Steel cord because of its high strength, wear resistance , heat fast , flexible , and many other excellent properties , is widely used in the production of radial tires . With the rapid development of China's automobile industry, automobile tires are increasingly demanding high performance , development of high-strength and ultra high strength steel cord can extend tire life and improve the safety performance of the tire , while reducing tire the amount of steel cord to reduce the production cost of the tire . Related predicted that by 2015 China's tire production will reach nearly 500 million , the rate of radial tires will reach more than 90% , excellent performance , reliable quality steel cord products have great market space in the future .
Over the last decade , China's steel cord products has made great progress , meridian tires 50% rate in 2003 increased to 87.3% in 2011 , but some high-intensity , high intensity , high value-added products, steel curtain wire rod still needs to import large quantities . The current Chinese enterprises in the production of steel cord quality wire rod and other lower levels of product quality must be further improved, a higher level of product quality is the need to intensify research and development research.
Our high-grade steel cord wire rod to be developed
At present , the domestic production of steel cord wire rod can have more than a dozen manufacturers , but can produce a higher level of product quality and stability of the manufacturers still small. To this end , China's steel cord wire rod producers still have a lot of space technology to improve the product .
Our products can be mass-produced steel cord level there are 72 , 82 , in recent years, Wuhan Steel, Anshan Iron and Steel successful trial 86 , 92 and 96 and other high-grade steel cord wire rod , but from achieve scale industrial production are still gaps . Baosteel Group in 1987, began the development of steel cord , commissioned in 1999 to achieve a high- speed wire rod mill with steel cord wire rod production , has been able to scale production of 72 , 82 , 86 and 92 products, and in recent years successfully developed 96 products. Wuhan Iron and Steel began in December 1999 to promote the development of 72A and 82A cord steel wire products , after 10 years of time , that level has been formed as WLX72A, WLX72AE, WLX82A, WLX82AE and many other brands of products , and the use of the converter - continuous casting process success developed a 92 ultra high strength steel cord wire rod . Qingdao Steel 's 72 and 82 levels of steel cord wire rod products are reliable , high quality and stability of recent years, the development of 92 market share is gradually improving . ( Baosteel, Wuhan and Qingdao Steel with steel cord wire rod production process conditions shown in Table 1 ) .
Insiders pointed out that the future development direction of China's steel cord steel there : one is to further stabilize and improve the current 72 , 82 steel cord products , continue to optimize the smelting process , the development of the molten steel of high purity direction , control type inclusions , shape, number and size optimized to reduce the slab casting technology center segregation , rolling optimize heating , rolling and controlled cooling technology to improve organizational performance and wire rod surface quality ; on the other hand , the relevant enterprises should intensify the development of 86 , 92 and 96 , such as a higher level of steel cord products , expanding market share of high-grade steel cord products , while enhancing their own competitiveness.
Seven factors, the two processes to good quality steel cord wire rod
Steel cord production process of steel cord wire rod is drawn into fine filaments (0.15mm ~ 0.38mm). In this process , the wire length is increased 1000 -fold to 1400 -fold , while the cross-sectional area is reduced to the original eight ten thousandths , and require interruption wire drawing process less than 1 second / 100 km, and then go through the high-speed double twisting machine twisted into rope . Therefore, the quality of steel cord wire rod with very strict requirements on the chemical composition range control , inclusion type, size , shape and volume controls are very strict requirements , while requiring segregation during solidification to minimize as much as possible , gold phase structure shall be uniform .
The main factors to improve product quality wire rod
No strict quality steel cord steel guarantee will easily produce broken wires and other issues affecting the production process and improve production costs. Affect the quality of wire rod are the following factors .
Chemical composition. Precise control of chemical composition, is the leading steel cord wire rod to ensure stable performance . Smelting process should enable the chemical composition of technical personnel to maintain a uniform , less volatile , cleaning rod to prevent the rod of instability, resulting in pulling off the wire. New GB GB/T27691-201l provides steel cord wire rod components ( see Table 2 ) .
Mechanical properties. According to the current capacity of the mill , the relevant new industry standard will LX70 and LX80 rod control rod tensile strength in the range of 970MPa ~ 1120MPa and 1070MPa ~ 1220MPa , the section shrinkage were not less than 40 % and 35 %.
Microstructure . Rod microstructure mainly sorbitic , the product should avoid the formation of martensite and cementite closed mesh and other harmful tissue , 70 level patenting rate ≥ 80%, 80 levels of patenting rate ≥ 85% , rod austenite grain size ≥ 6 levels.
