Reading designations
How to read BS 970 steel codes and the old EN numbers (EN8, EN19, EN24, 080M40, 817M40)
BS 970 names steels with a six-character code such as 080M40, in which the first three digits give the steel type, the letter says how the steel is specified and the last two digits give the carbon content. Older names such as EN8, EN19 and EN24 come from the British BS 970 EN series, not from European EN standards, and remain in everyday trade use.
- Code layout
- Three digits, a letter, two digits: 080M40
- First three digits
- 000–199 carbon and carbon-manganese (Mn × 100); 200–240 free-cutting; 250 silicon-manganese valve; 300–499 stainless and heat-resisting; 500–999 alloy
- Letter
- A = to chemical analysis, H = to a hardenability band, M = to mechanical properties, S = stainless
- Last two digits
- Mean carbon × 100 (080M40 ≈ 0.40% C); not carbon in stainless codes
- Old EN numbers
- EN1 to EN58 from the wartime and 1955 BS 970; "EN" here is not European Norm
- Status
- Superseded by European standards such as BS EN 10083 and BS EN 10088-3
Reading the six characters
The six-character system replaced the EN series in the 1970s. It packs the steel type, the way the steel is ordered and its carbon content into one code.
For carbon and carbon-manganese steels the first three digits are the manganese content times 100. For free-cutting steels the second and third digits give the sulphur content times 100. In the 500–999 alloy range the first three digits identify the alloy grade rather than a single element.
| Position | Meaning | In 080M40 |
|---|---|---|
| Digits 1–3 | Steel type; for carbon steels, Mn × 100 | 080: carbon steel with about 0.80% Mn |
| Letter | A analysis, H hardenability, M mechanical properties, S stainless | M: supplied to mechanical properties |
| Digits 5–6 | Mean carbon × 100 | 40: about 0.40% C |
Stainless codes such as 304S31
Stainless codes use the 300–499 range, and the first three digits follow the AISI type number. The letter is always S.
In stainless codes the last two digits are not carbon. They distinguish variants of the same type: 304S11 is the low-carbon, 304L-type variant, and 304S31 is the standard 304-type grade that suppliers list against 1.4301.
The old EN series: EN8 is British, not European
During the Second World War the British government and BSI issued emergency steel specifications that became the BS 970 EN series, from EN1 to EN58. The 1955 revision tightened the chemistry and added suffix letters (EN8D, EN36A) because the numbers could not be extended.
This "EN" is the prefix of the old British series, not an abbreviation of Europäische Norm (European Standard). EN8 has nothing to do with a European standard such as EN 10083. When the 1970s revision introduced six-character codes, EN8 became 080M40, EN19 became 709M40 and EN24 became 817M40.
A letter after an EN number on a stockist's list, as in EN19T or EN24T, is usually a BS 970 condition code. Codes P to Z give the tensile strength range after hardening and tempering; T is 850–1000 MPa, for example.
Why the old names are still used
BS 970 was superseded by European standards and has been formally withdrawn, yet EN8, EN19 and EN24 remain the names most buyers and machinists recognise in the UK. Indian engineering, forging and stockholding markets inherited the same British names and still quote them on drawings and price lists.
When writing a new specification, name the current standard and grade as well. Indian standards have their own names for these steels (40C8 is the closest IS 1570 grade to EN8), and European standards use names such as C40, 42CrMo4 and 34CrNiMo6.
Worked examples
Closest equivalents are given in region order (US · EU). They are near matches, not identical steels; check the full chemistry before substituting.
| Old EN name | BS 970 code | Reading the code | Closest equivalents (US · EU) |
|---|---|---|---|
| EN8 | 080M40 | Carbon steel, about 0.80% Mn, mechanical-property grade, about 0.40% C | 1040 · C40 (1.0511) |
| EN19 | 709M40 | Alloy range (1% Cr-Mo), mechanical-property grade, about 0.40% C | 4140 · 42CrMo4 (1.7225) |
| Often sold as EN19 | 708M40 | Sister 1% Cr-Mo grade with lower molybdenum than 709M40, about 0.40% C | 4140 · 42CrMo4 (1.7225) |
| EN24 | 817M40 | Alloy range (Ni-Cr-Mo), mechanical-property grade, about 0.40% C | 4340 · 34CrNiMo6 (1.6582) |
| EN36A | 655M13 | Alloy range (Ni-Cr case-hardening), mechanical-property grade, about 0.13% C | — · 15NiCr13 (1.5752) |
| EN58E (304S15) | 304S31 | Stainless, AISI 304 type, variant 31 (digits are not carbon) | 304 · X5CrNi18-10 (1.4301) |
Standards
Governing standards by region
| Region | System | Designation | 規格 | Match |
|---|---|---|---|---|
| UK | BS 970 six-character codes | BS 970Superseded; still widely quoted in trade. | BS 970 (1970s onward, Part 1:1991) | Same material |
| BS 970 (1955 EN series) | EN1–EN58Legacy names such as EN8, EN19, EN24, EN36; not European standards. | BS 970:1955 | Same material | |
| EU | European successor standards | EN 10083-2, EN 10083-3, EN 10084, EN 10088-3Engineering, case-hardening and stainless bar grades that replaced BS 970 in the UK. | Published in the UK as BS EN | Closest equivalent |
よくあるご質問
Common questions
What does EN8 mean?
EN8 is a medium-carbon steel from the old British BS 970 EN series. Its later BS 970 code is 080M40: about 0.80% manganese, supplied to mechanical properties, about 0.40% carbon. The closest grades are 1040 in the US and C40 (1.0511) in Europe.
Is EN8 a European EN standard?
No. The EN in EN8 is the British BS 970 numbering that began in wartime and was revised in 1955. It is unrelated to European Norms such as EN 10083, which now cover similar steels.
What is the modern equivalent of EN24?
EN24 became 817M40 in BS 970. Its closest European grade is 34CrNiMo6 (1.6582) and its closest US grade is 4340. In India the closest IS 1570 grade is 40Ni6Cr4Mo3.
What does the T in EN19T or EN24T mean?
It is usually the BS 970 condition code for the tensile strength range after hardening and tempering. T means 850–1000 MPa; other letters run from P (550–700 MPa) upward to Z.
What does the M in 080M40 mean?
M means the steel is supplied to a mechanical property specification. A means supplied to chemical analysis, H to a hardenability band, and S marks a stainless steel.
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Related references
References
Sources
- Steel strength and BS 970 designations (Roymech) — Digit ranges, letters A/H/M/S, carbon digits, condition codes P–Z, EN to BS 970 table
- BS970: an act of perseverance (West Yorkshire Steel) — History of the EN series, 1955 suffixes, 1970s six-character codes, withdrawal
- Stainless steel cross-references (West Yorkshire Steel) — 304S11 = 304L, 316S11 = 316L, 316S31 = 316
- Stainless steel 1.4301/304 datasheet (Righton Blackburns) — Lists 304S31 against 1.4301
- EN19 datasheet (Smith Metal) — BS 970:1955 EN19 and BS 970:1991 709M40; 42CrMo4, 1.7225
- IS 1570 (Part 4):1988 schedules for wrought steels, alloy steels (BIS, via Public.Resource.Org) — 40Ni6Cr4Mo3 composition; 15Ni13Cr3Mo2 noted as equivalent to EN36
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.