SU1696504A1 - Method of laser-arc treatment of low-carbon steel structures - Google Patents

Abstract

The invention relates to laser-arc processing and can be used in metallurgy and mechanical engineering for hardening steels. The purpose of the invention is to increase the strength properties. When processing using a laser beam and an electric arc. They combine a spot of heating the laser beam and an electric arc. A carbon-containing gas is supplied to the coaxial laser beam, and nitrogen is fed through the nozzle of the arc torch. The mixture has the following composition, vol.%: Nitrogen 30-40; carbon-containing gas else. The method allows refusing coatings to increase the absorption of laser radiation. 1 tab.

Description

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The invention relates to laser-arc processing in metallurgy and mechanical engineering and can be used to strengthen and increase the energy intensity of structures.

The purpose of the invention is to increase the strength properties and energy intensity of the structure.

The essence of the method is as follows.

The spots for heating the laser beam and the electric arc are combined, thus creating conditions for deep penetration and active mixing of the liquid metal in the treatment area, Nitrogen is supplied through the nozzle of the arc burner, and carbon-containing gas is coaxial to the laser beam. In the arc ionization of nitrogen atoms and decomposition of carbon-containing gas occurs with the release of free carbon. The atoms and ions of nitrogen, as well as carbon, diffuse into the liquid metal and, due to its active mixing, are evenly distributed throughout the depth of the reflow zone. Heating of the heat treatment zone of an electric arc leads to an increase in the absorption of laser radiation. In turn, the formation of a plasma torch when exposed to a metal laser beam makes it possible to stabilize the arc burning. As a result of the mutual positive effect, the efficiency of laser-arc processing is higher than that of laser and arc processing, which, with equal power, leads to an increase in both the width and depth of the laser-arc processing zone. After crystallization, the zone melted

about

Os SL O

-N

A path is formed, saturated with carbon and nitrogen, and consequently having increased hardness and strength.

The magnitude of the hardness and strength of the laser-arc zone is determined by the resulting microstructure. When mild steel is treated in an atmosphere of carbon-containing gases, it is carburized; however, when the liquid metal is saturated with carbon with more than 0.6%, after cooling, the structure consists not only of martensite (a solid component), but also of residual austenite (soft phase). In order to obtain maximum hardness, it is necessary to create such a mixture that would not lead to a carbon content of more than 0.6% in the steel.

Nitrogen is chosen as an additive to carbon-containing gas, and as it is introduced into the crystal lattice of iron, it increases the hardness i / t of the strength of the latter. However, the low solubility limit of nitrogen in iron (a few hundredths of a percent, depending on saturation conditions) requires a significant increase in hardness (by a factor of 2–3) of such alloying elements as aluminum, titanium, zirconium, chromium, etc. in order to obtain the steel is already alloyed, not low carbon.

Thus, in the course of the experiments, it was established that in the treatment zone of low carbon steel the optimum carbon content (0.6%) should be melted in an atmosphere consisting of 60-70% of carbon-containing gas. An additional increase in microhardness by 10–20% in the flash zone allows the use of nitrogen as the second component of the gas mixture instead of inert gas. The increase in hardness is due to the formation of nitrogenous martensite, which has a higher hardness than carbonaceous martensite. An increase in the nitrogen content of the mixture over 40% does not lead to an increase in the solubility of nitrogen in low carbon steel, since the limit of saturation of the melt zone with nitrogen is already reached at a content of 20% nitrogen in the mixture, and less than 30% cannot be, as this is with an excess of carbon-containing gases in the mixture of 70%. In addition, a reduction in carbon-containing gas of less than 60% in the atmosphere of the treatment zone leads to a decrease in the carbon content in martensite, which leads to a decrease in hardness and strength of the treatment zones,

The increase in carbon-containing gas more than 70% in the mixture leads to the formation of

in the structure of the treatment zone of residual austenite - a soft component, which reduces the overall hardness of the alloyed zone. Example. To implement the method

use Stz steel with a thickness of 5.0 mm. On both sides of the sheet, a pattern of reinforcement tracks is applied in the form of stacks with a step of 2.0; 2.5; 3.0; 3.5; 4.0 mm. After that, the samples for tensile testing are cut out of the sheet so that the angle between the longitudinal axis of the sample and the reinforcing tracks is 45 °,

Processing is carried out on a Coherent General laser power unit with a power of 1.0 kW, a beam diameter of 1.2 mm, and a beam travel speed on the sample surface of 10 mm / s.

As a source of electric arc using the installation of UAS-301. Arc current

1 50 A, voltage across the arc Od 23 8. In / as the plasma-forming gas, nitrogen and carbon-containing gases are used. Initially, the direct arc is ignited in nitrogen. The minus from the power source is supplied to the electrode. Then the laser beam gate in the laser head is opened and the spot of the heating of the electric arc and the focus of the laser radiation are combined. Next include the slide and put

reinforced track, and the treatment is carried out with the formation of the vapor-gas channel, melted the surface of the product in a mixture of gases consisting of 30 and 70%; 35 and 65%; 40 and 60%, respectively, of nitrogen and acetylene.

Acetylene is fed coaxially to the laser beam, and the composition of the mixture is adjusted by changing the flow rate of acetylene. After applying the track, allow the sheet to cool to its original temperature. Thus, a grid of reinforcing tracks is applied. The prepared samples are tested on a P10 tensile testing machine, the averaged results of tensile tests are given in the table. For each mode

five samples are tested.

The use of the proposed method for laser processing of low carbon steel structures provides the following advantages. In accordance with

the results of tests carried out laser-arc processing of sheets leads to

29% increase in yield strength

OQ2, at 18% temporary resistance

breaking about 1 ie the increase in strength properties while reducing the relative elongation by 11% relative to the known method. The energy intensity of work to destroy machined steel increases by 18%. It is possible to manufacture welded structures from parts that have been processed by the method, use multimode laser radiation, use lower power lasers to process parts of a given thickness, and replace parts of expensive laser energy with cheaper electric arc energy, and also reject coatings to increase laser absorption. radiation.

Claims (1)

Invention Formula The method of laser-arc processing of low carbon steel structures, in which a laser beam in carbon hardening tracks are created on the surface of the workpiece from two sides with a certain pitch and oriented at an angle to the loading axis, characterized in that. in order to increase the strength properties and power consumption of the structure, they additionally affect the treatment area with an electric arc burning in nitrogen medium, at the same time combining the spot of laser heating and electric arc, and heating is carried out in an environment having the following composition, vol.%: Nitrogen Carbon-containing gas 30-40 Else