DE1948839B2 - Aluminum-coated steel object - Google Patents

Description

is deformable. ...

This task is carried out in the case of an object

30 defined type according to the invention solved by that the base metal is a carbon steel or a

The invention relates to an aluminum alloy steel J ^ coated article made of steel for use and at least one Le ^ in chemical plants at a temperature between 0.1 to ¹ ^ ² ° J ™ ^ J ^ ° '™? ^Cr ^ ^ _ta inl'erSch having 150 and 65O ° C and in a corrosive sulfur 35 10 ^Gewlcht! F ^r0Zent with eTner Lu atmosphere of at least 1 ppm Schwefelverbin- and flat on its Metal Lobe with an aluminum ^{F yy} miniumhaltigen alloy layer in a thickness of

^ Material for chemical equipment or at least 0.05 mm (50 _μΓ η) and hoc ^ tenjW.J devices and the like for use in a high temperature (300 μ * is provided ^m * ^h ° ^ * "° £ S £ ratur- and high pressure atmosphere has been usual ₄ o a Alum.n.umgehalt of less than 30 'Gewichtslicherweise stainless steel of type 18-8 steel contains with percent and AIumin.um-Diffu, on be high chromium or with aluminum coated at a temperature between 800 and 950 C in a teter steel, etc. In the case of austenitic powder coating, stainless steel inevitably shows the coating according to the invention.

Disadvantage is that the steel is subject to the formation of stress as a pressure-resistant material and high-temperature corrosion cracks and is also expensive. Temperature and high pressure conditions as well as in a suIfid ^ al aluminum atmosphere which has come to practical use, as explained above, provided, coated steel is made in steel coated by hot dipping with up to a maximum temperature of 650 C and with aluminum a practically satisfactory one Strength of the diffusion-coated steel is classified, the former being expected to be 50 coated steel, while, in spite of its advantage of reasonable cost, there is often no particular limit subject to peeling of the aluminum coating in the allowable pressure. This means that the coated steel can only be used to a limited extent, while steel diffusion-coated against pressure fluctuations from 200 kg / cm up to aluminum is resistant to ultra-high pressures of 1000 kg / cm ² and under such pressures it can be satisfactorily used in industrial practice as a material in a high temperature. The applicable atmospheres were used. are sulphidic atmospheres with more than about 1 ppm of sulfur compounds, such as hydrogen sulphide, have the advantage that the surface film formed by aluminum-sulfur oxides, elemental sulfur or mercap diffusion processes can be used either in gaseous or in the same stable and liquid phase as the hot-dip aluminum steel and at the same time mixed with other thermal stability, high-temperature oxy-fluids such as hydrogen, water vapor, conden- sation resistance and corrosion resistance, hydrogen, etc. The erhndungsgemalJ is superior, so that from these properties comparable coated steel is advantageously suitable for the spreads for sootblower pipes in boiler systems, blowing 6 ₅ use in chemical plants as Destillalanzen for oxygen steel making process, etc. tion equipment for mineral oils, such . B. shale oil, benefit has been obtained. On the other hand, this petroleum oil, coal tar and the like of equipments for steel, however, has a serious disadvantage that its hydrofining, hydrodesulfurization or

Hydrocracking of these materials, from coal liquefaction equipment, Hydrogen Sulphide Extraction Plants, Sulfur Production Plants, Manufacturing Equipment for organic sulfur compounds as well as columns or columns and boilers, furnace tubes, Heat exchangers, piping, various piping components, etc. for such equipment and Investments. The steel according to the invention shows its industrial advantages particularly clearly when used on equipment and the like for use with petroleum or petroleum, in which the sulfur content rarely exceeds about 5 percent by weight.

According to DT-AS 12 04 493, which refers to a further development of the method cited at the beginning and in the case of which alone an improvement in the resistance to scaling is heat-resistant Chromium steels are to be achieved, it is provided that for this purpose layer thicknesses of only 0.02 to 0.03 mm, i.e. H. in other words, particularly thin layers that can only represent correct dimensions. Although it is explained that is extremely differentiated in the treatment of steel surfaces in the aluminum diffusion process apart from the composition of the steel of the base metal, especially the type of stress, which the steel treated in this way is exposed during its use, turned off must be, but always only from the point of view of improving the scaling resistance of heat-resistant steels, for the diffusion layer thicknesses between 0.02 and 0.03 mm are recommended, while thicker layers are expressly discouraged.

