defines two mechanical property classes for drill collar and BHA components. Class 1 requires minimum yield strength 120 ksi (827 MPa) and minimum UTS 140 ksi (965 MPa) - typically achieved with 4145H Q&T. Class 2 requires minimum yield strength 150 ksi (1034 MPa) and minimum UTS 160 ksi (1103 MPa) - a significantly higher strength level typically achieved with 4330V Q&T. Both classes require minimum elongation 13%, reduction of area 45%, and Charpy impact 54 J (40 ft-lbf) at room temperature. Class 2 is specified for more demanding BHA applications including deepwater drill collars, high-torque directional tools, and extended-reach well components where the higher strength provides better fatigue life and reduced drill collar diameter (allowing larger bore for mud flow at equivalent collapse resistance).

Question 5

Why does 4330V have better toughness than 4145H at high strength levels?

Accepted Answer

The toughness advantage of 4330V over 4145H at equivalent strength levels comes from three compositional features: (1) Vanadium (0.05-0.10%) - acts as a grain refiner during austenitising, producing finer prior austenite grain size. Finer grain boundaries reduce crack propagation rate and improve Charpy impact energy and fracture toughness. Vanadium also inhibits temper embrittlement by combining preferentially with carbon to form fine VC carbides. (2) Elevated silicon (1.45-1.80%) - raises the tempered martensite embrittlement (TME) threshold temperature, allowing higher tempering temperatures (510-560 degrees C vs lower temperatures for 4145H) without loss of strength, and producing better carbide dispersion. (3) Higher molybdenum (0.35-0.50% vs 4145H 0.15-0.25%) - further inhibits temper embrittlement (the reversible temper embrittlement mechanism that affects NiCrMo steels in the 375-575 degrees C range).

Question 6

Is 4330V available to NACE MR0175 for sour service?

Accepted Answer

4330V Q&T to API 7-1 Class 2 specification results in hardness of approximately 30-38 HRC - significantly above the NACE MR0175 / ISO 15156 limit of 22 HRC for CrNiMo alloy steels in H2S environments. Standard Class 2 4330V is therefore NOT NACE MR0175 compliant. For sour service drilling operations where H2S is present in the wellbore fluid, the operator must assess whether the specific H2S partial pressure and chloride concentration in the planned well triggers sulphide stress cracking (SSC) risk at the actual component hardness. In practice, most drill collar applications do not directly expose the drill collar material to formation fluids - the internal bore is protected by drilling mud. Consult Nifty Alloys technical team and the well engineering department for sour service drill collar applications.

Question 7

What sizes of 4330V are available in UAE?

Accepted Answer

Nifty Alloys supplies AISI 4330V / 4330 MOD from our Dubai, UAE warehouse in: Round Bar: 50-400 mm diameter (Q&T per AMS 6411 / API Spec 7-1 Class 2). Hollow Bar: OD 80-400 mm, various wall thicknesses (API 7-1 Class 2 Q&T, specify OD x ID x length). Note: 4330V has more limited stock availability than 4145H. Contact Nifty Alloys to confirm current stock before placing an order. For API Spec 7-1 Class 2 certified material with full CTR, AMS 6411 aerospace-certified material, or non-standard dimensions, contact our technical team.

Question 8

What certifications are supplied with 4330V from Nifty Alloys?

Accepted Answer

Standard supply includes EN 10204 3.1 Mill Test Certificates confirming chemical composition (including vanadium content), mechanical properties, and heat number traceability. For API Spec 7-1 Class 2 applications, a full Certified Test Report (CTR) is required, including: chemical analysis (with V and Si confirmation), Jominy hardenability test, tensile test (YS, UTS, elongation, RA), Charpy V-notch impact test results, and cross-section hardness survey. For AMS 6411 aerospace applications, AMS 2300 or 2301 cleanliness level documentation and ultrasonic/magnetic particle inspection records are available from our AMS-qualified mill sources. All certification requirements must be specified at enquiry stage.

