Why Inconel 600 is popular in high temperature and corrosion resistant valve?

Nickel-based alloy Inconel is widely used in the production of high temperature and corrosion-resistant valves. As specified in ASTM UNS N06600, the specified Inconel 600 is specified in ASTM A494 CY‐40. They are mainly used in stress corrosion resistant environments, especially for high concentration chloride media, when the Ni content is greater than 45%, it can be completely immune to chloride stress corrosion. In addition, it can resist the corrosion of boiling and concentrated nitric acid, fuming nitric acid, high-temperature gas containing sulfur and vanadium, combustion substances.

Inconel (ASTM B564 N06600) alloy is now widely used in boiler feedwater systems in nuclear power plants because it is safer than stainless steel. Inconel 600 or Inconel 625 high pressure (600 ~ 1500 LB) high concentration oxygen valves are commonly used in chemical fertilizer plants. The alloy valves of CY-40 and Inconel 600 take “In” as the material code, and the suitable operating temperature is -29~650℃.

The Inconel 600 has high strength and strong oxidation resistance at high temperatures. These alloys prevent stress corrosion cracking of metals caused by chloride ions in humid conditions. It is often used in large quantities in place of pure nickel to resist caustic corrosion and halogen corrosion at high temperatures, while not normally used in sulfuric acid units, but can be used at room temperature in low-concentration sulfuric acid media.

Inconel 600 has weak corrosion resistance to hydrochloric acid. It is resistant to all concentrations of pure phosphoric acid at room temperature, but the corrosion rate increases rapidly with increasing temperature. It also has good corrosion resistance to hot long chemical chain organic acids. Grease separation towers for stearic acid, oleic acid, and rosin acid are usually manufactured with Inconel 600 alloy.

The high Cr content of Inconel 600 alloy provides a good ability to prevent sulfur embrittlement. Therefore, it is often used in high-temperature alkaline media to replace Ni 201 containing S or where required high strength. Inconel 600, like all nickel alloys (except commercial pure Ni), is subject to stress corrosion when in contact with high temperature and high concentration alkaline media. Therefore, valves made of Inconel 600 should be completely stress-free before use to ensure minimal stress during operation.

Inconel 600 has good corrosion resistance to silver nitrate, also for optical processing and for hot, concentrated magnesium chloride. Inconel 600 was superior to Ni 200 in nitrite chlorides at temperatures greater than 43℃ (110 ℉). Inconel 600 can also be used in fasteners at 870 ° c (1 600℉) that require both high strength and oxidation resistance.

ASTM A494 specified CY-40 chemical composition and mechanical properties (table below) CY‐ 40 castings are usually supplied in as-cast condition and are not treated with the solution as the alloy is not sensitive to intercrystalline corrosion in the as-cast condition. It is suitable for industrial equipment which needs high strength, high pressure and closed state, has high corrosion resistance to chemical damage and harm, and has the ability to resist mechanical wear and oxidation under high temperature.

 

Chemical composition of CY-40, %

C

max

Mn

max

Si

max

P

max

S

max

CuMoFe

max

NiCr
0.401.503.000.030.03//11.0Remind14.0~ 17.0

 

The mechanical property of CY-40 

Tensile strength/MPayield strength/MPaElongation 50mm, %
48519530

 

Both of Inconel 600 and CY – 40 are high temperature and corrosion resistance of nickel-base alloy Ni ‐Cr‐ Fe alloy, their excellent properties of corrosion resistance to high temperature, high pressure make it widely used in the manufacture of nuclear industry or where need for high strength, high-pressure sealing, high corrosion resistance and high temperature resistant to mechanical wear and oxidation resistance of valve and equipment.

 

Classification of corrosion-resisting nickel-based alloys

Alloys with nickel above 50% are known as nickel-based corrosion-resistant alloys. Like Austenitic stainless steel, the microstructure of nickel-based alloys is single-phase austenitic without phase change in solid-state, and the grains of base metal and weld metal cannot be refined by heat treatment.

It has excellent corrosion resistance and high-temperature resistance performance that can withstand the erosion of various corrosive media even under the temperature range from 200 to 1090℃. It also has good strength, plasticity, processing and welding properties, has been widely used in the petrochemical, nuclear, aerospace and other industries.

According to the content of chemical elements such as Cr, Mo, Cu, Al, Ti and Nb, nickel-based corrosion-resistant alloys can be mainly divided into the following series: Ni-Cu, Ni-Cr, Ni-Mo, Ni-Cr-Mo.

