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What is the Treatment of Surface?What is the Chemical Treatment?
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What is the Treatment of Surface?What is the Chemical Treatment?

Views: 34     Author: Site Editor     Publish Time: 2018-03-16      Origin: www.fuchun-casting.com

What is the Treatment of Surface?

Surface treatment is a process of forming a surface layer on the surface of the matrix material, which is different from the mechanical, physical and chemical properties of the matrix.

The purpose of surface treatment is to meet the requirements of corrosion resistance, abrasion resistance, decoration or other special functions of products.

Surface protection can be divided into electroplating, coating, chemical treatment layer.Electroplating can include (galvanizing, copper, chromium, lead, silver, nickel, tin, cadmium, etc.); Coating can include (paint coating, electrostatic spray, spray technology); Chemical treatment can include (blackening treatment, phosphating treatment).



What is the Chemical Treatment?

Blackening is a common method of chemical surface treatment. The principle is to produce a layer of oxide film on the surface of the metal so as to isolate the air and achieve the purpose of rust prevention. The commonly used methods of blackening treatment are two kinds of traditional alkaline heating blackening and late normal temperature blackening. However, the blackening process at room temperature is not very effective for low carbon steel.

The main components of black liquor are sodium hydroxide and sodium nitrite. When the temperature is higher, it can get a good surface at about 135-155 C, but it takes only a little bit of time.



Phosphating is a process of chemical and electrochemical reaction to form phosphate chemical conversion film. The phosphate conversion film formed is called phosphating film.

The main purpose of phosphating is to provide protection for base metal and prevent corrosion of metals to a certain extent.

It is used for priming before painting, improving adhesion and corrosion resistance of paint film layer, reducing friction and lubrication in metal cold working process.



Nickel phosphorus plating is a chemical solution, which can react with carbon steel and other components, and form a layer of nickel phosphorus coating on the surface of the steel parts, effectively separating the contact between the steel components and the corrosive medium, thus achieving the purpose of anticorrosion.Its construction is to immerse the workpiece in the plating bath slowly, because it is completely soaked, so the reaction coating is even.




What are the differences between them

Surface Blackening Treatment:

1. Blackening treatment to improve rust resistance of metal products.

2. Because blackening is not easy to cause damage to metal products because of corrosion, it prolongs the service life of metal products.

Surface Phosphating Treatment:

The advantages of phosphating are the thicker film, better corrosion resistance, heat resistance, better adhesion and hardness, faster phosphating speed.

Its disadvantages are high working temperature, high energy consumption, high evaporation of solution, rapid change in composition, and often need to be adjusted, and the crystallization is not uniform.

Surface Nickel Phosphorus Plating:

1. The coating has good compactness. All the places where the solution can permeate can be well plated.

2. The coating is very smooth, and the dirt is not easy to be deposited.

3. The properties of the coating are similar to those of the metal, which do not affect the heat transfer coefficient of the heat exchanger.

4. The corrosion resistance of Ni-P plating is very high, and the temperature resistance can reach 500 degrees centigrade.



Scope of application

Surface Blackening Treatment:

The principle of surface blackening is to heat the metal to a very high temperature and quickly immerse in the cold water that dissolves a special agent to form a dense layer of oxide film on the surface of the metal, which is mostly blue.

When blackening, the size and finish of the workpiece have little effect on the quality and the size and appearance quality of the product will not be changed (compared with galvanizing and spray paint), so it is often used in precision instruments, optical instruments, tools, and hardness blocks.


Surface Phosphating Treatment:

Phosphating treatment is widely used in automobile, railway, electric vehicle, bicycle manufacturing, mechanical manufacturing, steel door steel window, instrument and instrument shell, high and low voltage electrical equipment, box cabinet shell and other steel structure parts for spraying, baking paint, spray plastic, rust proof, electrophoretic dip coating and so on.


Surface Nickel Phosphorus Plating:

ENP technology can be deposited on steel, copper, aluminum and other substrates. With good technological and excellent coating properties, it is widely used in electronic and computer, aerospace, chemical and chemical industry, petroleum and natural gas, machinery, automobile and motorcycle, precision instrument, food machinery, medicine, textile, municipal road administration and other industries.




  • What is 'multiple certification'?

    This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.

    For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.

  • What surface finishes are available on stainless steels?

    There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.

    The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.

  • Can I use stainless steel at high temperatures?

    Various types of stainless steel are used across the whole temperature range from ambient to 1100 deg C. The choice of grade depends on several factors:

    1. Maximum temperature of operation
    2. Time at temperature, cyclic nature of process
    3. Type of atmosphere, oxidising , reducing, sulphidising, carburising.
    4. Strength requirement

    In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.

    Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.

  • Can I use stainless steel at low temperatures?

    Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.

    Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.

    Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.

    In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.

    Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite. 

  • Is stainless steel non-magnetic?

    It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. 

    It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.

    In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.

    Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.

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