Definition of Alloy steel 4340 | 1.6511 | 36CrNiMo4 | EN24
Alloy steel 4340 is also called 1.6511, 36CrNiMo4, or EN24, is a nickel-chromium-molybdenum alloy steel with exceptional strength and toughness. It contains about 0.40% carbon, 1.8% nickel, 0.8% chromium, and 0.25% molybdenum. The nickel gives it deep hardening ability, so even large, thick parts harden all the way through. After quenching and tempering, it reaches 900–1300 MPa tensile strength. CNC shops machine it for critical parts like aircraft landing gear, crankshafts, connecting rods, axle shafts, and high-strength fasteners.
Properties of Alloy steel 4340 | 1.6511 | 36CrNiMo4 | EN24
| Property | Value |
|---|---|
| Mechanical Properties | |
| Ultimate tensile strength | 690 – 1080 MPa |
| Yield strength | 470 – 630 MPa |
| Young’s modulus (modulus of elasticity) | 205 – 213 GPa |
| Elongation at break | 15 – 22 % |
| Physical Properties | |
| Corrosion resistance | Moderate to Poor |
| Magnetism | Semi-Magnetic |
| UV resistance | Excellent |
| Weldability | Moderate |
| Thermal Properties | |
| Maximum service temperature | 613 – 652 °C |
| Thermal expansion coefficient | 11.5 – 13 × 10-6/ºC |
| Thermal conductivity | 35 – 50 W/(m⋅°C) |
| Electrical Properties | |
| Electrical resistivity | 18 – 27 μΩ*cm |
| Post Treatments | |
| Post-Processing | Tempering & Annealing |
| Anodizing compatibility | Not suitable |
| Common Applications | |
| High tensile applications | |
| General engineering parts | |
| Connecting rods & bolts | |
Why Alloy steel 4340 | 1.6511 | 36CrNiMo4 | EN24 Matters in CNC Workshops
- Critical high-strength applications: alloy steel 4340 is specified when parts must not fail. Aerospace, defense, oil/gas, and racing industries rely on it for load-bearing components.
- Deep hardening for large parts: alloy steel Unlike 4140, 4340 hardens through thick sections. This opens up large-diameter shaft and gear jobs that other steels cannot handle.
- Premium material, premium margins: alloy steel 4340 costs more than 4140 and commands higher machining rates. Customers pay for proven performance in safety-critical parts.
- Heat-treatment value add: Quenching, tempering, induction hardening, and nitriding all work well on 4340, letting you offer full-service finishing and increase order value.
Surface Finishes for CNC Machined ABS Parts
As-Machined
The default finish from CNC machining plastic stock (Delrin, nylon, HDPE, ABS). Visible linear tool path scallop marks across machined surfaces with a matte plastic sheen. No secondary operation suitable for functional components, jigs, fixtures, and internal parts where cosmetic appearance is secondary to dimensional accuracy.
Flame Polished
Quick post-fabrication process that passes a controlled flame over acrylic (PMMA) cut edges, melting the surface micro-layer to produce a crystal-clear, glossy, transparent edge. Fast and cost-effective for acrylic sheet edges produces optical clarity on cut borders without the labor of hand polishing. Ideal for display cases, signage, and acrylic enclosures.
Vapor Polished
Post-fabrication chemical process that exposes transparent plastic parts (acrylic, PC, PETG) to solvent vapor, melting and smoothing the surface micro-layer to dramatically improve optical clarity and gloss. Removes machining lines and produces crystal-clear transparent parts — essential for prototype lenses, light guides, display windows, fluidic chambers, and medical components requiring optical transparency.
Painted
Post-fabrication spray painting in any custom color (matte, satin, gloss, metallic) followed by screen printing or pad printing for logos, labels, buttons, and graphics. Applied over a primed plastic surface for uniform color and adhesion. Allows custom fabricated plastic parts to match production aesthetics widely used for control panels, instrument faces, enclosures, and marketing/showcase components requiring exact brand color and graphic printing.
Sanded
Post-fabrication sanding with progressively finer grit sandpaper (typically 240–600 grit) produces a uniform low-gloss matte non-reflective surface. Hides machining marks, scratches, and surface inconsistencies while providing a soft tactile feel. Used for HDPE, UHMW, and nylon components where a durable, non-glare, fingerprint-resistant matte appearance is desired for industrial and functional parts.
Heat Formed
Thermoforming process that heats plastic sheet (acrylic, polycarbonate, ABS) to its glass transition temperature and bends it over a form tool to create precise angles and curved shapes. Produces clean, smooth bend radii with consistent surface finish no tool marks at the bend. Used for display stands, guards, enclosures, signage, and custom fabricated parts requiring 3D formed shapes from flat sheet stock.
