What is the difference between EN8 and EN19 steel?

EN8 (080M40) is an unalloyed medium carbon steel. EN19 (708M40 / 42CrMo4) is a chromium-molybdenum alloy steel. EN19 through-hardens reliably to 65mm section versus ~40mm for EN8, and achieves 900–1100 N/mm² tensile in Q+T condition versus 550–700 N/mm² normalised for EN8. Choose EN8 for general shafts and machined parts; EN19 when you need higher tensile strength or larger section through-hardening.

Is EN19 stronger than EN8?

Yes — significantly. EN19 in the quenched and tempered condition achieves 900–1100 N/mm² tensile strength depending on section size. EN8 normalised achieves 550–700 N/mm². EN19 is approximately 50–70% stronger in the heat-treated condition.

Can I replace EN8 with EN19?

Yes in most cases. EN19 is a direct upgrade from EN8 — same machining characteristics in the normalised condition, better hardenability and higher tensile strength. The main reasons not to upgrade are cost (EN19 is more expensive) and applications where the lower strength of EN8 is deliberately specified for safety reasons (shear pins, designed-to-fail components).

Grade Comparison

EN8 vs EN19 — Key Differences.

EN8 and EN19 are the two most widely used engineering steel grades in the UK. Understanding when to choose one over the other saves money, prevents failures and avoids over-engineering. This page explains every difference that matters.

EN8 Data Sheet EN19 Data Sheet Get a Quote

Side by Side

Comparison Table.

Property	EN8 (080M40 / C40E)	EN19 (708M40 / 42CrMo4)
Carbon content	0.36–0.44%	0.35–0.45%
Alloy additions	None (unalloyed)	Cr 0.90–1.20%, Mo 0.15–0.40%
Tensile strength (normalised)	550–700 N/mm²	~850 N/mm²
Tensile strength (Q+T)	~700–900 N/mm²	900–1200 N/mm²
Through-hardening section	~40mm reliable	~65mm reliable
Surface hardness (flame/induction)	50–55 HRC	52–58 HRC
Machinability (normalised)	Good	Good (slightly harder)
Weldability	Fair — preheat 150–250°C	Difficult — preheat 200–300°C + PWHT
Fatigue resistance	Moderate	Good — Cr-Mo improves fatigue life
Relative cost	Lower	Higher (alloy premium)
International equivalents	C40E, AISI 1040, DIN C40	42CrMo4, AISI 4140, SCM440
British Standard No.	BS 970: 080M40	BS 970: 708M40
Bright bar range	6–150mm	6–150mm
Black bar range	16–250mm	20–300mm
3.1 cert available	Yes	Yes

The Core Difference

Hardenability — Why it Matters.

The single most important practical difference between EN8 and EN19 is hardenability — the ability of the steel to harden through a cross-section when quenched. This is where the chromium and molybdenum in EN19 do their most important work.

EN8: through-hardens reliably in sections up to approximately 40mm when oil quenched. Above this, the centre of the bar does not reach full hardness — it becomes a softer core surrounded by a harder outer zone.

EN19: through-hardens reliably in sections up to approximately 65mm when oil quenched. The chromium and molybdenum slow the transformation from austenite to softer microstructures, allowing martensite to form even in larger sections at lower cooling rates.

This means for a 50mm diameter shaft: EN8 will have a soft core after hardening, EN19 will be uniform through the section. For applications where a 50mm shaft must be through-hardened and have consistent properties centre-to-surface, EN19 is the correct grade.

For shafts under 40mm where full through-hardening is not required, EN8 is adequate and cheaper. The rule of thumb: if your section exceeds 40mm and you need reliable through-hardening, move from EN8 to EN19.

When to Choose Each Grade

The Right Grade for the Job.

Choose EN8 (080M40) when:

General engineering shafts and axles under 40mm
Keys, studs and stressed pins
Light to medium duty gears
Cost is a primary consideration and high tensile is not required
The component needs to be welded (easier than EN19)
Agricultural machinery driveline components
Flame or induction hardened wear surfaces on smaller sections

Choose EN19 (42CrMo4) when:

Shaft diameter exceeds 40mm and through-hardening is required
Tensile strength above 700 N/mm² is specified
The drawing specifies 42CrMo4, 4140, or 708M40
High fatigue resistance under cyclic or reversed loading
Automotive transmission shafts (global standard)
Oil and gas valve bodies and components
High-tensile bolting requiring 900+ N/mm²

Not sure? Call our sales team with the diameter, required tensile and application — we will recommend the correct grade. 01623 687 660

EN8 vs EN19 — Key Differences.

Comparison Table.

Hardenability — Why it Matters.

The Right Grade for the Job.

Stock Both Grades.