Choose the induction hardened chrome bar when the surface itself is the wear part: a case of at least HRC55, approximately 2 mm deep, formed in 45 steel before hard chrome plating. Choose the standard chrome bar — Yixin's 45 Steel Chrome-Plated Soft Shaft — when the bar will still be cut, machined or fitted after delivery and a base hardness of roughly HRC17 is acceptable. The deciding questions are simple: must the surface resist sliding wear, and will you remove material after receipt?
The Two Bars Side by Side
Terminology first. In this article "standard chrome bar" means a hard-chrome-plated shaft whose surface has not been induction hardened. Yixin sells that product as the 45 Steel Chrome-Plated Soft Shaft. "Soft" refers only to the absence of an induction-hardened case. It is not a flexible drive shaft, and nothing about the choice concerns bend radius or flexible transmission.
Both products start from Grade 45 steel to GB/T 699-2015 — comparable, for reference only, to C45, S45C and SAE 1045; chemistry limits differ between standards and are confirmed per order — and both receive hard chrome. The difference is where induction hardening enters the process route.
| Item | 45 Steel Chrome-Plated Soft Shaft | 45 Steel Induction-Hardened Chrome Shaft |
|---|---|---|
| Base material | 45 steel, not induction hardened | 45 steel |
| Hardness | ≈ HRC17 | Case ≥ HRC55; final core hardness is confirmed on the drawing and order |
| Case depth | None | ≈ 2 mm |
| Hardening step | No | Yes, before plating |
| Surface | Hard chrome | Hard chrome |
| Chrome thickness | 20–30 μm per side, up to 50 μm on request | 20–30 μm per side, up to 50 μm on request |
| Chrome hardness | HV800+ | HV800+ |
| Surface roughness | Ra ≤ 0.4 μm chrome | Ra ≤ 0.4 μm chrome |
| Downstream machining | Intended for shafts that still need turning, milling or drilling | Not intended for machining after the case is formed |
| Typical role | Bars that will be cut, machined or fitted further | Guide and wear surfaces that stay as delivered |
The process routes show the difference clearly. The 45 Steel Induction-Hardened Chrome Shaft runs cold drawing (up to Ø28) or peeling (Ø30 and above), roll straightening, centerless grinding, induction hardening, polishing, hard chrome (partner plant) and final polishing. The 45 Steel Chrome-Plated Soft Shaft follows the same family of operations, including hard chrome (partner plant), but stops short of the hardening step, so its hardness stays at the base level of approximately HRC17.
What the Induction-Hardened Case Actually Changes
Induction hardening converts the outer layer of the bar to a martensitic case of at least HRC55 to a depth of about 2 mm, while the core remains 45 steel; final core hardness is confirmed on the drawing and order. The result is a hard, wear-resistant shell on a comparatively ductile core.
Three consequences matter to a buyer.
First, the case resists localized deformation. A hard chrome layer 20–30 μm thick is mechanically thin; it follows the substrate beneath it. On a soft bar, point loads, edge loading and debris trapped under a seal can indent the surface and damage the chrome. A case of at least HRC55 limits that deformation, which is why induction hardened chrome bar is the usual choice for sliding guidance and rod surfaces.
Second, the case is a surface treatment only. It does not change the grade, the core strength or the dimensional class of the bar. If the shaft is loaded in bending or torsion and must resist permanent set, case hardness will not solve it — core hardness will, and that is a different product family.
Third, the case is not machinable in the ordinary sense. Once the surface is hardened and plated, cutting into it removes both the chrome and the hardened layer locally. The 45 Steel Chrome-Plated Soft Shaft is the product Yixin lists for shafts that still need turning, milling or drilling.
One specification habit follows from the route: in the induction-hardened route the dimensional work is done before hardening, and polishing follows it. State the diameter, tolerance, straightness and finish you need in the final plated condition, on the drawing, rather than assuming a pre-plating condition.
Choosing by Application and Downstream Process
Match the application, not the price list.
Sliding guidance and rod surfaces. If the bar functions as a guide rod, piston rod surface or wear surface and is installed as delivered, specify the induction hardened chrome bar. The hard case protects the surface against the contact conditions that soft bars tolerate poorly.
Linear bearings and recirculating ball bushings. Use the 45 Steel Chrome-Plated Linear Shaft. It follows the same route as the induction-hardened chrome shaft, and a tolerance of 0/−0.02 mm is typical for linear bearings. Induction hardening and shaft tolerance are separate decisions: the case gives wear resistance, the tolerance gives fit.
