SU1611982A1 - Method of carburizing steel articles - Google Patents

Abstract

The invention relates to metallurgy, in particular to chemical heat treatment using laser radiation, namely cementation, and can be used in mechanical engineering for surface hardening of machine parts made primarily of chrome-nickel steels. The purpose of the invention is to increase the wear resistance of the processed products when working in dry friction conditions by reducing the coefficient of dry friction. The method includes heating the processed products to the carburizing temperature by high-frequency currents, injecting graphite powder with a jet of inert gas into the zone of interaction of continuous laser radiation with the surface being treated, isothermally holding the processed products at 650-1100 ° C for 0.005-2 hours, and then quenching with a continuous laser beam without melting the surface. The use of this method provides an increase in the operational durability of pairs of dry friction by 1.5 times compared with the treatment by a known method due to a decrease in the coefficient of dry friction of steam by 1.1-1.5 times. 3 tab.

Description

;, the acquisition relates to metallurgy, i.i., in particular to chemical-thermal Koi: processing using laser radiation, namely cementation, 1 u.t can be used in machine-cipcfeh-sh for surface simpler- i ;; m .Etaly machines made pre- I1: precisely their thermally chromium-nickel steels.

The aim of the invention is to increase the wear resistance of the processed products when working under conditions of dry friction by reducing the coefficient of dry friction.

The method is carried out as follows.

The sample or product to be processed is placed in the inlet; the hector and high frequency currents (HDTV) are heated to an isothermal holding temperature; an injection powder and a laser beam are applied from the open end of the inductor. This part and the inductor, and the same with the moving table, sos; 1; ayut mixed; eB1C relative to the laser beam. After completion of the cementation process, the npii 650-1100 ° C isothermal aging is carried out in

00

to

0.005-2 hours, then the inductor is turned off and removed from the moving table, the workpiece is cooled in air, then, when the equipment reaches room temperature, it is quenched with a laser without melting the surface, while the laser beam repeats the trajectory that occurred during the laser cementation For laser jg effects using a JTT1-2 CO laser, the moving table has the ability to simultaneously move along two axes and rotate around the third axis. At the end of quenching, as in the 15 known method, cold treatment is performed by immersing the hardened product in liquid nitrogen for 30 minutes and low tempering at t60–200 ° C in low-temperature furnaces (drying cabinets 20). Saturation of the molten surface layer with carbon from the injected graphite powder allows the formation of a hardened layer up to 3 mm deep and a carbon content of 25 to 4.5%. Before heating the core, the ablation of the product before laser cementation allows to reach the depth of the hardened layer .4.5 mm with a carbon content of 5.25%. At the same time, the power of the laser beam is reduced during the cementation process to (0.03-0.8) 10 W.m. The isothermal overhead of the processed product after laser cementation at 650–11100 ° C (cemented layer) ensures the formation of the structure of ferrite and lamellar cementite in the surface layer, contributes to the decomposition of the austeddite. Subsequent quenching with a laser without melting the surface results in a solid (11–12 GPa) surface layer of up to 4.5 mm in depth, consisting of martensite and carbides. 45

The isothermal holding of the processed product after laser cementation at 650 (cemented layer) causes graphitization to occur in the carbon-saturated layer when the content of the latter is 2.5%, the isothermal holding at 65.0 (cemented layer) is 1100 ° C and the carbon content is in the cemented layer less than 2.5% is impractical. Formation as a result of isothermal exposure at 650 (cemented layer) - and subsequent quenching

50

55

5 d 5

0

five

With a laser without melting the surface of a solid (10–13 GPa) martensitic – cementitious structure of the surface layer with a regulated amount of graphite, the coefficient of dry friction decreases when metal surfaces interact, which favorably affects the wear resistance of the cemented layer. From the data given in table. 1 it follows that the isothermal holding temperature, the less must be its duration, thereby accelerating the entire process.

P r and m r. Samples of size 45x15 mm, of steel 14KhNZMA are placed in a heating induction device of a cylindrical shape with an open upper end and an internal diameter of 50 mm and a height of 30 mm.

When a sample or part is placed in an inductor, a non-enamel chromel-alumel thermocouple is fixed on its surface so that the junction of the thermocouple touches the surface of the workpiece about Laser processing during heating to 1100 ° C is carried out immediately after the surface reaches the specified temperature. In all other cases, heating of steel to lower temperatures (825 ° C and below) uses a three-minute peak. before the start of laser cementation. Heating is carried out by induction, cooling after disconnecting and removing the inductor in air. Thus, the total residence time of the product being processed does not exceed 3.3 minutes, and full (through) heating of products to a depth of over 10 mm does not occur, i.e. core properties do not undergo significant deterioration. At a distance of 4 mm from the upper surface of the specimen, a nozzle for injection of graphite powder is positioned at an angle to the surface. Laser cementation is carried out when the surface layer is melted by a LT1-2 continuous C02 laser at a power density of (O, 3-1, V) -10 W X m, injected into the melt zone of the GL-1 graphite powder in a jet sample relative to a laser beam 7–12, powder consumption 0.8–1.1 g-min, carrier gas consumption

--3 ..

-one

(14-18.) X10 m min. The cementation time of the sample surface of 535 mm is 8.3-15 seconds. The isothermal temperature (and low temp.) Temperature is determined with an accuracy of + 20 ° C. Laser quenching is carried out at a power density of (0.67-0.93) 10® laser beam speeds of 15 mm / s. After soaking in liquid nitrogen for 30 minutes (after stopping the nitrogen boiling), tempering at 160-180 ° C is carried out electric furnaces for 2 hours. The characteristics of the hardened layers, obtained by chemical-thermal treatment according to the proposed modes, are presented in Table. one.