Ni-Cu series

Alloys with Ni and Cu as the main elements are called Monel alloys, which are represented by 4000 series Numbers. Nickel-copper alloy is one of the most widely used nickel-based alloys. The addition of copper to nickel can improve the corrosion resistance in reducing medium while reducing the corrosion resistance of nickel in oxidizing medium and air. Monel alloy Ni70Cu30 is the earliest nickel-based corrosion-resistant alloy. It offers excellent strength and toughness as well as better resistance to the corrosion of reductive acid and strong alkali medium and seawater, etc. It is usually used in the manufacture of equipment for conveying hydrofluoric acid (HF), brine, neutral medium, alkali salt and reducing acid medium. Monel alloy has cast alloy and deformation alloy (rolled). The most commonly used Monel alloys are Monel 400 and Monel K500.

 

Ni-Cr-Fe series

This series includes Inconel and Incoloy alloy. The Ni-based alloy which contains more Cr than Fe is called Inconel alloy and is represented by 6000 series. While Incoloy alloy contains more Fe than Cr. The addition of Cr can significantly improve the corrosion resistance of Ni, especially the oxidation resistance of acid and salt, oxidation resistance and vulcanization. The Inconel 600 rolled product is ASTM UNS N06600 and the cast alloy CY‐ 40 alloy specified in ASTM A494.

 

Ni-Mo/ Ni-Mo-Cr series

Ni-Mo corrosion-resistant alloy was produced around 1930 and the earliest grades were Hastelloy A (20% Mo content) and Hastelloy B (30%Mo content). Nickel chromium-molybdenum alloy not only in some oxidizing medium, and excellent corrosion resistance in the reducing medium, especially in the F-, Cl- in the plasma of oxidizing acid, or in aerobic reducing acid or oxidant, oxidizing acid-reducing acid in mixed acid, wet chlorine and chlorine in aqueous solution, that all perform corrosion-resistant performance than other Nickel alloy materials.

A complete introduction of Hastelloy B,C,G alloy for chemical industrial

Ultra-low carbon Ni-Cr-Mo alloy is known as Hastelloy alloy. Hastelloy is a trademark of Haynes International company, consist of the letter “HA” in Haynes, “STELL” in STEILITE and “OY” in ALLOYS. As an advanced nickel-based alloy, Hastelloy offers excellent corrosion resistance to a variety of harsh corrosion environments such as wet oxygen, sulfurous acid, strong oxidizing salt medium, etc.

Hastelloy alloy has many series like Hastelloy A, B, C, D, F, G, N, W and X. The main companies producing Hastelloy alloy series are American Haynes International Inc (Hastelloy alloy research and development company), Special Metal (superalloy group) and ThyssenKrupp company of Germany. The alloys used in chemical plants are mainly Hastelloy B, C, and G, which mechanical properties are shown in the following table.

 

1)Hastelloy B

Series B includes Hastelloy B, Hastelloy 132, Hastelloy B3, etc. Hastelloy B alloy has the best corrosion resistance to hydrochloric acid,reducing its content of carbon to 0.02% and Si to 0.1%. that becomes Hastelloy b-2 alloy. Hastelloy B-2 can be used in hydrochloric acid medium of any concentration at boiling temperature and improves the resistance to intercrystalline corrosion in sensitization and post-welding.

In the 1990s, the invention of Hastelloy b-3 completely changed the defect of b-2 which was that it was easy to precipitate ni-mo precipitate at an intermediate temperature and improved the processing performance. However, Hastelloy B and Hastelloy B-2 alloys contain very low Cr and cannot be used in oxidizing environments. The corrosion resistance of this kind of Harley alloy under typical environment is shown in the table below.

MediumAverage corrosion resistance rate of Hastelloy B alloys (mm/a)
B-3B-2316LMonel400
50% Acetic acid0.0050.010.005/
40% Formic acid0.0130.0181.0410.053
55% Phosphoric acid0.0760.1520.4570.114
 50% Sulfuric acid0.0430.030>5004.699

 

2)Hastelloy C

Ni-Cr-Mo alloy Hastelloy C is a universal corrosion-resistant material suitable for all kinds of environments. The content of the C-series alloy is high. Element Cr and Mo play the role of oxidation-resistant medium and reducing medium corrosion respectively to resist local corrosion (pitting corrosion and crevice corrosion).

Hastelloy C alloy group consists of C, C-276, C-4, C-22 and C-2000. The first alloy Hastelloy C was produced in the 1930s, then C-4 in the 1970s, C-22 In the 1980s; alloy 59, 686, C-2000 and so on In the 1990s. Intercrystal corrosion, local corrosion, stress corrosion and passivation of Ni-Cr-Mo alloys were studied by electrochemical methods. S Ghosh study showed that C-276 alloy had better corrosion resistance than UNS N08367 and UNS N08028 in NaCl and H3PO4 solutions at 95℃. The corrosion resistance of class C alloys under typical conditions is shown in the table.

