Ground journal control
Calculate deflection limits for 4140 Turned, Ground, and Polished (TGP) chromoly alloy steel shafts and explore its machinability vs 4140 alloy steel.
While 4140 has a material cost premium (often 30-50% over 1045) and lower machinability (rating ~66%), its deep hardenability prevents warranty failures under extreme cyclic loads. Use it when 1045 fails fatigue limits, not as a default for moderate-load applications.
Though harder to machine than 1045, 4140 Q&T offers superior toughness, wear resistance, and torsional strength for demanding applications, significantly reducing tool wear and cycle times for large-batch OEM production.
At 205 GPa, 4140 is just as stiff as expensive alloys. Upgrading to 4140 stops yielding, not bending.
| Property | Typical Value | Notes | ||
|---|---|---|---|---|
| Tensile Strength | 850 - 1000+ MPa (123 - 145+ ksi) | Varies slightly with processing | ||
| Yield Strength | 655 - 900 MPa (95 - 130 ksi) | Point of permanent deformation | ||
| Endurance Limit (Fatigue) | 360 - 650 MPa | ~50-60% of UTS (crucial for reversing loads) | ||
| Hardness (Typical TGP) | HRC 28 - 32 (Pre-hardened Q&T) | Induction case hardens to HRC 55+ (0.8 - 2.5mm depth) | ||
| Standard Tolerance | ISO h6 / h7 | Optimal for linear ball bearings | ||
| Surface Finish | Ra 0.2 - 0.4 μm | Polished after centerless grinding | ||
| 0.80 - 1.10% | 0.15 - 0.25% | Chromium and Molybdenum respectively | ||
| Carbon (C) | Manganese (Mn) | Phosphorus (P) Max | Sulfur (S) Max | Cr / Mo | Iron (Fe) |
|---|---|---|---|---|---|
| 0.38 - 0.43% | 0.75 - 1.00% | 0.040% | 0.040% | - | Balance (~98.5%) |
Data Sources & Verification: Mechanical properties, chemical compositions, and fatigue endurance bounds are based on ASTM A108 (Cold-Finished Chromoly Alloy Steel),ASTM A29/A29M standards, and cross-referenced with ASM International fatigue datasets. Public standards do not guarantee a specific mill condition; final acceptance still depends on the MTR, drawing, heat-treatment certificate, and inspection plan. Data last reviewed: June 25, 2026.
Ground journal control
Stepped shaft machining
Keyway and thread features
4140 Chromoly Alloy Steel has poor corrosion resistance. If used in exposed environments, it must be hard-chrome plated, black oxided, or regularly oiled. For washdown environments, upgrade to 304/316 Stainless.
Use the calculator as a screening tool. The table below explains when the page output is reliable enough for RFQ preparation and when a drawing review should override the quick estimate.
| Decision | Use 4140 When | Escalate or Change Material When | Next Action |
|---|---|---|---|
| Stiffness | Deflection is acceptable after checking span, support, and diameter. | Deflection fails; changing from 4140 to 4140 alone will not solve elastic bending. | Increase diameter, shorten span, or add support. |
| Wear | Only journal surfaces need wear resistance and can be induction hardened then ground. | The whole shaft needs through-hardness or shock resistance. | Quote hardening targets, case depth, and grind allowance. |
| Environment | The shaft operates indoors with oil, plating, or planned corrosion protection. | Washdown, salt, condensation, or exposed outdoor service is expected. | Compare coating stack-up against 304/316 stainless. |
Send diameter stack, bearing fits, runout, heat treatment, coating, and volume so engineering can confirm the route.
Yes, 4140 has enough carbon for localized induction hardening on wear journals. Treat HRC and effective case depth as quote-controlled targets that must be verified after heat treatment.
4140 can be welded, but the medium carbon content makes it crack-sensitive without preheat, controlled filler selection, and post-weld stress relief. It is not as forgiving as low-carbon 1018.
TGP means turned, ground, and polished. For shafting, it signals a route intended to improve diameter control, surface finish, and bearing-interface consistency.
Choose 4140 when torsional shock, high-cycle reversing fatigue, or through-hardening requirements drive the risk. Do not choose it only to reduce elastic deflection, because the elastic modulus of both steels is identical (205 GPa).
Include material condition, diameter and length, bearing-fit tolerances, runout, straightness, finish requirements, heat treatment zones, coating, annual volume, and inspection method.
Only with a corrosion plan. Bare 4140 rusts readily, so outdoor or washdown applications usually need chrome, nickel, black oxide plus oil, or a stainless alternative.
Send drawings for precision turning, centerless grinding, and milling review. Include material condition, tolerance, finish, hardness, and annual volume so engineering can validate the route before quoting.
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Include drawings, material, finish, tolerances, quantity, and delivery location.