RU2534670C1 - Hard alloy strengthening method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: heat treatment method of a hard-alloy item involves sintering of a hard-alloy item and cooling. Sintering is performed at the temperature of 1650°C; then, vacuum tempering is performed with heating up to the temperature of 1050-1250°C and with exposure of 1 hour, and cooling is performed together with the furnace during 4 hours. Hardness, strength and resistance of items are increased.

EFFECT: simpler technical process of heat treatment of hard alloys.

1 dwg, 4 tbl

Description

The invention relates to mechanical engineering, mainly to methods of thermal hardening of powder metallurgy products, in particular to products from hard alloys used for cold and hot machining of metals and alloys, for example, by cutting.

A known method of heat treatment of products from carbide-containing hard alloys using quenching [M. Loshak Strength and durability of hard alloys. - Kiev: Naukova Dumka, 1984. - 218 p.], At which the quenching temperature is always chosen below the eutectic temperature of the components of the hard alloy: tungsten monocarbide and cementing cobalt binder. The disadvantages of this method are the low degree of hardening of the cutting plates of hard alloys and their low resistance to impact loads.

Closest to the claimed method is a method of heat treatment of products from carbide-containing hard alloys obtained by stationary sintering in the presence of a liquid phase, in which the processing temperature is selected in the temperature range 800-1400 ° C [Wu Yinfang. A survey of study on heat-treatment of cemented carbide. - Hard metals and hard materials. - 1993. - V.1, 1. - P.20-23 (prototype)], and the temperature range greater than 1280 ° C lies above the eutectic temperature (1280 ° C) of the components of the hard alloy. Thus, during heat treatment in the temperature range 1280-1400 ° C, the recrystallization of the hard alloy occurs. The disadvantages of this method are:

- a relatively small degree of hardening of carbide inserts:

- low resistance of hard alloy cutting inserts to impact loads.

The claimed invention is aimed at simplifying the technical process of heat treatment: lowering the temperature of heat treatment, the absence of the use of quenching baths, increasing the resistance.

The technical result of the invention is to simplify the technical process of heat treatment of hard alloys, increase resistance.

The technical problem is solved in that in the method of heat treatment of hard alloys, including sintering of hard alloys at a temperature of 1650 ° C, cooling, after sintering, leave in a vacuum furnace at a temperature of 600 ° C in an inert gas medium, incubated for 4 to 24 hours followed by cooling with the oven for 2.5 hours.

To explain the method, the drawing shows the appearance of carbide racks VK8 (a) and T14K8 (b), an increase of 1: 1.

The method is as follows:

Hard alloys were sintered at a temperature of 1650 ° C, cooled after sintering, tempering was carried out in a SGV2.3 / 15EM1 vacuum furnace at a temperature of 600 ° C (vacuum 5 × 10 ^-5 mm Hg), in an inert gas medium, the exposure time from 4 to 24 hours.

The essence of tempering is that a rarefied inert atmosphere is created in an airtight container. For this purpose, nitrogen is used. Inside the container, parts are placed that are connected to the negative pole of the constant voltage source - the cathode. The anode is the wall of the container. Between the cathode and the anode, a high voltage (500-1000 V) is turned on. Under these conditions, gas ionization occurs. The resulting positively charged nitrogen ions rush to the negative pole - the cathode. The electrical resistance of the gaseous medium near the cathode sharply increases, as a result of which almost all the voltage supplied between the anode and cathode falls on the resistance near the cathode, at a distance of several millimeters from it. This creates a very high electric field near the cathode.

Nitrogen ions, entering this high-tension zone, accelerate to high speeds and, colliding with the part (cathode), penetrate into its surface. In this case, the high kinetic energy, which had nitrogen ions, goes into heat. As a result, the part in a short time, about 15-30 minutes, heats up to a temperature of 600 ° C, when ions collide with the surface of the part, iron ions are knocked out of its surface. Due to this, the surface is cleaned of oxide films.

After tempering in a vacuum furnace, the cooling of hard alloys was carried out together with the furnace for 2.5 hours.

Before and after tempering in an inert medium, hardness (table 1, 2) and bending strength (table 3) were determined.