MediumCorrosion resistance rate of Hastelloy C alloys in different boiling medium(mm/a)
C-276C-22686C-2000C-59
ASTM 28A6.100.912.620.690.61
ASTM 28B1.400.180.250.100.10
10%HNO30.480.05//0.05
15%HNO319.051.325.87/1.02
50%H2SO46.107.82//4.47
5%HCL0.280.360.130.0380.08
10H2SO4+1%HCL2.228.99//1.78

 

(3)Hastelloy G

Ni-Cr-Cu-Mo alloy Hastelloy G, which is more resistant to sulfuric acid and phosphoric acid than Hastelloy C alloy. The alloy with high cr content has good corrosion resistance in sulfuric acid, phosphoric acid, sulfuric acid, phosphoric acid and wet-process phosphoric acid-containing F- and Cl-. Elements adding such as Si and B are able to withstand corrosion by concentrated sulfuric acid in HAS G alloy, which is characterized by high hardness and good abrasion resistance.

G series includes G, G-3, G-30, G-50 and etc. The birth of Hastelloy G-3, G-30 alloy solved the application of alloy in strong oxidation or mixed acid environment. The new Hastelloy G-35 is essentially a Ni-Cr-Mo alloy with a composition close to that of a C-series alloy. Because it is designed for strong oxidation and mixed acid environments and it is still included in the G series.

What’s the Power Metallurgy High Speed Steel?

Powder high-speed steel is a kind of metallurgical steel, which is made from molten steel by high-pressure atomization, through screening, compaction, vacuum sealing and hot-static pressing, and then forged and rolled.

Powder metallurgical steel is compacted by uniform and fine carbide particles. It overcomes a series of shortcomings caused by carbide segregation and forms a new component of high-speed steel which cannot be produced by smelting method. Compared with ordinary high-speed steel made by metallurgical process, the mechanical properties of powder metallurgical high-speed steel are greatly improved. The toughness of powder metallurgy M2 high speed steel is 20% higher than that of normal M2 high-speed steel. Powder high-speed steel has stronger hardness and more uniform structure after heat treatment. Only tools made by this process will not cause tooltip collapse because of the accumulation of carbides or the presence of large carbides.

 

Effect on the Technological Properties of Materials

  • Improving the grindability of materials

The grindability of most powder high speed steels is doubled than that of ordinary high speed steels. It is not easy to grind ordinary high speed steel when its V content is more than 3%, and it is almost impossible to grind if its V content is more than 5%. However, the V content of powder high speed steel T1 5 is 5%, which still has good grindability. Some powder high speed steels containing 9% V can still be grinded. Powder high-speed steel also overcomes the shortcomings of common high-speed steel such as forging difficulty, easy overheating, cracking and distortion in heat treatment.

  • New grade high-speed steel with higher alloying element content can be produced.

The chemical composition of powder high speed steel has made a great breakthrough because of no longer worrying about carbide segregation, grinding and forging. Firstly, the V content of steel is increased. Almost all the powder high speed steels contain more than 3% V, and some contain 9.8% V. At the same time, the carbon content of rigid steel is increased. Almost all the powder high speed steels are high carbon high speed steels with a carbon content of more than 1.2% and some of them as high as 2%.

  • Higher prices

Powder high-speed steel is more expensive than ordinary high-speed steel. Only gear cutters and special material cutters with special requirements can be used.

Brand and Composition of Powder High Speed Steel

At present, the main producers of powder high-speed steel are Sweden, the United States, Japan, Austria and other countries. Their brands and chemical compositions are shown in the table below.

CountryMaterialsChemical composition %
CWMoCrVCo
SwedenASP231.286.45.04.23.1/
ASP301.286.45.04.23.18.5
ASP532.454.23.14.28.0/
ASP602.306.57.04.26.510.5
AmericanCPM Rex T151.512.0/4.05.05.0
CPM Rex 761.510.05.33.83.19.0
CPM Rex2.4/1.35.39.8/
10V1.36.310.54.02.0/
CPM Rex 201.812.56.54.05.0/
JapanHAP 501.51.56.04.04.08.0
HAP 632.152.152.54.27.08.0
HAP 721.910.07.54.25.09.5
KNA33H0.975.95.84.03.4/
AustriaS390PM1.5510.74.94.95.28.2

 

Heat Treatment of Powder High Speed Steel

High-speed steels in different countries have their corresponding heat treatment specifications according to their grades and chemical composition. The following are some examples of heat treatment process parameters.

  • Annealing

The annealing specification recommended by Sweden for powder high-speed steels with four grades and chemical compositions is as follows: after heat preservation at 850 ~900, the cooling rate is less than 10 /h, and then slowly cooled to 700.