In the case of the aluminum-coated object according to the invention, however, it is not about the scale resistance, but exclusively about the influence of a sulphurous atmosphere at high temperatures and high pressure. It is true that the surface treatment used for this purpose is through aluminum diffusion also confirms the well-known advantage of the improved resistance to scaling, however Steels produced in this way have proven to be suitable for use at both high and high temperatures Pressure in a sulphurous atmosphere is considered unsuitable for the reasons given at the beginning.

In a manufacturing process for the aluminum-coated article according to the invention the measures listed below are particularly advantageous:

The base metal is a carbon steel or a material such as. B. molybdenum alloy steel, chromium-molybdenum alloy steel, nickel-chromium-molybdenum alloy steel or the like. Used. Steels such as CV ₂ -Mo-, 1-Cr-O ^ -Mo-, I ¹ A-Cr-V ₂ -Mo-, 2V ₄ -Cr-I-Mo-, 5-Cr-V ₂ - Mo- and 9-Cr-l-Mostahl can be used satisfactorily. The steel can be coated in practically any shape, such as plate, billet or bar, tube, cast steel and forged steel form. However, stainless steel is not suitable.

The aluminum diffusion coating itself can be carried out according to the powder, gas, ceramic adsorption, hot dip diffusion process and the like, the heating using suitable materials, electrical heating, high-frequency heating, low-frequency induction heating or plasma jet heating can be done. The coating is often carried out using a calorification process, although particular care must be taken to ensure that the base metal does not become significantly brittle. For example, the temperature must be erfindu'jgsgemäß set in a range of 800 to 950 "C. At a coating temperature of about 950 ⁰ C namely the crystal structure of the base metal a rapid grain growth would show, resulting in a marked deterioration in the toughness of the steel and thus to leads to a loss of serviceability of the coated steel, while it is difficult at a coating temperature ^{of below 800 ° C.}

ίο one of the high requirements according to the invention to obtain satisfactory coated steel. Further, it was found that the thickness of the formed coating film the iron-aluminum alloy layer according to the invention do not exceed 300 μm and the aluminum content of the surface area of the alloy layer is less than 30 percent by weight must be because the increase in the thickness of the coating film is a cause in some cases certain unfavorable conditions exist. For example, aluminum diffusion coated steel has with a thick alloy layer according to conventional practice conceded to have considerable corrosion resistance in sulphidic atmospheres, but is sensitive to intergranular corrosion

as due to the grain growth of the crystal grains of the steel, so that this steel is from the standpoint of sulfidation resistance is not satisfactory.

A coated steel according to the invention with a thickness of the alloy layer of at most 300 μm or usually from 20 to 200 μm, but preferably in the range from 50 to 150 μm, has against it regardless of its thinner alloy layer compared to conventional steels of this type Surprisingly satisfactory sulfidation resistance. So was z. B. a sample of the above coated steel in a corrosion test lasting several hours in an atmosphere from a Subjected to a gas mixture of hydrogen sulfide and hydrogen under high temperature and high pressure, no sulfide corrosion was shown, although it is also true that the corrosion resistance of coated steel generally with increasing aluminum content of the surface area the alloy layer is increased, the aluminum content according to the invention is reduced to a certain level Value limited to the alloy layer of the coated steel according to the invention a particularly to give high mechanical strength and stability. According to the invention it was found that dei Limit value of the aluminum content in the surface of the alloy layer at which the aforementioned Difficulties do not occur, at around 30 percent by weight. Usually an aluminum content is sufficient of about 20 percent by weight, an alloy layer which is satisfactory in practice in this regard Properties to deliver. For example, if the aluminum content of the surface area i the alloy: it would not be around 50%, isl given the possibility of a detachment of the alloy layer from the base metal, so that such a material not only has extremely poor processing properties, but also for use is unsuitable in cases in which frequent heat and pressure changes occur.

The following are the characteristics of the invention with reference to drawings on the basis of the at followed a series of experiments using an aluminum diffusion coating process

the various data obtained from the packed powder method. It shows

F i g. 1 is a graph showing the relationship between the aluminum diffusion coating temperature and the grain size of the base metal,

F i g. 2A to 2C micrographs of the texture of at various aluminum diffusion coating temperatures coated steel,

F i g. 3 is a graph showing the relationship between the (in the ordinate Charpy V notch toughness value and the measured value (plotted on the abscissa) Temperature and

F i g. 4 two photomicrographs illustrating the sulfidation resistance of an aluminum-coated Steel sample that has been subjected to a long-term practical test.