Segregation . Segregation will affect the disk of the steel cord tissue and cause broken wires , requiring no more than three levels of segregation .
Non-metallic inclusions. Non-metallic inclusions in steel cord control technology is the key to the production process with the rod , the industry 's level of non-metallic inclusions are strict requirements and maximum size ( see Table 3 ) .
Decarburization . 70 rod rod decarburization can not be greater than the nominal diameter of 1.2% , 80 rod rod decarburization of not more than 1.2% in nominal diameter.
Surface quality. Rod should not have cracks , folds , inclusions, such as the ears on the use of harmful defects ; pitting, dents, scratches and pressed into the iron oxide and other minor localized defects , the depth should not be greater than 0.10mm; surface oxide rod iron weight should be no more than 0.8%.
Inclusions in steel making process should be controlled to produce
Steel cord finally pulled into fine filaments , to get stability, we must first ensure that the steel cord wire rod production process with a uniform and stable chemical composition. The majority of our business on the basis of national standards were established more stringent requirements, carbon composition fluctuations generally controlled within ± 0.01% ~ ± 0.02%, silicon, manganese composition fluctuation general control ± 0.050%, P ≤ 0.02%, S ≤ 0.010%, the remaining ingredients in Table 2 . During the drawing of the nitrogen will cause the stress concentration broken filaments , and have adverse effects on the fatigue resistance of steel cord , so the standard explicitly requires N ≤ 0.006%.
The control of inclusions is the key to the production of quality steel cord products , especially in the presence of aluminum oxide is one of the main factors leading to broken wires and twisted steel cord occurs in the process of drawing . Therefore, the steel cord production process , the key is to control the inclusions reasonable control of aluminum oxide and titanium nitride inclusions inclusions . For this reason, the production process of steel enterprises should strictly control the aluminum content and nitrogen content , and develop a reasonable slagging system.
Recently , China has many companies and researchers on the nature of inclusions and more attention , a lot of research work. For example , Wuhan Iron and steel cord production process, using Si-Mn deoxidized molten steel to reduce dissolved oxygen , and with Ca-Si auxiliary oxygen, such as the use of LF, VD or secondary refining process control RH inclusions form, eventually content makes inclusions in aluminum oxide was controlled at about 20%. Shougang is fully programmable aluminum smelting process in the steel cord inclusions in aluminum oxide content is also controlled at around 20%.
Rolling process should be noted that three factors
In the rolling process , and the enterprises should pay attention to the surface decarbonization factors rod structure and surface quality of these three areas .
Surface decarburization. Companies want to reduce the decarbonization layer thickness , it should be based on their own equipment condition and develop an appropriate considering the quality slab heating system. At the same time , attention should be paid to the control of the furnace atmosphere . Wuhan Iron and technical measures taken are: one -stage heating using " high winds, low furnace pressure " operation, the furnace is an oxidizing atmosphere ; second heating zone would be appropriate to reduce the amount of air furnace gas as neutral or weak oxidizing atmosphere ; soaking segment a " small amount of wind, positive furnace pressure " operation, the furnace atmosphere is weakly reducing atmosphere ; determine the optimum air-fuel mixing gas . Surface decarburization layer thickness should be strictly controlled , some foreign advanced technology companies generally can do no produce wire rod surface decarburization , so rolling to strictly control the production of each segment within the furnace atmosphere furnace, establish reasonable heating system.
Rod tissue. Rod organizations patenting rate ≥ 85%, can not have martensite , bainite and cementite network organization . Also, the disc edges and central to cool evenly to ensure uniform organizational performance.
To this end, the Anshan Iron and Steel wire rod rolling line in Stelmor control air-cooled cooling process, try to create conditions for increasing the spinning circle diameter , increased by reducing the rolling speed and roll speed to control rod density overlap ; the same time, air-cooled line installation Jia Ling device , by changing the wind direction to ensure that the air-cooled cooling roller small differences in each region , in order to obtain a uniform disk of tissue.
Surface quality. Scratch is the most common steel cord wire rod surface quality problems, according to produce scratches links, Angang has taken the following measures : the sliding guide into the rolling mill guide and guard ; pallet descent to eliminate scratches, improved pallet fell way ; coiled head and tail plus protective pad , to prevent scratches when packing ; rod in the stacking process plus scratch pad ; playing packaging to prevent stacking, transportation , loading and unloading process occurs scratch .