  • Quenching

According to the basic principle of heat treatment, the heat treatment of powder high-speed steel should be the same as that of ordinary high-speed steel. The difference is that the carbide particles of powder high-speed steel are uniform and fine, and easy to dissolve into the matrix. Therefore, powder high-speed steel with the same chemical composition can choose a lower quenching temperature than that of ordinary high-speed steel, which can generally reduce the temperature by 5 ~8. Similarly, because the austenite of powder high-speed steel is easier to homogenize, a shorter holding time can be used, which can generally be shortened by 1/3 than that of ordinary high-speed steel.

Different countries have different grades and heat treatment specifications of powder high-speed steel. The quenching temperatures of four grades of powder high speed steels in Sweden are set at 1160 ~1180 C. The quenching temperature of American powder high speed steel CPM Rex42 is 1230 C and CPM Rex 20 is 1190 C.

  • Tempering

Because the carbides of powder high speed steel are uniform and fine, austenitizing is sufficient, tempering secondary hardening is more sufficient, and tempering effect of the same specification is better. The tempering temperature and holding time of powder high speed steel are approximately the same as those of ordinary type. Twice or thrice tempering is usually used. However, tempering temperature of some brands of powder high speed steel has been adjusted. For example, the tempering temperature of Austrian S390PM powder high speed steel is 500 C.

 

A brief introduction of mold steel

Last article, we have introduced the “Tool Steel Grades Definition System”. As we all know, tool steels can be classified to many different types according to different standards. According to their detail application, tool steels can be divided into cutting tool steels, mold steels and gauge steels. Here we introduce the classification of mold steel.

  • Cold working mold steel

Cold working mold steel is mainly used to manufacture the mold for pressing the workpiece under cold condition, such as cold stamping mold, cold stamping mold, cold drawing mold, stamping mold, cold extrusion mold, thread pressing mold and powder pressing mold. Cold working mold steels range from carbon tool steels, alloy tool steels, high speed tool steels to powder and powder high alloy tool steels.

  • Hot working mold steel

Hot working mold steel is mainly used to manufacture the dies for pressing the workpiece under high temperature as hot forging die, hot extrusion molded, die-casting mold, hot heading mold and so on. The commonly used hot working mold steels are: medium-high carbon content with Cr, W, Mo, V and other alloying elements added alloy mold steels; High alloy Austenitic heat resisting mold steel or heat working die steel for special requirements.

  • Plastic mold steel

Different kinds of plastics have different requirements on the properties of plastic mould materials. Many developed countries have specified the use range of plastic mold steel series, including carbon structural steel, carburized type plastic mold steel, hard plastic mold steel, age hardening plastic mold steel, corrosion resistant plastic mold steel, free cutting hardened plastic mold steel, the whole model of plastic mold steel, the maraging steel and mirror polishing with plastic mold steel, etc.

 

Steel requirements for different molds:

Generally, the mold is divided into five grades according to the service life. The first class is above one million times, the second class is between 500,000 and one million times, the third class is between 300,000 and 500,000 times, the fourth class is between 100,000 and 300,000 times, and the fifth class is below 100,000 times.

The steel material for first and second class mold that can be heat treatment and hardness can be up to HRC50 or so, otherwise the mold are easy to wear and injection molding product qualification rate is poor, so the choice of steel not only have better heat treatment performance but also have good cutting performance in the state of high hardness, that depends other problem should to be taken the consideration. Usually choosing Sweden 8407, S136, the United States 420, H13, Europe 2316, 2344, 083, or Japan SKD61, DC53 (the original metal mold materials, special circumstances use).

But for that strong corrosive plastics generally selected S136, 2316 420 steel, in addition to S136, 2316 420, SKD61, NAK80, PAK90, 718M for that with weak corrosion. The appearance requirements of the product will influence the choice of mold materials. For the transparent parts and the products with the surface requirements of the mirror surface, the available materials including S136, 2316,718s, NAK80, PAK90, 420. For the molds with extremely high transparency, S136 should be selected, followed by 420. There are many pre-hard materials for the third class mold, material like S136H, 2316H, 718H, 083H with the HB hardness between 270 to 340. P20, 718,738,618,2311,2711 are used for the fourth-class and fifth-class molds, and S50C, 45# steel may be used for the molds with extremely low requirements, that is the mold cavity is made directly on the mold blank.

