SU954529A1 - Method for thermal treatment of steel products having zinc plating - Google Patents

Description

(54) METHOD FOR THERMAL TREATMENT OF STEEL

PRODUCTS WITH GALVANIC ZINC COATING

The invention relates to electroplating and can be used in the heat treatment of zinc plated steel products. The need for heat treatment of products after electroplating is caused by the fact that galvanizing, and especially of cyanic electrolytes, is accompanied by hydrogenation of the steel base, which significantly impairs the reliability and durability of products due to the reduction of ductility of the steel. Exposure to steel products with coatings at elevated temperatures increases the diffusion of hydrogen from the metal and contributes to the restoration of ductility. The known method of heat treatment of steel products with galvanic zinc coating, providing for holding in vacuum at 200-400 ° C for 2-24 hours C. A method of thermal treatment of steel products with galvanic zinc coating, including holding in oil for 2 hours at 250 ° With ultrasonic treatment 2. The closest to the proposed technical essence and the achieved result is a method of heat treatment of steel products with zinc plating, in which after galvanizing The heating water is heated at a temperature of 150-250 ° C for 1-4 hours. However, the known treatment methods do not lead to the complete restoration of the original plastic properties, and sometimes further deterioration is observed. The purpose of the invention is to increase the ductility of steel products with galvanic zinc coating due to dewatering. The goal is achieved by the fact that in the method of thermal treatment of steel products with zinc plating, on / off, heating, isothermal holding and cooling, heating and cooling are carried out repeatedly in the temperature range (245 ± 5) (180 ± 5) ° С with holding at each temperature for 0.25-0.5 hours, after which the treatment is carried out with cold at a temperature not lower than 3954 minus 60 + 10 ° C. In this case, heating and cooling are carried out 2-8 times. The choice of the heat treatment boundary temperatures is due to the fact that zinc coatings embrittle at temperatures above 250 ° C and below minus 70 ° C. Thermal treatment according to the proposed method ensures the production of steel products with galvanic zinc coating with higher properties, due to the fact that thermal cycling (multiple heating and cooling) accelerates the process of hydrogen diffusion from the metal; cold treatment at the end of thermocyclic treatment (not less than minus 60 ± 10 ° C) leads to structural transformations in steel, which, as is well known, accelerate the release of hydrogen from a metal. Heat treatment according to the proposed method provides a significantly greater dehydration of galvanized steel products, and as a result, a more complete restoration of plastic, compared with the known method of providing isothermal aging at elevated temperatures (150-250 ° C). An example of the method. Test tape samples of size 18x120x0.25 mm from spring steel 65 g. Nag

a) Known method: holding at 250 ° C for 2 hours, air cooling

b) The proposed method:

 holding at 250, 180, 250 and 180 ° С for 0.5 hours at each temperature, i.e. two cycles, cooling at -60 ± 10 ° С

a) Known method: exposure at 200 ° C, 4 hours

b) The proposed method: eight cycles (exposures at 250 and 180 ° C for 0.25 hours at each temperature); cooling to -30 110 ° С

Non galvanized specimens

36

50

45

55

Claims (3)

: The samples in the furnace up to 810 + 10 ° С are quenched in oil, and then subjected to tempering to a hardness of 40 HRC at 410 ° С. Preliminary preparation of samples before coating consists of electrochemical (anodic) degreasing in an alkaline solution and etching in a solution of hydrochloric acid with hexamine. Zincing of samples is carried out from the electrolyte composition, g / l: zinc oxide 10-18; sodium cyanide 40-50; caustic soda 80-100; sodium sulfide 5, solution temperature 15-3Cf; C; cathode current density of 1-4 A / dm. The thickness of the deposited zinc coating is 6-7 microns. After cyanic zinc plating, the samples are subjected to heat treatment according to the following mode: heating to 245 + 5 ° С with a holding time of 0.25-0.5 h, cooling with a furnace to 180 + 5 ° C with a holding time of 0.25-0.5 h (one cycle), and so 2-8 cycles, at the end of thermal cycling cooling to a temperature of minus 3060110 ° C. The effectiveness of the processing method is evaluated by the plastic properties — the number of kinks before the destruction of the samples. In parallel, test samples subjected to processing by a known method. The test results are shown in the table. 5 Thus, the use of the proposed method of heat treatment of steel products with a zinc coating makes it possible to increase their plasticity 1.2-1.4 times as compared with the existing heat treatment regimes. This allows for greater restoration of the plastic properties of steel products, degraded as a result of the application of durable coatings on them, for example, springs and tongs of steel 65; G, which leads to a decrease in the marriage of these products, arising due to the embrittlement with hydrogen. Claim 1. Heat treatment of steel products with galvanic zinc coating, including heating, isothermal extraction and cooling, characterized in that, in order to improve n & nH, heating and cooling are carried out repeatedly (180 ± 5) by exposure at each temperature for 0.25-0.5 after which the treatment is carried out with an ode at a temperature not lower than minus 60 + 10 ° C. 2. Pop method, 1, characterized in that heating and cooling performed 2-8 times. Sources of information taken into account in the examination 1. Belaglazov S.M. The flooding of steel in electrical processes. L., Publishing House of Leningrad State University, 1975, p. 359. 2. In the same place 360. 3.Shchng, N.P., et al. Effect of current reversal and surfactant on hydrogenation of base metal and physical and hemanic properties of precipitation during cadmium plating and galvanizing. Sat N {water deposition of a metal during electrochemical processes, Izdan-vn Leningrad State University, 1974, p. 168.