In order to make steel have both good processing properties and high strength, bake hardening (BH) steel was developed using the age hardening principle.
The aging property is a characteristic in which carbon precipitates from the steel to form cementite after the steel is manufactured, thereby strengthening the structure and improving the performance. For ordinary stamping steel, the aging property has a great impact on the stamping performance of the steel. , so we must find ways to eliminate timeliness. However, through appropriate processes, the timeliness becomes the desired effect, which is not detrimental to the performance of the steel, but beneficial. Bake hardening steel takes advantage of this principle.
Bake Hardening Ability (BH) refers to the property that the steel plate has a low yield strength in the supply state after annealing and flattening, and the yield strength increases to a certain extent after stamping, spray painting and baking. BH properties are evaluated by BH value. The room temperature failure index AI value is used to measure the room temperature aging performance of bake-hardened steel plates.
According to the carbon content, bake-hardened steel is divided into low-carbon aluminum-killed high-strength BH steel and ultra-low carbon high-strength BH steel. It is obtained by adding a trace amount of niobium on the basis of low carbon aluminum-killed steel and ultra-low carbon steel. It is different from ordinary interstitial-free steel in that the carbon content is slightly higher and the niobium content is slightly lower. Its purpose The purpose is to control the atomic ratio of niobium and carbon so that the carbon content exceeds the number of carbides formed with niobium, that is, there are certain interstitial atoms in the steel, allowing them to form dislocations during processing and forming, resulting in work hardening. When baking at about 170°C after forming, solid solution carbon and dislocations work together. The solid solution carbon produces dislocation pinning, resulting in artificial strain age hardening, which increases the yield strength of the steel, thus achieving the goal of both forming and forming. , and has the purpose of good strength after forming, as shown in Figure 1-40. The effect of baking hardening is related to the content of solid solution carbon. The higher the content of solid solution carbon, the better the effect. However, the aging effect at room temperature is also very strong, which will cause natural aging before processing, so the content of solid solution carbon must be strict. control.
Bake-hardened (BH) steels are characterized by a significant increase (~10%) in the yield strength (YS) of the preformed parts after the paint operation during the manufacture of various automotive body parts (external door panels, exterior skins) . hood, fenders and trunk (trunk) lid, etc.). This increase in strength is called bake hardening response (BHR) and improves dent and impact resistance.
Motorists around the world rely on high-performance steel every day for reliable, safe operation. Use GNEE Steel's automotive-grade BH steel products to manufacture automotive components that keep the world running safely and efficiently. Contact us now for specific information!