SU1516496A1 - Method of isothermal hardening of articles - Google Patents

Abstract

The invention relates to heat treatment, in particular to a hardening method, and can be used in the isothermal hardening of carbon and alloyed steels. The purpose of the invention is to increase the hardenability of the products. The method includes cooling after austenitization in the molten salt with the addition of an aqueous solution of urea with a ratio of components of the solution, wt.%: Urea 18-26

water - the rest. 2 tab.

Description

one

(21) 4221391 / 23-02 (22) 04/06/87

(46) 23.10о89о Bulo 39

(71) Kramatorsk Research and Engineering Design and Technological Institute of Mechanical Engineering

(72) BoA Dziuba, AoC Moiseeva, N.Fo Kulachko, NaMo Kolesnik and YuoAo Bashnin

(53) 621о78 „066.6 (088.8)

(56) Lakhtin. Metal science and thermal processing of metals. M .: Metallurgi, 1984, with „215,

(54) METHOD PI30METppi4ECKOfl ZAKAL1SH PRODUCTS

(57) The invention relates to heat treatment, in particular to a quenching method, and can be used in isothermal quenching of carbon and alloyed steels. The purpose of the invention is to increase the hardenability of products. The method includes cooling after austenitization in molten salts with the addition of an aqueous solution of urea at a ratio of components solution, mas%: carbamide 18-26, water - the rest is about 2 table.

The invention relates to heat treatment, namely to salt bath compositions, and can be used in isothermal quenching of carbon and alloyed steels.

The purpose of the invention is to increase the hardenability of the products.

The quenching method includes austenitization, cooling and soaking in the molten salt with the addition of an aqueous solution of urea and the final cooling in air. In this case, an aqueous solution of urea contains components in the following ratio, wt.%:

Urea18-26

WaterEverything

Urea - (is white crystals, odorless, highly soluble in water, non-toxic, contain nitrogen 46.2%

The addition of an aqueous solution of urea to the melt increases the cooling capacity in the range of the lowest stability of austenite (in the range of pearlite transformation temperatures).

The nitrogen released at the melt temperature contributes to a higher fluidity, and thus accelerates the cooling capacity of the melt, which allows an increase in the hardenability of the products.

Example The increase in the cooling capacity of a melt in the pearlite temperature range is determined by measuring the hardenability of the cross section after quenching.

The solutions introduced into the bath to increase the cooling capacity of the melt were prepared by adding calculated amounts of urea into water while simultaneously peremeivaiva-

ate

about N X)

O5

Nonemo hardening ability of the medium is determined on samples with a diameter of 30 and 36 mm, a length of 200 mm, made of steel 60C2s,

Samples are heated in a chamber furnace of the CH3 type to 860 ° C, incubated for 40 minutes and cooled in a nitrate-pan composition: 55% KNOj + A5% NaNO, with the addition of a 0.7% carbamide solution of a certain consistency, which is introduced through a special A device that eliminates splashing, bursts and emissions 10–15 minutes before quenching begins, melts for 50 minutes and is cooled in air.

After cooling, templates with a thickness of 20 mm are cut out anodically and mechanically from the central part of the samples. After grinding the ends, the hardness is measured on a Rockwell device with a load of 150 two mutually perpendicular directions.

The presence of microcracks is determined after etching with a 10% solution of nitric acid in ethyl alcohol by visual inspection and with an ocular eye when magnified 10 times.

The compositions of the proposed and known solutions are given in Table. one

The used compositions of the solution introduced into the melt of the salts during isothermal quenching have the characteristics of hardenability given in Table 2.

TabLo 1 and 2 imply that the optimal content of urea I8

five

26% of salts added to the melt. The addition of urea to water and the introduction of perilite transformation in the temperature range increases the hardenability, creating uniform hardness in depth and prevents the formation of cracking.

When the content of urea in water is less than 18%, the cooling rate in the interval of the least stability of austenite is small and through-hardenability is not achieved. When the content of urea in water is more than 26%, the solution is oversaturated and, as a result, microcracks appear after quenching.

The application of the proposed method of isothermal quenching in molten salts with the addition of a urea solution improves the quality (durability) of parts by increasing the hardenability.

0

Claims (1)

Invention Formula The method of isothermal quenching of products, including austenitization, cooling and cooling in molten salts with the addition of water and final cooling for air, characterized in that, in order to increase the hardenability of the products, urea is preliminarily introduced into water in the following ratio of components, mas% : Urea18-26 WaterEverything Table I table 2