S235 (st37); S275 (st44); S355 (st52) according to the traditional German DIN17100 standard and the currently accepted international standards European EN 10025 (hot) and EN10130 (cold).

S235 (ST37):

Classified as structural carbon steel and generally used for structural steels.
Chemical Composition: This type of steel is a low carbon steel. It typically has a carbon content between 0.17-0.20%.
Mechanical Properties:
Tensile Strength: 370 to 510 MPa
Yield Strength 235 MPa.
Areas of Use: It finds a wide usage area in construction and machinery sectors. It is especially used in applications such as construction, automotive parts, heating equipment, steel constructions.

S275 (ST44):

A medium carbon steel with slightly higher mechanical properties than ST37.
Chemical Composition: This steel has a medium carbon content, usually between 0.22-0.26% carbon.
Tensile Strength: 440 to 570 MPa.
Yield Strength: 275 MPa.
Uses: ST44 can be used in more demanding conditions as it has higher strength than ST37. It is suitable for bridge construction, large industrial machinery, pressure vessels and various heavy industrial applications.

S355 (ST52):

A high quality structural steel with high strength. This steel has a higher carbon content than ST37 and ST44 and offers superior mechanical properties.
Chemical Composition: ST52 usually contains 0.22-0.26% carbon and small amounts of alloying elements.
Yield Strength: 355 MPa.
Tensile Strength: 520 to 680 MPa.
Areas of Use: ST52 is used for heavy machinery parts requiring durability, automotive industry, construction machinery, pressure vessels and construction industry. In addition, thanks to its high durability and strength, it is suitable for systems subjected to high pressure and heavy industrial machinery.