A chrome bar inspection checklist has four groups: documents and identification; diameter and length; chrome thickness and surface condition; and geometry, roughness and hardness. Each group is checked against the values written on the drawing and the order rather than against a general catalogue range, and each result is recorded together with the instrument and the measuring conditions used.
Which documents and identification should be checked first?
Start with the mill certificate, the commercial invoice and the packing list, and match grade, condition and quantity to the order before any measuring begins. A certificate of origin is arranged per order, and third-party inspection can be arranged on request; neither on its own replaces the incoming check.
Grade names are not interchangeable. Yixin Precision Machinery (Changzhou) works in Grade 45, 40Cr and 42CrMo. Other standards use comparable designations: C45, S45C and SAE 1045 are comparable to 45; 41Cr4 and SCr440 are comparable to 40Cr; 42CrMo4 and SCM440 are comparable to 42CrMo. Comparable grades are for reference only and the chemistry limits differ between standards, so if the drawing names a foreign grade, confirm the corresponding grade and condition on the order in writing.
Condition is a separate item from grade. A chrome bar may be supplied as a soft shaft, which means the surface is not induction hardened, as an induction-hardened chrome shaft, or as a quenched and tempered bar. The 45 Steel Induction-Hardened Chrome Shaft and the 45 Steel Chrome-Plated Linear Shaft carry an induction-hardened case of at least HRC55 to a depth of about 2 mm. Quenched and tempered products are not surface hardened and have no induction-hardened case, so a case-depth line does not apply to them. Grade 45 is supplied to GB/T 699-2015, and 40Cr and 42CrMo to GB/T 3077-2015.
How do you check diameter and length on receipt?
Measure the diameter with a calibrated micrometer at several points along each bar and around the circumference, compare the readings with the tolerance zone on the drawing, and check the cut length against the order. Record the values themselves rather than a pass or fail mark.
Yixin sizes are metric. The standard range is Ø4–140 mm, with up to Ø200 mm made to order. From Ø12 mm the standard tolerance zones are 0/−0.02 mm, −0.01/−0.03 mm or −0.02/−0.05 mm, chosen on the order. From Ø4–11 mm the standard range is −0.02/−0.05 mm; quenched and tempered bars start at Ø8 mm, so that range applies to them at Ø8–11 mm, while the 40Cr Q&T Ground Round Bar starts at Ø5 mm. The 45 Steel Chrome-Plated Linear Shaft is supplied at a typical 0/−0.02 mm for linear bearings.
Length is defined by the order. Full bars come in 4 m, 6 m, 7.5 m or 8.1 m, and CNC cut lengths start from 200 mm with ends left as sawn. If the drawing calls for a different end condition, it has to be stated in the enquiry and confirmed on the order.
How thick should the chrome be, and how is it verified?
Hard chrome on Yixin bars is 10–50 μm per side, chosen per order, with a chrome hardness of HV800 or higher. The thickness is a line on the drawing and the order, and that line is the acceptance criterion rather than a general range.
Thickness and hardness are specified together because they answer different questions: thickness sets how much wear material is present and how the finished diameter is built up, while chrome hardness describes the layer itself. Both are confirmed on the drawing and the order for the specific product, so a figure copied from another project should not be assumed to apply.
Chrome-plated products are the 45 Steel Chrome-Plated Soft Shaft, the 45 Steel Induction-Hardened Chrome Shaft, the 45 Steel Chrome-Plated Linear Shaft, the 45 Steel Q&T Chrome-Plated Bar, the 40Cr Q&T Chrome-Plated Bar and the 42CrMo Q&T Chrome-Plated Bar. Ground products have no chrome layer, so a chrome thickness line does not apply to the 45 Steel Ground Round Bar, the 45 Steel Q&T Ground Round Bar or the 40Cr Q&T Ground Round Bar.
Where independent confirmation is needed, third-party inspection can be arranged on request, and such a check applies to the sample or the order it covers. Salt-spray performance is not part of the standard specification. Where a rating is required, we specify a thicker chrome layer and can have the order tested by a third-party laboratory.
How do you check straightness, surface finish and hardness?
Record straightness, surface roughness and hardness as three separate results, because they are three separate requirements. On Yixin bars, straightness is approximately 0.1 mm/m from Ø25 mm and approximately 0.2 mm/m below Ø25 mm; surface roughness is Ra ≤ 0.4 μm on chrome surfaces and Ra ≤ 0.8 μm on ground surfaces.
