GCr15/52100 Chromium: What the 1.30–1.60 wt% Window Settles on a Certificate, and What It Cannot Tell You

Chromium outside 1.30–1.60 wt% is the first thing to reject

Read the chromium line before anything else on the sheet. Two composition tables give AISI 52100 the same window, 1.30–1.60 wt% Cr^1,14, and a third places the whole 52100/En31/100Cr6/SUJ-2/GCr15 family at a mean of about 1C-1.5Cr¹¹.

A figure inside that band is consistent with all three; a figure outside it is not covered by any source here as acceptable. That makes Cr the cheapest single check you can run.

It is one number, it sits on every mill certificate, and it is the one where the sources converge most tightly. The carbon and residual lines are where the tables start to drift apart, which is the next thing to look at.

One caution on scope: the agreement is on the 52100 designation and on the family mean, not on a quoted clause. No source in this set reproduces the GB/T 18254 or ASTM A295 text, so treat 1.30–1.60 as the window the published tables support rather than as a verbatim standard limit.

Match the whole sheet to the standard it invokes, not to a remembered table

Chromium passing does not make the certificate good. The sources agree that carbon sits around 0.95–1.10 wt% and that phosphorus and sulphur are held low, at or below roughly 0.025 wt%^1,14.

They do not agree on the rest of the window. Manganese is given as 0.20–0.50 with Si below 0.35 in one table¹, and as Mn 0.25–0.45 with Si 0.15–0.35 in two others^3,14.

Carbon's upper limit is 1.10 in two tables^1,14 but 1.05 in the GCr15 description³. A sheet that is compliant against one of these and non-compliant against another is not a defective sheet — it is a sheet being judged against the wrong reference.

So the acceptance basis is the standard the certificate names, not a table you remember. Ask which designation and edition the mill certified to, then check every element against that document.

If the supplier cannot name it, the certificate has no basis you can audit against.

What the Cr number does and does not predict

Chromium's role is stated consistently: it forms chromium carbides and contributes to hardenability and wear resistance¹⁴. And the fine carbide dispersion is what gives 52100 its rolling-contact fatigue life and wear resistance after hardening and tempering¹⁰.

Low retained austenite in 52100 is attributed to the chromium addition together with a cold treatment¹⁰. GCr15 is described at grade level as having high contact fatigue strength and good dimensional stability⁵.

None of that is a curve. No source here gives an ideal critical diameter, a Jominy band or a CCT shift for a specific Cr level inside 1.30–1.60, and none gives retained-austenite percentages as a function of Cr^10,14.

The same holds for fatigue: composition is said to matter, and small composition changes can influence heat-treatment behaviour, hardness uniformity and fatigue resistance¹⁸. But no source documents a fatigue penalty for Cr below 1.30 or above 1.60^5,10,18.

What you can do with the Cr figure is therefore narrow. Use it to accept or reject chemistry.

Do not read a high-normal or low-normal Cr value as a hardenability or life grade, and do not let a supplier present it as one. If retained austenite matters to your application, note that cryogenic treatment to reduce it carries a reported micro-cracking risk with loss of toughness and fatigue² .

That is a heat-treatment decision to raise separately, not something the Cr line answers.

Traceability checks before you accept the sheet

Chemistry on paper only means something if it is tied to the parts you receive. Small composition shifts affect heat-treatment response, hardness uniformity and fatigue resistance, which is why the traceability documents below are worth asking for up front¹⁸.

• ✓Mill test certificate naming the grade and the standard edition certified to
• ✓Spectral analysis report for the actual heat, not a generic grade datasheet
• ✓Heat number stated on the certificate and matched to the marking on the delivered bar or part
• ✓Batch traceability from heat number through to the delivered lot
• ✓Cleanliness and carbide-distribution requirements stated where the application demands them
• ✓A verification route agreed in writing: ASTM A295/A295M or ISO 683-17 plus your cleanliness and microstructure requirements
• ✓Hardness profile, retained-austenite evidence and furnace-lot traceability defined as release criteria

Section size decides whether plain GCr15/52100 is the right grade

Plain 52100 is described as only moderately hardenable, with sections above roughly 20–30 mm said to need the Mn-Si variant 100CrMnSi6-4 (SUJ3)¹⁰. That threshold comes from a vendor-tier source, so treat it as a prompt to check rather than a measured limit.

A second source puts the GCr15SiMn crossover at wall thickness above 12 mm⁵, and a bearing maker describes SUJ3 as the thick-section grade with SUJ5 adding Mo for large and extra-large bearings¹³.

If your part is thick, the chromium line on a plain 52100 certificate will pass and still leave you with the wrong grade. Decide the grade from section size first, then check the chemistry of whichever grade you specified.

Alternative grades the sources do not cover

The question invites a comparison with other through-hardening grades, and the evidence stops short of it. The only alternative the sources place against 52100 is corrosion resistance: 52100 is described as having none, with stainless bearings using 440C¹⁰.

No Cr range and no fatigue data for 440C appear in this set, so you cannot judge a 440C certificate on the same basis. Case-hardening grades such as 8620 or 4320, and high-alloy grades such as 8Cr4Mo4V, are not covered at all.

One steelmaker does describe BQ-Steel and IQ-Steel variants of 100Cr6 as optimised for fatigue strength and cleanliness⁷ . That is the supplier's own positioning of its product line, not an independent comparison, and it carries no composition figures.

If your application needs one of the uncovered grades, source its specification separately. A 52100 certificate cannot stand in for it, and the Cr window above does not transfer.

Commercial terms the certificate cannot settle

Nothing in this evidence set carries price, minimum order quantity, lead time or heat-treatment cost. You will not find a premium for the Mn-Si or Mo variants here, and you should not infer one from the alloy content.

What you can do is make the quote answer the questions the certificate cannot. Ask the supplier to state the grade and standard edition being quoted, to confirm the heat number will appear on the certificate and on the delivered goods.

And to say whether the section size of your part is within what that grade is intended for¹⁸. Those are the terms that decide whether the delivered lot matches what you accepted on paper.

Treat any commercial difference between plain and modified grades as something to be quoted and confirmed, not derived from the chemistry.

Where the composition tables disagree

These are the two places where a certificate can look wrong and be right, or look right and be wrong. Neither is a defect in the sources — they describe different designations and different levels of detail.

The point for you is that a single remembered number is a weak basis for rejection.

Before you request a quote

• Request certificate numbers, issuing bodies, scope and validity for the exact model and destination market.
• The evidence leaves this open — put it to the supplier: no Cu, Ni, Mo residual limits or oxygen/titanium limits for 52100/GCr15 are given — request the full certified analysis rather than the Cr line alone.
• The evidence leaves this open — put it to the supplier: no ideal critical diameter, Jominy band or CCT data showing how hardenability changes with Cr inside 1.30–1.60 — ask for hardenability test data if section size is critical.
• The evidence leaves this open — put it to the supplier: no retained-austenite percentages, and no Cr-specific tempering or cryogenic response — ask for retained-austenite measurement on the actual heat treatment.
• The evidence leaves this open — put it to the supplier: no documented Cr-versus-fatigue relationship, and no fatigue-life penalty for Cr outside 1.30–1.60 — do not accept a life claim resting on the Cr figure.
• Request the complete specification sheet with units, test conditions and configuration assumptions.
• The evidence leaves this open — put it to the supplier: no certificate test methods, sampling frequency, acceptance criteria or third-party inspection requirements — agree the inspection route in the purchase order.
• Request a written quote with price basis, MOQ, tooling, payment terms and production lead time.