4140QT Alloy & Carbon Round Bar
AISI 4140 (Q&T condition) · JIS SCM440 (Q&T condition) · DIN 42CrMo4 (Q&T, 1.7225)
4140QT is AISI 4140 (JIS SCM440, DIN 42CrMo4) supplied in the pre-quenched and pre-tempered condition, typically to a hardness range of 28–34 HRC (approximately 280–330 HB). The "QT" designation indicates that the heat treatment — austenitising, quenching, and tempering — has been performed at the mill before delivery, producing a consistent through-hardness that eliminates the need for heat treatment after machining in many applications.
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Material Properties
4140QT round bar is supplied with uniform through-hardness across the cross-section (verified by hardness testing). The typical hardness range of 28–34 HRC corresponds to a tensile strength of approximately 930–1 100 MPa. Machinability at this hardness is practical for CNC turning and milling using appropriate carbide insert grades. The steel retains the characteristic chromium-molybdenum toughness: Charpy impact values are typically 60–100 J at room temperature, ensuring resistance to dynamic and shock loading.
This supply condition is commercially significant for machine shops and component manufacturers who either lack in-house heat treatment capability or need to avoid the distortion risk associated with hardening complex machined geometries. Components that can be machined directly from 4140QT round bar to finished dimensions include hydraulic cylinder rods, fastener stock, jig and fixture components, and general structural shafts.
The distinction from our annealed SCM440 is purely in supply condition — the chemistry is equivalent. Choose 4140QT when the target hardness falls within the pre-tempered range, or SCM440 (annealed) when a higher or lower final hardness is required with custom heat treatment.
Chemical Composition (%)
| Element | Content (%) |
|---|---|
| C | 0.38 – 0.43 |
| Si | 0.15 – 0.35 |
| Mn | 0.60 – 0.90 |
| Cr | 0.90 – 1.20 |
| Mo | 0.15 – 0.30 |
| P | ≤ 0.030 |
| S | ≤ 0.030 |
Mechanical Properties
| Property | Value |
|---|---|
| Hardness (Supply Condition) | 28 – 34 HRC (280 – 330 HB) |
| Tensile Strength | 930 – 1 080 MPa |
| Yield Strength (0.2%) | 780 – 935 MPa |
| Elongation | ≥ 12% |
| Impact Toughness (KU2) | ≥ 63 J |
Heat Treatment
As Supplied
Ready to machine. No further heat treatment required for hardness in the 28–34 HRC range.
Stress Relief (optional)
After heavy machining operations, stress relieve at 450–550°C for 2–4 hours if dimensional stability of finished part is critical.
Typical Applications
Frequently Asked Questions
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Alloy & Carbon Round Bar
Related Grades
Other grades in the same product family that may suit your application.
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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-4340qt-alloy-bar.jpg
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4340QT
Alloy & Carbon Round Bar
Nickel-chromium-molybdenum alloy steel supplied in the Q&T condition — offering the highest strength and toughness combination among our alloy bar grades, ideal for heavy-duty shafts and critical structural components.
View Details →product-s45c-alloy-bar.jpg
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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 4140QT 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.