In recent years, as car manufacturers are required to reduce parts, cost, lightweight and high strength. Especially, in the overseas to get more competitive than emerging automobile manufacturers price advantage, must be to minimize the cost of production is competitive in the local car. At the same time, in order to deal with the problem of environmental protection, to reduce CO2 emissions, to reduce fuel consumption, must try to reduce body weight.
To reduce the cost of parts, but also to reduce the cost of bolt. The production cost of the bolt, the blank costs accounted for the major part, the most effective way is to reduce the cost of materials. The Japanese auto manufacturers to reduce the cost of material supply, is studying the use of overseas cheap materials. However, due to the cleanliness of the quality of some of the production of bolt wire rod or plate than high, can not fully meet the requirements of the quality of Japanese automobile industry, so the current use of overseas steel car manufacturers are few.
On the other hand, in the light, the automobile manufacturers have carried out various studies. For the above to meet the requirements of users, making bolt manufacturers have also been to study on lightweight bolt. As the lightweight bolt measures, some use of aluminum or titanium and other light metal, some reduced bolt size. In these measures, although aluminum is much lighter than iron, but low strength. Although titanium is lighter than iron, and iron has the same strength, but is not easy to process, and the material cost is quite high. Based on the above reasons, the car with the bolt on the lightweight effective examples are few.
Reduce the bolt size can reduce weight, but if the decrease in the same strength grade bolt size, due to the reduced area of the bolt, the bolt fastening force will decline. Therefore, in order to ensure the same degree of strength, but also to reduce the size of the bolt, we must increase the strength of the bolt.
In the current JIS and other public standards and car manufacturers own standards, only the strength of the following 12.9 bolts to make provisions. When the strength is more than 12.9, the fracture characteristics of the ordinary quenched and tempered bolts will become worse. In some 10.9 and 12.9 high strength bolts has been used, if want to achieve the lightweight by reducing the size, we must use intensity more than 12.9 bolts, and use some methods to improve the delay fracture characteristics.
Quenched and tempered bolts to achieve high strength, and some by adding alloy elements to improve the delay fracture characteristics. Although the addition of alloying elements can improve the delay fracture characteristics, but because of the high cost of alloying elements, the cost of the rise is inevitable.
Another measure is the use of non quenched and tempered bolts. The bolt is in non quenched and tempered without tempering after forming (heat treatment), mainly through the work hardening material to ensure the strength of. Metal structure and bolt bolt of the non quenched tempered is completely different, it has a strong characteristic of delayed fracture resistance. The bolt is the use of non quenched and tempered carbon content than quenched and tempered high material bolt, by controlling the cooling and heat treatment at the billet stage, can obtain high section shrinkage rate, by drawing formed after work hardening, the hardening in the forming stage of bolt further ensures the bolt strength. Ordinary bolt in the forming after although not quenched and tempered, but in order to pass the cold forging to eliminate internal strain bolts, so it must be barffing. The disadvantage is the hardness of material than quenched and tempered high, very difficult to forming.
At present, for non quenched and tempered bolts of the engine strength is 1600MPa, for non quenched and tempered the strength of the bolt body has reached 1400MPa. Can be expected for high strength bolts of this demand will be further expanded in the future.