Process method for controlling hot rolling cracking problem of low-zinc brass cast ingot

Abstract

The invention relates to a low-zinc brass casting technology, in particular to a process method for controlling the hot rolling cracking problem of a low-zinc brass cast ingot. The quality problem that surface cracking and pressing always occur in the hot rolling process of the low-zinc brass material is solved. A technological method for controlling the hot rolling cracking problem of a low-zinc brass cast ingot comprises the steps that in the low-zinc brass casting process, CuRe 10% rare earth alloy is added; hundreds of grams of CuRe 10% rare earth alloy are added into each ton of low-zinc brass; and the casting temperature of the low-zinc brass is 1160-1200 DEG C. In the casting process of the low-zinc brass, a covering agent prepared by mixing borax, sodium chloride, potassium chloride, dietary alkali and refractory clay is used as a covering material. According to the method, the effect of refining the grains of the low-zinc brass product is finally achieved, and the problem of hot rolling surface cracking is solved.

Description

Technical Field

[0001] The invention relates to a low-zinc brass casting technology, in particular to a process method for controlling the hot-rolling cracking problem of a low-zinc brass ingot. Background Art

[0002] There are many high-end copper alloy materials for connectors in China, which are mainly used in electronic information, new energy vehicles and other fields, and some materials have successfully replaced imported materials. Among them, low-zinc brass materials are high-strength medium-conductor products, which are mainly used in automotive connector materials and other fields, and the surface quality requirements of materials are very strict. However, this kind of product will always have quality problems such as surface cracking and pressing during the hot rolling process, which directly affects the subsequent processing quality of the product. If it is not discovered during the rough rolling and fine rolling process, then the quality problem of stratification will occur during the stamping process, which will directly affect the service life of the parts, and then affect the reliability of the car, causing serious consequences. Summary of the invention

[0003] The invention aims to solve the quality problem of surface cracking and pressing of low-zinc brass materials during hot rolling, and provides a process method for controlling the hot rolling cracking problem of low-zinc brass ingots.

[0004] The invention discloses a process for controlling the hot rolling cracking problem of low-zinc brass ingots, comprising adding a CuRe10% rare earth alloy during the casting process of the low-zinc brass; the CuRe10% rare earth alloy contains, by mass percentage, 10% of Re element, 0.1% of Fe element, 0.01% of Si element and 0.01% of Ni element, and the remainder is Cu content; and during the casting process, 0.3-0.5% of the CuRe10% rare earth alloy is added to each ton of molten copper.

[0005] Furthermore, the casting temperature of low zinc brass is 1160°C-1200°C.

[0006] Furthermore, in the casting process of low-zinc brass, a covering agent made of a mixture of borax, sodium chloride, potassium chloride, edible alkali and refractory clay is used as a covering material. The covering agent is calculated by mass ratio: 100 parts of borax, 2 parts of sodium chloride, 4 parts of potassium chloride, 1 part of edible alkali and 2 parts of refractory clay.

[0007] Furthermore, borax, sodium chloride, potassium chloride, edible alkali and refractory clay are mixed in proportion, stirred and baked to obtain a covering agent.

[0008] The invention solves the cracking problem of the low-zinc brass ingot during hot rolling by strictly controlling the temperature of the molten copper during the smelting process of the low-zinc brass (mainly referring to the zinc content ≤5% in the invention), preparing a suitable covering agent, and finally adding a certain amount of rare earth alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Phase diagram of Cu-Zn binary alloy.

[0010] Figure 2 Schematic diagram of low-zinc brass grains, with high-temperature grain structure on the left and low-temperature grain structure on the right.

[0011] Figure 3 Schematic diagram of the comparison of low zinc brass grains before and after refinement, Figure a is before refinement, and Figure b is after refinement.

[0012] Figure 4 Macroscopic grain structure diagram of the cross section of low-zinc brass without the addition of rare earth elements.

[0013] Figure 5 Macroscopic grain structure diagram of low zinc brass cross section when rare earth elements are added. DETAILED DESCRIPTION

[0014] 1. Theoretical analysis Low-zinc brass ingots often crack during hot rolling. This is a surface crack caused by non-hot rolling overheating. From the Cu-Zn binary alloy phase diagram ( Figure 1 As shown in the figure, low zinc brass (zinc content ≤ 5%) is α single-phase brass, and as the temperature continues to rise, the higher the purity of α+ liquid, the higher the purity, the lower the strength of the material, and the higher the temperature, the coarser the grains (such as Figure 2 As shown in the figure, the high-temperature microstructure of low-zinc brass is closely related to the extrusion temperature. As the extrusion temperature increases, the stress concentration phenomenon caused by the phase change begins to intensify. When the phase morphology becomes strip or block, the stress concentration phenomenon begins to weaken. That is to say, during high-temperature rolling, the plastic range of brass is narrow.

[0015] After comparing and analyzing the internal grain structure of low-zinc brass materials, it was determined that the main cause of cracking was that the coarse grain structure inside the ingot caused cracking on the surface of the hot-rolled billet.

