The surface hardness of the super-standard spring flat steel is affected by the finish rolling temperature, the stack cooling temperature and the cooling rate. If the finishing temperature is too low or the cooling rate is too fast, the stack cooling temperature will be too low, which will lead to excessive hardness. For 65siMnvB and 50crvA flattening, controlling the cooling rate is particularly important, because the presence of elements such as antimony, boron, and chromium will greatly improve the hardenability of steel, and the cooling rate has a greater impact on 5siMnvB and 50CrvA. 60SiZMn is sensitive. If the finishing temperature and cooling rate are not properly controlled during production, it will be difficult to ensure that the flatness (HB) is less than 321.
There are many reasons for the bending of the flattening after the side-bending and flat-bending hot rolling. There are three main points: First, the heating temperature of the billet is uneven along the cross-section direction, which causes the flat steel after rolling to have a temperature difference in the width and is easy to produce during the cooling process. The side bend; the second is that the rolling amount of the rolled piece in the two sides of the hole is not uniform. The thickness of the flat steel is different, the flat steel will produce side bends to the thicker side; the third is the flat steel during the cooling process. The surface heat dissipation rate is not uniform, which will cause the flat steel to produce side bends or flat bends. Other reasons, such as the hot flat steel staying on the transport roller for too long or the flat steel crosses when the stack is cold will also lead to flat bending.
The reasons for the scratching of the flat surface of the scraping wire are also various, mainly the influence of the guide and the conveying roller, and are analyzed separately below. The influence of the guides on the guides in the guides has a great effect on the scratches on the flat surface. The use of the sliding guide to produce the scratch line is mainly due to the sticking of the guide plate under high temperature sliding friction. The lower the hardness of the guide material, the more serious the sticking phenomenon, and the bond is an oxidized deposit of iron. After the guide plate is adhered to the steel, it will continue to be used, which will inevitably scratch the sides of the rolled piece.
In addition, the improper installation height of the upper and lower guide plates of the outlet will cause the upper and lower surfaces of the rolled piece to be scratched. If a rolling inlet guide is used, the chance of scratching will be much reduced, but if the roller is not properly lubricated and cooled, or the surface is not highly accurate, scratches will occur.
The influence of the shaft feeding roller path In the actual production, the guide plate is often provided on the roller table. Because there is welding bead on the roller surface of the welding guide plate, the angle of the mounting plate is not suitable, or the friction between the welding rod and the rolling piece will cause Scratch line generation. Generally speaking, the scraping line caused by the conveying roller is irregular and intermittent, and the scraping line caused by the guiding is long and regular. Among the common defects in the production of warp flats, the cause of the warping is more complicated. The slag is slag inside the billet. During the rolling process, the roll shape (especially the rough pass) is too large, or there are pits and sticking steel on the hole type. The design of the extended hole type and the vertical roll type is unreasonable and incorrect. The adjustment method may cause warping.
When using the "second fired material" of the initial rolling blank, if the flat surface of the flattened surface is warped, it is generally regular. Most of the warping is caused by the hole type of the rough rolling pass, and a strip is formed on the surface of the rolled piece. Convex. In the middle rolling and finishing rolling process, due to the poor plasticity of the spring steel, the extension of the strip-like tenons is larger than the extension of the base of the rolling stock, forming a thin strip of warping. When using a continuous casting billet to "single fire", the production of some warps is irregular.
Metallographic analysis found that some of these irregular skins have decarburization on the surface, which may be related to the surface quality of the continuous casting blank; some of the warping is not decarburized, which may be due to the surface of the rolled piece during transport. The impact or the crater is caused by the impact, and the curling edge or the pit portion cannot be welded during the subsequent rolling process to form a warp.
Key points for quality control of each production process The spring slab billet before preparation for heating shall be finished and ground. The usual method is to use a grinder to clean up the surface defects observed by the naked eye. Some spring flat steel manufacturers carry out long-length grinding on the surface of the blank, and the grinding amount is 2-3mm. Some manufacturers first pickle the blank, so that the defects on the surface of the blank are fully exposed and then repaired. The method of repairing by grinding or pickling will increase the production cost, which is uneconomical, and the hydrogen fragile is liable to cause "hydrogen embrittlement" phenomenon when the billet is pickled. Therefore, relying solely on finishing and grinding to improve the quality of the blank is not the best choice in terms of economy and technology. It should start from the aspects of smelting, refining and continuous casting, and fundamentally improve the quality of the spring steel.
The optimization of the chemical composition of steel will also play a significant role in the quality of the flat. In 60siZMn steel, silicon increases the activity of carbon, so the content of carbon and silicon plays a large role in the decarburization of steel, but silicon is the key element to improve the anti-ballistic properties of steel, so the strength of steel is guaranteed. In the case of anti-ballistic reduction, it is advisable to control the content of carbon and silicon in the steel according to the standard lower and lower limits.
Rolled spring steel should be rhythmically rolled and balanced. It is better not to use a common boring type for the rough rolling hole type to ensure accurate cross-section shape of the rolled piece. In the hole design, the equalization reduction ratio and rolling force should be considered, and a reasonable hole type and compression ratio should be adopted. Generally, the extended hole type selects a smaller groove bottom width and a larger groove bottom fillet and roll gap fillet, and it is not suitable to use a diamond one-hole type system.
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