Elements that constrain the quality of the spring

Chemical composition fluctuations and segregation The strength of steel is mainly determined by the carbon content of the steel. Chemical composition fluctuations and segregation are mainly fluctuations and segregation of carbon content. For example, if a factory uses the same batch number 70 steel wire rod to pull to a6.0mm for heat treatment, the strength of the steel wire after quenching is large, and the corresponding data obtained by carbon sampling after sampling (smelting analysis C mass fraction is 0.74). %, intensity fluctuations do not take into account heat treatment factors). It can be seen that the maximum difference in intensity fluctuation is 225 MPa. If drawn to a2.6 mm finished steel wire, the $Rb will reach 334 MPa according to the KN Tu Linkov formula. At the same time, due to the large segregation and fluctuation of the composition, the wire treated with lead bath The impact of organizational performance is also large. If the austenitization is not uniform, the eutectoid phase precipitates first, and other structural transformations occur, which will affect the mechanical properties and process properties of the steel wire. In severe cases, the steel wire will break during drawing and use.

The effect of purity and internal defects is due to the low purity of domestic wire rods, the variety of inclusions, high content, large particles, and internal defects such as residual shrinkage, looseness, cracks, uneven tissue, etc. When twisted and entangled, it is easy to become a source of cracks, eventually leading to fracture.

Influence of various factors in the production process Heat treatment temperature fluctuation and technical operation At present, most manufacturers adopt automatic temperature control coal-fired muffle furnace and horizontal take-up unit. Since the temperature of the steel wire is indirectly obtained by measuring the temperature of the furnace, the temperature of the furnace in the production is greatly affected by factors such as the coal quality, climatic conditions, and the position of the thermocouple insertion. Therefore, the actual production process temperature of the heat treatment can only maintain a staged stability. The state changes with the above several conditions. During the change process, the automatic temperature control system is often out of control, causing the furnace temperature to be unstable and causing the line temperature to fluctuate. In addition, there are differences in the temperature between the furnace holes in the furnace and the temperature distribution in the lead tank, which has a great influence on the uniformity of the steel rod.

In terms of technical operation, there are four key links that are the main factors affecting quality. First, when the specifications are changed, the lead wire is not used as required or the part of the wire that is affected during the threading process is not cut off. Second, because the temperature difference between the furnace and the wire is small during the time of the wire threading, the wire temperature is too high and the oxidation is often caused. Third, the number of threads in the furnace and the number of threads per hole also have a certain influence on the temperature difference between the furnace and the steel wire. Fourth, the steel wire caused by the lower wire is stopped in the furnace, so that the steel wire in the furnace is over-fired. Peroxidation, austenite grains are coarse, and a section of steel wire that stays at the outlet is precipitated along the austenite grain boundary during cooling, and is transformed into reticular ferrite by lead quenching, and the steel wire structure deteriorates. Although the above four points are relatively clear, they are often ignored in the production of many manufacturers.

The influence of the drawing process is due to the low level of equipment and equipment of most manufacturers, and some even self-made simple equipment can not meet the requirements of producing high-quality spring steel wire. There are two aspects that have great influence: (1) cooling Insufficient or uneven. The heat generation in steel wire drawing is a common phenomenon. How to effectively dissipate the heat in the steel wire is a problem that the steel wire industry has been trying to solve. Therefore, the mechanical energy consumed on the drawn steel wire is converted into heat in the deformation zone of the die hole, so that the temperature of the wire in the drawing is suddenly increased to more than 300e due to insufficient or uneven cooling, and the static strain of the wire is aging. Intensified, this will not only cause the unevenness of the strength of the wire rod, but also reduce the bending and torsion performance of the steel wire; (2) The speed ratio of the wire drawing machine does not meet the requirements of the drawing process. In the production, the speed ratio of the front and rear roads in the drawing is often changed due to the wear of the reel and the tower wheel. Pulling according to the normal mold-binding process will inevitably increase the twist of the steel wire on the cross-wheel and slip on the tower wheel. The result is the finished steel wire. Producing large torsional stress and quality problems such as wool, flat wire and over tolerance, which not only affect the winding performance of the steel wire, but also affect the mechanical properties of the steel wire.

The influence of the middle/three mixed 0 in each step of production/three mixed 0, that is, the mixed steel number, the mixed furnace number, and the mixed specification, often occur in two cases. First, due to poor management, blanks and semi-finished products are stored without obvious signs and mixing, resulting in / three mixed 0; Second, some small enterprises have a low quality awareness, using raw materials regardless of steel number, number, only production is not tested, all qualified factory.

The impact of non-standard operation such as cutting corners and materials is due to the fierce competition in the market price of carbon spring steel wire. Some unscrupulous producers and operators have participated in market competition to reduce costs, use cutting corners, shoddy and other improper means, and disrupt the market. Order has brought many quality hazards and caused great economic losses to the country and the people. The specific performances are as follows: (1) eliminating the necessary surface treatment and heat treatment processes, and directly drawing the finished products; (2) specifically selecting waste and defective wire rods that are processed at low prices by some steel mills or purchasing wastes of some production plants. (3) replace the high carbon steel wire rod with medium carbon steel (such as 45 steel) wire rod; (4) large compression ratio drawing to reduce the intermediate drawing process; (5) improper promotion Means to sell inferior products. The existence of the above situation not only hinders the overall image of the steel wire market, but also harms the interests of regular manufacturers.

Production Introduction

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