The heat treatment of H13 hot steel

H13 is the most commonly used hot work steel, it has higher thermal strength and hardness, wear resistance and toughness, better heat resistance fatigue performance, has been widely used in the manufacture of various forging die, hot extrusion die and aluminum, copper and its alloy casting mold. Hot-working tool steel undertakes a lot of impact load, friction, intense cold and heat cycle caused by thermal stress and high-temperature oxidation, often produce a series of failure forms such as crack, collapse, wear and so on.

H13 steel is a type of hypereutectoid alloy steel, and its metallographic structure has many defects such as non-metallic inclusions, carbide segregation, loose center and white spots, which can reduce the strength, toughness and thermal fatigue resistance of die steel. Heat treatment technology has a great influence on the structure and performance of the H13 steel mold.

Forging process
H13 steel contains quite high alloy elements, offering poor thermal conductivity and low eutectic temperature, easy to cause overburning. For the blank with Ø 70 mm H13 steel block in diameter, it should be preheated within the range of 800 ~ 900 ℃, at first, then in the forging heating temperature 1065 ~ 1175 ℃, repeatedly pulling long upsetting forging, be noted that the forging ratio should be greater than 4.

Spheroidization annealing process
The purpose of spheroidization annealing is to uniform structure, reduce hardness, improve cutting performance and prepare the structure for quenching and tempering. The annealing process is insulated at 845 ~ 900℃ (1h+1min) /mm, then cooled to 720 ~ 740℃ isothermal (2h+1min) /mm, and finally cooled to 500℃ and out of the furnace, spheroidization annealing structure is pellet pearlite and hardness less than 229HBS.

Quenching and tempering process
The best heat treatment process of H13 steel is that the oil cold quenched or fractional quenched after heating at 1020 ~ 1080℃, and then it is tempered at 560 ~ 600℃ twice. The microstructure is tempered torstenite + tempered sostenite + residual carbide, and the microhardness is 48 ~ 52HRC. For high thermal hardness requirements of the mold (die casting die) can be taken upper limit heating temperature quenching. The lower limit heating temperature can be used to quench the mold (hot forging mold).

 

In addition, the manufacture of H13 steel mold has to go through a series of processes such as forging, annealing and machining. Improper operation in each process will cause premature failure of the mold and reduce its service life. Therefore, attention must be paid to the influence of preheating, cooling and lubrication of the mold, forging, cutting, grinding and EDM on H13.

The welding of stainless steel-carbon steel clad plate

The clad plate is produced by bonding two or more metals together into a single steel sheet or plate. Stainless steel-Carbon steel clad plates combined the stainless steel and carbon steel material through the explosion and rolling process, which make the metal plate more corrosion resistant, abrasive resistance and high temperature and pressure resistance. But the welder will face the new problem that is the welding, everyone knows that the two different material welding will be more complex and difficult.

Generally speaking, The welding sequence of the stainless steel cladding steel plate is generally as follows: first weld the inside of the base layer, then weld the outside of the base layer after root removal on the back and finally weld the transition layer and cladding layer (groove diagram). However, for the welding of the longitudinal girth weld of the small-diameter cylinder (diameter below 500), the outer groove shall be selected. Therefore today let’s learn the welding process of a pressure vessel made by small diameter stainless steel cladding plate.

Hydrogen sulfide tower bottom reboiler (or U-tube heat exchanger). The medium containing ammonia, the container is made of Q245R + S31603 stainless steel clad steel plate, the design pressure of 1.18 MPa, the design temperature of 189 ℃, Φ 600 mm in diameter.

Groove design

Due to the small diameter of the shell body, it can only be welded from the outside, so the outer groove – single side welding type is adopted. This groove adopts GTAW+SMAW welding on the outside of the barrel, and the welding sequence is as follows: cladding welding, transition welding and base welding. Different from the previous welding sequence, this welding sequence brings about the selection of welding materials.

 

Welding material

Considering the dilution effect of the base material, the welding material with higher chrome-nickel content should be selected. The welding material of the base layer is generally stainless steel, the covering layer is generally ER316L (H03Cr19Ni12Mo2Si) welding wire, and then the welding electrode A042 (e309mol-16) is used to weld the transition layer and the base layer.