 

Attachment: various countries steel codes:

  1. AISI Code:

P1-P19:LowCarbon Steel

P20-P39:Low Carbon, High Alloy Steel(Plastic mould steel)

2XX,3XX,4XX,6XX:Stainless Steel

H1-H19:Chromium base (Hot working steel)

Wx:Water Hardening Steel

Sx:Shock Resisting Steel

Ox:Oi lHardening Steel

Ax:Air Hardening Steel

Dx:High Carbon, High Chromium Steel

Mx:Molybdenum base (H.S.S)

 

  1. DIN Code:

1.2738:Low carbon, high alloy (P20 – Plastic mould steel)

1.2311:Lowcarbon, high alloy (P20 – Plastic mould steel)

1.2312:Lowcarbon, high alloy, free Machine (P20-free cutting)

1.2083:StainlessSteel (420 – Acid resistant steel)

1.2316:High performance stainless Steel (420 – High acid resistant steel)

1.2343:Chromiumbase (H11–hot working steel)

1.2344:Chromiumbase (H13–hot working steel)

1.2510:Low alloy steel (O1- Oil steel )

1.2379:High carbon, high chromium steel

 

  1. JIS Code:

SxxC:Plain Carbon steel

SUSxx:Stainless Steel ( Acid resistant steel- 420)

SCrx:Chromium Steel

SCMx:Chromium Molybdenum Steel(P20)

SKx:Carbon Tool Steel

SKSx:Low Alloy Steel (Oil steel – O1)

SKD11:Medium-High Alloy Steel(D2)

SKD6:Medium-High Alloy Steel(H11)

SKD61:Medium High Alloy Steel(H13)

SKHxx:High Speed Steel (M 2)

SUMx:Free Cutting Steel

SUJx:Bearing Steel

 

Application of Nickel-based alloy surfacing welding in waste incineration power plant

Waste incineration power generation is an effective way to deal with household waste. Due to the complexity and heterogeneity of waste composition, various highly corrosive gases such as chloride and sulfide will be produced in the incineration process. Waste furnace flue gas mainly includes HCl and SO2, and the content of HCl is significantly higher than that of SO2, so chlorine corrosion is the most important corrosion in waste incineration power plant.

Chlorine tends to occur in incinerators as gaseous HCl, Cl2, and metallic chlorides such as KCl, NaCl, ZnCl2, and PbCl2. In addition to the direct gas phase corrosion, these metal chloride low melting salt deposition and the surface of metal oxide film Redox will reaction each other, which lead to corrosion of metal matrix. They also jointly with other inorganic salts in the flue gas deposits formed on the wall in the high-temperature molten salt corrosion, in the dust – local liquid metal interface, forming the electrochemical corrosion environment. The further diffusion of corrosion forms a layer of loose outer oxide film on the external surface of the molten chloride. Due to the high diffusion rate of metal ions in the molten salt, this electrochemical process seriously erodes the metal components in the water wall and superheater of the boiler, leading to early degradation and even failure of its performance.

 

The corrosion of the sulfur element on the heating surface tube of waste furnace cannot be ignored. The corrosion of sulfur mainly comes from the thermal corrosion of alkali metal salts, namely Na3Fe(SO4)3 and K3 Fe(SO4)3. At the same time, a large amount of ash powder produced by garbage combustion scours the surface of a heating surface tube, resulting in different degrees of wear. Under the combined action of multiple factors, the heating surface pipe is continuously oxidized, corroded and worn from the outside to the inside, and local burst occurs when it cannot bear the pressure of water vapor in the pipe.

 

As an economical and rapid material surface modification method, surfacing welding is to bead welding the corrosion resistant material like austenitic stainless steel, nickel-based alloy on the inner surface of equipment, which is widely used in the manufacturing and repair of various industrial equipment parts such as valves, pipes, fittings, flanges, plates, etc. For example, surfacing welding of alloy 625 in the waste incineration power generation system forms a corrosion resistant layer and protect the inner surface of the equipment from corrosion, extending the service life of the equipment. Low dilution parent material and high deposition rate are usually used to maximize the performance of the overlying layer.

In theory, all corrosion-resistant alloys can be surfacing welding like Inconel 625, Incoloy 825, C276, Monel 400, etc. Chromium-nickel austenitic stainless steel surfacing in various hydrogenation reactors can effectively prevent hydrogen corrosion on the steel surface. The inner wall of the urea synthesis tower is welded with ultra-low carbon molybdenum-containing austenitic stainless steel. In order to reduce the overall project cost, we can implement a 2-3 mm thickness surfacing welding with alloy C276, C22 or 625 alloy layer on the metal material surface of all kinds of large equipment and accessories.

