{"id":3265,"date":"2026-06-02T05:23:03","date_gmt":"2026-06-02T05:23:03","guid":{"rendered":"https:\/\/spiralbevelgearbox.xyz\/?p=3265"},"modified":"2026-06-02T05:23:03","modified_gmt":"2026-06-02T05:23:03","slug":"spiral-bevel-gearbox-materials-explained-20crmnti-gears-42crmo-shafts-and-hrc-hardness-standards","status":"publish","type":"post","link":"https:\/\/spiralbevelgearbox.xyz\/es_es\/application\/spiral-bevel-gearbox-materials-explained-20crmnti-gears-42crmo-shafts-and-hrc-hardness-standards\/","title":{"rendered":"Explicaci\u00f3n de los materiales de las cajas de engranajes c\u00f3nicos espirales: engranajes de 20CrMnTi, ejes de 42CrMo y est\u00e1ndares de dureza HRC."},"content":{"rendered":"
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The performance of a caja de engranajes c\u00f3nicos espirales<\/strong> over its service life is determined not only by its geometric design but by the material properties of every load-bearing component. The selection of gear steel alloy, heat treatment process, carburizing depth, shaft material, and housing iron grade are engineering decisions with direct consequences for load capacity, fatigue life, shock resistance, and maintenance intervals. This guide explains every material specification used in Ever Power spiral bevel gearboxes \u2014 what each material is, why it was selected, and what it delivers in service.<\/p>\n

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1. Gear Material: 20CrMnTi Alloy Steel<\/h2>\n

The spiral bevel gear sets in all Ever Power gearboxes are manufactured from 20CrMnTi<\/strong> \u2014 a Chinese national standard (GB\/T 3077) carburizing alloy steel that corresponds closely to 16MnCr5 (DIN\/EN), SAE 5120, and JIS SCM415 in terms of composition and properties. The material contains chromium (1.0\u20131.3%), manganese (0.8\u20131.1%), and titanium (0.04\u20130.10%) as key alloying elements, with a base carbon content of 0.17\u20130.23%.<\/p>\n

Why 20CrMnTi for spiral bevel gears?<\/strong><\/p>\n

The low base carbon content (0.17\u20130.23%) allows the core of the gear to remain tough and ductile after heat treatment \u2014 essential for absorbing the impact loads that occur during belt conveyor starts, agricultural PTO engagement, and mining lump ore loading. The alloy additions enable the surface to be carburized to high hardness, giving the tooth face the wear resistance needed for millions of mesh cycles in service.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\nValue<\/th>\nEngineering Significance<\/th>\n<\/tr>\n<\/thead>\n
Surface Hardness (after carburizing + quenching)<\/td>\nHRC 58 \u2013 62<\/td>\nHigh contact fatigue resistance; resists pitting and spalling<\/td>\n<\/tr>\n
Core Hardness<\/td>\nHRC 33 \u2013 40<\/td>\nTough core absorbs bending impact without brittle fracture<\/td>\n<\/tr>\n
Carburized Case Depth (standard)<\/td>\n1.0 \u2013 1.4 mm<\/td>\nSufficient case depth to survive contact fatigue at rated load<\/td>\n<\/tr>\n
Carburized Case Depth (heavy duty)<\/td>\n1.2 \u2013 1.6 mm<\/td>\nDeeper case for mining and heavy shock applications<\/td>\n<\/tr>\n
Tensile Strength (core, after treatment)<\/td>\n900 \u2013 1,100 MPa<\/td>\nHigh core strength supports gear tooth root bending capacity<\/td>\n<\/tr>\n
Approximate International Equivalents<\/td>\n16MnCr5 (DIN), SAE 5120, JIS SCM415<\/td>\nGlobally recognised carburizing steel; established performance data<\/td>\n<\/tr>\n
Gear Precision Grade (after grinding)<\/td>\nISO Grade 5 \u2013 6<\/td>\nPrecision profile enables 60 \u2013 68 dB noise level and high contact ratio<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

2. The Heat Treatment Process: Carburizing, Quenching and Grinding<\/h2>\n

The transformation of a 20CrMnTi steel blank into a precision spiral bevel gear involves a defined sequence of heat treatment steps that must be controlled precisely to achieve the target surface and core hardness combination:<\/p>\n

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Step 1: Carburizing at 900\u2013950\u00b0C<\/strong><\/p>\n

The rough-machined gear is placed in a controlled carbon-rich atmosphere at 900\u2013950\u00b0C. Carbon diffuses from the atmosphere into the steel surface, raising the surface carbon content from 0.20% to 0.80\u20131.0% to a depth of 1.0\u20131.6 mm. The core carbon content remains unchanged.<\/p>\n<\/div>\n

Step 2: Controlled Oil Quenching<\/strong><\/p>\n

The carburized gear is quenched in oil at 60\u201380\u00b0C. The high surface carbon content transforms to martensite at HRC 58\u201362. The low core carbon content transforms to a mixture of ferrite and bainite at HRC 33\u201340. Controlled atmosphere quenching prevents oxidation of the carburized surface.<\/p>\n<\/div>\n