Question 9

What is the double tempering practice for 4330V?

Accepted Answer

Double tempering (tempering twice at the same temperature) is the recommended heat treatment practice for 4330V and is specified in many AMS 6411 and API 7-1 procurement documents. The reason is metallurgical: the first tempering cycle converts the majority of martensite but leaves some retained martensite and austenite. When the part air cools from the first temper, the retained martensite re-transforms. The second tempering cycle then tempers this newly formed martensite. The result of double tempering is: more uniform carbide distribution, reduced retained austenite, better and more reproducible Charpy impact results, and higher dimensional stability. The procedure is: temper at target temperature for 2-4 hours, air cool to room temperature (minimum 1 hour), then repeat at the same temperature for 2-4 hours. Both cycles at identical temperature. Double tempering adds cost but consistently produces better toughness - always specify double temper for critical Class 2 and AMS 6411 aerospace applications.

Question 10

When should I specify 4330V instead of 4340 for BHA applications?

Accepted Answer

4330V is the upgrade from 4340 when maximum toughness at high strength levels is required. 4340 achieves excellent strength (930-1080 MPa Q&T standard engineering) and good toughness, but at Class 2 strength levels (1034 MPa YS min) the toughness margin of 4340 narrows. 4330V is preferred over 4340 when: (1) API 7-1 Class 2 mechanical requirements must be met with the highest possible Charpy impact energy; (2) Deepwater or arctic drilling subjects the drill collar to low temperatures where 4330V nickel content and vanadium grain refinement provide better low-temperature toughness; (3) High-cycle fatigue environments (hard rock, high rotary RPM, extended drilling programs) where the finer grain structure of 4330V improves fatigue crack initiation resistance; (4) AMS 6411 aerospace quality documentation is required alongside API 7-1. For standard onshore UAE drilling at Class 1 requirements, 4145H remains the most economical and widely available specification.

Standard	Designation	Notes
AISI / SAE	4330	Base grade designation.
Common Name	4330V	Common name for the modified grade.
Common Name	4330 MOD	Variant common name (used interchangeably).
Common Name	4330 Modified	Variant common name (used interchangeably).
UNS	G43300	UNS number for base 4330.
AMS	AMS 6411	Primary specification for bar/tube.
Common Name	4330V Class 2	API Spec 7-1 Class 2 material designation. No DIN/EN or BS equivalent - AMS 6411 is the primary procurement reference globally.

Standard	Status	Notes
EN 10204 3.1	Suitable	Mill Test Certificate - standard with all supply.
EN 10204 3.2	Conditional	Independent third-party MTC - available on request.
NACE MR0175 / ISO 15156	Requires Confirmation	Standard Class 2 Q&T hardness (approx 30-38 HRC) exceeds the 22 HRC limit - consult for sour service applications. Verify at order stage.
API Spec 7-1	Conditional	API Spec 7-1 Class 2 CTR available from qualified mill sources - specify at order stage.
AMS 6411	Conditional	AMS 6411 aerospace certification available from qualified mill sources - specify at order stage.

