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300M Alloy Steel Bar: AMS 6257, AMS 6417, AMS 6419
- John
When engineering challenges demand materials that refuse to fail, 300M Alloy Steel rises to the occasion. SteelPro Group specializes in delivering 300M steel solutions trusted by engineers worldwide.
This article unpacks the science, applications, and products of 300M Alloy Steel. Let’s explore what makes 300M the backbone of high-stakes engineering.
What Is 300M Steel?
300M steel is a durable alloy enriched with silicon, vanadium, carbon, and molybdenum. It is a refined version of AISI 4340. With excellent strength, toughness, and good elongation, it outperforms many aerospace alloys. Its through-hardening capability ensures uniform strength, even in thick sections. However, 300M is sensitive to hydrogen embrittlement and requires protection like oxidation or coating. Its corrosion resistance is limited, making it inappropriate for uses that demand high levels of corrosion protection.
Certified to AMS 6257, AMS 6419, and MIL-S-8844 standards, SteelPro Group 300M is trusted in aerospace applications such as landing gear and rotors.
300M Steel Specifications
- AMS 6257
- AMS 6419
- AMS 6417
- MTL 1201
- MIL-S-8844
- Boeing BMS 7-26
- BS S155
- GJB 5063
- GB/T 38809
These certifications ensure 300M performance in aerospace and defense applications.
300M Steel Chemical Composition
| Element | Content |
| Carbon (C) | 0.4 – 0.45 |
| Silicon (Si) | 1.45 – 1.8 |
| Manganese (Mn) | 0.6 – 0.9 |
| Phosphorus (P) | ≤ 0.01 |
| Sulfur (S) | ≤ 0.01 |
| Chromium (Cr) | 0.7 – 0.95 |
| Nickel (Ni) | 1.65 – 2 |
| Copper (Cu) | ≤ 0.2 |
| Molybdenum (Mo) | 0.3 – 0.5 |
| Vanadium (V) | 0.05 – 0.1 |
300M Steel Mechanical Properties
| Property | Longitudinal Value | Transverse Value |
| Yield Strength (0.2% offset) | 1550 MPa (225 ksi) | 1550 MPa (225 ksi) |
| Tensile Strength | 1900 – 2100 MPa (≥ 275 – 305 ksi) | 1900 – 2100 MPa (275 – 305 ksi) |
| Elongation (%) | 8% | 5% |
| Reduction of Area (%) | 30% | 20% |
300M Steel Products Specification
We supply certified 300M steel in different forms with custom sizes. Our stock includes bars and rounds in a wide range of sizes, adhering to AMS, MIL, and global specifications. For specialized dimensions or unique project requirements, we offer tailored solutions.
| Product Form | Size Range (Metric) | Size Range (Imperial) | Standards | Surface Finish Options |
| Bar | Diameter: 6–305 mm | Diameter: 0.25–12 in | AMS 6257, AMS 6417, AMS 6419 | Cold-Drawn, Ground, Hot-Rolled |
| Rounds | Diameter: 10–150 mm | Diameter: 0.4–6 in | AMS 6257, AMS 6419 | Precision Turned, Polished |
| Custom Sizes | Lengths: 3–12 m | Lengths: 10–40 ft | MIL-S-8844, BMS 7-26 | Custom Machining Available |
300M Steel Applications
300M alloy steel excels in high-stress environments requiring strength, fatigue resistance, and reliability:
- Aerospace: Landing gear, flap tracks, high-strength bolts.
- Defense: Armored vehicle parts, weapon systems.
- Transportation: Driveshafts, turbochargers, EV motor components.
- Energy: Oil/gas valves, turbine shafts.
- Industrial: Heavy machinery gears, high-pressure tools.
300M Alloy Steel Properties Overview
- Superior Fatigue Resistance
It’s ultra-clean microstructure, refined through vacuum arc remelting.
- Uniform Hardness
300M maintains consistent hardness throughout thick sections, eliminating weak points in critical components.
- Balanced Toughness
It retains ductility at high strength levels, preventing fractures from sudden impacts or overloads.
- Thermal Stability
The silicon-enriched composition allows for higher tempering temperatures, reducing brittleness while preserving hardness.
- Aerospace-Grade Reliability
300M meets strict industry standards for purity and traceability, ensuring performance in flight-critical systems.
300M Steel vs 4340 Steel
300M steel is a high-strength alloy for aerospace, while 4340 steel is a versatile, medium-strength alloy. 300M offers better strength and fatigue resistance.
- Composition
300M is an upgraded version of 4340, incorporating additional silicon, vanadium, increased carbon, and molybdenum. It’s made using vacuum arc remelting (VAR), ensuring higher purity.
- Performance
300M is tougher, more durable against fatigue, and less likely to experience brittle fracture under stress. 4340, while strong, doesn’t match 300M’s durability in extreme conditions.
- Applications
300M is used in aerospace components like landing gear. 4340 is used in automotive and industrial parts.
- Cost
300M is more expensive due to its production process and enhanced properties, while 4340 is more affordable for general use.
Aerospace-Grade 300M Steel From SteelPro Group
At SteelPro Group, we supply certified 300M steel that meets AMS 6257, MIL-S-8844, and Boeing BMS 7-26 standards. Every piece, whether bar, round, or custom-cut, undergoes rigorous testing to ensure it meets the demands of aerospace, defense, and high-stress industrial applications.
Need a tailored solution?
We offer precision-sized stock, surface finishes, and heat treatment protocols, all optimized for your project. With global logistics and traceable certifications, we ensure fast, reliable delivery with no delays or uncertainty.
