Several culprits of stainless steel rust

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Many people believe that stainless steel will not rust. In fact, everything has a life span. Stainless steel is also a kind of metal, which will be oxidized and corroded in nature, causing rust; The only difference is that the material or protection degree is different, which can delay the probability and time of rusting to the greatest extent. However, in many cases, stainless steel will also be “rusted”. Here are the main culprits of stainless steel rust:

1、 Presence of chloride ions in the service environment

Chloride ions mainly exist in purified liquids and gases. The use of stainless steel in the presence of chloride ions will accelerate its corrosion, even exceeding that of ordinary low-carbon steel. Therefore, there are requirements for the use environment of stainless steel, and it needs to be wiped frequently to remove dust and keep it clean and dry.

2、 Without solution treatment

Solution treatment: refers to the heat treatment process that heats the alloy to the high-temperature single-phase area and maintains the constant temperature, so that the surplus phase can be fully dissolved in the solid solution and then rapidly cooled to obtain the supersaturated solid solution. Its purpose is to fully dissolve various phases in the alloy, strengthen solid solution, improve toughness and corrosion resistance, eliminate stress, and soften, so as to continue processing or molding. If the alloy elements are not dissolved in the matrix material, the alloy content in the matrix structure is low and the corrosion resistance is poor.

3、 Natural intergranular corrosion

Under the action of a corrosive medium, a corrosion phenomenon between grains of stainless steel is called intergranular corrosion. When the stainless steel with intergranular corrosion is subjected to stress, it will fracture along the grain boundary and the strength will almost disappear. This is the most dangerous form of stainless steel damage.

Stainless steel will not rust because the content of chromium (Cr) and nickel (Ni) has reached a certain standard. These two alloys are the key to rust prevention in stainless steel. Generally, stainless steel produced by small factories will rust, mainly because of the low nickel content (the cost price of nickel largely reflects the benchmark price of stainless steel); If the nickel content reaches the standard required by various stainless steel, no matter how you cut it, it will not rust.

4、 Mechanical stress corrosion

When stainless steel materials are made into products, they need to go through such processes as stamping, shearing, punching, stretching, grinding, shearing, bending, planing, thermal cutting, or welding. Because of the external stress loading, the machined parts and their edges will be damaged by their own stress to a large extent, which will lead to the intergranular transformation; Therefore, it destroys its corrosion resistance and speeds up the rusting process.

5、 Damage to surface passivation protective layer

Passivation is a method to change the metal surface into a state that is not easy to be oxidized, thus delaying the corrosion rate of the metal. Passivation is due to the interaction between metal and oxidizing substances. During the interaction, a very thin, dense, well-covered, and firmly adsorbed passivation film is formed on the metal surface. Once this “protective film” is damaged by external forces (mainly large scratches), the stainless steel is like a body without resistance, which is easy to react with the outside world to rust and corrosion.

The application practice of stainless steel pipes tells you where the advantages are!

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Stainless steel material is a recognized healthy material that can be implanted into the human body and is used in almost all fields involving human health. It has been widely used. The Stainless steel water pipe is an environmentally friendly material that meets health requirements, can be 100% recycled, saves water resources, reduces transportation costs, reduces heat loss, and avoids sanitary ware pollution. The details are as follows:

1. Lifespan

Stainless steel tubing has the longest service life. From the analysis of the use of stainless steel abroad, the service life of stainless steel water pipes can reach 100 years, or at least 70 years, which is as long as the life of buildings.

2. Corrosion resistance

One of the most prominent advantages of stainless steel pipe is its excellent corrosion resistance, which is the best among all kinds of pipes. Because stainless steel can passivate with oxidant, a tough and dense chromium-rich oxide protective film Dr2O3 is formed on the surface, which can effectively prevent the further oxidation reaction.

