Steel Grade Comparison: International vs Chinese GB

Grade Mapping and Mechanical Data

Common callout	Chinese GB grade	Condition	Tensile strength	Hardness	Typical use at KGL
1018 / 20 steel	20 (GB/T 699)	Hot rolled, normalized	approx. 410 MPa	HB 120-150	Fixtures, welded brackets
1045 / C45	45 (GB/T 699)	Normalized or quenched and tempered	600-750 MPa	HB 170-220	Shafts, plates, jig bases
4140 / 42CrMo4	42CrMo (GB/T 3077)	Quenched and tempered	1,000-1,100 MPa	HRC 28-34	High-strength shafts, gears
4340 / 40CrNiMo	40CrNiMoA (GB/T 3077)	Quenched and tempered	1,100-1,250 MPa	HRC 32-38	Heavy duty pins and shafts
P20 / 1.2311	3Cr2Mo (GB/T 1299)	Pre-hardened	approx. 1,000 MPa	HB 280-320	Mold bases, cores
718H / 1.2738	3Cr2NiMo	Pre-hardened	approx. 1,000 MPa	HB 330-370	Large mold cores
H13 / 1.2344	4Cr5MoSiV1 (GB/T 1299)	Quenched and tempered	approx. 1,400 MPa	HRC 45-50	Die casting dies, hot work
D2 / 1.2379	Cr12Mo1V1 (GB/T 1299)	Hardened	not applicable	HRC 58-62	Wear inserts, cutting dies
Inconel 718	GH4169 (GB/T 14993)	Aged	1,270+ MPa	HRC 40-44	High temperature hardware

Tensile values are typical ranges for the stated condition, cross-checked against the KGL engineering standard (2022-01-08), GB/T 699 and GB/T 3077 mill data, and the Mechanical Design Handbook 6th ed. Vol. 1; your drawing callout and the lot certificate govern acceptance. Substitution proposals always ship with mill certificates for approval.

Machinability Reference

Relative machinability on the 45 steel cutting-speed basis (K = 1.0 to 1.5), from the Mechanical Design Handbook 6th ed. Vol. 1. This is how the families above compare at the machine:

Material family	Relative machinability K	What it means at the machine
Aluminum alloys, leaded brasses	8 to 20	Highest speeds and longest tool life
Free-cutting steel	2.5 to 3	High-volume turned parts, short chips
Medium-carbon steel: 45 / C45 / 1045, gray cast iron	1.0 to 1.5	Baseline for chip control and tool wear; best band 170 to 230 HBW
Hardened 65Mn, austenitic stainless 304/316L	0.15 to 0.65	Work hardening, lower speeds, sharp positive-rake tools
Titanium alloys, heat-resistant alloys (GH4169)	0.04 to 0.14	Lowest speeds, high-pressure coolant, rigid setups, ceramic or carbide grades

Steel Grade FAQ

Is 42CrMo the same as 4140?

Functionally yes: 42CrMo (GB/T 3077, also EN 42CrMo4) matches AISI 4140 in carbon and molybdenum content and is the grade our mills supply for 4140 callouts. Mechanical properties after the same heat treatment are equivalent for practical purposes.

Which grade replaces P20 if I buy in China?

3Cr2Mo is the GB equivalent of P20 (1.2311); for the nickel-improved 718H, 3Cr2NiMo is the match. Both are supplied pre-hardened around HB 280-320.

Do you have a substitution risk policy?

Yes: any grade substitution is proposed in writing with the mill certificate comparison attached, and your approval is required before material is cut.