St3sp steel: properties, composition, equivalents

St3sp is the Russian and CIS carbon structural steel of GOST 380: 245 MPa yield to 20 mm, 370–480 MPa tensile, killed, and the direct counterpart of S235JR.

Last updated 26 September 2026

What is St3sp?

St3sp — Ст3сп in Cyrillic — is the ordinary-quality carbon structural steel that carries most of the structural steelwork produced in Russia, Kazakhstan, Belarus and the wider CIS. It appears on almost every mill certificate arriving from the region, and it is the grade an S235JR enquiry is normally answered with.

The name has three parts. St is *stal* (steel), 3 is the position on the GOST 380 ladder from St0 to St6, and sp is *spokoynaya* — killed steel. The suffix matters: kp is rimmed, ps semi-killed and sp fully killed, and only the silicon content changes between them. Structural work outside a heated building is ordered sp, because rimmed steel has neither the silicon nor the consistency for a welded structure.

The second thing to know is that GOST 380 contains no mechanical properties at all. It defines grades and chemistry. Yield, tensile, elongation and impact come from the product standard — GOST 535 for sections and bar, GOST 14637 for heavy plate — which is why a complete certificate names two standards and an incomplete one names only the first.

The third is the category number. St3sp and St3sp5 are not the same order: the digit sets what was tested. Category 1 requires no impact test, category 3 is tested at +20 °C, category 4 at −20 °C and category 5 at −20 °C after mechanical ageing. Reading an S235J2 requirement across to "St3sp" without a category is reading half of it.

St3sp chemical composition

GOST 380-2005 ladle analysis for St3sp. The suffix is the deoxidation practice and it changes only the silicon: **sp** (спокойная, killed) 0.15–0.30 %, **ps** (полуспокойная, semi-killed) 0.05–0.15 %, **kp** (кипящая, rimmed) ≤ 0.05 %. Carbon, manganese, phosphorus and sulphur are the same across all three. Like Q235 and unlike S235JR, St3sp carries a carbon *minimum*.

St3sp mechanical properties

Mechanical values are not in GOST 380 at all — they come from the product standard that calls the grade up: GOST 535 for sections and bar, GOST 14637 for heavy plate, GOST 16523 for thin sheet. That is why a genuine St3sp certificate always names two standards, and why a certificate quoting GOST 380 alone is incomplete.

Impact toughness

St3sp requires a minimum Charpy V-notch energy of 27 J at 20 °C (category 3 and above; KCU converted from J/cm²). The impact requirement is set by the **category number** (1 to 6) written after the grade, not by the grade itself. St3sp alone carries no Charpy test; **St3sp category 3** is tested at +20 °C, **category 4** at −20 °C and **category 5** at −20 °C after mechanical ageing. GOST states impact as KCU in J/cm² on a U-notch piece, so the figures are not directly comparable with European KV values on a V-notch piece — a conversion, not an equivalence.

St3sp equivalent grades

Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for St3sp →

Old and superseded designations

Product forms and tolerance standards

Product forms: hot-rolled sections: I beam (GOST 8239 / 26020), channel, angle, heavy plate to GOST 14637, thin sheet and coil to GOST 16523, round, square and flat bar to GOST 2590 / 2591 / 103, welded pipe to GOST 10704 (chemistry called up from GOST 380).

Dimensional tolerances: heavy plate: GOST 19903; thin sheet: GOST 19904 (cold) / GOST 19903 (hot); I beam: GOST 8239, wide-flange GOST 26020; round bar: GOST 2590.

Key property values

St3sp yield strength

245 MPa minimum up to 20 mm, stepping to 235 MPa at 20–40 mm, 225 MPa at 40–100 mm and 215 MPa above. Note that the first step is at 20 mm and not at 16 mm as in EN 10025-2 — the two ladders do not line up, and in the 16–20 mm band St3sp is nominally the stronger of the two.

St3sp tensile strength

370–480 MPa. The band is tighter than the European 360–510 MPa and sits inside it, so St3sp material satisfies an S235JR tensile requirement on both limits.

St3sp chemical composition

C 0.14–0.22 %, Si 0.15–0.30 %, Mn 0.40–0.65 %, P ≤ 0.040 %, S ≤ 0.050 %, with Cr, Ni and Cu each limited to 0.30 % as residuals. The carbon *minimum* of 0.14 % is the practical difference from S235JR, which only caps carbon at 0.17–0.24 % by product and thickness.

kp, ps and sp — what the suffix changes

Only the silicon, and therefore the deoxidation. kp (rimmed, Si ≤ 0.05 %) has a clean surface skin and a segregated core; it is sheet and light-gauge material, not structural. ps (semi-killed, 0.05–0.15 %) is a compromise used for sections. sp (killed, 0.15–0.30 %) is the structural and weldable choice, and the only one that should be accepted against a European structural grade.

The category digit

Written after the grade — St3sp5 — it sets the test scope, not the strength. 1: chemistry and tensile only. 2: plus elongation. 3: plus impact at +20 °C. 4: impact at −20 °C. 5: impact at −20 °C and after mechanical ageing. 6: impact at −40 °C. Category 5 is the usual structural order in the CIS and the one to ask for against S235J2.

KCU and KV are different tests

GOST reports impact energy as KCU in J/cm² on a U-notched specimen; EN reports KV in joules on a V-notched one. There is no exact conversion — the U-notch is blunter and absorbs more energy — so a GOST impact figure cannot be placed directly beside an EN one. Where a design needs 27 J KV, ask the mill for a V-notch test to EN 10045 / ISO 148 as a supplementary requirement.

Weldability

St3sp is fully weldable by all arc processes in normal structural thicknesses and needs no preheat below about 25 mm at ordinary ambient temperatures. Two cautions carry over from the specification. The carbon minimum of 0.14 % means material can legitimately sit harder than a typical European S235JR heat, so a procedure qualified on European plate should be re-checked on the declared analysis. And the suffix must be sp: rimmed St3kp has a segregated, low-silicon core and is not a structural welding material whatever the yield figure says. Consumables are the ordinary mild-steel classes; CIS practice uses UONI-13/45 and equivalents, which correspond to E7015/E7016.

Machining, forming and heat treatment

Machinability is good and predictable for a low-carbon steel — better than S235JR on average, because the carbon minimum keeps the material out of the very soft range where low-carbon steel smears. Cold bending and roll forming are acceptable in the killed variants; GOST sets no yield ceiling, so spring-back varies between heats. For pressing and deep drawing the correct GOST specification is the 08kp / 08ps / 08Yu forming grades of GOST 16523, not St3.

Typical applications

• Building and industrial steelwork across Russia, Kazakhstan, Belarus and Central Asia
• Welded frames, platforms, stairs, ladders and gantries
• Heavy plate for hoppers, chutes, silos and tank shells with no pressure duty
• Hot-rolled sections rolled to GOST 8239 and GOST 26020 profiles
• Welded pipe for structural and low-pressure service (GOST 10704)
• Material offered against an S235JR or A36 requirement on export orders

St3sp compared with related grades

Frequently asked questions

Related grades

Verified against GOST 380-2005; mechanical values per GOST 535-2005 and GOST 14637-89; GOST 380-2005 — Carbon steel of ordinary quality. Grades; GOST 535-2005 — Rolled sections and bars. General specifications; GOST 14637-89 — Hot-rolled heavy plate of ordinary-quality carbon steel. Last checked: September 2026.