A method for high-precision control of the surface oxide layer of welding wire

Abstract

The application provides a method for high-precision control of the surface oxide layer of welding wire and relates to the technical field of welding. The method comprises the following steps: cooling the billet in a crystallizer to 250-300 DEG C under a nitrogen environment; performing 2-3 times of cyclic heat treatment, wherein the cyclic heat treatment comprises temperature rising treatment and temperature dropping treatment in sequence, so that the surface of the billet changes from ferrite to austenite, and an austenite layer is obtained; the final temperature of the temperature rising treatment is 900-950 DEG C, and the final temperature of the temperature dropping treatment is 100-150 DEG C; and performing oxidation treatment on the billet comprising the austenite layer in a gas containing oxygen, so that the austenite layer is oxidized into a ferrous oxide dense layer. The method for high-precision control of the surface oxide layer of welding wire provided in the application controls the form and thickness of the oxide layer in the welding wire preparation process, so that the oxide layer can be accurately and completely removed, and high-quality welding wire is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a method for high-precision control of the surface oxide layer of welding wire. BACKGROUND

[0002] Welding wire is a metal wire welding material used as filler metal or as both filler metal and current-carrying electrode. In gas welding and tungsten inert gas welding, the welding wire is used as filler metal; in submerged-arc welding, electroslag welding and other gas tungsten arc welding, the welding wire is both filler metal and current-carrying electrode.

[0003] In the related art, the main component of the welding wire is low-carbon steel, and the main component of the low-carbon steel is ferrite. The oxide layer formed at high temperature is relatively loose. Although most of the oxide layer can be removed by mechanical removal of the oxide layer before rolling, due to the discontinuous island shape of the oxide layer, there will still be residual oxide layer in the local area where the oxide layer is relatively thick and the oxidation degree is relatively deep after the mechanical removal of the oxide layer. The residual oxide layer will be pressed into the base material during the rolling process, and finally the uneven composition will result in poor quality of the welding wire formed by subsequent wire drawing. SUMMARY

[0004] The present application provides a method for high-precision control of the surface oxide layer of welding wire, which can prepare high-quality welding wire by controlling the morphology and thickness of the oxide layer during the preparation of the welding wire. The technical scheme of the present application is as follows:

[0005] A method for high-precision control of the surface oxide layer of welding wire, comprising:

[0006] cooling the steel billet in the crystallizer to 250-300℃ under a nitrogen environment;

[0007] carrying out 2-3 times of cyclic heat treatment, the cyclic heat treatment comprising in turn temperature rising treatment and temperature dropping treatment, so that the surface of the steel billet changes from ferrite to austenite, and an austenite layer is obtained; wherein the final temperature of the temperature rising treatment is 900-950℃, and the final temperature of the temperature dropping treatment is 100-150℃;

[0008] carrying out oxidation treatment on the steel billet including the austenite layer in a gas containing oxygen, so that the austenite layer is oxidized into a dense ferrous oxide layer.

[0009] Optionally, the temperature rising rate of the temperature rising treatment is 100-150℃ / s, and the final temperature is kept for 3-8s.

[0010] Optionally, the temperature dropping rate of the temperature dropping treatment is 200-300℃ / s, and the final temperature is kept for 2-3s.

[0011] Optionally, after each cooling treatment, a temperature recovery treatment is further included, and the final temperature of the temperature recovery treatment is 150-200 DEG C.

[0012] Optionally, the temperature recovery rate of the temperature recovery treatment is 10-20 DEG C / s, and the holding time at the final temperature is not more than 5 min.

[0013] Optionally, during the temperature rising treatment, carburizing powder is sprayed on the surface of the billet to increase the carbon concentration of the surface layer of the billet to 0.4-0.6%, wherein the carburizing powder comprises carbon powder and barium carbonate powder.