And other metal pipes, such as galvanized water pipes and copper pipes, have little passivation ability, which is the key reason why the corrosion resistance of copper pipes of galvanized pipes is far less than that of stainless steel pipes. Stainless steel does not corrode uniformly like carbon steel, and no protective coating is required for use; with stainless steel water pipes, there is no limit to the chemical composition of water, because stainless steel has good performance in water of various oxygen content, temperature, PH and hardness Corrosion resistance; stainless steel water pipes can withstand high flow rates, even if the flow rate is greater than 40 m/s, it still maintains a very low corrosion rate, no more than 0.003 mm/year, especially suitable for high-rise water supply.

Stainless steel generally does not suffer from localized corrosion. The chloride content that 304 stainless steel can withstand is up to 200ppm, and the chloride content that 202 stainless steel can withstand is up to 1000ppm. This conclusion is based on exposure experimental data and has been confirmed by experience. The thermal expansion coefficient of stainless steel pipe is similar to that of copper pipe, which is 1.5 times that of ordinary steel pipe. Compared with stainless steel pipe, it has the characteristics of slow thermal expansion and cold contraction.

3. Heat resistance and heat preservation

The thermal conductivity of stainless steel pipe is 1/25 of copper pipe and 1/4 of ordinary steel pipe, especially suitable for hot water transportation. The most commonly used stainless steels in the water industry are 202 and 304 stainless steels, which can meet the vast majority of water treatment and delivery conditions.

4. Strength

The tensile strength of 304 stainless steel pipe is 2 times that of steel pipe and 8-10 times that of plastic pipe. The strength of the material determines whether the water pipe is strong, crash-resistant, safe, and reliable. Safety and reliability are the most important requirements for building water supply. Under the circumstance of being hit by an external force, the possibility of leakage of the stainless steel water pipe is extremely small. The working pressure of a high-rise water supply system is generally greater than 0.6Mpa, which requires higher pressure on pipes.

Let’s talk about steel.

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How to prevent copper oxidation during copper alloy surface treatment?

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In the process of copper alloy surface treatment, after a period of storage, the surface of copper alloy will appear blackened and oxidized. After the surface of copper alloy is oxidized, it will seriously affect the quality, appearance, and service life of the product. In the process of copper alloy surface treatment, anti-oxidation treatment is a very important process. So, how to prevent copper oxidation during copper alloy surface treatment?

At present, the methods to prevent copper oxidation include passivation, electroless plating, electroplating, sealing, painting, and other processes. Among them, copper alloy passivation treatment is mature and easy to operate, which is favored by copper alloy surface treatment plants.
The copper alloy passivation treatment process includes copper degreasing, copper derusting, copper polishing, copper passivation, and other processes. The pretreatment degreasing and rust removal processes are very important, they determine the quality and yield of the final product, and the passivation process determines the role of rust prevention and discoloration prevention.

In general, copper alloy passivation agent is a chromium-free passivation agent with good environmental protection performance and stable physical and chemical properties.

Copper alloy passivation agent is non-toxic, odorless, non-volatile, non-deliquescent, non-decomposing, non-sublimating, and does not absorb dust and harmful gases such as H2S and SO2.

The copper parts treated with copper alloy passivation agent can effectively resist the erosion of copper alloys by hot and humid salt spray and bacteria, and have good wettability and high corrosion resistance.

The copper alloy passivation agent has the triple functions of dehydration, discoloration prevention, and rust prevention, and the generated passivation film has better electrical properties.

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The production process and welding quality of titanium plate determine its quality!

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A notable feature of titanium plates is their strong corrosion resistance, which is due to their great affinity for oxygen. It can form a dense oxide film on its surface, which can protect titanium from medium corrosion. It has good stability in acidic, alkaline, neutral saline solutions and oxidizing media, and is better than existing stainless steel and other commonly used non-ferrous metals in corrosion resistance.

The quality of titanium plate largely depends on the smelting process of the titanium plate manufacturer, including the chemical composition of titanium, the cleanliness of titanium water (gas, harmful elements, inclusions), and the quality of cast slab (composition segregation, decarburization, and surface conditions), which are the key control points of smelting operation.

