Introduce St 37.4 Black Phosphate Hydraulic Seamless Tube

In industries like construction, mining, and agriculture, hydraulic systems face extreme pressure and corrosion, making the reliability of their components absolutely critical. Traditional hydraulic tubes often struggle under these harsh conditions, leading to frequent failures, unplanned downtime, and escalating maintenance costs. These challenges not only disrupt operations but also compromise overall system safety and efficiency.

Enter St 37.4 Black Phosphate Tubes – a solution engineered specifically to address these pain points. With its unique black phosphate treatment, these seamless tubes exhibit enhanced corrosion resistance and durability under high-pressure environments. This innovative approach significantly extends the lifespan of hydraulic systems while reducing maintenance efforts and costs.

By integrating advanced material properties with precise manufacturing techniques, St 37.4 Black Phosphate Tubes deliver superior performance where it matters most, ensuring reliable operation even in the most demanding industrial applications.

Technical Specifications of St 37.4 Black Phosphate Hydraulic Seamless Tube

Applicable Standard: DIN 2391/EN10305-1

Material grade: St 37.4

Surface Finish: Black phosphate coating

OD: 6-60mm

WT: 1-8mm

L: 6000mm or customized length

Heat treatment: NBK normalized

Dimensional standard: EN 10305-4

What is St 37.4 material?
St 37.4 is a carbon structural steel commonly used for cold-drawn or cold-rolled seamless precision steel tubes, as specified in German standards DIN 2445 and DIN 2391. It is valued for its excellent mechanical properties and reliability in various industrial applications.

What is Phosphating?

Phosphating is a chemical treatment that forms an insoluble phosphate protective layer on the surface of steel through a chemical reaction. This phosphate coating enhances the adhesion and corrosion resistance of paint layers, improves the decorative appearance of metal surfaces, and provides lubrication in certain metal cold-working processes.

Phosphating is commonly applied to the inner and outer surfaces of precision seamless steel tubes to achieve a highly wear-resistant, corrosion-resistant, and uniformly colored phosphate protective film.

Phosphating Process:

Pre-treatment: Before phosphating, oil, rust, and other impurities on the workpiece surface must be thoroughly cleaned to ensure effective phosphating.

Process Control: The temperature, concentration, and duration of the phosphating solution must be carefully controlled to achieve high-quality phosphate coating.

Post-treatment: After phosphating, the workpiece should be promptly rinsed and dried to prevent contamination and corrosion of the phosphate layer.

Why Do Phosphated Seamless Precision Tubes Appear Black?

The black appearance of phosphated hydraulic precision tubes is due to the inherent characteristics of the phosphate coating formed during the phosphating process.

- Composition of Phosphate Coating

Phosphating can be classified into different types, such as zinc-based, manganese-based, and iron-based phosphating:

Manganese and iron phosphating typically result in a black coating.

- Zinc phosphating usually produces a gray or light-colored coating.

Black phosphating mainly involves manganese or iron phosphating, where the phosphate coating consists mainly of manganese phosphate or iron phosphate. These compounds are naturally dark or black, giving the surface its black appearance.

- Influence of Phosphating Solution Composition

Black phosphating uses a specialized phosphating solution that contains oxidizers (such as nitric acid or nitrites). These oxidizers promote the formation of magnetite (Fe₃O₄, black iron oxide) during the reaction, contributing to the black coloration of the phosphate layer.

- Microscopic Structure After Phosphating

The phosphated surface forms a porous phosphate crystal layer, which can absorb anti-rust oil or other treatment agents, further deepening the black appearance. Additionally, high-temperature treatment or sealing processes can make the black color more uniform and stable.

Dimensions of St 37.4 Precision Hydraulic Seamless Steel Tube

Advantages of Black Phosphating Coating

Enhanced Corrosion Resistance:

The phosphating layer forms a microporous structure on the metal surface, helping to absorb rust-preventive oil or protective agents, thereby improving rust resistance.

Effectively reduces the risk of rust in humid or corrosive environments, extending the service life.

Increased Surface Hardness and Wear Resistance:

The phosphating process enhances the surface hardness compared to raw carbon steel, improving wear resistance.

Reduced Friction Coefficient:

The phosphating coating provides excellent lubrication, minimizing friction and wear between moving parts.

Suitable for high-pressure hydraulic systems, reducing internal pipeline friction and improving fluid transmission efficiency.

Improved Coating Adhesion:

The phosphating layer serves as an excellent base, enhancing the adhesion of subsequent coatings such as paint, electroplating, or other surface treatments, preventing peeling or blistering. 

Aesthetic Black Appearance:

Black phosphating treatment gives the metal surface a uniform matte black finish, enhancing visual appeal and anti-glare performance.

Main Applications of St 37.4 Precision Seamless Black Phosphate Tube

- High-performance hydraulic and fuel transmission pipelines

- High-pressure brake pipes and steering system pipelines

Our Supply Capability

We specialize in the production and supply of high-quality St 37.4 black phosphated hydraulic seamless tubes. Utilizing high-precision cold-drawing processes and strict quality control, we meet the demands of global customers in high-pressure hydraulic systems, the automotive industry, construction machinery, and rail transit. Contact us for a quote!

St 37.4 Black Phosphate Hydraulic Seamless Tube