The term "ST 35" refers to ​​historical German steel grades​ defined by the old ​​DIN standards​, specifically for pipes. It's important to understand its context and modern equivalents:

​​Origin & Standard:​

​​ST 35​ was primarily defined in the old ​​DIN 1626 (Steel tubes and pipes - General delivery technical conditions)​ and ​​DIN 2448 (Wrought steel pipes - Dimensions)​ standards.

The "ST" stands for ​​Stahlrohre​ (steel pipes). The number "35" indicates the ​​minimum yield strength (Rp0.2) of approximately 35 kp/mm²​, which converts to ​​approximately 343 MPa (or often rounded to 335-355 MPa range)​. The specified minimum was usually ​​235 MPa (N/mm²)​ for earlier classes.

​​Modern Equivalent:​

The old DIN standards were largely superseded by European standards. The direct material equivalent of ST 35 for ​​seamless and welded tubes for pressure purposes​ is now ​​P235GH (according to EN 10216-1 / EN 10216-2)​.

​​P235GH​ breaks down as:

P: Pressure purpose

235: Minimum Yield Strength (ReH) at room temperature in MPa (~235 MPa).

GH: Indicates it's suitable for elevated temperatures (G = Hauptgruppe "main group" for temp use, H = temperature limits defined).

​​Key Properties (Typical for ST 35 / P235GH):​

​​Chemical Composition (typical ranges):​

Carbon (C): 0.10 - 0.17%

Manganese (Mn): 0.40 - 0.80%

Silicon (Si): ≤ 0.35%

Phosphorus (P): ≤ 0.025%

Sulfur (S): ≤ 0.015%

Low alloy content. Primarily a Carbon-Manganese steel.

​​Mechanical Properties (at Room Temperature):​

​​Yield Strength (ReH / Rp0.2):​ ≥ ​​235 MPa​ (P235GH specified min).

​​Tensile Strength (Rm):​ 360 - 510 MPa (common range).

​​Elongation (A5):​ ≥ 25% (minimum values specified based on specimen size).

​​Hardness:​ Typically around 120-140 HB.

​​Impact Toughness:​ Required values specified in standards (e.g., EN 10216) depending on delivery condition and application, often tested at +20°C.

​​Delivery Condition:​ Typically supplied in ​​normalized (N)​ or ​​normalized rolled (NR)​ state to achieve the required properties and microstructure.

​​Weldability:​ Generally ​​good​ due to low Carbon Equivalent (CEV). Standard welding procedures applicable, though preheating might be needed for thicker sections or restrictive joints.

​​Common Applications:​

Seamless and welded ​​boiler tubes​ and ​​heat exchanger tubes​ operating at ​​moderate temperatures and pressures​.

General ​​pressure piping systems​ for steam, water, and gases in industrial plants.

Structural tubing applications where moderate strength and formability are required.

Pipes conforming to standards like ​​EN 10255 (formerly DIN 2448, DIN 2462)​ for water and gas applications (though DIN 2448 ST 35 pipes are now also covered under materials like ​​S235JRH or P235TR1/P235TR2 in EN 10255​).

​​Standards & Variants:​

​​DIN 17175:​ Covered seamless tubes of heat-resistant steels (similar grades existed here).

​​EN 10255:​ Non-alloy steel tubes suitable for welding and threading (formerly DIN 2448/DIN 2462). Uses designations like ​​S235JRH​ (Structural steel, min yield 235 MPa, J impact at +20°C, H=Hollow section) or ​​P235TR1/P235TR2​ (Pressure purpose, min yield 235 MPa, TR=Tube, test category 1 or 2).

​​ISO 65:​ Carbon steel tubes suitable for screwing according to ISO 7/1 (similar scope to old DIN 2448).

​​ASTM A106 Gr. A / ASTM A53 Gr. A:​ Similar US equivalents in terms of strength level and application.

​​In summary:​

​​ST 35 is an obsolete German designation​ for pipes made from a carbon-manganese steel with a ​​minimum yield strength of approximately 235 MPa​.

Its primary ​​modern European equivalent is P235GH​ (EN 10216-1/2), used for pressure applications at moderate temperatures.

For non-pressure pipe applications like water/gas lines (previously covered by DIN 2448), modern equivalents are ​​S235JRH​ or ​​P235TR1/P235TR2​ (EN 10255).

Its defining characteristics are ​​moderate strength, good weldability, ductility, and suitability for normalized condition​.

If you encounter "ST 35" in documentation, refer to the specific standard mentioned (e.g., DIN 2448, DIN 1626) to understand the exact requirements, which are now best fulfilled by materials defined in the applicable current standards (EN 10216, EN 10255, etc.).