DE1533332B1 - USE OF A STEEL ALLOY AS A MATERIAL FOR OBJECTS THAT MUST BE PERMANENT AGAINST SULFURIC ACID - Google Patents

Description

Process of steel production required reducing agent surcharge. The upper limits of 0.03% for phosphorus and 0.03% for sulfur indicate those limits beyond which it is difficult in the steelmaking technique to reduce the total amount of these elements present. Since phosphorus also tends to promote corrosion, it is essential to limit its proportion to the above-mentioned value. Although there is copper in an element, the larger acts in the sense of switching corrosion resistance, an addition of less than 0.2% is ineffective, and amounts of copper about 0.6 ° / ₀ also lead to difficulties in the process of steel manufacture. Chromium in a content range of 0.3 to 0.9% with the simultaneous presence of copper causes corrosion resistance, but a chromium content of less than 0.3% no longer imparts the property of corrosion resistance. On the other hand, a chromium content of more than 0.9% causes poor machinability. As already mentioned above, the steel alloy to be used according to the invention is characterized by the addition of antimony or tin or of both substances for the purpose of a considerable improvement in the corrosion resistance. An antimony content of more than 0.5% lowers the melting point of the material and thus impairs its hot formability, while an antimony content of less than 0.05% does not improve the corrosion resistance. The content range for tin from 0.05 to 0.5% is determined on the basis of the same facts as that for antimony. For example, a tin content of over 0.5% has a considerable negative impact on the hot formability, while a tin content of less than 0.05% no longer increases the corrosion resistance. The simultaneous presence of tin and antimony in the content range of 0.05 to 0.5% will serve to improve the corrosion resistance of the steel alloy at more than 75% sulfuric acid and more than 115 ⁰ C.

The cumulative effect caused by the simultaneous presence of tin and antimony is effective are stronger than in the case of an additive consisting either only of tin or only of antimony Case is. The reason for setting the sum of the tin and antimony contents on the area from 0.05 to 0.5%, that it is difficult below the lower limit of 0.05% is a satisfactory one To achieve corrosion resistance behavior, while above the upper limit of 0.5% the Hot workability deteriorated. The addition of 0.30 to 0.80% of nickel affects the corrosion resistance the steel alloy does not. Nickel also prevents the other additive elements from building up between the interfaces of the crystal particles, caused by the selective oxidation of the iron component is caused during hot deformation, and therefore acts in the sense of conveying the desired Corrosion resistance. To ensure

ίο satisfactory thermoforming properties too under difficult operating conditions it is necessary to select a lower content limit of 0.30%, whereas if the upper content limit of 0.80% is exceeded, the corrosion resistance of steel alloys gradually decreases. This range of nickel content is also suitable an appropriate equilibrium ratio to the proportions of the other added elements to train. . - ■ ..

Alloying a small amount of nickel prevents the hot workability from deteriorating and the further processability of the steel alloy, as achieved by the addition of elements which are capable of imparting the desired corrosion resistance, so that it this enables various steel products including special steel plates, structural steels, To produce steel pipes and the like, for which precise dimensional accuracy is strictly required.

If elements such as Cu, Sb and Sn are added to the alloy, these elements form a solid solution in Ferrite, and if then the iron component takes precedence over these elements, an oxidation process is subject, the concentration of the solid solution of Cu, Sb and Sn increases, which ultimately leads to precipitation and accumulation of these elements at the grain interfaces. It is believed that this causes a lowering of the melting point at these interfaces, which then leads to it cracking occurs and poor hot working properties are caused. Against it an addition of nickel has the effect of preventing rapid oxidation of the iron. It also mixes precipitated and at the grain boundaries

■ 45 aggregates copper, antimony and tin with the nickel and forms masses with a high melting point, which contributes to the maintenance of the good hot working properties.
Chemical compositions of typical samples according to this. Embodiments of the invention and control samples are listed in Table 1 below:

Table 1
Chemical composition of typical samples according to the invention and of control samples

sample

Si

Cu

Cr

Ni Sb Sn Mo

A (control sample)

B (sample according to the invention)
C (sample according to the invention)

D (control sample)

E (sample according to the invention)
F (sample according to the invention)

G (control sample)

H (control sample)

I (control sample) .........

0.12
0.09
0.11
0.13
0.13
0.09
0.13
0.07
0.07

0.21

0.24

0.28

0.30

0.31

0.24.

0.19

0.42

0.55

0.40 0.38 0.35 0.38 0.42 0.46 0.45 0.50 0.98 0.017
0.017
0.018
0.020
0.019
0.016
0.012
0.083
0.036

0.015
0.015
0.015
0.017
0.014
0.015
0.015
0.010
0.010

0.34
0.41
0.30
0.42
0.41
0.39

0.29

0.54
0.68
0.48
0.53
0.53
0.52

0.53
18.68

0.48
0.64

0.54
0.40

8.48

0.48
0.25
0.42
0.15
0.17
0.20

0.11
0.12
0.11

Each of these samples was immersed in a series of corrosion tests for a period of 5 hours in sulfuric acids of different concentrations and different temperatures. The test results are in the table below! received. As can be seen from this table, the samples according to the invention, namely samples B, C, E and F, which all contained nickel, showed less corrosion than the control samples. In Table 2, the percentages denote the concentration of sulfuric acid, the data in ° C relate to the sulfuric acid temperatures, and the other figures provide a measure of the degree of corrosion, expressed in mg / cm ^a / 5 hours.

