St35.8, St45.8, 17Mn4, 19Mn5 Seamless Steel Tubes for Elevated Temperatures

Introduction

St35.8, St45.8, 17Mn4, and 19Mn5 are widely used seamless steel tube grades manufactured for applications involving elevated temperatures. These steels are known for their high mechanical strength, excellent heat resistance, and good weldability, making them ideal for boiler tubes, heat exchangers, and pressure vessels in industries such as power generation, petrochemicals, and thermal processing.

This article provides a technical overview of these steel grades, highlighting their material properties, specifications, chemical and mechanical characteristics, and applicability in high-temperature environments.

Material

These grades are part of the DIN 17175 standard, which specifies seamless steel tubes used in high-temperature service. They are non-alloy or low-alloy heat-resistant steels, produced through hot rolling or hot extrusion, and often undergo normalizing or annealing treatments to improve mechanical properties and heat resistance.

• St35.8: Non-alloy steel for average pressure applications.

• St45.8: Similar to St35.8 but with higher tensile strength.

• 17Mn4 & 19Mn5: Low-alloy steels with added manganese for enhanced strength and oxidation resistance at elevated temperatures.

Specification

• Standard: DIN 17175

• Manufacturing Process: Seamless (hot-rolled or cold-drawn)

• Delivery Conditions: +N (Normalized), +A (Annealed)

• Outer Diameter (OD): 10.2 mm – 711 mm

• Wall Thickness (WT): 1.6 mm – 100 mm

• Length: 6 – 12 meters or custom

• End Types: Plain, beveled, or threaded

• Surface Condition: Black (bare), varnished, or oiled

Key Features

• ✅ Excellent High-Temperature Strength

• ✅ Reliable Creep Resistance

• ✅ Good Weldability

• ✅ High Pressure Resistance

• ✅ Consistent Microstructure due to Seamless Construction

• ✅ Dimensional Accuracy with Tight Tolerances

Chemical Composition

Mechanical Properties

Steel Grade Overview

• St35.8: For moderate temperature and pressure, offering basic strength and weldability.

• St45.8: Enhanced strength, used in higher pressure conditions than St35.8.

• 17Mn4: Manganese-alloyed for improved mechanical properties at elevated temperatures.

• 19Mn5: Higher Mn content for improved heat resistance and creep performance.

Application

These steel grades are widely used in:

• Boiler Tubes

• Heat Exchangers

• Superheaters

• Steam Pipelines

• High-Temperature Pressure Vessels

• Chemical and Thermal Processing Plants

• Power Generation Systems

Possible Alternative Grades

Depending on the service condition, alternatives may include:

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