In addition, industrial titanium plate also requires sufficient hardenability to ensure uniform microstructure and mechanical properties of the whole spring cross-section. The main reason for fatigue cracks is oxide inclusions in titanium, and the damage of type D inclusions to fatigue life is greater than that of type B inclusions. Therefore, foreign titanium factories and automobile factories put forward higher requirements for oxide inclusions in industrial titanium plates. For example, the Swedish SKF standard requires that the oxygen content in titanium be less than 15 × 10-6, and class D inclusions are lower than class B inclusions. Especially Al2O3 and tin inclusions do great harm to the fatigue life of titanium springs. In order to produce high-quality industrial titanium plates, special smelting methods such as electric furnace electro slag remelting or vacuum arc remelting were usually used in the past.

Because titanium plate has special physical and chemical characteristics, their welding process is very different from other metals. Titanium welding is a TIG welding process that effectively protects the welding area with inert argon. Before using argon, check the factory certificate on the bottle body to verify the purity index of argon, and then check whether the bottle valve leaks or fails.

When welding titanium plates, the following must be ensured:

The metal in the welding area shall not be polluted by the active gas n0h and the harmful impurity element clean above 250 ℃. Argon with purity not less than 99.98% and water content less than 50mg / M32: industrial grade I pure argon.

A coarse crystal structure cannot be formed. The welding process shall be carried out according to the predetermined construction sequence, and no large welding residual stress and residual deformation shall be generated. Therefore, the quality control of the whole process shall be carried out in strict accordance with the procedure quality management standards, so that the factors of human, machine, material, and method are under good control, so as to ensure the quality within a reasonable construction period.

Copper Nickel Alloy C71500 BFe30-1-1 Copper Rod Steel Plate Forgings

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Copper-nickel alloy C71500 cupronickel alloy is widely used in heat exchangers and condensing pipes for coastal power stations and ships due to its excellent corrosion resistance and anti-fouling properties. The excellent corrosion resistance of cupronickel alloy is attributed to the Cu 2 O film formed on its surface, which effectively prevents further contact between the substrate and the solution. As the main additive elements of cupronickel alloy, iron and manganese have an important influence on improving the corrosion resistance of cupronickel alloy, but there is no consensus on the influence mechanism of iron and manganese in it.

As a forgeable material, cupronickel alloy is suitable for both hot working technology and cold working technology and can be used to produce various profiles required. According to the processing process of cupronickel alloy, the maximum cold working deformation before annealing can reach 50%. The cupronickel alloy pipe is usually bent during use. When bending, the smooth bending method can prevent the influence of non-end flow on the service life of the pipe [DD. Under normal circumstances, the phenomenon of stress corrosion does not occur in cupronickel alloys, but when the cold working temperature is extremely low, stress relief heat treatment must be carried out, and the heat treatment temperature is 300 ° C ~ 400 ° C.

The complete annealing temperature of B10 alloy is 700℃~800℃, and the complete annealing temperature of B30 alloy is 750℃~850℃. The specific time and temperature of complete annealing depend on the degree of cold working, section thickness, degree of annealing treatment, and grain size of the alloy. Sure. Before heat treatment, the oily residue on the surface of the alloy must be removed to avoid the formation of the carbonaceous film. The carbonaceous film can cause pitting corrosion on the surface of the cupronickel alloy. Under certain working conditions, it will increase the sensitivity of impact corrosion, thereby reducing cupronickel alloy. Service time in practical application

Both B10 and B30 cupronickel alloys exhibit good resistance to seawater corrosion and biofouling under many conditions. Among them, the cupronickel alloy of B10 has better anti-biological accumulation ability. When the water speed is greater than 1m/s, the tiny organisms attached to the metal surface will be easily separated and removed. When the material does not have the ability to resist bioflooding, organisms in seawater will strongly adhere to its surface and grow in large numbers, resulting in a reduction in the service life of the material. Although some materials have good biofouling resistance, they do not have the ability to resist seawater corrosion, which will also reduce the service life. In addition, when the cupronickel alloy components in seawater are attached to the joints and surfaces of the components, the crevice corrosion resistance of cupronickel alloys is better than that of other common alloys. Cupronickel exhibits good corrosion resistance even under static or stagnant conditions that may occur during plant commissioning or overhaul

BFe30-1-1 cupronickel alloy has good solderability. However, this welding method is rarely used, because the joint strength obtained by this welding method does not meet the actual service requirements of cupronickel alloy, and the galvanic metal corrosion will be aggravated in a corrosive environment. Traditional brazing methods can be used, but a high silver filler metal is recommended, which minimizes the chance of corrosion of cupronickel. Copper-phosphorus and copper-silver-phosphorus solders should not be used because their use increases the risk of intergranular corrosion and hydrogen embrittlement. Re-cold-worked cupronickel alloy materials should be recrystallized and annealed before brazing to avoid excessive penetration and cracking between the brazing alloy and the base metal.