The corrosion of waste heat boiler heating surface tube can be solved by surfacing a layer of high temperature resistant nickel-based alloy material on the outer wall of boiler tube. The traditional surfacing welding method has serious damage to the base material of the boiler tube, and the dilution rate of 10% ~ 20% is difficult to meet the requirements. CMT (Cold Metal Transfer) welding system is adapted to surfacing a layer of Inconel 625 material with high-temperature resistance and corrosion resistance on the heating surface of the boiler, which can effectively solve the corrosion problem of the heating surface pipe and extend the service life of the boiler. In the case of high-load operation, the service life of steel pipe can reach more than 5 years, and solve the problem of heating surface corrosion and pipe wall ash, greatly improve the thermal conversion efficiency and power generation.

The welding of duplex stainless steel S32750

Compared with Austenitic stainless steel, super duplex stainless steel has more Cr and Mo contents, which is beneficial to form ferrite and improve the corrosion resistance of the steel. The addition of Ni, N, Cu and Cu can improve the corrosion resistance of steel to non-oxidizing medium. Super duplex stainless steel has good weldability without welding hot and cold cracks. Under the influence of welding heat cycle, Ferrite increases and the grain size enlarge, while too slow cooling will also lead to the precipitation of harmful phase, which may destroy the balance between Austenite and Ferrite, affect the mechanical properties and corrosion resistance of welded joints. Here this article will introduce the welding process of S32750 stainless steel.

 

Welding methods

Tungsten argon arc welding is characterized by energy concentration, a small amount of heat input, easy to control the welding quality. Reasonable control of the welding heat input, multi-layer welding, multi-channel and low deposition rate, the tungsten electrode argon arc welding and auxiliary to 99.99% pure argon gas protection weld molten pool implementation super duplex stainless steel welding, can get better welding quality and good mechanical properties and corrosion resistance.

 

Welding materials

According to the chemical composition and mechanical properties of the base material, ER2594 wire is an ideal choice. The weld metal is allowed to be called “super duplex stainless steel” when the PRENE(pitting resistance equivalent value) is greater than 40.

 

Welding parameter

Sample operation is specified in ASME B31.1andASME Ⅸ。

Firstly, take the base material sample S32750 pipe with the specification f114.3mm 6.02mm and open the V-shaped groove. The groove and weld bead is shown in the figure.

The welding material model is ER2594 with the specification f2.0mm. Note that too much current is easy to burn through, too little current is easy to cause incomplete fusion or incomplete welding. In the process of operation, the weld groove Angle can be appropriately increased to control the fusion ratio and adjust the metal composition of the weld.

Secondly, it is strictly prohibited to start the arc and test current on the surface of the base metal outside the groove to prevent arc damage to the base metal. The quality of the starting and ending arc should be guaranteed during welding. The same welding material and welding process as the root pass shall be used for welding positioning weld. The number of locating solder joints shall be 2, 3 or 4 points and shall be fixed on average. The thickness shall not exceed 2/3 of the pipe wall to ensure that the welding seam will not crack and remove defects during the formal welding process.

Welding shall be done in strict accordance with the relevant parameters selected. In order to make the welding can cover the actual construction of large-diameter, thick-wall pipe should be used as wide as possible range of parameters. Controlling interpass temperature less than 120 ℃, the welding heat input 1500 j/mm or less, on the premise of guarantee the quality of welding, as far as possible use small current, fast welding, small heat input and welding layer, bead for welding.

 

It is worth noting that the groove and the surface 50mm away from the groove shall be cleared before welding, and there shall be no water vapor, phosphating substances, carbon-containing materials (such as oil, paint, scale, rust, burr and halogen, etc.) and cracks, interlayer and other defects. Proper measures such as isolation and stacking should be taken to prevent the contamination of the super duplex stainless steel by iron elements. Super duplex stainless steel has good weldability and is not easy to produce hot cracks, been widely used in seawater and wastewater treatment equipment, papermaking, petrochemical equipment and other environments where require strict corrosion resistance.

What’s the effect of Co for carbide alloys?

Cobalt (Co) is a magnetic and scarce metal element. Cobalt resources are widely but imbalanced in the world. The reserves of Congo (DRC), Australia and Cuba account for 70% of the total global reserves, of which Congo accounts for 47.89%. Cobalt resources are mostly associated with copper-cobalt ore, nickel-cobalt ore, arsenic-cobalt ore and pyrite deposits.

As one of the important strategic resources, Co plays an important role in many applications. Cobalt alloys or mixtures of metals, make up half the cobalt used each year. Currently, the largest consumption and application of cobalt are mainly lithium battery, of which the positive electrode material is lithium cobalt oxide. In addition, Cobalt is also used in the traditional areas of super heat-resistant alloys, tool steels, and type of magnetic materials. The cobalt compounds are mainly used as catalysts, desiccants, reagents, pigments and dyes, which is essential for industrial processing.