 

Welding test

ProcessLayer NoMaterialSize(mm)ElectrodeElectricity(A)Arc voltage(V)Speed(cm/min)Heat input(kJ/cm)
CTAW1ER316L2.0DCEN100-40011-1414-16≤8.4
SMAW2A0423.2DCEP90-11021-2314-16≤10.8
SMAW3-4A0424.0DCEP140-16023-2616-18≤15.6

After passing NDT, the samples were tested for mechanical properties and intergranular corrosion. It can be seen from the test results that the tensile strength, bending performance, impact performance and intergranular corrosion of the welded joint meet the standard requirements, which proves the welding process and welding material w.

 

The experiment shows that the stainless steel clad plate can be welded in this order: cladding weld – welding transition weld – base weld. After welding the overlaying seam, the welding material of the base should be stainless steel. Adopting the process of  GTAW+SMAW to weld the stainless steel cladding plate of small diameter barrel on the outside side with the correct welding material, which can completely meet the standard requirements.

3 tips for Ni-based high temp alloy cutting

In the last article we discussed what’s the high temp alloy, we know nickel-based alloy is the most commonly used high temperature alloy used in aerospace, aviation and other fields at about or above 1000℃. Because it contains many high-melting-point alloy elements such as Fe, Ti, Cr, Ni, V, W, Mo, etc., which forms austenitic alloy with high purity and dense structure, and some elements from metal and non-metallic compounds with high hardness, small specific gravity and high melting point with non-metallic elements such as C, B, N, making its poor machinability. Its relative machinability is only 5 ~ 20% of that of plain carbon steel. The superalloys are characterized by difficulty cutting, do you know why they are difficult to cut? There are some features you should know before answer the question.

  • High content of fortified elements

In the process of cutting, a large number of abrasive metal carbide, intermetallic compound and other hardpoints are formed, which has a strong scratch on the knife, and is easy to produce deposition and clipping, affecting the quality of the processed surface.

  • High temp strength and work hardening tendency

The cutting process produces great plastic deformation resistance and cutting load, and the cutting temperature is high. The unit cutting force of nickel-based superalloy is 50% higher than that of medium carbon steel. The working hardening and residual stress of the surface layer after processing are large, and the hardening degree can reach 200% ~ 500%, leading to serious edge and edge wear, groove wear is also easy to occur.

Now that we know that Nickel-based high temp alloys are difficult to cut, here we will discuss 3 tips should pay attention to in cutting.

  • Metal Cutting Tools

Superalloys must have special tool materials for cutting. The most commonly used are carbide cutters, or high speed steel for machining complex surfaces with very low cutting speed. Hot-working grades with better performance are most commonly used in practice. In addition, Si3N4 ceramics tools are the best option for high temp alloy due to its higher resistance to adhesion, heat resistance and hardness than cemented carbides and are also suitable for semi-finishing and finishing of superalloy.

  • Tool Feeds and Speeds

The cutting of superalloy materials also requires the geometric parameters of cutting tools, such as forging, hot rolling and cold drawing. The rake angle of the tool (γ0) is about 10 degrees while the casting superalloy is about 0 degrees. The cutter’s back angle (a) = 10 ~15. The cutter inclination angle (λs) is – 5 10 in rough machining and lambda s = O 3 in finish machining. The main deviation angle (κr) is 45 ~75. The arc radius (r) of the tool tip is 0.5-2 mm, which is large in rough machining.

  •  Cutting Parameters and Conditions

The choice of cutting amount is basically the same as stainless steel, the most important is the cutting speed. For carbide tools, cutting speed (Vc) =20 ~ 50m/min; Feed quantity (f) should be small, generally f=0.1 ~ 0.5mm/r, the large value should be taken for coarse turning, the small value should be taken for fine turning. Backdraft (ap) should not be too small. For coarse turning, ap=2 ~ 4mm, and for fine turning, ap=0.2 ~ 0.5mm.Vc=5 ~ 10m/min for high temperature alloy machining with HSS endmill; Fn =0.05 ~ 0.12mm/r, ap+1 ~ 3mm.The carbide face milling cutter is Vc=20 ~ 45m/min. Fn =0.05 ~ 0.1mm/r, ap=1 ~ 4mm.

What are high temp alloys?