What is the difference between 316Ti stainless steel and 316L stainless steel?

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316Ti stainless steel is based on 316 stainless steel by adding Ti to improve the resistance to intergranular corrosion. It is also a variant of 316 stainless steel and is used in equipment resistant to sulfuric acid, phosphoric acid, acetic acid, and acetic acid. Physical properties: 316 stainless steel chemical composition C: ≤0.08 Si≤1.00 Mn≤2.00 P≤0.035 S≤0.030 Ni 11.00~14.00 Cr 16.00~19.00 1 Mo 1.80~2.50 Ti≥5*C%~0.70 Usually also called Mo2Ti3163 (00Cr17Ni14Mo2) is an ultra-low carbon steel of 0Cr17Ni12Mo2, which has better resistance to intergranular corrosion than 0Cr17Ni12Mo2 (SUS316). 316L stainless steel chemical composition C≤0.03 Si≤1.00 P≤0.035 S≤0.03 Ni: 12.0-15.0 Cr: 16.0-18.0 Mo: 2.0-3.0 Tensile strength (Mpa) 620 MIN Yield strength (Mpa) 310 MIN Elongation ( %) 30 MIN Area reduction (%) 40 MIN Features: due to the addition of Mo, its corrosion resistance, atmospheric corrosion resistance, and high-temperature strength are particularly good, and can be used under harsh conditions; excellent work hardening (non-magnetic); Excellent high-temperature strength; non-magnetic in solid solution state; cold-rolled products have the good gloss and beautiful appearance; compared with 304L stainless steel, the price is higher.

copper-nickel-90-10-pipe

UNS C70600 in Seawater Service

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The performance and application of titanium forgings!

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Titanium forgings have high strength, low density, good mechanical properties, good toughness and corrosion resistance. In addition, titanium forgings have poor technological performance, are not easy to cut, are easy to absorb impurities such as hydrogen, oxygen, nitrogen, carbon, etc. during hot processing, and have poor wear resistance and complex production processes. The industrial production of titanium began in 1948, and with the development of the aviation industry, the titanium industry is growing at an average annual rate of about 8%. At present, the global annual output of it has reached more than 40,000 tons, and there are nearly 30 types of it. The most widely used titanium forgings are Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (TA7) and industrial pure titanium (TA1, TA2 and TA3).

Titanium forgings are mainly used in the manufacture of compressor components for aircraft engines, followed by structural parts for rockets, missiles and high-speed aircraft. In the mid-1960s, titanium and its alloys were used in general industries such as making electrodes for the electrolysis industry, condensers in power stations, heaters in oil refining and desalination, and in environmental pollution control devices. Titanium and titanium alloys have emerged as corrosion-resistant structural materials. In addition, it is used in the production of hydrogen storage materials and shape memory alloys.

Standard: National Standard GB/T 16598-1996

American Standard: ASTM B381

Material: TA0, TA1, TA2, TA3, TC4

Delivery state: Annealed state (M) Hot working state (R) Cold working state (Y) (annealing, ultrasonic flaw detection)

Packing: carton or wooden box

Surface treatment: car light, chamfering

Surface quality: The surface roughness Ra of the two end faces should not be greater than 3.2m (subject to the requirements of ultrasonic flaw detection), and the surface roughness Ra of the inner and outer sides should not be greater than 12.5m (Ra should not be greater than 3.2 m during cylindrical ultrasonic flaw detection). Circumferential surface required), the chamfering radius is 5 ~ 15mm. There should be no visible defects such as cracks, folds, double skins, etc. on the surface of the product. Local surface defects can be removed by grinding, the cleaning depth should not exceed the dimensional tolerance, and the minimum allowable size should be guaranteed. The ratio of the cleaning depth to the width of the two end faces should not exceed 1: 6, the inner and outer sides should not exceed 1: 10, and the outer grinding should be carried out in the axial direction.

