Development of Advanced High-Strength Steel in China
The development of advanced high-strength steels (AHSS) plays an important role in the development of modern vehicle manufacture and steel processing industries and is beneficial to Chinas economic development. In this regard, due to the low consumption of advanced high strength steel in China, it is necessary to increase the consumption of advanced high strength steel in the near future.
Advanced high strength steels (AHSS) are steels that possess beyond traditional high strength properties, with strength level of the order of several hundreds of megapascals. These steels are used to meet the growing demand for lighter weight vehicles and components. AHSS generally refers to a range of steels that are produced with enhanced mechanical properties through variations in composition, and changes to the austenite grain size, processing parameters and the final heat treatment process.
The introduction of advanced high strength steels (AHSS) to the Chinese steel industry began in the late 1990s and has seen significant advances in production capability and applications. China has adopted a number of ASTM, DIN and other international standards to enable the production of AHSS. The production processes and material properties of AHSS are divided into three categories: Dual-Phase (DP), Transformation-Induced Plasticity (TRIP), and Martensitic Steels.
The most widely used advanced high-strength steels in China are the dual-phase (DP) and transformation-induced plasticity (TRIP) steels. Dual-Phase steels combine the high strength of a martensitic phase, with the improved plasticity of a ferritic phase. The presence of a ferritic phase makes the steel more formable, while the addition of a martensitic phase yields high strength and improved fatigue properties, as well as enhanced welding properties. Contemporary car bodies often use such steels in order to lighten the car structure. DP steels are typically produced from high-manganese (Mn) grades and displayed under the family of CSA105, CSA165 and CSA245.
In contrast to DP steels, transformation-induced plasticity (TRIP) steels exhibit higher strength by forming a mixture of martensite, bainite and retained austenite, with the latter two phases providing excellent ductility and simultaneous high strength. The most common TRIP grade in China is XGL210, which is widely used in car bodies due to its excellent formability, strength and welding properties. Other grades of TRIP steels such as XGL390, XGL450 and XGL500 are increasingly being used in cars as well.
Last but not least, martensitic steels are produced by a heat treatment process that alters the microstructure in order to generate an ultra-high strength and excellent wear resistance. The introduction of microalloying elements, such as niobium, vanadium and titanium, makes these steels even better. Common martensitic steels used in China are XGL750 and XGL1000, which are mainly used in automotive components due to their high strength and wear-resistant properties.
In conclusion, advanced high-strength steels (AHSS) have become increasingly important in the Chinese steel industry in recent years, with development focusing on the production and application of dual-phase (DP), transformation-induced plasticity (TRIP), and martensitic steels. The use of these steels provides lighter weight and improved formability, strength and wear-resistant properties in a range of applications.