Bars that will be machined after receipt. Use the 45 Steel Chrome-Plated Soft Shaft, or a ground bar if plating is not yet required. Where the finished part needs threads, flats or cross-holes, define those features on the drawing so the sequence between machining, hardening and plating is settled before production.
Shafts loaded in bending or torsion. Case hardness is the wrong tool. Yixin's Q&T options address the core: the 45 Steel Q&T Chrome-Plated Bar has a quenched and tempered core of HRC25–28, the 40Cr Q&T Chrome-Plated Bar reaches HRC28–35 and is made to order, and 42CrMo is supplied in the Q&T condition only, at HRC30–38 after quenching and tempering, with a minimum order of 1 t.
When the fit tolerance drives everything. Linear bearings, housings and mating bores are often specified in ISO fit codes such as f7, g6 or h6. Yixin publishes tolerances as millimeter limits rather than ISO fit codes, so convert the fit into a limit tolerance and confirm it on the drawing.
Specification and Inspection Checklist
The induction hardened chrome bar is defined by several independent values. Confirm each one rather than assuming a single "hardened" label covers them.
| Check | What to state on the drawing or order | Yixin standard capability |
|---|---|---|
| Diameter | Finished diameter | Ø4–130 mm from stock (cold drawn to Ø28, peeled from Ø30); other sizes reviewed against the drawing |
| Tolerance | Limit tolerance in the final condition | Ø4–11 mm: −0.02/−0.05 mm. From Ø12 mm: 0/−0.02, −0.01/−0.03 or −0.02/−0.05 mm |
| Case hardness | Minimum surface hardness | ≥ HRC55 |
| Case depth | Depth of the hardened layer | ≈ 2 mm |
| Chrome thickness | Per side | 20–30 μm per side, up to 50 μm on request |
| Chrome hardness | Minimum | HV800+ |
| Straightness | Per meter | ≈ 0.1 mm/m from Ø25; ≈ 0.2 mm/m below Ø25 |
| Surface roughness | Chrome and ground conditions | Ra ≤ 0.4 μm chrome; Ra ≤ 0.8 μm ground |
| Length | Cut length | Standard 1 m, CNC cut to length with approx. 3 mm cutting allowance |
| Order documents | Documentation set | Commercial invoice, packing list and mill certificate; certificate of origin per order |
Inspection should follow the same order. Verify the delivered diameter and tolerance in the plated condition, check straightness over the full length, confirm surface roughness, and confirm case hardness and chrome thickness against the drawing and the inspection record agreed for the order. If a value matters to function, put it on the drawing rather than in an email.
When Neither Product Is the Right Answer
Induction hardening and hard chrome solve wear and guidance. They do not solve corrosion, high core strength or application-specific material requirements.
Designs calling for materials outside this family require a separate material decision; none of those materials is a Yixin catalogue product. If your design calls for one of them, treat it as a material decision outside this product family and select the closest Yixin product explicitly: soft shaft or ground bar for machining stock, induction-hardened chrome shaft for wear surfaces, Q&T chrome-plated bar where core strength governs.
Foreign grade names help sourcing conversations, but they are comparisons, not equivalents. Grade 45 (GB/T 699-2015) is comparable to C45, S45C and SAE 1045; 40Cr (GB/T 3077-2015) is comparable to 41Cr4 and SCr440; 42CrMo (GB/T 3077-2015) is comparable to 42CrMo4 and SCM440. Chemistry limits differ between standards, so confirm the exact grade and condition per order.
Summary
Choose the induction hardened chrome bar when the surface is the wear part: a case of at least HRC55, approximately 2 mm deep, under hard chrome of 20–30 μm per side at HV800+, in a bar that stays as delivered. Choose the 45 Steel Chrome-Plated Soft Shaft when the bar will still be machined, cut or fitted and an approximately HRC17 base is acceptable. Choose the Q&T chrome-plated series when the core, not the surface, carries the load. Specify diameter and tolerance in the final plated condition, add case hardness, case depth, chrome thickness, straightness and roughness to the drawing, and confirm the grade per order rather than by a foreign grade name alone.
References
- ISO fit codes (f7, g6, h6) — cited here only as common buyer terminology; Yixin publishes millimeter limit tolerances and does not publish ISO fit codes.
- GB/T 699-2015 (Grade 45) and GB/T 3077-2015 (40Cr, 42CrMo) — the standards Yixin's grades are made to.
- EN designations: C45, 41Cr4, 42CrMo4 — comparable grades, for reference only.
- SAE designation: 1045 — comparable grade, for reference only.
- JIS designations: S45C, SCr440, SCM440 — comparable grades, for reference only.
- Product specifications and process routes: https://yxrod.com/en