Table 2
Immersion corrosion tests carried out on samples according to the invention and on control samples

sample

20% Test conditions 40 ° / o 50% 60% 70% 80% 0.49% 30 ⁰ C 50 ⁰ C 60 ⁰ C 75 ⁰ C 100 ⁰ C 130 ⁰ C 30 ° C 2.1 17.5 37.5 13.2 8.2 12.4 0.7 1.6 12.1 33.4 15.0 7.4 13.7 0.6 2.4 19.7 42.2 14.3 8.2 15.6 1.1 2.8 16.0 40.6 18.4 7.0 14.8 0.7 3.2 19.1 50.2 15.6 6.9 10.3 1.0 2.4 17.2 48.1 17.0 9.2 18.0 0.8 12.6 19.3 241.2 13.5 7.0 14.5 2.2 15.3 248.0 380.6 20.6 8.3 20.5 19.5 2.0 65.7 229.6 176.2 179.6 208.7 0.04

90% 160 ⁰ C

A (control sample)

B (sample according to the invention)
C (sample according to the invention)

D (control sample)

E (sample according to the invention)
F (sample according to the invention)

G (control sample) ....

H (control sample) .....

I (control sample) ...

44.7 45.4 48.1 35.9 32.0 37.6 60.2 65.2 42.7

These results are shown graphically in FIG.

With a view to determining the particularly specific properties of the steel alloys according to these embodiments of the invention, a method was used to determine the maximum melt-out during flame cutting, expressed as a percentage of the non-melted part of the sample, in which the test piece was inserted into a Mannesmann- Drilling machine introduced and the ratio of that length portion of the test piece in which no crack formation was noticeable to the total length of the test piece was determined and determined as the maximum melt-out, expressed as a percentage of the part that was not melted out. When the roll clearance of the Mannesmann drill was set to 20 mm, a frustoconical test piece, which at one end had a diameter of 25 mm, at the opposite end a diameter of 30 mm and a length of 150 mm, was inserted into the roll clearance and processed. The percentage of the part not melted out was set equal to 100 7o in the absence of crack formation. The maximum melt-out is obtained by dividing the difference between the total length of the specimen and the length of that part in which cracking occurred by the total length of the specimen and expressing the quotient obtained in this way as a percentage. According to this method the specimens listed in Table 1 according to the invention C and F as well as the control samples A and I pierced at temperatures of 1150 and 1200 ⁰ C and then their properties were investigated with respect to hot workability. The results of the tests are shown in Table 3 and in FIG. 1 reproduced.

35

Table 3

Maximum melt-out, expressed as a percentage of the part that has not been melted out the sample

40 sample Sample) ..
Sample) .. ■ \
tempo
1150 / request
saturation in ⁰ C
1200 I 1250 50%
90%
63 7o
43% A.
G
F.
45 I. (Control sample)
(according to the invention
(according to the invention
(Control sample). 32%
55 7o
54%
26% 37%
61%
60 7o
34%

These results clearly show that by adding nickel to that used in the present invention Alloy, which contains various corrosion

Contains preventive elements including antimony, steel alloys with significantly improved hot formability can be obtained.

Macrostructures of specimens that have been subjected to the above test procedure

were, are in the pictures according to FIG. 3 and 4 reproduced, from which the excellent quality is clear the internal structure of the steel alloys according to the invention emerges. The flexibility the internal structure of each of the in the

F i g. 3 and 4 shown specimens is lost as the temperature of the specimen decreases, blurring the interfaces between the grains will. This condition is more pronounced in the in FIG. 3 shown control samples,

especially with the 18/8 stainless steel (Fig. 3b). The in Fig. 3 shown, antimony-containing specimen has at a temperature of 125O ⁰ C, the temperature suitable for drilling, a very good loading

creation of the internal structure, but here the melt-out was expressed as a percentage of the unmelted part of the sample, to 50%. In contrast, FIG. 4 shows the inner Structure of the test pieces C and F containing nickel according to the invention. How out of this Figure can be seen, here are both the internal structure and the melting, expressed as a percentage of the unmelted part, much improved. The percent melt-out for samples C and F is 90 and 63%, respectively.

The steel alloys used according to the invention are suitable for steel pipes or steel plates in the Low temperature range of boiler systems that burn heavy oil, where operating conditions arise in which corrosion from sulfuric acid can occur. Due to the presence of a relatively small amount of nickel is the hot formability and further processability of the Steel alloys are significantly improved, and it can thus at low cost such steel products, such as special steel plates, structural steel members, steel pipes and the like. Manufacture in which one is extremely

ίο exact compliance with the dimensions is required. These products can be found in steam power plants, petroleum refineries, town gas refineries, in the chemical Synthesis technology as well as in the chemical-large-scale production of ethylene, olefins and their Use of derivatives.