From the data table. 1 it follows that the discrepancy between the parameters of the isothermal holding (temperature and time) does not lead to obtaining a satisfactory quality of the demental layer. Thus, the absence of isothermal aging after cementadium or a decrease in temperature does not lead to a complete decomposition of residual austenite in the cemented layer. Increasing the duration of isothermal exposure for more than 2 hours does not lead to new properties of the hardened layer, but only causes additional overhead costs. The use of isothermal holding temperatures above 1100 ° C leads to decarburization at any, even small, isothermal holding periods (Table 1. Clause 6).

As a result of passing the full heat and chemical treatment of the proposed method, a surface hardened layer with a depth of 1.0-4.25 mm and a carbon content of 0.70-5.25% and a hardness of 59-63 HRC was obtained. When processed by a known method, a shallower carburization depth is achieved at a lower c content. him carbon

(tab. 1).

In order to obtain more complete information on the change in the coefficient of dry friction after carrying out chemical-thermal treatment using the proposed method, tests were carried out on an SMT-4 friction machine at a speed of 5

e p10

1982

The relative movement of the rubbing surfaces is 0.840.1 m-s with a specific load of 150 ± 15 MPa according to the disk (block) scheme.

A pair of friction is made of steel 14KhNZMA in various variants of chemical heat treatment (HTO).

A: WHO according to a known method; B: Laser cementation according to the proposed method (Table 2).

The cleanliness of the surface of friction pairs prior to the start of testing corresponds to Class B

The results of measurements of the coefficient of dry friction are given in table 3. According to the proposed method, the details of the rotary-loading mechanism of the blast furnace were processed. The operating conditions exclude lubrication of the mechanism (dustiness and operating temperatures of up to 300 ° C). The main reason for the breakdown of the mechanism is the jamming of the rubbing parts and bending of the structural elements. In the course of accelerated tests, they flew, processed by the proposed method, showed operational stability by 1.5 times. More than those processed by a known method due to a decrease in the coefficient of dry friction of the pair by 1.1-1.5 times.

15

20

25

thirty

f

p m u. and a

gaining

The method of cementation of steel products made from chromium-nickel s / hoists, including heating the surface of the workpiece to the temperature of cementation, specifically csment-dich., Isothermal aging and hardening, about tl and h and with that, 4Td, with an increase chain wear resistance of processed products by reducing the coefficient of dry friction, heating to saturation temperature is carried out by high frequency currents, saturation is carried out by injecting graphite powder with a stream of inert gas into the interaction zone of a continuous laser radiation was the surface izstermi- ieskuyu exposure is carried out at 650 0.005-2.0 hours and subsequent zakalku-- continuous laser beam without fusing surface.

55

Table 1

with radiation power (0.7-1.8) -10 watts. x m, beam moving speed 7-12 MMJt, graphite powder consumption 0.8-1.1 g. min

Heating up to 650 ° C5 shutter speed 3 min, laser cementation according to claim 1 with a power density (0.3-0.8) "10® W X

km., isothermal exposure (t) laser hardening, cold working, low tempering;

t 0,054 h

t 1 h

t 2 h

t 10 h

. Same as in claim 2, but isothermally aged at 600 ° C:

t 0.05 h t 1 h t 2 h

Heating up to 825 ° C, holding for 3 minutes, laser cementation according to claim 1, at a laser radiation power density (0.15-0.50) x

k10 W m isothermal exposure (t) laser hardening, cold treatment, low tempering:

t 0.05 h

t 0.5 h t 1 h

t 2 h

Heating up to 1100 ° C, exposure 3 min, laser cementation according to claim 1 with a laser beam power density (0.03-0.10) -1Q W M- isothermal shutter speed (t), laser hardening, cold working.

0.5-3.0

1.0-3.7 1.0-3.7 1.0-3.9 1.0-3.8

1.0-3.5 1.0-3.5 1.0-3.5

1.3-4.1 1.3-4.2 1.3-4.4 1.3-4.4

0.76-4.50 Martensite +

carbide + residual aus-. tenit (up to 15%)

Martensite + carbides

0.72-4.10 0.75-4.40 0.72-5.20 .0.7 2-4 ,. 5 o

0.73-4.10 0.73-4.10 0.73-4.10

MarteNsit -t- carbides + residual austenite (up to 15%)

Martensite + carbides decarburization

0,80-5,00 0,80-4,30 0,80-0,25 0,65-0,20

low holidays: t 0,005 h

1.7-4.5

t 1 t 1

1.7-4.5 2.9

t 2 h

Same as in claim 5, but isothermal and vydorzkka at 1150 C

t 0,005 h

1.7-4.5

1.8-4.0

Processing according to the well-known scheme; cementation gas, at 930-950 C for 12 h, isothermal aging at 580-600 ° C 4 -h, quenching from furnace heating from 780 ° C 30 min to oil, cold working, low tempering

Continued table. one

61-63

0,80-5,25 Cementite martexit +

42

0.09-0.37 0.21 (with the initial 2.45)

free graphite

Sharp decarburization

23-27

38-46

0.33 (with a decarbon-starting living 2.45)

39-61

Martensite + 0.8-0.9 carbides

Claims (1)

The method of cementing steel products mainly from nickel-chromium steels, including heating the surface of the workpiece to a cementation temperature, cementation itself, isothermal aging and hardening, which is different in order to increase the wear resistance of the processed products by reducing. dry friction coefficient, heating to 45 saturation temperature is carried out by high-frequency currents, saturation is carried out by injection of graphite powder with an inert gas stream into the zone of interaction of continuous laser radiation with the surface, isothermal exposure is carried out at 6501100 ° C for 0.005-2.0 hours, and the subsequent quenching - continuous laser beam without surface fusion.