[0014] Optionally, the cooling treatment comprises spraying salt water on the surface of the billet, the pressure of the nozzle for spraying the salt water is 0.3-0.5 MPa, the flow rate of the salt water is 1-2 m / s, and the flow is 30-50 L / min·m2; wherein the salt water comprises 5-10 wt% of sodium chloride solution.

[0015] Optionally, the oxidation treatment comprises increasing the temperature to 920-1400 DEG C at a rate of 1-5 DEG C / min, the partial pressure of oxygen is 10 -14 ~10 -8 atm, and the holding time is 8-10 h.

[0016] Optionally, after the oxidation treatment of the billet comprising the austenite layer in the gas containing oxygen, the following steps are further included:

[0017] The billet is subjected to an operation of removing the oxide layer by high-pressure water, wherein the pressure of the high-pressure water is 20-25 MPa.

[0018] Optionally, the billet in the crystallizer is cooled to 250-300 DEG C at a cooling rate of 300-350 DEG C / min in a nitrogen environment.

[0019] Compared with the prior art, the present application has at least the following beneficial effects:

[0020] By adopting the method of cyclic heat treatment, a fine-grained austenite layer with micron-level thickness is formed on the surface of the ferrite-based billet, and the austenite layer on the surface of the billet is subjected to active and controllable oxidation treatment, so that the austenite layer is oxidized into dense sheet-shaped ferrous oxide. On the one hand, the dense sheet-shaped ferrous oxide can grow uniformly, and the obtained ferrous oxide dense layer is dense and uniform in thickness and can be controlled according to the oxidation time, that is, the oxidation layer can be uniformly removed after subsequent wire drawing. On the other hand, the generated ferrous oxide dense layer grows to 2-5 microns to form a protective layer to prevent external oxygen from oxidizing the internal iron matrix. In this way, without removing the ferrous oxide dense layer, direct rolling is performed, and the subsequent rolling process will not erode and oxidize the inside to form a new oxidation layer. Finally, only the ferrous oxide dense layer needs to be completely removed after rolling into a welding wire, and then copper or other metals are plated to obtain a finished welding wire. Therefore, the morphology and thickness of the oxidation layer in the welding wire preparation process are controlled with high precision, so that a high-quality welding wire is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is a microcrystalline phase diagram of the billet after heat cycle treatment in the embodiments of the present application;

[0023] Figure 2 is an SEM diagram of the ferrous oxide dense layer in the embodiments of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0025] The embodiments of the present application provide a method for high-precision control of the surface oxidation layer of a welding wire, comprising:

[0026] The billet in the crystallizer is cooled to 250-300 DEG C under a nitrogen environment;

[0027] 2-3 times of cyclic heat treatment, which includes temperature rising treatment and temperature dropping treatment in sequence, so that the surface of the billet changes from ferrite to austenite, and an austenite layer is obtained; wherein the final temperature of the temperature rising treatment is 900-950°C (hypoeutectoid steel above 50-100°C, and the final temperature of the temperature dropping treatment is 100-150°C (lower than Ms point but higher than room temperature, Ms is martensite start temperature);

[0028] The billet including the austenite layer is subjected to oxidation treatment in a gas containing oxygen, so that the austenite layer is oxidized into a dense ferrous oxide layer.

