Steel Material Grades

European (EN 10025)

American (ASTM)

Sub-grades & Toughness

Weldability

EN 10025 — European standard for hot-rolled structural steel. Minimum yield strength (f_y) is specified at t ≤ 16 mm. Values reduce with increasing thickness.

Grade	f_y ≤16mm (MPa)	f_y 16–40mm (MPa)	f_y 40–63mm (MPa)	f_y 63–80mm (MPa)	f_u (MPa)	Elongation A (%)	C_E max
S235	235	225	215	215	360–510	≥ 26	0.35
S275	275	265	255	245	410–560	≥ 23	0.43
S355	355	345	335	325	470–630	≥ 22	0.45
S420	420	400	390	370	520–680	≥ 19	0.47
S460	460	440	430	410	550–720	≥ 17	0.53
S500	500	480	460	440	590–770	≥ 17	0.56

ASTM standards — American Society for Testing and Materials. F_y = minimum yield strength; F_u = minimum tensile strength. Values in MPa (ksi shown in brackets).

Grade	F_y (MPa / ksi)	F_u (MPa / ksi)	Elongation (%)	Typical use
A36	250 / 36	400–550 / 58–80	≥ 20	Plates, bars, legacy sections
A572 Gr.42	290 / 42	415 / 60	≥ 20	General structural
A572 Gr.50	345 / 50	450 / 65	≥ 18	W-shapes, plates — most common AISC grade
A572 Gr.60	415 / 60	520 / 75	≥ 16	High-strength plates
A572 Gr.65	450 / 65	550 / 80	≥ 15	High-strength plates
A992	345 / 50	450 / 65	≥ 18	W-shapes for seismic design (F_y/F_u ≤ 0.85)
A913 Gr.50	345 / 50	450 / 65	≥ 18	HSLA Q&T — seismic sections
A913 Gr.65	450 / 65	550 / 80	≥ 15	HSLA Q&T — seismic/high-strength
A514	690–760 / 100–110	760–895 / 110–130	≥ 16–18	Q&T high-strength plates (bridges, cranes)

EN ↔ ASTM Approximate Equivalents

European (EN)	American (ASTM)	f_y (MPa)
S235	A36	235 / 250
S275	A572 Gr.42	275 / 290
S355	A572 Gr.50 / A992	355 / 345
S420	A913 Gr.60	420 / 415
S460	A913 Gr.65	460 / 450

Sub-grades define Charpy V-notch impact toughness at a test temperature. Choose based on minimum service temperature and fracture consequence class.

Sub-grade	Test temp (°C)	Min. energy (J)	Application guidance
JR	+20 °C	27	Internal unexposed steelwork only. Not for external or cold environments.
J0	0 °C	27	General building structure. Sheltered external locations.
J2	−20 °C	27	Standard for most European building design. External structure in temperate climates.
K2	−20 °C	40	Fracture-critical members. Cold climates (Nordic countries, alpine regions).
M	−20 °C	27	Thermomechanically rolled (TMCP). Good through-thickness properties.
N	−20 °C	27	Normalised. Similar to M, different production route.
ML / NL	−50 °C	27	Extreme cold climates. Offshore structures in arctic conditions.
QL	−60 °C	27	Quenched & tempered. Extreme cold environments, LNG structures.

Tip: EN 1993-1-10 (Steel toughness selection) provides a systematic procedure for selecting sub-grade based on element thickness, stress level, lowest air temperature, and consequence class. Always apply this to fracture-critical elements such as tension flanges of major beams and column bases.

Carbon Equivalent (C_E) is the key indicator of weldability. Higher C_E = higher risk of hydrogen-induced cold cracking = more stringent preheat required. Formula per IIW: C_E = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15

Grade	C_E max	Weldability	Preheat (t ≤ 25mm)	Preheat (t = 50mm)
S235	0.35	Excellent	None	None
S275	0.43	Very Good	None	None to 50°C
S355	0.45	Good	None	50–75°C
S420	0.47	Moderate	25–75°C	100–125°C
S460	0.53	Moderate	50–100°C	125–150°C
S500+	0.56+	Demanding	100°C+	150°C+
A36 (ASTM)	~0.40	Good	None	None to 50°C
A572 Gr.50	~0.45	Good	None	50°C
A913 Gr.65	~0.38	Good (TMCP)	None	None to 25°C

Preheat temperatures are indicative. Always calculate preheat using BS EN ISO 17663, AWS D1.1 Annex I, or SEISI guidance for the specific heat input, material thickness, and hydrogen content of the welding process used.