Property	AISI 4330V / 4330 MOD — AMS 6411 — Quenched & Tempered (Q&T)Default	AISI 4330V / 4330 MOD — API Spec 7-1 — Q&T API 7-1 Class 2	AISI 4330V / 4330 MOD — ASTM A29 / A29M — Normalised
Tensile Strength (UTS)range	1103–1310 MPaTypical: 1207 MPaCondition: Room temp, longitudinalNotes: Class 2 range. For aerospace tempers: up to 1580 MPa achievable. Per AMS 6411.	1103 MPaTypical: 1172 MPaCondition: Room temp, longitudinalNotes: API Spec 7-1 Class 2 minimum 160 ksi (1103 MPa). Confirmed on CTR.	1034–1172 MPaTypical: 1100 MPaCondition: Room tempNotes: 4330V normalises to high strength - comparable to many Q&T grades due to high hardenability and alloy content.
Yield Strength (0.2% Proof Stress)range	1034–1172 MPaTypical: 1100 MPaCondition: Room tempNotes: Class 2 min 1034 MPa (150 ksi). Aerospace higher strength tempers: 1172-1380 MPa.	1034 MPaTypical: 1103 MPaCondition: Room tempNotes: API Spec 7-1 Class 2 minimum 150 ksi (1034 MPa). The defining Class 2 requirement.	758–930 MPaTypical: 850 MPaCondition: Room temp
Elongationmin	13 %Typical: 16 %Condition: 50 mm gauge	13 %Typical: 16 %Condition: 50 mm gauge lengthNotes: API Spec 7-1 Class 2 minimum 13%.	10 %Typical: 14 %Condition: 50 mm gauge
Reduction of Areamin	45 %Typical: 55 %Condition: Longitudinal	45 %Typical: 55 %Condition: LongitudinalNotes: API Spec 7-1 Class 2 minimum 45%.	30 %Typical: 45 %Condition: Longitudinal
Hardnessrange	30–38 HRCTypical: 34 HRCCondition: Surface, Rockwell CNotes: Class 2 standard range. Aerospace tempers: 38-46 HRC.	30–38 HRCTypical: 34 HRCCondition: Surface and cross-section surveyNotes: Full cross-section hardness survey required per API 7-1. Verify vs NACE 22 HRC limit if sour service.	310–370 HBTypical: 335 HBCondition: BrinellNotes: Higher than 4145H normalised due to higher Ni and alloy content.
Impact Energy (Charpy V-notch)min	54 JTypical: 81 JCondition: Room tempNotes: API 7-1 Class 2 minimum 54 J. 4330V typically exceeds this significantly due to V grain refinement and double temper. [VERIFY]	54 JTypical: 95 JCondition: Room temp, V-notchNotes: API Spec 7-1 Class 2 minimum 54 J (40 ft-lbf). 4330V typically achieves significantly higher values due to V grain refinement and double temper. Superior Charpy performance vs 4145H Class 2.	—
Impact Energy (Charpy)typical	—	—	27 JCondition: Room tempNotes: Lower than Q&T. DO NOT use normalised 4330V for API 7-1 or AMS 6411 applications - must Q&T. [VERIFY]

Property	AISI 4330V / 4330 MOD — AMS 6411 — Quenched & Tempered (Q&T)Default	AISI 4330V / 4330 MOD — API Spec 7-1 — Q&T API 7-1 Class 2	AISI 4330V / 4330 MOD — ASTM A29 / A29M — Normalised
Density20 degrees C	7.85 g/cm3	7.85 g/cm3	7.85 g/cm3
Modulus of Elasticity25 degrees C	210 GPa	210 GPa	210 GPa
Thermal Conductivity100 degrees C	36 W/m.K	36 W/m.K	36 W/m.K
Coefficient of Thermal Expansion20-100 degrees C	12.3 um/m.degC	12.3 um/m.degC	12.3 um/m.degC
Specific Heat Capacity20 degrees C	475 J/kg.K	475 J/kg.K	475 J/kg.K
Melting Point / RangeSolidus	1425 degrees C	1425 degrees C	1425 degrees C

AISI 4330V / 4330 MOD

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Standard

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Overview

Frequently Asked Questions

What is AISI 4330V / 4330 MOD steel used for?

What is the difference between 4330V and 4145H for drill collar applications?

What does AMS 6411 specify for 4330V?

What is API 7-1 Class 2 and how does it differ from Class 1?

Why does 4330V have better toughness than 4145H at high strength levels?

Is 4330V available to NACE MR0175 for sour service?

What sizes of 4330V are available in UAE?

What certifications are supplied with 4330V from Nifty Alloys?

What is the double tempering practice for 4330V?

When should I specify 4330V instead of 4340 for BHA applications?

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