SU1382863A1 - Method of thermal treatment of cold-rolled steel in bell furnace - Google Patents

Description

(21) 3868138 / 23-02

(22) 03/19/85

(46) 03/23/88. Bul № 11

(71) Institute of Ferrous Metallurgy

(72) V.I. Kusov, A.I. Yatsenko, N.I. Repin, N.P.Kusova, G.V. Kruglikova,

A.P.Shapovalov, A.K.Gruznov, Yu, A.Mukhin, E.I. Bulatnikov, A.N. Tinkov, K.F.Losev and V.I. Kulichkov

(53) 625.783 (088.8)

(56) USSR Author's Certificate No. 428026, cl. C 21 D 1/26, 1968.

Guseva S.S. et al. Continuous ter-. Automotive steel machining. - M .: Metallurgi, 1970, p.19-22.

(54) METHOD FOR THERMAL PROCESSING OF COLD-ROLLED STEEL IN BULK FURNACE

(57) The invention relates to heat treatment of products in the ferrous metallurgy, namely to heat treatment in bell-shaped furnaces of cold-rolled steel, intended primarily for finishing cutting of parts. The purpose of the invention is to reduce the duration of the heat treatment process while maintaining stable heat treatment performance for a wide range of productivity. This is achieved by increasing and maintaining stable cooling rates of the charge by cold purging with protective gas with a flow rate equal to 0.85-1.5 of the volume of the charge. The specified flow rate of protective gas allows maintaining a cooling rate of 15.5–16.5 ° C / h and obtaining an annealed metal with ferritic grains of 9–10 points without inclusions of tertiary cement along the boundaries of ferritic grains.

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the processing of products in the ferrous metallurgy, namely, the heat treatment in cold-rolled steel bell-type furnaces, designed primarily for the final cutting of parts.

The purpose of the invention is to reduce the duration of the heat treatment process while maintaining stable heat treatment quality indicators for a wide range of capacities, including heavy load tanks, ranging from 85 to 120 tons.

The stable qualities of thermal processing are achieved due to constant cooling rates of 15.5-16.5 C / h and, as a result, elimination of termination of tertiary cementite at the boundary l

equal to 0.85-1.5 volumes of the set, is chosen based on the optimal ratio between the gas flow rate, the average cooling rate of the coil foot and the structural characteristics of the annealed sheet.

Increasing the gas flow rate in the purge, for example, to 1.6-2.0 m / h of the bulk of the charge and is more economically inexpedient, since the cooling rate of the foot of the coils practically remains at the same level.

Cold blowing is terminated after the metal reaches a temperature of 400-350 ° C, since below these temperatures the process of releasing tertiary cementite slows down. Besides.

ren, i.e. The quality of metal is maintained at between 400 and 350 ° C with slow cooling for the production of parts for final cutting.

The method is implemented in the following way.

A stack of rolls is formed on the stand, covered with a muffle, and a cold purge of the baffle space with protective gas is performed within 1-2 hours by opening the inlet and outlet pipes. Then, in the process of heating for 4-8 hours, a hot purge is carried out and the discharge pipe is closed. After the coils are heated up to the annealing temperature, the heating cap is removed and the discharge pipe is opened so that the flow through the coils

protective gas was 0.8-1.5 / h "m volume of the charge

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After cooling the stack of coils to 400-350 ° C, the discharge pipe is closed and further cooling, for example, to 120-140 ° C, is carried out by circulating the protective gas under the muffle in a closed loop.

The duration of the heat treatment process is reduced by shortening the cooling time, which is achieved as a result of cold purging with protective gas, from the removal of the heating cap until the metal reaches 400-350 ° C, in an amount of 0.85-1.5 per 1 m volume of cages. Mixing cold protective gas with a temperature of not more than 20-25 ° C, with a protective gas circulating in the dark-walled one.

space, lowers the temperature, increases the heat transfer process.

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The process of thermal aging of methane occurs, which have a favorable effect on the stabilization of mechanical properties.

The end of cold blowing above 400-350 ° C and, consequently, a decrease in the cooling rate leads to the release of tertiary Cementite at the grain boundaries, i.e. to lower quality

annealed metal.

Example. At the stand, a three-roll stock was formed from steel 08U with a strip width of 1230 mm and 0.8 mm, with a total mass of about 90 tons, and is heated to 690 ° C. After the metal has reached the temperature at the station, the heating cap is removed and the discharge pipe is opened to the smoke hogs. The flow of protective gas in the purge of 1.0 m / h of the volume of the charge. With a set up volume of 11.5 m, the absolute gas consumption is 11.5–12 m / h.

After the metal reaches the lagging point, the discharge pipe is closed and further cooling is carried out with the protective gas circulating around the closed loop to the unpacking temperature of 110 ° C using a bench thermocouple.

The cooling temperature is up to 16 s / h. The productivity of the cooling process in this case increases by 20–22%, and that of the annealing process, by 11–12%.

These microstructural studies show that the annealed metal has ferritic

313828634

Grain 9-10 points, cementite - P-1 with a ballast gas with open discharge pipe, inclusions of tertiary cementite, heating of the charge and subsequent cooling of the boundaries of ferritic grains. Exhibiting with a removed heating cap of suitable parts as a result of a clean one, characterized in

YOU cutting down povpiyaetsya 5-6% mail, t the purpose of reducing the duration

compared with the known method. The heat treatment process with preservation

stable quality indicators of the formula of the invention of processing for a wide range

10 productivity, after the removal of the method of thermal treatment of the heating cap.

steel-hardened steel in the bell furnace, which gives the pipe and produces cold

including cold and hot purging with protective gas at the flow rate,

Ku of the under-muffled space of protection equal to 0.85-1.5 m / h of the volume of the charge.

Claims (1)

Claim A method of heat treating cold rolled steel in a bell furnace, including cold and hot purging of the semi-muffle space with a protective gas with an open exhaust pipe, heating the cage and subsequent cooling with the heating cap removed, characterized in that, δ, to reduce the duration of the heat treatment process while maintaining stable quality indicators heat treatment for a wide range of performance, after removing the heating cap open the outlet pipe and produce a cold purge for itnym gas with a flow rate of 0,85-1,5 m ³ / h-m ³ volume cages.