More precisely, F i g. 1 shows a curve that was produced by evaluating and plotting the results obtained when measuring the grain size according to ASTM Standard, Part 1, 1435, E 19-46 method, for various coated steels, the steels using a 2V ₄ - Cr-1-Mo steel as the base metal and implementation of the aluminum diffusion coating at temperatures of 870, 900, 950, 1000 and 1050 ⁰ C were produced. As can be seen from the curve, some change in grain size occurs at 900 to 950 ^° C and a radical change is observed when the temperature rise exceeds ^{the range from 950 to 1000 ° C.} In this experiment, the coating time for the temperature range from 870 to 950 ^° C. was set to 10 hours and for the temperatures of 1000 and 1050 ^° C. it was reduced to 5 hours, although the time shown in FIG. 1 showed changes in grain size. The same tendency as mentioned above was also shown when the same aluminum diffusion coating was applied to other kinds of base metals.

The influence of the coating temperature on the microcrystalline structure is from the photomicrographs

ίο the aluminum diffusion coated steel according to F i g. 2 clearly visible. The for the respective coated steels according to FIG. 2 applied diffusion coating conditions were 870 ⁰ C and 10 hours for the case (A), 920 ° C and 20 hours for case (B) and 1050 ° C and 5 hours for case (C). As can be clearly seen from these micrographs of the microstructure, the coated steel (C) has, due to the diffusion coating at 1050 ° C, an exceptional

ao neat coarse grain growth, which leads to an embrittlement of the base metal X. It can also be seen that the thickness of the alloy layer Y in the case of the coated steel (A) is below 150 μm and in the case of the coated steel (B) is below 200 μm.

In addition, it should be noted that the in FIG. 2 with Z designated area shows an additional layer already mentioned at the beginning. This outer surface layer of the coated steel including this additional layer is normally applied prior to application of the coated steel peeled off and removed.

The following are the mechanical properties of the aluminum diffusion coated according to the invention Stahls on the basis of FIG. 3 and Table I explained in more detail.

Table I.

Mechanical properties of Al diffusion-coated steel pipe

Base metal

Coating conditions Tensile strength test Bending test

Temperature time tensile strength elongation

( ⁰ C) (hours) (kg / mm ^! ) (%) (180 ° C bend)

Flattening test

2V ₄ -Cr-1-Mo steel reason reason 51.0 30th no cracking no cracking metal metal 2V4-Cr-1-Mo steel 870 10 54.0 29 no cracking no cracking 2V ₄ -Cr-1-Mo steel 900 20th 54.7 24 no cracking no cracking IVi-Cr-l-Mo steel 920 20th 54.8 21 no cracking no cracking 2V ₄ -Cr-1-Mo steel 950 20th - - no cracking no cracking 2V4-Cr-1-Mo steel 1050 5 71.6 11.0 - no cracking

Table I illustrates the results of on a test piece of 2 ^l / ₄ -Cr-l-Mo steel carried out as the parent metal measurements and clearly shows the influence of deposition temperature on the material with respect to the elongation which is an important factor for the mechanical strength of the steel represents. These tests proved that the coated steel at a coating ^{temperature of 1050 °} C. completely loses its suitability for use under high temperatures and pressures.

F i g. 3 illustrates the results of the Charpy V Notch toughness test, which demonstrates that there is little difference between the Charpy V Notch toughness value of an uncoated steel (indicated by solid dots) and that of an uncoated steel (indicated by circular dots) in accordance with the invention at 860 ⁰ C coated steel, while at the same time no deterioration in toughness is found.

It should be noted, however, that in the case of a ^{coated steel treated at a temperature above 95O 0} C a considerable increase in its transition temperature was observed. In the sulfur-resistant, aluminum diffusion-coated steel according to the invention for use under high temperatures and pressures, the film of the alloy layer formed by the above-mentioned coating method is particularly stable,

7 8

so that not only the weldability of the coated steel has been put into operation under steel, but also the workability of large and varied conditions in complicated shaped workpieces can be improved. For example, in an atmosphere of 11.4 mole percent. It is therefore possible to weld with hydrogen sulfide, 62 mole percent hydrogen and performance of satisfactory strength and sulfide- 5 26.4 mole percent hydrocarbon gas, as well as under ionic stability by using welding conditions of high temperature and high pressure, rods for example from 9-Cr-1-Mo steel, stainless ie at temperatures of 220 to 450 ⁰ C and a steel of the type 18-8 or the like. To produce. While pressure of 125 kg / cm ² . The steel coated in this way using the conventional aluminum diffusion coating showed the satisfactory effectiveness of longer pipe sections inevitably leading to their deformation in terms of mechanical strength and sulphidation, the subsequent straightening of the resistance under all of the conditions mentioned.
Deformations, cracks in the coating alloy The conditions and results produced are described below in the coating according to the invention of comparative tests which did not result in any difficulties in the case of steel itself, laboratory and practical tests and the problems involved. In the treatment of 15 in particular, the behavior of aluminum-coated workpieces, such as molded valve parts, steel objects in a sulfur-containing atmosphere, is practically created in the coating according to the invention at high temperature and the \ table no deformation of the workpieces, so that they are excellent sulfidation resistance properties

