SU1073340A1 - Steel-stripping melt - Google Patents

Abstract

MELT FOR CLEANING STEEL, containing caustic soda and sodium nitrate, characterized in that, in order to reduce metal losses and improve the quality of surface cleaning, the melt additionally contains cryolite in the following ratio of components, wt.%: Caustic soda. 65-80 Nitrate 15-25 Sodium Cryolite 5-10 (GB)

Description

with

00

The invention relates to chemical cleaning of corrosion-resistant steels, in particular, to melts of heat-rolled pipes from scale and technological lubricants, and can be used in metallurgy and other fields of technology. Alkaline NaOH-based melts with NaNo, N & 202 NagCrO oxidants are known, which are widely used in domestic metallurgical and engineering plants, as well as in the USA, England, Germany and other countries. (Hook process) to remove scale from the surface of corrosion-resistant, acid-resistant, heat-resistant and other steels and alloys i. However, the introduction of oxidizing agents, combined with high process temperature, accelerates the process of metal oxidation and the formation of a significant oxide film, which requires additional etching in solutions acid (clarification) i.e. results in significant metal loss. The closest to the present is an alkaline melt containing sodium hydroxide and sodium nitrate 1 which is used for Shaving the carbon-containing grease and descaling the surface. The treatment of the pipe is carried out at 420-450 ° C for 20 minutes C2. The disadvantages of the known alkaline melt are the need to perform processing at 420-450 ° C, which leads to increased corrosion loss of the metal, which the composition is 0.5-1.0%; the formation on the metal surface of a significant oxide film of golden-brown color, under which there is a residue of a carbon-containing lubricant rolled into the metal, resulting in a carburized state during further heat treatment Surfaces: steel and an increase in intergranular corrosion rejects (according to YuTZ 4: aSb ° KLS, ° .S5 .: irreducible etching in 10-23% H2S04 solution at 45-60 ° C for 2-5 min or in a nitrogen-fluorine solution (ng + nco) to remove the oxide film (but the inclusion of cm is not removed). The purpose of the invention is to reduce metal losses and improve the quality of surface cleaning. This goal is achieved by the fact that the melt for cleaning steel containing caustic soda and sodium nitrate, additionally contains cryolite in the following ratio of components, wt.% :. Caustic soda Cryolite sodium nitrate (NajAIF) The introduction of cryolite ensures complete dissolution of the AIFelc ions by the carbon-containing lubricant, while metal does not oxidize to form an oxide film. The cleaning process is carried out at 250-300 ° C. Under these conditions, NaN03 only plays the role of a corrosion inhibitor (passivates the surface), since the decomposition of nitrate with the formation of nitrite and oxygen (NaNO: | 0) occurs at a higher temperature. 380 ° C. The introduction of cryolite into the melt of less than 5% does not completely remove the lubricant from the metal surface, and the cryolite content of more than 10% leads to a significant increase in the melt temperature (300 s) and large corrosion losses of the metal. If the content of UaHOj in the melt is lower than 15%, then the site has a pasture bore on the metal surface, and the concentration of sodium nitrate above 25% leads to an increase in the melting point and time of etching. . When the content of NaOH is 65-80%, the optimum technological parameters of the process are ensured (low melting point and high liquid mobile). .. Melt preparation procedure and process parameters are as follows. Caustic soda is loaded into the bath and melted, then sodium nitrate and cryolite are added. Process temperature 250-300s; duration 10–20 min (depending on the content of cryolite in. The technological scheme for the chemical treatment of heat-rolled pipes made of corrosion-resistant steels includes the following operations: washing with hot HL ° –rai. melt for 10–20 min, washing with hot water ; passivation (clarification) in a 10-15% solution at 45-60 0 for 2-3 with cold water from a fire engine. Example: A comparative test of the proposed alkaline and known melts was carried out in the laboratory. The samples of steel 12X18H10T were processed ;} 20 km and a length of 50 mm after warm rolling at the KhPT YuTZ mill in Nikopol with graphite-containing lubricant,%: NaKOg 55-40, graphite 5-8, Ca (OH) 5-8. Table 1 shows the compositions of alkaline melts (1 and 2 known.

Table 1

80

B; LOCAL soda

82

Sodium nitrate 20

14

Cryolite

For each variant, 10 samples were processed and, in options 1 and 4, 20 samples of pipes. Test propensity to

Melt temperature, ° С

320

Processing temperature, ° С

450

Duration about 20, min

Corrosion loss of metal a,% 1.15 0.95

Zolvvid obtistorabotki measles neva film with grease strips

Tendency to intercrystallite corrosion {method AM-GOST 6032-75),%

80

72.5

65

63

15

20

25

26

7.5

ten

D1

MMK was carried out according to the method of AM oGOST-6-032-75 ..

; The parameters of the process of processing and the results of the tests are given in Table. 2 ..

20

180 180

230

300

300

250

250

350

ten

ten

20

20

0.27 0.12

0.25

1.0

SerebSvetristola white

clean surface clean surface with traces of spreading

BOB

/ Not

Not

Not

51073340

From the data obtained, it follows that 100-200C and thus the saving of electricity in the case of the application of the proposed racial energy and the increase in durability

flotation of chemical processing of heat equipment; complete removal of grease-rolled pipes from corrosion-resistant and obtaining a light surface /

their steels are reduced by corrosive contamination of the etching operation and metal batery by 4–9 times, providing for ICC, as well as improving

The complete removal of the lubricant, and, as a result, a consequence, is ruled out for ICC.

Thus, the use of the predla- economic effect is responsible for

Melt glue for chemical melt for chemical treatment

workings of corrosion-resistant pipes for corrosion-resistant heat-rolled pipes

bakes reduction of corrosion only in the conditions of the Nikopol South metal loss by 4–9 times; the reduction of the pipe plant is more than

processing temperature on 60 thousand rubles. in year.

Claims (1)

MELT FOR CLEANING STEEL, containing caustic soda and sodium nitrate, characterized in that, in order to reduce metal loss and improve the quality of surface cleaning, the melt further contains cryolite in the following ratio of components, wt.%: \ Sodium hydroxide 65-80 Nitrate sodium 15-25 Cryolite (NagAI F ₆ ) 5-10 > ♦