SU1548218A1 - Method of surface thermal strengthening of steel articles - Google Patents

Abstract

The invention relates to heat treatment of steel with concentrated energy sources and can be used in mechanical engineering and ferrous metallurgy in the manufacture of rolls. The purpose of the invention is to improve the surface quality by increasing the depth of the hardened layer and the uniform distribution of hardness over the depth of the hardened layer. The method includes heating by an electron beam and moving the product relative to the beam. Moreover, the heating is carried out with an electron beam with a power density of 0.1-10 MW / cm ² and an electron energy of 0.3-4 MeV, and the beam diameter and the linear velocity of the surface of the product are chosen from the condition of adiabaticity of heating the surface layer from the ratio D / V = (0.01-0.3) Τ, where D is the beam diameter on the surface of the product

V is the linear velocity of the surface under the beam

Τ is the time of thermal diffusivity to the depth of the electron path. 1 ill., 1 tab.

Description

The invention relates to heat treatment of steel by concentrated (energy sources) and can be used in mechanical engineering and ferrous metallurgy in the manufacture of rolls.

The purpose of the invention is to improve the surface quality by increasing the depth of the hardened layer and the uniform distribution of hardness over the depth of the hardened layer.

When the beam power density is less than 0.1 MW / cm2, the heating time of the surface layer becomes comparable with the thermal diffusivity time, i.e. the adiabatic condition of heating is violated, as a result of which there is a sharp deterioration in the hardening. When the power density is higher than 10 MW / cm2, the surface is disturbed due to its melting, and an increase in the speed of movement of the product will require an extremely complicated implementation device.

When the electron energy is less than 0.3 MeV, the structural transformations necessary for strengthening do not have time to occur in the irradiated material. When the energy of electrons is more than 4 MeV, the thickness of the heated layer exceeds 2 mm, and the cooling rate of the layer due to heat transfer into the interior of the material is J

315

It becomes 200 ° C / s, which is the limit for quenching on marten sieves, i.e. there is a decrease in strength. If the heating time determined by the ratio of the beam diameter and the speed of movement of the surface becomes greater than 0.3, self-hardening mechanism is also violated. When the heating times are less than 0.0lЈ, the structural transformations in the material do not have time to complete, as a result of which the strength decreases.

The beam diameter and the linear velocity of the surface movement of the product are chosen from the condition of adiabaticity of heating the surface layer, for example, from the ratio

d (0.01-0.3) Ј-v,

where d is the beam diameter on the surface

products;

v is the linear velocity of the surface under the beam, m / s; Ј - time of thermal diffusivity to the depth of the electron path

The drawing shows a graph of the change in the microhardness of the material in depth after processing by the proposed method.

Strengthen the sample from non-hardened steel; The electron energy is 0.8 MeV, the beam current is 7.8 mA, the beam diameter is 1.2 mm, and the surface displacement rate is 1.7 m / s. The curve has a characteristic form: the microhardness is almost constant up to the depth of the electron path, and its level is much (more than 4 times) higher than the initial level of microhardness.

The proposed heat treatment method is carried out as follows.

Heat treatment of rolling rolls of steel are electron beam with an energy of 1.5 MeV, a current of 8 mA and a diameter of 2 mm on the surface of the roll. This provides a power density of 0.4 MW / cm2. An electron accelerator with a beam power of up to 60 kW and a device for the concentrated release of beams into the atmosphere is used. Roll with a diameter of 55 mm rotate with an angular speed of 800 rpm

and simultaneously move along the axis at a speed of 13 mm / s. In this mode of heat treatment, adiabetic heating of the surface is ensured84.

metal layer with a depth of 0.7 mm (this is the electron mileage at an energy of 1.5 MeV), since the heating time of each point of the surface layer is 1 ms, and the characteristic time of thermal diffusivity is ms.

To substantiate the specific values of the mode of operation of the method using the results of heat treatment of the side surfaces of cylindrical specimens made of steel in the delivery state. Samples with a diameter of 65 mm are fixed in cones-centers and are driven in rotation by an electric drive with an adjustable speed from 90 to 5000 rpm. The other electric drive produces a progressive movement of the sample with a speed that ensures uniform processing of the cylindrical surface. The electron beam is generated by an accelerator with the release into the atmosphere and adjustable beam power up to 60 kW.

The electron beam escapes from the accelerator discharge device, the divergence angle depends on the electron energy. By changing the distance from the outlet device to the sample, a beam diameter on the sample surface is d 1 mm. The beam current is determined by calculation from the condition that the temperature of each point of the treated surface reaches 1350 ° C.

The physico-technical characteristics and heat treatment modes, as well as microhardness results are shown in the table, with modes 1,2,7 and 8 obtained by calculation using extrapolation of experimental results of modes 3-6 (modes in examples 1 and 8 have value).

These tables show that the positive effect is achieved exactly in the indicated intervals of values of power density, electrode energy, beam diameter and linear velocity of the surface of the product and is absent.

Using the method of surface heat treatment of products provides in comparison with the known increase in hardness by 1.5-2 times, obtaining uniform hardness over the depth of the hardened layer, as well as increasing the wear resistance of the surface, by 3-4 times.

5154821

Claims (1)

Invention Formula The method of surface thermal hardening of steel products, including heating for quenching by an electron beam with given power density, electron energy and diameter, and moving the product relative to the beam, characterized in that, in order to improve the surface quality by increasing the depth of the hardened layer and the uniformity 0 eight" the hardness distribution over the depth of the hardened layer, heating is carried out with a beam with a power density of 0.1-10 MW / cm2, an electron energy of 0.3-4.0 MeV and a beam diameter d it (0,01-0,3) v, where v - the speed of movement of the product relative to the beam, m / s; # - time of thermal diffusivity to the depth of the electron path, s. Mode one Physicotechnical specifications process Electron energy The parameters of the hardening process for example LIZTLrLTLCEL Ii MeV0.2 0.3 0.8 0.8 1.5 2.4 4.0 2 Beam current, mA 50 50 7.8 4.2 5 6 3.8 3 Movement speed v, cm / s 1200 1200 170 100 100 100 10 4D / v ratio, ms 0.08 0.08 1 1 1 15 5 5 Depth of run electrons cm 0.005 0.01 0.04 0.065 0.085 0.15 0.22 0.32 6V time of thermal diffusivity V, ms 0.05 0.2 10 18 22 80 245 560 7 Ratio (d / v) / 1.6 0.3 0.15 0.05 0.0450.0120.025 0.009 8 Density of power, MW / cm 2 0.08 0.1 0.34 0.5 0.75 1.4 10 13.8 9 Depth strengthened 0, 03 0.2 0.4 0.5 1.0 1.0 1.8 Occurs 5 4,2 ten foot layer, mm Not ten eleven The averaged microhardness, kgf / mm2 250 500 1200 1100 1000 950 500 Relation to the initial microhardness - hardening coefficient 1 2JO 4.8 4.5 3.8 Note. With a beam diameter on the sample surface of 0.45 mm The parameters of the hardening process for example 5 4,2 ten surface melting 3.8 then uoq yooo 800 600 hgfm | liQO 0.51.0 mi Depth of hardened layer