High temp alloy is the alloy based on the element of Fe, Ni and Co, a kind of metal material that can work for a long time under the action of high temperature above 600℃ and certain stress; It has good high-temperature strength, oxidation resistance, corrosion resistance, fatigue performance, fracture toughness and other comprehensive properties. High-temperature alloy is single Austenite structure and has good stability and reliability at various temperatures. Based on the above performance characteristics and the high content alloy, also known as “superalloy”, widely used in aviation, aerospace, petroleum, chemical, an important material for ships.

Classification of high temp alloys

Superalloy materials can be classified according to the following three ways: matrix element type, alloy strengthening type, material forming mode.

According to the matrix element, it is divided into Fe-based, Ni-based, Co-based superalloys. The service temperature of Fe-base superalloy can only reach 750~780℃ generally. For the heat-resistant parts used at a higher temperature, nickel-based and refractory metal-based alloys are adopted. Ni-based high temp alloy occupies a special important position in the whole superalloy field. It is widely used in the manufacture of aviation jet engines and the hottest end parts of various industrial gas turbines.

 

By matrix element type

  • Fe-Ni-Cr/ Fe-Cr-Mn high temp alloy

Iron-based superalloy can also be called heat-resistant alloy steel, that adding a small amount of Ni Cr and other alloy elements on the basis of Fe. Heat-resisting alloy steel can be divided into Martensite, Austenite, Pearlite and Ferrite heat-resisting steel according to its normalizing requirements.

  • Nickel-based high temp alloy

The nickel-based superalloy contains 50% or more nickel, and the solid solution and aging treatment can greatly increase the creep resistance and compressive and yield strength. At present, the application range of nickel-based superalloy is far more than that of iron base and cobalt based superalloy. The turbine blades and combustion Chambers of many turbine engines and even turbochargers are made of nickel-based alloys.

  • Co-based high temp alloy

A cobalt-based superalloy is about 60% cobalt-based alloy, and the addition of Cr, Ni and other elements improves its heat resistance. Although this kind of superalloy has better heat resistance, the cobalt production ratio is less, so it is difficult to process. It is usually used for parts under high-temperature conditions (600 ~ 1 000℃) and high temperature under extreme complex stress for a long time, such as the working blade of aero engine, turbine disc, hot end parts of the combustor and aero engine. In order to obtain better heat resistance, elements such as W, Mo, Ti, Al and Co should be added in preparation under general conditions to ensure their superior thermal and fatigue resistance.

 

By alloy reinforced type

According to the type of alloy strengthening, superalloy can be divided into solid solution strengthening superalloy and aging precipitation strengthening the alloy.

  • Solid solution enhanced superalloy

Solid solution enhanced superalloy means that some alloy elements are added to iron, nickel or cobalt-based superalloy to form single-phase austenite structure. Solute atoms distort the matrix lattice of the solid solution, increasing the slip resistance in the solid solution and strengthening it. Some solute atoms can reduce the delamination energy of the alloy system and increase the dislocations’ decomposition tendency, leading to the difficulty of cross slip.

  • Aging precipitation strengthened superalloy

The so-called aging precipitation strengthening is the alloy workpiece after solid solution treatment, cold plastic deformation, in higher temperature or room temperature to maintain its performance of a heat-treatment process. For example, Inconel 718 alloy has a maximum yield strength of 1 000 MPa at 650℃, and the alloy can be made at 950℃.

 

By material forming method

According to the material forming method, it is divided into casting superalloy (including common casting alloy, single crystal alloy, directional alloy, etc.), deformed superalloy, powder metallurgy superalloy (including common powder metallurgy and oxide dispersion strengthened superalloy).

 

High temp alloy has been widely used in aerospace and energy fields due to its excellent comprehensive performance and has become an irreplaceable key material for hot end components of aero engine, even its consumption accounts for 40%~60% of the total amount of engines. Take Inconel 718 alloy as an example, it is the most widely used brand mainly used in the bolts, compressors, wheels and oil spinner of turbo-shaft engines as the main parts. In addition, it is also used in casing, ring, afterburner and nozzle. Superheater and resuperheater use high-temperature alloy tubes with good creep resistance and excellent corrosion resistance in the ultra-supercritical power boiler with high parameters for coal electricity. Turbine blades and guide blades for gas plants, steam generators for heat pipes for nuclear power, etc.

 

 

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.