An HRC reading and an HV reading on a chrome bar report are not interchangeable. They come from different indenters, they are taken with different test forces, and on a plated bar they are often taken on different layers. Before you compare a number with your drawing, fix four things: the scale, the force, the location and the layer that was tested. Conversion between scales is approximate and is not a basis for acceptance.
Which scale is on my report, HRC or HV?
HRC is a Rockwell C reading taken with a diamond cone indenter; HV is a Vickers reading taken with a diamond pyramid indenter and is always reported together with the test force that was used. If the report gives a number without the scale, ask the laboratory what was measured before you accept the lot.
Three details decide whether the number can be compared with your drawing at all:
- The scale designation. Rockwell has several scales, and only the C scale matches a drawing that asks for HRC; a figure written as HR with no letter is not usable. Vickers results are normally written as HV followed by a load index, and two HV values taken at different loads are not the same test.
- The force. Put the force on the drawing where the requirement is critical. A value reported at one force cannot be checked against a limit written at another force.
- The sample condition. Surface preparation, curvature and whether the area was polished all affect what the indenter actually measures. The report should state how the surface was prepared.
A report that answers these three points is an inspection record you can file against the lot. A report that gives only a number is a production note, and it will not settle a dispute.
Which layer does the number refer to, the chrome or the steel?
Both can appear on a chrome bar report, and they mean different things. A chrome-plated bar has a thin hard chrome layer over a steel substrate, so a hardness figure is only meaningful when the layer is named.
On bars from Yixin Precision Machinery (Changzhou), hard chrome is 10–50 μm per side, chosen per order, and chrome hardness can reach HV800+. Because that layer is thin, its hardness is normally reported in HV, and the load index matters more than the number itself. The steel underneath is normally reported in HRC.
The routes behave differently, and the report should follow the route. On the 45 Steel Induction-Hardened Chrome Shaft, the induction-hardened case in the steel is at least HRC55 and about 2 mm deep, and the hard chrome sits on top as a separate layer; a case reading and a chrome reading must never be compared with each other. On a quenched and tempered route such as the 45 Steel Q&T Chrome-Plated Bar, the surface hardness is HRC25–28 or HRC28–32, chosen per order, and the core is softer because grade 45 has limited hardenability. That is a surface figure, not a through hardness, so a reading taken at a sawn end or after machining may not match it.
Where on the bar was the reading taken?
A hardness figure without a location is only half a result. Ask for the distance from an end, the position around the circumference and the number of readings behind the reported value.
Location matters because the measurement can land on something other than the layer you are buying. On an induction-hardened bar the hardened case is about 2 mm deep, so a reading taken below that depth measures base steel rather than case. On a bar cut to length the ends are left as sawn, and a reading on a sawn end does not describe the ground or plated barrel. On a plated bar, a reading taken through the coating reaches the substrate, and a reading taken on the coating describes the chrome only.
A report that gives a minimum and a maximum from a stated number of readings is more useful than a single value, because it shows the spread. For acceptance work, agree in the RFQ how many readings are taken, where they are taken and whether the lowest reading or the average is the accept/reject figure. Where hardness is a critical item, put that location on the drawing so the laboratory and the supplier work to the same point.
Can I convert HV to HRC and compare the two?
You can convert, but the converted number is an estimate and it is not a sound basis for acceptance. Conversion tables are empirical: they depend on the material group, the test force and the pair of scales, and they do not make a coating reading comparable with a steel reading.
The common mistake is to convert across layers. If your drawing asks for HRC on an induction-hardened case and the report gives HV800+ on the chrome, no conversion will bridge the two, because the chrome is 10–50 μm per side and the case is about 2 mm deep — different layers, different tests, different purposes. Convert only within the same layer, and only to check that a figure is in the expected region.
In practice: specify the scale you want on the drawing; require the report to show the original scale, the force and the layer; where a conversion is used, ask for the measured value, the converted value and the table used, so the conversion can be audited later. Confirm any conversion table against the applicable standard before it goes into a purchase specification.
Which figure belongs to which Yixin product route?
Match the number to the product route and to the layer first, then compare it with your drawing. The table summarizes the hardness figures that belong to each chrome-plated route in the standard catalogue.
| Product route | Layer or property the figure describes | Typical figure |
|---|---|---|
| 45 Steel Chrome-Plated Soft Shaft | Base steel, not induction hardened | Base ≈ HRC17 |
| 45 Steel Induction-Hardened Chrome Shaft | Induction-hardened case in the steel, about 2 mm deep | At least HRC55 |
| 45 Steel Q&T Chrome-Plated Bar | Quenched and tempered surface (core softer) | HRC25–28 or HRC28–32, chosen per order |
| 40Cr Q&T Chrome-Plated Bar | Q&T hardness | HRC28–35 |
| 42CrMo Q&T Chrome-Plated Bar | Q&T hardness | HRC30–38 |
| All chrome-plated routes above | Hard chrome layer, 10–50 μm per side | Chrome hardness can reach HV800+ |
These are typical process capability figures for the named routes; the final value for a given order is fixed on the drawing and order. Note that the HV figure belongs to the plating, while the HRC figures belong to the steel — the two are reported separately for a reason.
What to put in your RFQ
- The product route and the grade as named on the drawing, for example Grade 45 to GB/T 699-2015 in the quenched and tempered condition, or 40Cr to GB/T 3077-2015.
- The layer to be hardness checked: the steel substrate, the induction-hardened case, or the hard chrome layer.
- The scale and the force, for example HRC on the case or HV with a stated load index on the chrome.
- The acceptance figure, whether it is a minimum or a range, and whether it applies to the lowest reading or an average.
- The measurement location: distance from the end, position around the circumference, and number of readings.
- The chrome thickness you want, chosen from 10–50 μm per side, so that the chrome reading and the layer thickness are consistent.
- The sampling plan, and whether third-party inspection is required; inspection of an order by a third-party laboratory is arranged on request.
- A request for the steel mill certificate for each heat, which is forwarded unaltered.
Summary
Read a chrome bar report in this order: scale, force, layer, location, then the figure. HRC belongs to the steel and HV normally belongs to the thin hard chrome layer, and a conversion across the two is an estimate rather than an acceptance criterion. When you write the enquiry, name the route, the layer, the scale, the acceptance figure and the measurement location, and the report you receive will match the drawing you sent.