Suitable for medium and high-strength mechanical parts, shaft components, gears, connectors, quenching and tempering parts, wear-resistant parts, fixtures and jigs, as well as alloy structural steel materials requiring good overall mechanical properties.
40Cr is a commonly used medium-carbon alloy structural steel, belonging to the chromium-based quenched and tempered steel, featuring good strength, toughness, hardenability, wear resistance, and comprehensive mechanical properties. Compared to 45# steel, 40Cr can achieve better strength, hardness, and fatigue performance after quenching, tempering, quenching, and tempering, making it suitable for manufacturing shaft parts, gears, connecting rods, screws, pins, sleeves, fixtures, and medium- to high-strength mechanical structural parts. It is commonly used in metal parts that need to withstand certain loads, friction, impact, or fatigue conditions.
By focusing on application scenarios, boundaries of advantages, and non-recommended scenarios, it helps sales, customer service, and quoting staff quickly determine whether the material meets current part requirements.
High strength, good toughness, hardenability better than 45# steel, good wear resistance, heat-treated strengthening, suitable for quenching and tempering, suitable for medium to high load structural parts, shaft and transmission parts, and stable overall mechanical properties.
Shaft parts, pins, gears, sprockets, screws, connecting rods, sleeves, connectors, transmission parts, clamps and jigs, mechanical brackets, wear-resistant parts, mold auxiliary parts, automotive mechanical parts, construction machinery parts, medium and high load structural parts, and functional parts after quenching and tempering.
Highly corrosive environmental parts, long-term exposed outdoor parts, food direct contact parts, medical implant parts, highly elastic snap-fit parts, strong welded structural parts, ultra-lightweight parts, metal parts requiring rust-free maintenance, parts requiring stainless steel appearance and corrosion resistance, and extremely high-temperature long-term load-bearing parts.
The following parameters come from product information and material knowledge fields, used for design review, quotation communication, and preliminary judgment before material selection.
| Material positioning | Suitable for medium and high-strength mechanical parts, shaft components, gears, connectors, quenching and tempering parts, wear-resistant parts, fixtures and jigs, as well as alloy structural steel materials requiring good overall mechanical properties. |
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| Precision performance | 40Cr is suitable for CNC turning, milling, drilling, tapping, grinding, wire cutting, and post-heat treatment finishing. CNC machining can achieve better dimensional accuracy; After heat treatment, dimensional accuracy is affected by deformation, and key dimensions usually require grinding or secondary finishing. It is recommended to mark tolerances and machining requirements separately for shaft parts, gears, hole positions, threads, mating surfaces, and wear-resistant surfaces. |
| Dimensional tolerances | For CNC machining of 40Cr, the standard dimensional tolerances can be referenced as ±0.02mm-±0.10mm, while ordinary structural parts can be evaluated at ±0.10mm-±0.20mm; If the part requires quenching and tempering, quenching, high-frequency quenching, nitriding, or surface treatment, dimensional changes or deformation may occur after heat treatment. It is recommended to heat treat key dimensions before finishing. These values represent the standard reference range and do not guarantee absolute tolerances for all structures. Actual confirmation must be based on process, dimensions, structure, heat treatment, and post-processing. |
| Minimum Wall Thickness | The wall thickness of ordinary CNC machined structures is recommended to be no less than 0.8mm-1.0mm. Small non-stressed areas can be further optimized according to structure and processing methods, but it is not recommended to make large areas that are too thin. Areas requiring heat treatment, tapping, load-bearing, wear resistance, or assembly should be appropriately thickened to avoid processing deformation, heat treatment deformation, cracking, or insufficient strength. |
| Recommended wall thickness | For ordinary structural parts, 1.5mm-3.0mm is recommended; for shaft parts, mounting seats, threaded connection points, fixtures, fixtures, wear-resistant surfaces, and load-bearing positions, 2.0mm or more is recommended; for parts requiring quenching and tempering, quenching, surface quenching, or nitriding, increase machining allowance based on deformation risk and reserve grinding or finishing allowance at key dimensional positions. |
| Minimum aperture | CNC machining can achieve smaller hole diameters, but controlling deep small holes and hole position accuracy after heat treatment is more challenging. For general designs, the recommended aperture is no less than 1.0mm. For precision holes, threaded holes, positioning holes, pin holes, and fitting holes, it is recommended to reserve machining allowance. If necessary, drill, ream, boring, or grinding should be performed after heat treatment. |