Well, the above is all about the performance and application of titanium forgings. I hope you like it!

Refinement of Titanium Alloy by Hydrogen Treatment

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Ultrafine-grained titanium alloy has a series of outstanding advantages, its room temperature strength can be improved to a certain extent, and it has a great elongation when stretched at high temperature. Refined grains are usually obtained by large deformation methods, such as equal-diameter angular extrusion, high-pressure torsion, multi-axis forging, and cumulative coil pressure welding. In addition, hydrogen treatment can also be used for titanium alloys.

In the 1970s, the Moscow Aircraft Manufacturing Research Institute studied the influence of hydrogen on the processing properties of titanium alloys, and proposed the concept of “hydrogen plasticization”, using hydrogen as a temporary alloying element, through hydrogen infiltration, eutectoid decomposition, vacuum hydrogen removal, and other processes. , using hydrogen-induced plasticity, hydrogen-induced phase transformation, and the reversible alloying of hydrogen in titanium alloys to improve processing properties and refine the microstructure of materials.

Hydrogen treatment can be used to refine the grain structure of titanium alloy castings and forgings and improve their mechanical properties. It has been reported in the literature that the microstructure of TiAl alloy can be refined by hydrogen treatment, and its compressive strength and yield strength have been significantly improved. In practical applications, the hydrogen treatment technology can usually be combined with the corresponding subsequent heat treatment and thermal deformation treatment, so as to obtain a very fine grain structure. Studies have shown that large-scale deformation of hydrogenated titanium alloys at a high temperature can form equiaxed fine grains with a grain size of about 1 μm, and even nano-scale grains. The research on Ti-6.3Al-3.5Mo-1.7Zr (%, mass fraction) alloy shows that the hydrogen atomic fraction is 14%-16% in hydrogen treatment, the deformation temperature is reduced to 550 ℃, and then through the deformation process and metastable phase, The decomposition process finally obtained nanocrystalline grains with a grain size of 40 nm. Comparing the engineering stress-strain curves of Ti-6Al-4V alloys with different grain sizes, it can be seen that the ultra-fine-grained materials exhibit high yield strength and high elongation compared with the coarse-grained or general fine-grained materials.

Let the titanium alloy absorb a large number of hydrogen atoms (protium), and then let these hydrogen atoms (protium) desorb under a high-temperature vacuum, this process is called protium treatment. For α + β titanium alloys, the protium treatment includes the following three processes: (1) protium absorption in a hydrogen atmosphere; (2) martensitic transformation and hot working eventually cause dispersive hydride precipitation; (3) final protium desorption treatment and recrystallization. It is reported that the Ti-6Al-4V alloy is treated with protium, and the alloy absorbs 0.5% of protium and desorbs at 873K, showing an ultra-fine equiaxed grain structure with large-angle grain boundaries and grain size in the range of 300-500 nm. Studies have shown that protium treatment increases the content of the β phase in the α matrix. Tensile tests show that the yield strength of the alloy increases at room temperature, and the maximum elongation of 1123K alloy reaches 9000%. It is also reported that the Ti-6Al-4V sheet was treated with protium with a protium content of 0.5%, then quenched at 1223K, hot-rolled at 1023K to a thickness reduction rate of 80%, and desorbed at 873K. In the uniform structure of equiaxed crystals, the grain size is 0.3 ~ 0.5μm. The test results show that the mechanical properties such as superplastic elongation of the alloy increase significantly with the decrease of grain size.

Although the hydrogen treatment method shows great potential for refining titanium alloys, compared with other conventional methods, the hydrogen treatment method has a higher cost, and for larger structural parts, this treatment method also suffers from uneven hydrogen distribution and equipment condition requirements. Higher problems still need further research to solve.