Table 1 Carbide grade Vacation time, h Hardness, hv Medium Hardness, HV one 2 3 Average 600 ° C - inert medium VK8 four 1354 1354 1402 1370 (1331) 1330 1354 1332 1332 1339 1332 1332 1187 1307 VK8 8 1427 1427 1427 1427 (1359) 1360 1267 1267 1268 1267 1354 1402 1378 1378 VK8 16 1427 1378 1427 1410 (1409) 1410 1415 1415 1415 1415 1402 1402 1408 1404 VK8 24 1354 1332 1533 1400 (1403) 1400 1378 1332 1427 1379 1378 1402 1533 1437 T14K8 four 1427 1402 1402 1410 (1449) 1450 1478 1452 1478 1469 1478 1478 1452 1469 T14K8 8 1452 1402 1427 1427 (1427) 1430 1402 1427 1452 1427 1402 1452 1427 1355 T14K8 16 1428 1428 1533 1479 (1469) 1470 1427 1402 1505 1444 1402 1452 1452 1435 T14K8 24 1427 1452 1402 1427 (1458) 1460 1452 1452 1533 1479 1452 1452 1505 1469 T14K8 source 1452 1427 1378 1419 1420 VK8 source 1302 1332 1282 1305 1310 1312 1318 1305 1327 1302 1302 1278 1294

Talitsa 2 t h T14K8 VK8 four Hardness and strength increased by 10%. Hardness and strength increased by 10%. 8 Hardness increased by 20%, strength - by 30%. Hardness and strength increased by 20%. 16 Hardness increased by 40%, strength - by 90%. Hardness and strength increased by 40%. 24 Hardness increased by 30%, strength - by 50%. Hardness and strength increased by 30%. Table 3 Carbide grade Vacation time, h Strength, N / mm ² The average strength, N / mm ² one 2 3 Average 600 ° С - inert medium VK8 four 2154 2154 2202 2170 2130 2154 2132 2132 2139 2107 2107 2127 2107 VK8 8 2127 2127 2127 2127 2160 2167 2167 2168 2167 2154 2102 2178 2178 VK8 16 2427 2378 2427 2410 2406 2378 2378 2378 2378 2402 2402 2402 2402 VK8 24 2354 2332 2533 2406 2400 2378 2332 2427 2379 2378 2402 2533 2437 T14K8 four 1727 1702 1702 1715 1720 1778 1752 1778 1769 1678 1678 1652 1669 T14K8 8 2145 2102 2080 2100 2140 2140 2200 2145 2180 2210 2252 2147 2200 T14K8 16 2701 2532 2602 2661 2880 2942 2903 2933 2938 3050 3060 3010 3040 T14K8 24 2378 2378 2363 2370 2360 2513 2402 2505 2476 2472 2452 2152 2229 T14K8 source 1502 1498 1502 1501 1500 VK8 source 1800 1869 1800 1823 1830

The results of studies at this stage showed that vacuum tempering is effectively carried out for the T14K8 alloy. With an increase in exposure time from 4 to 24 hours, hardness increases from 10% to 40%, strength - from 10% to 90%. The best tempering regime with a exposure time of 16 hours: hardness increased by 40%, strength by 90%.

For VK8 alloy, tempering in an inert atmosphere leads to an increase in hardness and strength by 10–40%.

The effect of annealing temperature on surface wear (table 4) of VK8 and T14K8 hard alloys was studied in the following series of experiments. Cutting was carried out by end turning from the center to the periphery n = 400, t = 1 hour, s = 0.1 mm / rev. The coefficient of resistance (defined as the ratio of wear resistance before and after tempering in an inert atmosphere) increased by 3-6 times.

We analyzed the results of experimental work to improve the physicomechanical properties of hard alloys of VK and TK groups and compared with the prototype (table 4). Heat treatment was carried out with heating the samples in an inert medium at a temperature of 600 ° C, with a holding time of 4 to 24 hours. Hardness increased from 10 to 40%, strength - from 10% to 90%, the coefficient of resistance increased by 3-6 times.

Table 4 Material grade Type of processing Tensile strength, MPa Hardness, hv Coefficient of resistance, K VK8 Source 1830 1310 3 4 hours vacation 2130 1330 four 8 hours holiday 2160 1360 5 16 hours vacation 2406 1410 6 24 hours vacation 2400 1400 four T14K8 Source 1500 1420 3 4 hours vacation 1720 1450 3,5 8 hours holiday 2140 1430 four 16 hours vacation 2880 1470 5 24 hours vacation 2360 1460 4,5

Claims (1)

A method of heat treatment of a carbide product, including sintering a carbide product and cooling, characterized in that the sintering is carried out at a temperature of 1650 ° C, then vacuum tempering is carried out with heating to a temperature of 1050 ° C-1250 ° C and holding for 1 hour, and cooling is carried out together with oven for 4 hours.

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