[0029] In the embodiment, to solve the problem that after the mechanical removal of the oxide layer in the background art, the oxide layer still remains in the parts where the local oxide layer is thick and the oxidation degree is deep, the residual oxide layer is pressed into the billet matrix during the rolling process, and finally the uneven composition leads to the problem of poor welding wire quality formed by subsequent wire drawing, the embodiment adopts a cyclic heat treatment method to form a micron-thick fine-grained austenite layer on the surface of the steel billet mainly composed of ferrite. After obtaining the austenite layer, the austenite layer on the surface of the steel billet is subjected to active and controllable oxidation, i.e. oxidation treatment, which can oxidize the austenite layer into dense sheet-shaped ferrous oxide. On the one hand, the dense sheet-shaped ferrous oxide can grow uniformly, and the obtained dense ferrous oxide layer is dense and uniform in thickness and can be controlled according to the oxidation time, which is convenient for subsequent uniform removal after wire drawing; on the other hand, the generated dense ferrous oxide layer does not grow indefinitely, and the thickness of the dense ferrous oxide layer grows to 2-5 microns to form a protective layer to prevent external oxygen from oxidizing the internal iron matrix. In this way, without removing the dense ferrous oxide layer, direct rolling is performed, and the subsequent rolling process will not erode the inside to form a new oxide layer. Finally, after rolling into a welding wire, the dense ferrous oxide layer is completely removed, and then copper or other metals are plated, so that a finished welding wire is obtained.

[0030] It should be noted that the density of the oxide film formed during the oxidation of iron is directly related to its crystal structure. When the metal has a face-centered cubic (FCC) lattice, it is easier to form a dense and continuous oxide film. Among the two allotropic forms of iron, the FeO layer formed by γ-Fe (austenite, face-centered cubic structure) during high-temperature oxidation is the densest, and grows in a layered / sheet-like manner. The atomic packing density of the FCC lattice is high, and the diffusion rate and path of oxygen ions ( ) and iron ions ( ) in the lattice are low and regular, which is conducive to the uniform epitaxial growth of the oxide film and the formation of dense sheet-shaped FeO.

[0031] In the present embodiment, the rapid heating treatment in each cycle of the cyclic heat treatment can form a large number of austenite crystal nuclei on the ferrite surface, with a size of 1-3 μm. After the cooling treatment, a large number of austenite is changed into banded martensite due to the change in temperature and the rapid cooling, with a width of about 0.2 μm. In each cycle, the second heating triggers the reverse phase change (martensite→austenite), and nanoscale austenite crystal nuclei (100-500 nm) are generated at the interface of the lath martensite. The second cooling converts the newly generated austenite into finer martensite (lath width ≤0.1 μm), and the austenite layer is pushed outwards and thickened.

[0032] In the present embodiment, the low-carbon steel for preparing the steel blank can be added with 1.0-1.5% wt Mn or 0.5-1.0 wt% Ni, which can increase the performance of the low-carbon steel and expand the γ phase region and improve the stability of austenite.

[0033] In the present embodiment, the thickness of the austenite layer obtained after each cycle of the heat treatment is 15-20 μm, and the controllable thickness growth of the austenite layer is realized.

[0034] In some embodiments of the present application, the heating rate of the heating treatment is 100-150℃ / s, and the holding time at the final temperature is 3-8 s.

[0035] In the present embodiment, the heating rate is 100-150℃ / s to above 900℃, and the holding time is short, which can cause the explosive formation of austenite crystal nuclei (density ) at the ferrite grain boundaries. In addition, the short holding time can prevent grain coarsening.

[0036] In the present embodiment, the rapid heating can be realized by a high-frequency induction heating furnace, with an induction frequency of 1-10 kHz and a power density of 1.5-3.0 kW / cm².

[0037] In some embodiments of the present application, the cooling rate of the cooling treatment is 200-300℃ / s, and the holding time at the final temperature is 2-3 s.

[0038] In the present embodiment, the cooling rate (>critical value, about 200℃ / s) inhibits carbon diffusion and fixes the austenite-martensite interface.

[0039] In some embodiments of the present application, after each cooling treatment, a re-heating treatment is further included, and the final temperature of the re-heating treatment is 150-200℃.

[0040] In the present embodiment, the re-heating treatment can release the stress generated in the cooling treatment and retain high hardness.

[0041] In some embodiments of the present application, the temperature rising rate of the temperature rising process is 10-20℃ / s, and the holding time at the final temperature is no more than 5min.

[0042] In the present embodiment, the holding time should be controlled within 5min, and a longer holding time will cause the carbide to coarsen.

