What it is
Alloy steels like 42CrMo (AISI 4140), 40Cr, and 20CrMnTi contain chromium, molybdenum, and manganese for high strength and hardenability, used in shafts, gears, bolts, and mould bases. The alloy content is exactly what a buyer cannot see, so passing plain medium-carbon steel off as 42CrMo — or shipping bar that was never properly heat-treated — is the characteristic fraud.
Grades & standards buyers order
| Grade | Standard | Notes |
|---|---|---|
| 42CrMo / 42CrMo4 | GB/T 3077 / EN 10083 | The workhorse Cr-Mo grade; equivalent to AISI 4140 / SCM440. |
| 40Cr / 5140 | GB/T 3077 / AISI | Chromium grade for moderately stressed parts. |
| 20CrMnTi | GB/T 3077 | Case-hardening gear steel; chemistry must match for correct carburizing. |
How it's sold: Sold by metric ton as round bar, flat, or forged blanks; specify grade, delivery condition (hot-rolled, annealed, or quenched-and-tempered), diameter, and required hardness (HB/HRC).
What drives the price
- Alloy content (Cr/Mo) — molybdenum is expensive and volatile
- Delivery / heat-treatment condition (Q+T costs more)
- Diameter and forged vs rolled
- Required hardness range and testing
Lock these into the contract before you pay
Exact grade + full chemistry
42CrMo, 40Cr, and plain 45# steel look identical; require a Cr/Mo/Mn analysis tied to a heat number and confirm with PMI.
Delivery / heat-treatment condition
Bar sold as quenched-and-tempered but shipped as-rolled will fail in service; specify the condition and hardness.
Hardness (HB/HRC) and test
Require a hardness certificate and, for critical parts, a third-party hardness/tensile test.
Scams most common to alloy steel
Grade Substitution (lower grade shipped than ordered)
Plain medium-carbon steel (e.g. 45#) or a leaner alloy shipped as 42CrMo — invisible without spectrometer/PMI testing.
Forged Mill Test Certificates (MTC / EN 10204 3.1)
A forged certificate showing 42CrMo chemistry and Q+T hardness for bar that is neither.
Bait-and-Switch Quality
A correct-chemistry sample bar followed by off-spec production tonnage.
Red flags in a quote or sample
- 42CrMo priced barely above plain carbon bar
- No Cr/Mo figures on the chemistry certificate
- Delivery condition (annealed / Q+T) left unstated
- Refusal to allow PMI or hardness testing before balance payment
Already paid and something's wrong?
If you received off-spec alloy steel, a certificate that doesn't match, or your supplier has gone quiet after a deposit, move quickly. Recovery odds drop with every day that passes on a wire transfer.
Buying alloy steel from China: FAQ
What grades of alloy steel can I buy from China?
The most commonly ordered grades are 42CrMo / 42CrMo4, 40Cr / 5140, 20CrMnTi. Always pair the grade with its standard on the purchase order so the mill test certificate can be matched to what you actually receive.
What is the most common scam when buying alloy steel from China?
Grade Substitution (lower grade shipped than ordered). For this product specifically: Plain medium-carbon steel (e.g. 45#) or a leaner alloy shipped as 42CrMo — invisible without spectrometer/PMI testing. The defense is to specify the exact grade and standard, require a verifiable mill test certificate, and commission independent pre-shipment inspection.
What should I check before paying for alloy steel?
Lock down exact grade + full chemistry, delivery / heat-treatment condition, hardness (hb/hrc) and test in the contract, verify the supplier is a real manufacturer, and never release the balance until an independent inspection confirms the goods.
I already paid a Chinese supplier for alloy steel — what now?
Act fast: contact your bank about a recall on the wire, gather all contracts and communications, report the pattern so others are warned, and review the documented cases to understand your options. The sooner you act on a redirected or disappeared payment, the better the odds.
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