In cobalt-based alloys, the addition of Co increases strength and hardness especially the red hardness, permits higher quenching temperatures. It also intensifies the individual effects of other major elements in more complex steels. The consumption and application of carbide alloys are the Tungsten carbides. It is mainly used for cutting tools, molds, cobalt heads, nozzles, perforating tools and corrosion-resistant and wear-resisting parts, such as sealing rings, cylinder linings, ball-point pens, etc.

Cutter steel with a certain amount of cobalt has good wear resistance and cutting performance. Cobalt combines other metal carbide grains in the alloy composition to make the alloy more ductile and less sensitive to impact. This alloy is welded to the surface of the parts, which can increase the service life of the parts by 3-7 times. Sterlite carbide containing more than 50% cobalt will not lose its original hardness even if heated to 1000 ℃.

The cobalt-based alloy still shows good performanceunder high temperature above 1038 ℃, especially used for the production of high temperature engines and steam turbines, so it is widely used in aerospace and modern military field. The use of cobalt-based alloys containing 20-27% chromium in the structural materials of aero-turbine engines can achieve high oxidation resistance without any protective coating. A thermal-medium turbine engine in a nuclear reactor heating studio can operate continuously for more than one year without maintenance.

What’ s metal cladding plate?

Metal cladding plate is composed of base steel (plain carbon steel) and composite layer (corrosion resistant metal) through the explosion and rolling process. The base material can be ASTM A 516 Gr70, ASTM A36, ASTM A283, ASTM A387 and other ordinary carbon steel and special steel. The cladding material can be ordinary stainless steel such as 304, 304L, 316L, S31603; Commercial pure titanium Gr1, Gr2, titanium alloy Gr.5, etc. Duplex stainless steel like 2205, 2507,904L; Nickel alloys such as Hastelloy C-276, C-22, Monel 400, Inconel600, Inconel 825, etc and other metal like Copper and Aluminum, etc. Metal cladding plate offers good process performance and can be hot pressing, cold bending, cutting, welding.

 

In theory, all kinds of malleable, corrosion-resistant and high-strength specialty metals can be used to make cladding materials. Cladding plates reduce the use of precious metals, their material and thickness can be produced by demands, combined the advantages of low cost and high performance. It has been widely used in petrochemical, coal chemical, fluorine chemical, fine chemical, acetic anhydride, PTA, chlor-alkali, salt, metallurgy, medicine, electric power and other fields. There are two main methods for industrial production of metal cladding plates: explosive cladding and hot rolling cladding.

 

Explosive cladding

Also known as explosive welding. superimposed the cladding layer on the base layer to make them keep a certain distance. The explosive instantly produces huge energy, which causes these two metals to collide at high speed to form plastic deformation, melting and welding together. Ideally, the shear strength per square millimeter can be up to 400 Mpa, which can meet almost any processing requirements.

The features of explosive cladding:

1. Cold processing, can produce a variety of metal cladding plate, such as titanium, copper, nickel, aluminum and a variety of non-ferrous metals.

2. Explosive cladding can produce metal with thickness up to hundreds millimeter for used in some large water conservancy project base and ultra-thick tube plate. It’t suitable for the production of composite steel plates with a total thickness less than 8 mm.

3. Less investment and can be small-scale production or mass production, also achieved a small number of pipe &plate or special-shape workpiece combination. The cladding layer can be spliced and polished before the explosion.

4. Due to the characteristics of explosives limited by weather and other technological conditions, explosive compound production efficiency is low. In addition, explosives can cause vibration, noise and smoke pollution, usually produces in the remote outdoor factory.

 

Hot rolling cladding

The hot rolling cladding is the process that the cladding material and the base material are overlapped and assembled into the slab to be rolled. In order to improve the bonding strength, a series of technical measures such as vacuum hot rolling or shielded gas rolling should be taken. The features of hot rolling cladding:

1. Using large plate mill and hot continuous rolling mill, so it offers high production efficiency and fast production speed.

2. More choice of product thickness, the stainless steel coating thickness of more than 0.5mm can be produced. Limited by the compression ratio of steel rolling, hot rolling production cannot produce a thickness of more than 50mm cladding steel plate, it is not convenient to produce round and other special shape clad plates.

3. Cladding plates of 6, 8 and 10 mm is ideal for this process. Under the condition of hot continuous rolling, the scale production can be realized and the length can be determined according to the needs to meet the needs of users.

4. Limited by technical conditions, the hot rolling process to directly produce titanium, copper, aluminum and other non-ferrous metal composite need to be improved.

 

Both explosive and rolling cladding are in accordance with GB/T-8165-2008 standard, by which main technical indicators are the same or higher than the Japanese standard JIS G3601-1990. They specified in different standards for pressure vessels. From the terms of cost accounting, the rolling cladding is calculated by ton while explosive cladding is calculated by explosive area. Some engineers concluded that from the actual production: with the limit of 20mm, the thick steel plate should be explosive composite while the thin steel plate should be rolled composite.