[0043] In some embodiments of the present application, during the temperature rising process, carbonizing powder is sprayed on the surface of the billet to increase the carbon concentration of the surface layer of the billet to 0.4-0.6wt%; wherein the carbonizing powder comprises carbon powder and barium carbonate powder. In this way, the critical temperature of austenite transformation can be significantly reduced , and the formation of austenite is promoted.

[0044] It should be noted that the concentration needs to be controlled, and the surface carbon concentration during carbonization is controlled to be 0.4-0.6wt% to avoid the precipitation of brittleness , and the carbon concentration can be monitored and collected according to the dew point instrument or oxygen probe.

[0045] In some embodiments of the present application, the temperature rising process includes spraying salt water on the surface of the billet, the pressure of the nozzle for spraying salt water is 0.3-0.5 MPa, the flow rate of the salt water is 1-2 m / s, and the flow rate is 30-50 L / min·m²; wherein the salt water comprises 5-10wt% of sodium chloride solution.

[0046] In the present embodiment, the high-pressure and high-flow salt water spraying and flushing can rapidly cool the billet. In addition, it can also flush away the residual carbon to prevent the excessive accumulation of carbon from increasing the carbon content of the billet, so that the increase in the surface carbon concentration during each spraying of carbonizing powder is fixed to 0.4-0.6wt%. It should be noted that the forced convection of salt water with a flow rate of 1-2 m / s can eliminate the soft spots caused by the vapor film.

[0047] In some embodiments of the present application, the oxidation process includes increasing the temperature to 920-1400℃ at a rate of 1-5℃ / min, the partial pressure of oxygen is 10 -14 ~10 -8 atm, and the holding time is 8-10h.

[0048] In the present embodiment, 920-1400℃ is the stable zone for the formation of austenite, and increasing the temperature at a rate of 1-5℃ / min can reduce the thermal stress-induced cracking of the oxide film, and the partial pressure of oxygen is 10 -14 ~10 -8 atm, which can inhibit the formation of iron oxide.

[0049] In some embodiments of the present application, after the oxidation process of the billet including the austenite layer in the gas containing oxygen, it further includes:

[0050] The operation of removing the oxide layer by high-pressure water on the billet; wherein the pressure of the high-pressure water is 20-25 MPa.

[0051] In some embodiments of the present application, the billet in the crystallizer is cooled to 250-300℃ at a cooling rate of 300-350℃ / min under nitrogen environment.

[0052] In the present embodiment, the cooling at a cooling rate of ≥300℃ / min can inhibit the formation of coarse grains.

[0053] In order to more clearly illustrate the technical solutions and advantages of the present application, the following will be described in detail through several embodiments. Embodiment

[0054] The billet in the crystallizer is cooled to 260℃ at a cooling rate of 370℃ / min under nitrogen environment.

[0055] Two cycles of heat treatment are performed, and the heat treatment includes, in sequence, a heating treatment, a cooling treatment and a re-heating treatment, so that the surface of the billet is changed from ferrite to austenite, and an austenite layer is obtained; wherein the final temperature of the heating treatment is 920℃, the heating rate is 107℃ / s, 80wt% carbon powder and 20wt% barium carbonate powder are sprayed during the heating, the final temperature is maintained for 5s, the final temperature of the cooling treatment is 130℃, the cooling rate is 230℃ / s, the final temperature is maintained for 3s, the final temperature of the re-heating treatment is 180℃, the re-heating rate is 17℃ / s, and the final temperature is maintained for 4min.

[0056] The temperature is increased to 1150℃ at a rate of 3℃ / min, the partial pressure of oxygen is 10 -11 atm, and the holding time is 10h.

[0057] After the oxide layer is removed by high-pressure water, a rolling process is performed, and the temperature during the rolling process is controlled at 975±50℃.

[0058] The product wire rod obtained by rolling is formed into a coil and is drawn at a drawing temperature of 960℃, and a welding wire is obtained.