For this purpose 2 sheets of drawings

209534/320

Claims (1)

1 2 Claim- sulfuric acid is one of the operating conditions. ■ As is known in the art, apply Use of a steel alloy consisting elements such as chromium, and copper. The like., Generally of less than 0.15% carbon, less than suitable components to steel alloys, a Be-0,40 ° / ₀ silicon, less than 0.5 ° / ₀ Manganese, 5 to impart resistance to sulfuric acid (cf. less than 0.03% phosphorus, less than 0.03% Austrian patent specification 112 813). It has now been found sulfur, 0.2 to 0.6% copper, 0.3 to 0.9%, that through the alloying and the chromium, 0.05 to 0.5% antimony or tin or the simultaneous presence of a suitable one Amount of both elements together, 0.3 to 0.80% antimony or tin or both elements from a nickel, the remainder iron and impurities, as a steel-based material, which is a small amount of material for objects that are against sulfur-chromium, Contains copper and carbon, practically acidic in concentrations of 0.5 to 50% with usable steel alloys, temperatures of 30 to 60 ° C can be created sufficiently, which must have excellent corrosion resistance at all times, especially as pipes if one of the operating conditions or plates for boilers that burn heavy oil is the presence of sulfuric acid or corrosive systems that include gases of the same chemical type operated in the low temperature range. It was going to be. now found that the corrosion resistance of this improved steel alloy can be increased even further can if you add 0.30 to 0.80% nickel to it. It is accordingly the aim of the invention to propose the components carbon, copper, chromium, antimony and a steel alloy which contains a ^ and / or tin and nickel as a material for a relatively small amount of alloy - W Objects which contain sufficient constituents against sulfuric acid and which must be resistant to a high level of resistance. 25 against the corrosive effects of sulfuric acid Usually it is steel that does not possess certain. Contains elements and does not contain any special surface 'The steel alloy treatment to be used according to the invention has been subjected to liquid sulfurization consists of less than 0.15% carbon, Feic acid of a concentration below 60% quickly less than 0.40% silicon, less than 0.5% manganese, attacked and disbanded. At concentrations above 3 ° less than 0.03% phosphorus, less than 0.03% 60% the corrosion progresses violently as soon as the sulfur, 0.2 to 0.6% copper, 0.3 to 0.9% chromium, Sulfuric acid is heated. 0.05 to 0.5% antimony or tin or both As a result, the normal service life of ge elements together is 0.3 to 0.80% nickel, the remainder Domestic iron and steel are very limited, iron and impurities. This steel alloy if the material is used under operating conditions 35 is used as a material for objects that with which it is with sulfuric acid or with one against sulfuric acid in concentrations of 0.5 Corrosive gas that condenses sulfuric acid up to 50% at temperatures from 30 to 60 ° C forms, comes into contact, and which must be sufficiently resistant, so in particular Loss of steel and iron as a result of such corrosion as pipes or plates for heavy oil burning sion are therefore very high. Although so far 40 boiler systems that affect the low temperature range considerable research expenditure by the companies. Dedicated to the search for metallic materials. The invention is explained with reference to the following, which are resistant to the corrosive effects of writing, drawings and pictures, and sulfuric acid. In the drawings and pictures, m means - in most of the 45 F i g found or found. 1 the relationships between the heat wound materials around pure metals or steels, cutting temperature and the maximum removal, which contained a high proportion of expensive alloy - expressed as a percentage of the non-removed components, and cheap steel alloys, part of the sample, a small amount of alloy components Fig. 2 the results of corrosion tests, are not yet easy to produce 50 using hot sulfuric acid and are not widely available. the new steel alloy as well as with counter samples When an exhaustive investigation is carried out with regard to the effect of various elements in relation to FIG. 3 pictures showing the the corrosion resistance of different steel materials caused by flame cutting tests against sulfuric acid or corrosive gases 55 reproduce the structure, of the same chemical type were now cheap figs. 4 images, which the at the invention Steel alloys found which cause a lower amount of steel alloys by flame cutting attempts Contain alloy components, and reflect the th macrostructures, under the above-mentioned conditions an extremely With regard to the individual components included in the have high resistance to sulfuric acid. 6.0 alloy steels according to the invention in use In particular, extensive undertakings should be mentioned: Is carbon in Searches made with the aim of cheap steel - larger proportions than 0.15% applied, so Creating alloys that contain a small amount of Le-not only degrades the corrosion-resistant alloy components included, and the example speed, but there also occurs an undesirable increase should be suitable for such components, such as strength with the simultaneous presence of others Steel pipes, as they are in the low temperature range of elements. The stated salary ranges for Heavy oil burning boiler systems used silicon and manganese of less than 0.4 and less, respectively where the presence or formation of than 0.5% denotes the proportion range of the at