RU2585151C1 - Method of hardening steel surface - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, specifically to chemical-thermal treatment, and can be used in machine building to ensure increase of operational characteristics of machine parts. Method of surface hardening of steel item includes application of boron-containing coating and subsequent thermal treatment. Boron-containing coating applied on surface of steel article is a homogenised mixture consisting of phenol-formaldehyde resin with coke number in hardened condition of not less than 52 % (A), boric anhydride (B) and iron carbonyl (C) in ratio A:B:C from 90:8:2 to 50:40:10, followed by two-step heat treatment. First step involves heating to 200-350 °C for 2-8 minutes using an infrared lamp, and second step involves heating to ensure temperature of coating of 850-1,000 °C due to action of gas-flame burner for 10-30 minutes.

EFFECT: higher efficiency of penetration of boron-containing components, reduced temperature and time of saturation of steel surface and simple process.

1 cl, 1 tbl, 1 ex

Description

The invention relates to metallurgy, namely to chemical-thermal treatment, and can find application in mechanical engineering, providing an increase in the operational characteristics of machine parts.

A known method of hardening a steel surface by diffusion boronation of steel parts, including applying a boron-containing grease to the steel surface and subsequent diffusion exposure at saturation temperature, carried out in the melt electroslag bath at 1500 ° C (patent RU No. 2016138 - prototype).

The disadvantage of the prototype is the high holding temperature (1500 ° C), while, starting from a temperature of 1000 ° C, an inevitable increase in the grain of steel occurs, leading to a decrease in its mechanical properties, as described in many works in metallurgy.

In addition, boron is slightly soluble in iron and steel (0.1 ÷ 0.15%), and its melting point is 2000 ÷ 2500 ° C. Therefore, the use of conventional boron mixtures as coatings does not allow efficient boron saturation of steel surfaces, given the large particle sizes.

In addition, the known method requires the use of large equipment and a long boron process using electroslag baths and molten fluxes at 1500 ° C.

The objective of the present invention is to increase the penetration efficiency of boron-containing components - reducing the temperature and time of saturation of the steel surface and simplifying the process technology by using a coating containing components in the form of a homogenized mixture to molecular sizes.

The task is achieved in that as a boron-containing coating, a homogenized mixture is applied to the surface of the steel product, consisting of a phenol-formaldehyde resin having a coke number in the cured state of at least 52% (A), boric anhydride (B) and iron carbonyl (C) in the ratio A: B: C from 90: 8: 2 to 50:40:10, followed by a two-stage heat treatment - at the first stage, heating to 200 ÷ 350 ° C for 2 ÷ 8 minutes with electric heaters, and then, at the second stage, by exposure gas flame burner for 10 ÷ 30 minutes, about espechivaya wash temperature of 850 ÷ 1000 ° C.

Example 1

Cooking plaster

200 parts by weight are charged into a stirred reactor. ethyl cellosolve, after which add 48 wt.h. boric anhydride and stirred until complete dissolution of the latter. Next, 65 parts by weight are added to the boric anhydride solution. phenol-formaldehyde resin brand "Bakelite liquid" (GOST 4559-71) in terms of dry product and 6 wt.h. liquid carbonyl iron.

The mixture is stirred for 10 minutes at + 20 ° C, after which the solvent is distilled off in an amount of 190 parts by weight and is caught. The remaining 10 parts by weight ethyl cellosolve provide a pasty state of the obtained coating, in which all components are homogenized to a molecular state. The resulting composition is packaged and stored in storage conditions for at least 1 month.

The implementation of the boronation process

The finished coating is applied with a 1 mm layer on the steel surface, after which, in the first stage, they are heated by the action of an infrared lamp to 300 ° C for 5 minutes, as a result of which the phenol-formaldehyde resin cures and partially cokes. After that, for the steel product coated with coating, immediately (or after a sufficiently long break), the second stage is carried out, subjecting it to a flame and providing a surface temperature of 900 ° C for 15 minutes, while iron carbonyl decomposes, forming extremely active particles of iron of atomic size, which instantly react with boron atoms resulting from the reduction reaction of boric anhydride with decomposing coke, forming iron borides, which easily penetrate the steel surface, saturating I have this surface and increasing its hardness to HB350, which exceeds the hardness of the abrasive.

Examples 2 ÷ 4 carry out analogously to example 1, changing the parameters in accordance with table 1.

In all examples, surface hardness reaches the level of HB 350.

Claims (1)

A method of hardening the surface of a steel product, including applying a boron-containing coating and subsequent heat treatment, characterized in that as a boron-containing coating, a homogenized mixture consisting of phenol-formaldehyde resin having a coke number in the cured state of at least 52% (A) is borne anhydride (B) and iron carbonyl (C) in a ratio of A: B: C from 90: 8: 2 to 50:40:10, followed by a two-stage heat treatment, and in the first stage they are heated to 200-350 ° C for 2 -8 m chickpeas using infrared lamps, and then the second step is carried out with a heating temperature providing wash 850-1000 ° C by the action of the burner flame for 10-30 minutes.