Step 3: Tempering at 160\u2013200\u00b0C<\/strong><\/p>\n

After quenching, the gear is tempered to relieve quench stresses and improve toughness of the martensite surface layer without significantly reducing hardness. Surface hardness after tempering: HRC 58\u201362 (unchanged). Brittleness of as-quenched martensite is reduced.<\/p>\n<\/div>\n

Step 4: Precision Grinding to ISO Grade 5\u20136<\/strong><\/p>\n

Heat treatment introduces distortion in the gear tooth geometry. Precision grinding on a Gleason or Klingelnberg machine removes this distortion, correcting the tooth profile back to within ISO Grade 5\u20136 tolerance (pitch error below 6 microns, profile error below 8 microns).<\/p>\n<\/div>\n<\/div>\n

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3. Shaft Material: 42CrMo Alloy Steel<\/h2>\n

42CrMo<\/strong> (GB\/T 3077) is a medium-carbon chromium-molybdenum alloy steel, broadly equivalent to 42CrMo4 (EN 10083-3), SAE 4140, and JIS SCM440. It contains 0.38\u20130.45% carbon, 0.9\u20131.2% chromium, and 0.15\u20130.25% molybdenum, providing a combination of high hardenability, good toughness, and excellent fatigue resistance.<\/p>\n

Ever Power uses 42CrMo for input and output shafts, normalized and tempered to HRC 25\u201330 through-hardness \u2014 not just surface hardened. Through-hardening means the full shaft cross-section is at the target hardness level, not just a surface layer. This is critical for shafts carrying combined bending and torsional loads, where bending fatigue initiates from the surface but propagates through the material cross-section.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\n42CrMo (HRC 25\u201330)<\/th>\nSignificance<\/th>\n<\/tr>\n<\/thead>\n
Tensile Strength<\/td>\n900 \u2013 1,100 MPa<\/td>\nHigh shaft strength; resists torsional overload<\/td>\n<\/tr>\n
Yield Strength<\/td>\n750 \u2013 950 MPa<\/td>\nConservative safety factor on yielding at rated torque<\/td>\n<\/tr>\n
Fatigue Limit (rotating bending)<\/td>\nApprox. 420 \u2013 500 MPa<\/td>\nLong fatigue life under continuous cyclic bending from belt pull forces<\/td>\n<\/tr>\n
Impact Toughness (Charpy)<\/td>\n60 \u2013 100 J<\/td>\nAbsorbs shock without brittle fracture \u2014 critical for mining and agricultural drives<\/td>\n<\/tr>\n
International Equivalent<\/td>\n42CrMo4 (EN), SAE 4140, JIS SCM440<\/td>\nGlobally recognised and specified alloy<\/td>\n<\/tr>\n
Machinability<\/td>\nGood (65% of free-cutting steel)<\/td>\nAllows precision-ground journal finish for bearing fit<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

4. Housing Material: Cast Iron vs Ductile Iron<\/h2>\n

The gearbox housing carries the gear mesh separation forces and provides the rigid structure that maintains shaft alignment under load. Ever Power offers two housing material options with different performance profiles:<\/p>\n

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Grey Cast Iron \u2014 HBS 190\u2013240<\/strong><\/p>\n

Standard housing material for general industrial applications. Excellent machinability, good vibration damping (graphite flakes in the microstructure absorb vibration energy), adequate compressive strength. Elongation at fracture: 0.5\u20131% \u2014 meaning grey iron shatters under extreme shock rather than deforming. Standard service factor up to 1.75.<\/p>\n<\/div>\n

Ductile Iron \u2014 GGG50 (EN-GJS-500-7)<\/strong><\/p>\n

Nodular graphite microstructure gives elongation at fracture of 5\u201315% \u2014 the housing deforms before it fractures under shock. Tensile strength 500 MPa vs 200\u2013300 MPa for grey iron. Specified for mining conveyors, agricultural PTO drives, forestry equipment, and any application with service factor above 2.0 or shock loads above 3x nominal torque.<\/p>\n<\/div>\n<\/div>\n

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5. Sealing Materials: NBR vs FKM<\/h2>\n
\n\n\n\n\n\n\n\n
Seal Material<\/th>\nTemperature Range<\/th>\nOil Compatibility<\/th>\nWhen to Specify<\/th>\n<\/tr>\n<\/thead>\n
NBR (Nitrile)<\/td>\n-30\u00b0C to +120\u00b0C<\/td>\nMineral and GL-4 EP oils<\/td>\nStandard industrial; mineral oil; operating temp below 100\u00b0C<\/td>\n<\/tr>\n
FKM (Viton)<\/td>\n-20\u00b0C to +200\u00b0C<\/td>\nSynthetic PAO, esters, GL-5 hypoid<\/td>\nSynthetic oil; high temperature; chemical environments; mining duty<\/td>\n<\/tr>\n
PTFE lip seal<\/td>\n-60\u00b0C to +260\u00b0C<\/td>\nUniversal \u2014 all lubricants<\/td>\nExtreme temperature; aggressive chemicals; very high shaft speed<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

6. Material Certificates and Documentation<\/h2>\n

Ever Power<\/strong> provides material documentation at three levels depending on application requirement:<\/p>\n