4340QT Alloy & Carbon Round Bar
AISI 4340 · JIS SNCM439 · DIN 36CrNiMo4 (1.6511)
4340QT is AISI 4340 (JIS SNCM439, DIN 36CrNiMo4) supplied in the pre-quenched and pre-tempered condition. The addition of approximately 1.8% nickel over 4140/SCM440 is the defining feature of 4340 — nickel enhances toughness, particularly at low temperatures, and improves hardenability to ensure consistent through-hardness in larger cross-sections (up to 150 mm diameter and beyond). This makes 4340 the go-to grade when both high strength and high toughness are required simultaneously.
product-4340qt-alloy-bar.jpg
Image placeholder
Material Properties
At a given hardness level, 4340 consistently outperforms 4140 in toughness (impact energy) — typically by 30–50% at equivalent hardness. This is directly attributable to the nickel addition which stabilizes the austenite, refines the martensite, and reduces susceptibility to hydrogen embrittlement. Hardenability is excellent: sections up to 150 mm can be through-hardened to high hardness via oil quench. The steel is particularly valuable in applications involving shock loading, thermal gradients, or cryogenic service temperatures.
4340 was originally developed for aircraft landing gear and other safety-critical aerospace applications, where the combination of high tensile strength (>1 000 MPa), excellent fatigue strength, and resistance to brittle fracture is non-negotiable. These same characteristics make it indispensable in heavy mining equipment, marine shafts, large industrial gears, and oil & gas drill collars.
PT. Precision Special Steel supplies 4340QT in round bar form. The "QT" designation means the bar is pre-hardened at the mill, typically to 28–34 HRC, ready for direct machining to finished component dimensions.
Chemical Composition (%)
| Element | Content (%) |
|---|---|
| C | 0.38 – 0.43 |
| Si | 0.15 – 0.35 |
| Mn | 0.60 – 0.80 |
| Cr | 0.70 – 0.90 |
| Mo | 0.20 – 0.30 |
| Ni | 1.65 – 2.00 |
| P | ≤ 0.025 |
| S | ≤ 0.025 |
Mechanical Properties
| Property | Value |
|---|---|
| Hardness (Supply Condition) | 28 – 34 HRC (280 – 330 HB) |
| Tensile Strength | 1 000 – 1 200 MPa |
| Yield Strength (0.2%) | 860 – 1 060 MPa |
| Elongation | ≥ 11% |
| Impact Toughness (KU2) | ≥ 78 J |
| Fatigue Limit | ~540 MPa (R = -1) |
Heat Treatment
As Supplied
Pre-hardened Q&T. Ready to machine for most applications in the 28–34 HRC range.
Stress Relief (optional)
450–550°C for 2–4 hours after heavy machining for dimensional stability in critical parts.
Re-hardening (if required)
Austenitise at 800–845°C, oil quench, temper at 540–680°C to target hardness. Contact PSS technical team.
Typical Applications
Frequently Asked Questions
What forms is 4340QT available in?
What are the international standard equivalents for 4340QT?
Do you offer cutting and machining services for 4340QT?
Is 4340QT supplied with a mill test certificate?
Alloy & Carbon Round Bar
Related Grades
Other grades in the same product family that may suit your application.
product-scm440-alloy-bar.jpg
Image placeholder
SCM440
★Alloy & Carbon Round Bar
Chromium-molybdenum alloy steel for high-strength shafts, gears, and structural parts. Excellent combination of strength, toughness, and fatigue resistance in the quenched and tempered condition.
View Details →product-4140qt-alloy-bar.jpg
Image placeholder
4140QT
Alloy & Carbon Round Bar
AISI 4140 chromium-molybdenum steel supplied in the quenched and tempered condition (28–34 HRC) — ready for machining into high-strength components without further heat treatment.
View Details →product-s45c-alloy-bar.jpg
Image placeholder
S45C
★Alloy & Carbon Round Bar
Standard medium-carbon steel round bar for general machinery components. Widely available, readily machinable, and heat-treatable — the workhorse of industrial manufacturing.
View Details →Need 4340QT in Indonesia?
Get a competitive quote within 1 business day. Material in stock at our Cikarang warehouse — available for same-day cutting and in-house CNC machining.