therefore proves to be satisfactorily applicable. to prove.

' . Furthermore, it has been confirmed by practice that at the 20th
described coating in principle no

brittleness of the base metal was caused, and the τ. Laboratory tests
ⁿ mechanical strength of steel is that of

^ ¹ - steels coated in the conventional way (1) preparation of test pieces

^ ^: ·· superior. In addition, the alloy layer of the 25th

^ Steel is so stable that the steel is easily directed on the surface of plates made of a carbon

n ^ · can be, with its weldability strong material steel on the one hand and a 27 ₄ -Cr-l-Mo steel

^{i! 1} "has been improved so that the steel has a broader look with the aid of the aluminum diffusion process

">? ^T turnaround area is developed. Even under consideration with powder coating an aluminum-containing upper

'vfi- viewing the fact that the 3 ° surface layer according to the invention is formed with a thickness of 100 μm. the

wi coated steel priced the conventional aluminum plates in the diemnsion of 10 X 15 X 2 mm

Minium hot-dip steel is not superior, it is popular for aluminizing its surface over

the stability of the alloy layer, which was held for 10 hours at a temperature of 870 ° C.

reliability of weldability etc. incomparable The other conditions corresponded to the conditions

HT more advantageous. He also keeps each comparison with 35 genes that were also used in the previous example

stainless steel with regard to the sulfidation resistant templates.

strength and firmness stood so that he with regard to his

Economic efficiency is several times cheaper than (2) examination procedures

stainless steel. - ^

The following is a preferred embodiment 40. Each of the test pieces was placed in a quartz tube

the invention described using an example. 70 mm in diameter after pumping out the air

. . . a 100% H ₈ S-GaS by a vacuum pump

Example exposed, wherein the quartz tube is electrically heated

It has been a packing material through thoroughly.

Mixing 0.3 to 0.5 percent by weight Ammo 45 After 500 to 1000 hours after Ernium chloride with aluminum-iron alloy powder reach a temperature of 550 ⁰ C in the tube (Al content 50 %) prepared such a particle size that The weight gain was measured by weighing the Gedas powder in a normal sieve with a mesh size as large as the weight in a porcelain bowl,
of about 0.30 mm (50 mesh) passed, and thoroughly This measuring method was prepared after every 500 or more times the ingredients were mixed. A 5 ° 1000 hour heating in the aforementioned variety of atmospheres of workpieces of the spheres listed below to determine the weight increase was placed in an iron vessel, whereupon fetches. For comparison purposes, the same experiment was filled with the packing material on the vessel and _{closed or sealed with a carbon steel, a 27 4} -Cr-1-Mo steel. Subsequently, a low-carbon steel 18 Cr - 8 Ni, ie the closed vessel was heated in a furnace to 86O ⁰ C 55 a stainless steel according to AIME type 304L, and for 10 to 15 hours on this temperature-containing 18 Cr - 8 Ni stainless steel (AIME temperature left, making the aluminum diffusion type 321) made to effect the respective weight coating. to determine the increase. In all cases of these comparative steel sheets, shells formed on the upper tube, 274-Cr-1-Mo steel about 12.5 to 60% area, which softened when heated in the aforementioned

Switch off 460 mm atmosphere. Care was taken that

Elbow, 27 "Cr-l-Mo steel ... about 12.5 until the weight gain is determined

460 mm falling shells were also weighed.

Flange, 27 ₄ -Cr-l-Mo steel 19 to 460 mm

Valve, 27 ₄ -Cr-l-Mo steel 1 19 to 254 mm 65 ₍₃ ) result

5-Cr-7 ₂ -Mo steel J No. 1500

Connection fitting, 27 ₄ -Cr- The results of the test are in the following

1-Mo steel - reproduced in the following table.