[0059] Comparative Example 1

[0060] After the oxide layer of the billet in the crystallizer is removed by high-pressure water, a rolling process is performed, and the temperature during the rolling process is controlled at 975±50℃.

[0061] The product wire rod obtained by rolling is formed into a coil and is drawn at a drawing temperature of 960℃, and a welding wire is obtained.

[0062] Comparative Example 2

[0063] The steps in Comparative Example 2 are basically the same as those in Example 1, except that no cyclic heat treatment was performed.

[0064] The product obtained in Example 1 has a structure in which ferrite is encapsulated in nanoscale austenite. Figure 1 At the same time, a layered ferrous oxide dense layer can also be obtained on the outermost layer. Figure 2 Therefore, the product obtained in Example 1 is less prone to wire spatter during use.

[0065] The product obtained in Comparative Example 1 clearly shows localized blackening of the welding wire, which is caused by a loose oxide layer remaining on the welding wire. During use, the residual oxide layer is prone to welding wire spatter.

[0066] The product obtained in Comparative Example 2 did not form austenite outside the ferrite. The oxide layer obtained after oxidation treatment was loose and thick. After removing the oxide layer with high-pressure water, the product had more oxide residue. There was more oxide residue inside the welding wire, and the spattering was more serious than that in Comparative Example 1.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for high-precision control of the oxide layer on the surface of a welding wire, characterized in that, include: The steel billet in the crystallizer is cooled to 250~300℃ in a nitrogen atmosphere; The steel billet undergoes 2-3 cycles of heat treatment, which includes heating and cooling processes in sequence, to transform the surface of the steel billet from ferrite to austenite, thereby obtaining an austenite layer. The final temperature of the heating process is 900-950°C, and the final temperature of the cooling process is 100-150°C. The steel billet including the austenitic layer is subjected to oxidation treatment in a gas containing oxygen, so that the austenitic layer is oxidized into a dense ferrous oxide layer.

2. The method according to claim 1, characterized in that, The heating rate of the heating process is 100~150℃ / s, and the temperature is held at the final temperature for 3~8s.

3. The method according to claim 1, characterized in that, The cooling rate of the cooling process is 200~300℃ / s, and the temperature is maintained at the final temperature for 2~3s.

4. The method according to claim 1, characterized in that, After each cooling process is completed, a warming process is also included, with the final temperature of the warming process being 150~200℃.

5. The method according to claim 4, characterized in that, The temperature recovery rate of the temperature recovery treatment is 10~20℃ / s, and the holding time at the final temperature does not exceed 5 minutes.

6. The method according to claim 1, characterized in that, During the heating process, carburizing powder is sprayed onto the surface of the steel billet to raise the carbon concentration on the surface of the steel billet to 0.4~0.6wt%; wherein the carburizing powder includes carbon powder and barium carbonate powder.

7. The method according to claim 1 or 6, characterized in that, The cooling process includes spraying brine onto the surface of the steel billet. The pressure of the nozzle used for spraying the brine is 0.3~0.5 MPa, the flow rate of the brine is 1~2 m / s, and the flow rate is 30~50 L / min·m². The brine includes a 5~10 wt% sodium chloride solution.

8. The method according to claim 1, characterized in that, The oxidation treatment involves heating to 920-1400°C at a rate of 1-5°C / min, with an oxygen partial pressure of 10. -14 ~10 -8 ATM, heat preservation time is 8~10 hours.

9. The method according to claim 1, characterized in that, After the steel billet including the austenitic layer undergoes oxidation treatment in a gas containing oxygen, the process further includes: The steel billet is subjected to high-pressure water to remove the oxide layer; the pressure of the high-pressure water is 20~25MPa.

10. The method according to claim 1, characterized in that, The steel billet in the crystallizer is cooled to 250-300℃ in a nitrogen atmosphere at a cooling rate of 300-350℃ / min.

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