 

How to make titanium alloy easy to machine?

As everyone knows, Titanium and its alloys are difficult to machine and process due to their high strength, low thermal conductivity and chemical reactivity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life. In addition, a relatively low Young’s modulus leads to spring-back and chatter leading to poor surface quality of the finished product. During turning and drilling, long continuous chips are produced; causing their entanglement with the cutting tool and making automated machining near impossible. In the last article, we explained what-makes-alloyed-titanium-grade5-so-difficult-to-machine in details.  Today I will discuss what should I do to makes Titanium easy to machine and supplied several tips about the  processing of most commonly used alloy Titanium grade 5 alloy ( 6Al-4V) :

 

  • Using carbide cutting tools. Tungsten-cobalt cemented carbides are characterized by high strength and good thermal conductivity and are not easy to react with titanium at high temperature. They are suitable for processing titanium alloys.
  • Select reasonable geometry parameters of tools. In order to reduce the cutting temperature and tool bonding, the front Angle of the tool can be appropriately reduced and the contact area between the chip and the front cutter surface can be increased to dissipate heat. At the same time, the rear angle of the cutter is increased to reduce the phenomenon of tool bonding and the precision of the machined surface is reduced due to the rebound of the machined surface and the friction contact between the machined surface and the machined surface. The tip should use arc transition to enhance tool strength. It is necessary to maintain the sharpness of the sharpener frequently to ensure that as little cutting heat as possible is generated during the processing.
  • Appropriate cutting parameters. Lower cutting speed – high cutting speed will lead to a sharp increase in cutting temperature; Moderate feed — large feed leads to high cutting temperature, while small feed leads to accelerated wear of the blade due to long cutting time in the hardened layer; Greater cutting depth — cutting beyond the hardened layer on the titanium alloy surface of the tip improves tool life.
  • Maintain a high cutting fluid flow and pressure. Sufficient continuous cooling of the machining area is required to reduce the cutting temperature.
  • Avoid machine tool vibration. Vibration can cause blade breakage and blade damage. Choose a larger cutting depth, but the titanium alloy machining rebound, the larger clamping force will aggravate the workpiece deformation, finishing can consider the use of jigs and other auxiliary tools to meet the stiffness requirements of the processing system.
  • The climbing milling methods by which milling is carried out. In titanium alloy processing, the milling cutter caused by reverse milling is much more damaged than the milling cutter caused by climbing milling.
  • Grinding with a green silicon carbide grinding wheel. The sticky chips will cause the blockage of grinding wheel and the surface burns of parts. Therefore, it is appropriate to use the green silicon carbide grinding wheel with sharp grinding particles, high hardness and good thermal conductivity. The grinding wheel size can be F36 ~ F80 that depending on the surface finish. The hardness of the grinding wheel should be soft so as to reduce the adhesion between grinding particles and grinding chips and the grinding heat. At the same time to ensure a small grinding and low speed, sufficient emulsion.
  • Drilling. Standard drill bits need to be polished during drilling to reduce burners and broken bits. Grinding method: increase the top Angle and decrease the front angle of cutting part, increase the back Angle of cutting part, double the number of taper of cylindrical edge. During processing, the cutting times should be increased and the drill bit should not stay in the hole, sufficient emulsion cooling, timely removal of chips and observe whether the drill bit becomes blunt.
  • Titanium alloy reaming needs to be calibrated. The width of the blade belt should be less than 0.15mm. Multiple reamer sets can be used for multiple reamers. The diameter of each reamer increase shall be less than 0.1mm. Reaming with this method can meet the requirement of a high finish. Handle cleaned titanium alloy parts should wear clean gloves, to avoid sodium chloride stress corrosion.
  • Tapping is the most difficult process in titanium alloy processing. Excessive torque causes rapid wear of the tap cutter teeth, and the rebound of the processed part can even break the tap in the hole. Ordinary tap processing should be according to the diameter size appropriate to reduce the number of the chip to increase the space, set aside on the calibration of tooth belt should be after 0.15 mm width of blade Angle increases to about 30 °, remove tooth back 1/2 ~ 1/3, calibration tooth number 3 after increases taper pouring. If you want to achieve better processing results, jumping wire is a good choice, which can effectively reduce the cutting tool and the workpiece contact area.

 

It is worth noting that: It is important to use non-combustible or non-combustible tools to transfer titanium chips and ensure that the cutting area has fire protection facilities. Trace cutting of titanium chips once a fire can be dry powder extinguishing agent or dry soil, dry sand extinguishing.