1.3818 Cr-Mn-N Steel Round Bar

Product Description

1.3818 (X40MnCrN18-12) is a high-nitrogen, austenitic manganese-chromium steel. While similar to 1.3817, this specific grade is optimized for even higher mechanical loads and is a staple in the heavy electrical and power generation industries.

Technical Profile: 1.3818 (X40MnCrN18-12)

This material is a specialized non-magnetic steel. Its chemistry is designed to maintain a stable austenitic structure even after significant cold deformation, which is the primary method used to achieve its exceptionally high yield strength.

Chemical Composition (Typical %)

The high manganese and nitrogen levels are the "secret sauce" for its strength, replacing the need for expensive nickel while providing superior hardening capabilities.

• Carbon (C): 0.35 – 0.45%

• Manganese (Mn): 17.00 – 19.00%

• Chromium (Cr): 11.00 – 13.00%

• Nitrogen (N): 0.20 – 0.40%

• Silicon (Si): 0.30 – 0.80%

Mechanical Advantages

1. Work Hardening: Unlike standard steels that are quenched and tempered, 1.3818 gains its strength through cold expansion or cold working. This allows it to reach yield strengths ($R_{p0.2}$) exceeding 800–1000 MPa depending on the degree of processing.

2. Stress Corrosion Resistance: It is highly resistant to stress corrosion cracking (SCC) in chloride-containing environments and moisture, which is a common failure point for other high-strength steels.

3. Magnetic Permeability: It maintains a very low magnetic permeability, making it invisible to magnetic fields—essential for components rotating at high speeds within electromagnetic fields.

Primary Applications

You will typically find 1.3818 round bars being processed into:

• Retaining Rings: The "end-rings" for large turbo-generators that hold the copper windings in place against massive centrifugal forces.

• Drill Collars: Used in oil and gas "Measurement While Drilling" (MWD) tools where non-magnetic properties are required to avoid interfering with directional sensors.

• High-Load Fasteners: Specialized bolts in magnetic resonance imaging (MRI) equipment or fusion research reactors.

Comparison: 1.3818 vs. 1.3817

While both are Cr-Mn-N steels, 1.3818 generally contains higher Chromium and Nitrogen levels compared to 1.3817. This results in:

• Better corrosion resistance (due to the $\approx$12% Cr vs $\approx$4.5% Cr in 1.3817).

• Higher potential yield strength through nitrogen-strengthening.

Machining & Fabrication

• Machinability: Difficult. It work-hardens instantly. Constant feed rates and heavy-duty tooling are required. If the tool dwells, the surface will harden to the point where the next pass may fail.

• Welding: Generally not recommended for high-strength applications as the heat-affected zone (HAZ) will lose the strength gained from cold working.