SU1470786A1 - Method of hardening steel articles - Google Patents

Abstract

The invention relates to the field of metallurgy, and more specifically to the heat treatment of railway rolling stock components. The aim of the invention is to increase the resistance to fatigue and durability and reduce energy costs. The method includes heating the local zones above the temperature A _c ** 3 by surfacing layers of low carbon steel and cooling the blown surface to be cooled to a temperature of the adjacent zone below 700 K with a temperature gradient of 50-250 ° C / cm. The use of the invention allows to increase the durability of parts and reduce the energy intensity of the heat treatment process. 2 hp ff, 2 tab.

Description

one

The invention relates to metallurgy, and more specifically to the heat treatment of cast bearing parts of railway rolling stock.

The aim of the invention is to increase the resistance to fatigue and long-term life and reduce energy costs.

Hardening of cast beams was made of 20L steel I-beam with a section with a predominant wall thickness of 10 mm, a height of 80 mm, a flange width of 60 mm, and a span between the supports of 500 mm. The surfacing was performed with the Sv-08A wire in the lower corners of the T-joint mating in the longitudinal direction of the beam for the entire span. The weld area in the cross section of the I-beam was 4.,. 6% of the total area of the section.

During surfacing, the temperature of the hardened surface (z-iapysHou of the surface of the shelf) was 900 Cj, which was the result of heating the metal during surfacing at the corners of the brand.

Cooling; the cd of the zone heated during the surfacing from the side of the outer surface of the shelf was made by blowing an air-water mixture with different moisture content and different flow rates up to 700 K (427 ° C) weld area of the I-beam. The temperature gradient in the direction normal to the surface being hardened was (50 ... 250) degrees / cm.

The modes of surfacing and cooling of the pack, - of the hand zone, are given in Table. one,.

The results of fatigue tests are given in table. 2

zhzga

xfffiEa

V: a53

Uh

For comparison, such beams strengthened by a known method (Example 16) were tested: heating up to 930 ° C in a furnace, aging for 3 hours and differential, j, diffusion cooling by an air / water mixture at the optimum for the proposed method, but up to temperature interface 550 ° С.10

Fatigue tests of I-beams were carried out on a hydropulse-to-switch machine TsDM-YuPu in the mode of a constant asymmetry factor O, .29 on the basis of 10 cycles. The limit of endurance was determined by the test results of 6 beams of each variant. Hardening (examples 2, 3, 4, 7, 8, 11, 12, 14, and 15) increases the endurance limit by an average of 37.2%. This 20 is explained by a higher level of residual compressive stresses arising in the lower flange of the I-beam under differential cooling to 700 K and lower, in contrast to the 25 known method in which forced cooling ends above a temperature of 820 K, the lowest. the limit of excellence was obtained in examples 1, 6, and 10, with 30 lower claimed limits, the temperature gradient DT. To achieve the required minimum temperature gradient of 50 degrees / cm, it is necessary that the specific heat transfer rate is not lower than 5.0 kW / cm, the moisture content of the water / air mixture is at least 0.5% by volume, and the mixture consumption is not less than 0.10. Measuring the levels of residual stresses in the hardened zone using comparable methods, performed by the slotting method, showed that with the optimal hardening mode of the proposed method, the average value of j exact stresses is 230 MPa, while by the known method 156 MPa . When the temperature gradient is more than 250 degrees / cm, the residual compressive stress is over 300 MPa, which exceeds the yield strength of low-alloyed low-alloy steel and causes distortion of the reinforced zone of the beams.

When hardening, the duration of the process is reduced by more than

5 times with less energy: for the optimal hardening mode by a known method, the energy capacity is 91.5 MJ, and for the optimal variant 3 according to the proposed method; 56.9 MJ. According to the test results of the three parts, the average durability to failure amounted to 8.4-I D cycles, while similar parts strengthened by a known method were held to break only 3 j 2 10® cycles.

The application of the proposed method in industrial production and in the repair of load-bearing parts of freight car trucks will increase the load-carrying capacity of cars and the safety of two-way trains without an increase in metal consumption.

Claims (3)

1. The method of hardening steel parts, mainly cast profile ones, including heating the hardened surface to a temperature above oi, y conversion, and differential cooling, which is so that, in order to increase resistance to fatigue and durability and reduce energy costs, local deposition of layers of low carbon steel in the corners of the joint adjacent to the reinforced surface of the walls, providing heating of the strengthened surface to the quenching temperature, and cooling is carried out by blowing n by this surface until the water-air mixture in the build-up temperature region lower than 700 K at a temperature gradient in a direction normal reinforcement by this surface (50 ... 250). hail / cm 2. A method according to claim 1, characterized in that the local heating is carried out by arc welding at a specific heat input (5 ... 20) kW / cm. 3. Method according to paragraphs. 1 and 2, characterized in that the heat sink from the hardened surface is produced by an air / air mixture at a content of (O, 5 ... 3.5)% by volume of water and consumption (0.1 ... 054). Table 1 Table Tested with warping.