[0016] 2. Experimental process Experiment 1 Adding rare earth alloys to low zinc brass As an additive, rare earth alloy can also be used to refine grains. It can mainly react with harmful substances in copper (such as oxygen, sulfur, lead, bismuth, etc.) to generate crystal cores, so that the copper structure is refined. On the other hand, rare earth gathers on the grain boundaries and is easy to fill the surface defects of the new phase grains being generated in the solution, forming a film that hinders the continued growth of the grains, inhibiting the growth of the grains, and thus refining the grains. Other elements in the rare earth alloy used in the present invention can also play a role in strengthening the grain boundaries of the ingot and improving the hot workability. For example, Re, an element present in the rare earth alloy, will precipitate preferentially at the grain boundaries during the cooling process during the dissolution casting, and will be enriched on the phase interface (grain boundaries) during crystal growth. They can not only hinder the growth of existing crystals, but also form a large concentration of supercooling to promote nucleation, and can also make the branches of the crystals form thin necks, which is easy to produce crystal reproduction, and thus can significantly refine the ingot grains (such as Figure 3 As shown in the figure), the grain boundaries can be strengthened, making it difficult for cracks to occur during hot working.

[0017] The rare earth alloy used in the present invention is a CuRe 10% alloy, with Re as the main element, Fe, Si, Ni as the auxiliary elements, and the rest being Cu. This rare earth is cheap, and the amount added does not need to be too much. Only a few hundred grams per ton are needed to achieve a good effect, so it has a very high cost performance.

[0018] Figure 4 This is a low-magnification grain structure diagram of a low-zinc brass cross section that was prone to cracking. Figure 5 This is a low-magnification grain structure diagram of the brass cross section after rare earth elements are added during the experiment of the present invention. It can be clearly seen from the figure that after adding rare earth elements, the grains become very fine from the coarse state before adding rare earth elements, and the thickness of equiaxed crystals reaches 50-80mm after adding rare earth elements.

[0019] Experiment 2 Controlling the melting temperature of low zinc brass The inventors made a conclusion through low-power observation in practice: when other influencing factors are the same, the grain size of low-zinc brass will gradually increase with the increase of temperature (such as Figure 4 ), and the fluidity of copper water below 1160℃ will deteriorate, it is easy to contain ash, affecting the surface quality of the ingot. After many experiments, the inventor set the casting temperature of low-zinc brass at 1160℃-1200℃, which not only ensures the fluidity of copper water during casting, but also prevents the expansion of grain structure (such as Figure 5 as shown).

[0020] Experiment 3: Improving the covering agent during casting Our comparative experiments found that the use of a single covering agent (borax) in the casting process of low-zinc brass has a negative effect on the insulation, fluidity and grain size of the molten copper in the crystallizer. Therefore, we have developed a method of mixing a certain amount of borax, sodium chloride, potassium chloride, edible alkali and refractory clay in proportion, stirring and baking (100Kg borax with 2Kg sodium chloride, 4Kg potassium chloride, 1Kg edible alkali and 2Kg refractory clay), which can effectively reduce the cooling rate of molten copper, increase the fluidity of molten copper, and thus facilitate the refinement and uniformity of the grains.

[0021] 3. The following is a comparison of data before and after the experiment of the present invention: Table 1 Statistics of hot-rolled batches and cracking proportions of low-zinc brass products from September 2023 to May 2024.

[0022] .

[0023] The results show that the average proportion of hot-rolled cracking batches of low-zinc brass products is 9.8%.

[0024] Table 2 Statistics of hot-rolled batches and cracking proportions of low-zinc brass products from June to November 2024.

[0025] .

[0026] Table 1 is a statistical analysis of the percentage of batches of low-zinc brass ingots produced before the experiment that cracked during hot rolling. Table 2 is a statistical analysis of the percentage of batches of low-zinc brass ingots produced by the present invention after adding a special rare earth alloy and controlling the casting temperature to a certain range that cracked during hot rolling. It is obvious that the experiment was successful and effectively solved the problem of hot rolling cracking of low-zinc brass.

[0027] Through theoretical analysis and experiments, the present invention finally found an innovative method to completely solve the hot rolling cracking of ingots caused by casting problems, that is: adding a certain proportion of rare earth alloy, controlling the smelting temperature to a certain range, and using our improved covering agent. The above methods are combined to finally achieve the effect of refining the grains of low-zinc brass products and solve the problem of hot rolling surface cracking.

Claims

1. A process for controlling the cracking problem of hot-rolled low-zinc brass ingots, characterized in that: During the casting process of low-zinc brass, CuRe10% rare earth alloy is added; the CuRe10% rare earth alloy contains 10% Re element, 0.1% Fe element, 0.01% Si element and 0.01% Ni element by mass percentage, and the rest is Cu content; during the casting process, 0.3-0.5% CuRe10% rare earth alloy is added to each ton of molten copper in a mass ratio.

2. A process for controlling the hot rolling cracking problem of low-zinc brass ingots as claimed in claim 1, characterized in that: The casting temperature of low zinc brass is 1160℃-1200℃.

3. A process for controlling the hot rolling cracking problem of low zinc brass ingots as claimed in claim 1 or 2, characterized in that: During the casting process of low-zinc brass, a covering agent made of a mixture of borax, sodium chloride, potassium chloride, edible alkali and refractory clay is used as the covering material. The covering agent is calculated by mass ratio: 100 parts of borax, 2 parts of sodium chloride, 4 parts of potassium chloride, 1 part of edible alkali and 2 parts of refractory clay.

4. A process for controlling the cracking problem of hot rolling of low-zinc brass ingots as claimed in claim 3, characterized in that: The covering agent is prepared by mixing borax, sodium chloride, potassium chloride, edible alkali and refractory clay in proportion, stirring and baking.

Images