Study on Properties and Microstructure of HSLA Series Steel for Automotive

Aiming at the low alloy series high strength (HSLA) steel for automobile, the material characterization methods such as metallographic microscope, tensile testing machine, scanning electron microscope and transmission electron microscope were used to conduct in-depth comparative study on its properties and microstructure. The results show that Nb element is added to the low alloy series high strength steel. With the increase of Nb content, the average grain size grade of ferrite increases gradually and the strength increases. The test steel has good comprehensive mechanical properties, and its yield ratio exceeds 0.7, and the maximum value reaches 0.82. However, the two grades of HC260LA and HC300LA have obvious yield platform phenomenon. In addition, HC420LA shows a certain degree of excess performance. In terms of micro-texture, incomplete γ fiber texture (<111>//ND) is formed in HC380LA and below strength grade steel, while HC260LA also contains α fiber texture (<110>//RD) which is unfavorable to deep drawing performance. The size of NbC precipitates in the steel is mainly concentrated in the range of tens of nanometers, and the maximum is not more than 100 nm. With the increase of the number of NbC precipitates, the dispersion strengthening effect increases, which plays an important role in series HSLA steel. Based on the comparative analysis of the properties and microstructure characteristics of series HSLA steel, the targeted composition system adjustment and process optimization design ideas were proposed to further improve the comprehensive performance of the material.