Hardness depends on the product, so the inspection certificate should name the product and the measurement position. The 45 Steel Chrome-Plated Soft Shaft and the 45 Steel Ground Round Bar have a base hardness of about HRC17. The 45 Steel Induction-Hardened Chrome Shaft and the 45 Steel Chrome-Plated Linear Shaft have an induction-hardened case of at least HRC55, about 2 mm deep. The 45 Steel Q&T Ground Round Bar and the 45 Steel Q&T Chrome-Plated Bar are quenched and tempered to a surface hardness of HRC25–28 or HRC28–32, chosen per order; the core is softer because grade 45 has limited hardenability. The 40Cr Q&T Ground Round Bar and the 40Cr Q&T Chrome-Plated Bar are HRC28–35, and the 42CrMo Q&T Chrome-Plated Bar is HRC30–38.
Because a surface reading and a core reading differ on quenched and tempered bar, agree the measurement position before the order is placed. Cylindricity and run-out are separate requirements from diameter, so list them separately if the application needs them.
What does a receiving inspection plan look like?
The table below can serve as the receiving record for a chrome or ground bar order. The right-hand column lists Yixin standard capabilities, which are confirmed on the drawing and order; the drawing value always replaces the general figure.
| Check item | What to record | Yixin standard capability, confirmed on the drawing and order |
|---|---|---|
| Grade and condition | Grade, heat treatment condition, comparable grade if named | Grade 45, 40Cr, 42CrMo; soft, induction hardened, quenched and tempered |
| Diameter | Micrometer readings, positions, instrument | Standard range Ø4–140 mm, up to Ø200 mm made to order; Ø4–11 mm −0.02/−0.05 mm; from Ø12 mm 0/−0.02, −0.01/−0.03 or −0.02/−0.05 mm |
| Length and ends | Cut length, end condition, quantity | Full bars 4 m, 6 m, 7.5 m or 8.1 m; CNC cut from 200 mm, ends as sawn |
| Chrome thickness | Drawing value, verification method | 10–50 μm per side, chosen per order; chrome hardness HV800 or higher |
| Surface roughness | Ra value and measurement direction | Ra ≤ 0.4 μm chrome; Ra ≤ 0.8 μm ground |
| Straightness | Measuring length and support | Approximately 0.1 mm/m from Ø25 mm; approximately 0.2 mm/m below Ø25 mm |
| Hardness | Scale, position, instrument | Soft shaft and ground bar about HRC17; induction-hardened case at least HRC55, about 2 mm deep; 45 steel Q&T surface HRC25–28 or HRC28–32; 40Cr Q&T HRC28–35; 42CrMo Q&T HRC30–38 |
| Documents and packing | Certificate, invoice, packing list, packing condition | Mill certificate with commercial invoice and packing list; bubble film and wooden cases for export; no steel straps on finished bars |
What to put in your RFQ
- Grade and condition: Grade 45, 40Cr or 42CrMo, and whether the bar is soft, induction hardened, quenched and tempered, ground, chrome plated or both ground and chrome plated.
- Diameter and tolerance zone: nominal diameter, the tolerance zone, and the quantity or total weight.
- Length and ends: full bar length of 4 m, 6 m, 7.5 m or 8.1 m, or the CNC cut length from 200 mm, plus the required end condition.
- Chrome specification where applicable: thickness in μm per side within the 10–50 μm range, and the chrome hardness requirement.
- Surface and geometry: Ra value, straightness, and any cylindricity or run-out requirement, each listed separately.
- Hardness: the scale, the required value and the measurement position, and whether an induction-hardened case is required.
- Inspection and documents: mill certificate, whether third-party inspection is to be arranged on request, and whether a certificate of origin is required.
- Packing and marking: wooden cases for export, and whether your brand is to be printed on the packing.
For a first order, note that the minimum order quantity is 1 t and samples of 20–50 kg are available; lead time depends on whether bars are cut from stock, in a non-standard diameter or in a custom heat treatment.
Summary
An incoming inspection checklist for chrome and ground bars works when every requirement is written on the drawing and checked as a separate result: grade and condition, diameter and tolerance zone, length and end condition, chrome thickness, roughness, straightness and hardness. Yixin standard capabilities, such as 10–50 μm of chrome per side at HV800 or higher, Ra ≤ 0.4 μm on chrome and Ra ≤ 0.8 μm on ground surfaces, and straightness of approximately 0.1 mm/m from Ø25 mm, give the receiving team a starting point, and the drawing value replaces them on every order. Third-party inspection can be arranged on request, and the certificate package follows the order.