Reference

Steel and cast iron grade equivalents

Specifying one designation with no stated equivalent is how a drawing turns into a six-week mill order. These are the grades that actually appear on machine frame drawings, grouped by strength class so you can see what substitutes for what.

Filter — grade, standard or region

Grade	Standard	Region	Yield min (MPa)	Tensile (MPa)	Note
Mild structural steel — 235–250 MPa yield
Q235B	GB/T 700	China	235	370–500	Most widely stocked plate in Asia
S235JR	EN 10025-2	Europe	235	360–510	JR = 27 J at +20 °C
A36	ASTM A36	USA	250	400–550	North American workhorse
SS400	JIS G3101	Japan	245	400–510	No impact requirement
St37-2	DIN 17100	Germany	235	340–470	Superseded by S235JR
E24-2	NF A35-501	France	235	360–510	Superseded by S235
Low-alloy structural steel — 345–355 MPa yield
Q355B (was Q345B)	GB/T 1591	China	355	470–630	Renamed Q355 in the 2018 revision
S355J2	EN 10025-2	Europe	355	470–630	J2 = 27 J at −20 °C
S355JR	EN 10025-2	Europe	355	470–630	JR = 27 J at +20 °C
A572 Gr.50	ASTM A572	USA	345	450 min	Usual US equivalent to S355
SM490A	JIS G3106	Japan	325	490–610	Weldable structural
St52-3	DIN 17100	Germany	355	490–630	Superseded by S355J2
Pressure-vessel plate — guaranteed notch toughness
Q245R	GB 713	China	245	400–520	Normalised, impact tested
P265GH	EN 10028-2	Europe	265	410–530	Elevated temperature service
A516 Gr.60	ASTM A516	USA	220	415–550	Fine-grain, notch tough
Q345R	GB 713	China	345	510–640	Higher strength vessel plate
P355GH	EN 10028-2	Europe	355	510–650
A516 Gr.70	ASTM A516	USA	260	485–620	The one most often over-specified
Grey cast iron — machine bases and beds
HT200	GB/T 9439	China	—	200 min	Light-duty bases
HT250	GB/T 9439	China	—	250 min	Standard machine base iron
HT300	GB/T 9439	China	—	300 min	Higher strength beds
EN-GJL-250	EN 1561	Europe	—	250 min	Was GG25 under DIN 1691
EN-GJL-300	EN 1561	Europe	—	300 min	Was GG30
Class 35B	ASTM A48	USA	—	241 min	Roughly HT250
Class 40B	ASTM A48	USA	—	276 min	Roughly HT300
FC250	JIS G5501	Japan	—	250 min	Roughly HT250

How to use these

These are practical equivalents — same strength class, comparable weldability, interchangeable on a machine frame in the great majority of cases. They are not certified substitutions. A pressure-retaining part, a fatigue-critical joint or anything governed by a customer specification needs the actual grade verified against the mill certificate.

On a machine frame the grade barely affects performance, because stiffness comes from Young's modulus and that is essentially identical — around 200 GPa — across every carbon and low-alloy steel on this table. Specifying a higher-strength grade does not make the frame stiffer. Frames are deflection-limited, not stress-limited.

The note that removes the problem

Plate: Q355B / S355J2 / A572 Gr.50, or approved equivalent
with minimum yield 345 MPa. EN 10204 3.1 mill certificates required,
heat numbers traceable to plates in the assembly.

One sentence, and the deviation request never has to happen. The longer argument is inchoosing a steel grade for a machine frame, and the schedule consequences are inplate availability is what sets your lead time.

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Free to quote, reference or link with attribution. The calculation method is stated above so it can be checked rather than taken on trust.

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