ι.ϊ

Test pieces

Weight gain (mg)

after after

500 hours 1000 hours

Al-coated carbon steel 0.1 0.1 Al-coated 0.1 0.2 27, -Cr-l-Mo steel Carbon steel 580 1000 27 ₄ -Cr-Mo steel 340 590 A1ME type 3O4L steel 1.5 2.5 AIME type 321 steel 1.4 2.4

From the table above it follows that the aluminum-coated steels according to the invention with respect to Their sulfidation resistance properties largely match the stainless steels used in the test were superior.

20 II. Practical experiments

(1) Experimental procedure

As a test piece, an aluminum-coated plate of 30 × 60 × 5 mm was inserted into a channel inside a heat exchanger of a plant for hydrodesulphurisation of heavy oil introduced and in it exposed to a gas with sulfur compounds for about 1 year. From the test piece Cross-sectional photomicrographs were taken at the beginning and after the experiment.

The material used for the test _{piece was an aluminum-coated 2V 4} -Cr-1-Mo steel, the coating of which was produced as under I, and a thickness of 90 μm.

The atmosphere and temperature conditions within the heat exchanger to which the test piece is to be placed were exposed to:

Temperature ( ⁰ C) 365 to 420

Gas pressure (kg / cm ² ) 138 to 139

Gas composition

(Mole percent) H ₂ S: 5 to 9,

H ₈ : 60 to 65
CO ₂ : 24 to 26,
H ₂ O: 0.07 to 0.08

Duration of experiment (h) 7370

(2) Result

The result is shown in photomicrographs 1 and 2 in FIG. 4 reproduced. The photomicrograph 1 shows the microstructure of the enlarged cross-section of the sample before the test, while the Photomicrograph 2 showing the microstructure inside the heat exchanger at the end of the experiment reproduces the aforementioned atmospheric conditions. The magnification is 150 times. The analysis of the two photographs shows that the aluminum-coated steel according to the invention is hardly below the Suffered sulfidization attack.

If one compares the cost of a tube used for the heat exchanger from one according to the invention aluminum-coated steel (base metal: 274-Cr-l-Mo steel) and made of an 18 Cr - 8 Ni stainless steel, then one comes to the conclusion that with the steel coated according to the invention the Half the cost is saved.

For this purpose 3 sheets of drawings

Claims (2)

mechanical strength is so poor that the use of this steel as a material 1. Aluminum-coated article made of steel ^b ; ^um ^, ^he _{D k} is accompanied by certain dangers. for use in chemical plants with a 5 and nonem _{wdse bejnem} process for temperature between 150 and 65O ⁰ C and in corro- bo, is _{change-resistant surfaces} on a warm sulphurous atmosphere of at least P ^r ^ " ^g \ _{ubstances according to} the DT- AS 12 00 096 belppm sulfur compounds, characterized by a surface diffusion process for which the basic principle H is a known _material properties for high carbon steel or an alloyed steel with the verb «« ™ £ ^d £ _{, namely} this concerns the maximum 0.5 weight percent C and min- Jemper "u _known surface treatment least one alloy component from the group appli g _{of Zunderfestigkejt of warm.} from 0.1 to 1.2 Gew.chtsprozent Mo, up to 10 overall ™ ^r ^ ^rh ° J ^ _s S _len ^'to _e f _{bean deviations} ^ _h. in this Beaufweist and on its metal surface of an x ₅ ^' ^^ nut 'at high temperatures and wight percent Cr and up to 4.5 M. Gew.chtsprozent fesfön Ch Seispäteren strain of aluminiu A thick layer of alloy in a handlun thickness. ^ P _Οχ . β of at least 0.05 mm (50μΐη) and at most Stah ^ »g ^^ _{at the elevated} Tempe 0.3 mm (300 _μ m) provided, st, soft near the other Ouöauon _{£ J adhere erzie be} t _t) surface an aluminum content of less than »^« J, ^ 5 _{of iff} 1.5 usionszone to 30 per cent by weight and Alummium- "if ^ a ^'Ge ha'U _{$ Gnindwefkstoffes} be diffusion, a temperature between 800 and« ^ ^ _d * _Invention now consists in a 95O ⁰ C in a Pu verumhullung is made. uie Auigauc uci _Γ * _η ^ _αη Λ _71I create rW 2. Use of an aluminum-coated aluminum coated Ge ^ ns ^ ™ Khaffen, jdw steel according to claim 1 for chemical plants for an increased ™ chan.sche ^ ^ns P ™ £ ™ Hydroraffinieruig hydrodesulphurisation and hy-. ^^^^^ drocracking of mineral oils. S high temperature conditions weldable as well