| Assembly clearance | For precision metal assembly, one side can be reserved at 0.02mm-0.10mm according to fitting requirements; for ordinary plug-in and assembly, it is recommended to reserve 0.10mm-0.30mm per side. If parts require heat treatment, blackening, electroplating, galvanizing, powder spraying, painting, nitriding, or rust prevention treatment, combine heat treatment deformation and surface treatment thickness to increase assembly allowance to avoid overtightening or surface scratches. |
| Detailed performance | 40Cr is suitable for machining holes, grooves, steps, chamfers, threads, shaft shoulders, positioning surfaces, keyways, tooth profiles, wear-resistant surfaces, and ordinary mechanical structural details. Under CNC machining, detail performance is good, and after heat treatment, key surface quality can be improved through grinding. Small text, logos, and markings are recommended to be achieved through laser marking, engraving, stamping, or etching. |
| Surface effect | The original machined surface of 40Cr is usually silver-gray or gray-black metallic and may have oxide scale, knife marks, scratches, or rust spots. After grinding and polishing, a relatively smooth metal surface is obtained; after blackening, a black rust-resistant appearance is achieved; after galvanizing or electroplating, a silver-white or glossy metallic effect can be achieved; after painting or powder spraying, multiple colors and better protection can be achieved. If long-term appearance stability is desired, reliable anti-rust treatment or stainless steel materials should be used. |
Based on material characteristics and suitable product ranges, customer needs are broken down into easier application directions to determine.
Shaft parts, pins, gears, sprockets, screws, connecting rods, sleeves, connectors, transmission parts, clamps and jigs, mechanical brackets, wear-resistant parts, mold auxiliary parts, automotive mechanical parts, construction machinery parts, medium and high load structural parts, and functional parts after quenching and tempering.
Suitable for medium and high-strength mechanical parts, shaft components, gears, connectors, quenching and tempering parts, wear-resistant parts, fixtures and jigs, as well as alloy structural steel materials requiring good overall mechanical properties.
40Cr compared to ordinary carbon steel, it has better hardenability and overall mechanical properties. After quenching and tempering, it achieves a good balance of strength and toughness. It is more suitable than 45# steel for mechanical parts that withstand higher loads, impacts, and fatigue, but it also requires higher control for processing and heat treatment. 40Cr is a rust-prone steel material that oxidizes and corrodes easily in exposed environments, typically requiring surface protection such as blackening, galvanizing, electroplating, painting, phosphating, and anti-rust oil.
Based on wall thickness, hole position, assembly clearance, dimensional tolerances, and material usage risks, determine in advance whether the part structure is suitable for 40Cr.
Post-processing of 40Cr affects appearance, dimensions, hole position, assembly clearance, and usage validation results, and should be explained in advance during quotation, DFM review, and sample confirmation stages.
Post-processing should focus on appearance display, dimensional fitting, connection assembly, and testing verification. Parts involving assembly positions need to be reserved in advance for machining, coating, and trial assembly allowances.
For common issues such as threads, snaps, strength, temperature resistance, and weather resistance, identify in advance whether the material needs to be replaced or if another processing method should be used.
When customer demand exceeds 40Cr material boundaries, it is necessary to combine strength, temperature resistance, toughness, long-term stability, and mass production goals to promptly recommend alternative materials or processing technologies.
If lower cost and ordinary strength are needed, 45# steel can be chosen; If higher strength, toughness, and fatigue performance are required, 42CrMo can be chosen; If better corrosion resistance is required, 304 stainless steel, 316 stainless steel, or 17-4PH stainless steel can be chosen; If lighter weight is needed, 7075 aluminum alloy, 6061 aluminum alloy, or TC4 Titanium Alloy (Ti-6Al-4V) can be chosen; If higher wear resistance and mold performance are required, mold steels such as Cr12, Cr12MoV, and H13 can be chosen.
If customers require better strength, toughness, hardenability, and fatigue performance than 45# steel, 40Cr is a suitable choice. If it is just ordinary low-cost structural parts, 45# steel or Q235 may be more economical. If parts need to be used outdoors for long periods, in humid or corrosive environments, it is not recommended to use exposed 40Cr directly; stainless steel should be chosen or reliable surface protection should be added. If the part is subjected to heavy loads, high impact, or high fatigue life requirements, higher-grade alloy steels such as 42CrMo can be further evaluated.
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