Monel R-405 is a nickel-copper alloy (approximately 67 percent nickel, 23 percent copper) that is a free-machining variant of Monel 400. The key difference is the addition of a controlled amount of sulfur (typically 0.025 to 0.060 percent), which breaks chips into small segments during machining. This significantly improves machinability, especially in automatic screw machines, while maintaining corrosion resistance comparable to Monel 400.

The nominal chemical composition of Monel R-405 is: nickel (plus cobalt) 63.0 to 70.0 percent, copper 28.0 to 34.0 percent, iron up to 2.5 percent, manganese up to 2.0 percent, sulfur 0.025 to 0.060 percent, silicon up to 0.5 percent, carbon up to 0.3 percent.

Mechanical properties (typical, annealed condition):

● Tensile strength: 450 to 550 MPa

● Yield strength (0.2% offset): 170 to 240 MPa

● Elongation: 30 to 40 percent (slightly lower than Monel 400 due to sulfur)

● Density: 8.80 g/cm³

● Hardness: typically 60 to 80 HRB

Corrosion resistance: Monel R-405 offers excellent resistance to seawater, brine, reducing acids (hydrofluoric, sulfuric, hydrochloric) under moderate conditions, alkalis, and salt solutions. It is resistant to stress corrosion cracking and has good performance in marine atmospheres. However, the sulfur addition makes it less suitable for welding or hot working; Monel R-405 is primarily used in the as-machined condition without subsequent welding.

Standards: Commonly manufactured to ASTM B164 (rod and bar). Other specifications include ASME SB164, QQ-N-281, and AMS 4674.

Typical applications of Monel R-405 include:

● Automatic screw machine components: valve stems, nuts, bolts, fittings, and fasteners.

● Instrumentation components for chemical and marine service.

● Pump shafts, plungers, and small precision parts where good machinability is required.

● Water meter parts and other high-volume machined components.

Comparison with Monel 400: Monel R-405 has similar corrosion resistance but slightly lower ductility and impact strength. It is not recommended for welding or hot forming. Monel 400 is preferred for sheet, plate, tube, and weldments. Monel R-405 is selected specifically for bar and rod products that will be extensively machined, especially on automatic lathes.

Selection guidance: Choose Monel R-405 when complex, high-volume machining is required and the application does not involve welding or severe impact loading. For welded structures or components requiring maximum ductility and toughness, use Monel 400. For higher strength with similar corrosion resistance, consider Monel K-500 (which is precipitation-hardenable).