Miroslav Német

IF Steel Effect of Rate Deformation on the Fracture Surface Change

Strain rate is a significant external factor and its influence on material behaviour in forming process is a function of its internal structure. In this contribution the influence of loading on the deformation IF steel is investigated using rotate hammer. To study the influence of rate deformation from 8.33 x 10-3 s-1 to 4000 s -1 to changes in the fracture of steel sheet used for bodywork components in cars. Experiments were performed on samples taken from interstitial free (IF) grade strips produced by cold rolling and hot dip galvanizing. Material strength properties were compared based on measured values, and changes to fracture surface character were observed.

Changes in Mechanical Properties and Microstructure after Quasi-Static and Dynamic Tensile Loading

Dual phase (DP), interstitial free (IF) and advanced high strength low alloy steel (HSLA)sheets have been successfully used for different components of car body. DP and HSLA are used ascrash resistant and IF as cover or “skin” of car body. The development of new vehicles nowadays isbeing driven by the need to simultaneously reduce mass and increase of passenger and pedestriansafety as well as costs saving through cold forming instead of hot forming. Limited publishedinformation is available on the changes in microstructure of these steel grades at different highstrain rates [1-3].This paper deals with changes of mechanical properties, microstructure and fractography of threesteel grades, which were tested at quasi static (10-3 s-1) and high strain rate (3000 s-1). Themicrostructures were characterized in terms of ferrite grain size, aspect ratio of ferrite andelongation of constituent phases. Deformed and undeformed specimens were compared to assess thechanges in the microstructure. The fracture appearance analysis indicates that the fracture patternunder high strain rates is mainly ductile, regardless of steel grades. The microstructure changessignificantly during the deformation process under both quasi-static and dynamic tension in allinvestigated steels. The plastic deformation in ferrite dominates in this process.

Changing the Hardness Automotive Steels at Different Strain Rate

Currently, the automotive industry used sheets of different qualities. The most common include IF (inter Interstitial Free) steel and alloyed steel. Use the sheet quality depends on the point of application in the production car. Testing and product testing is a standard part of the process of innovation and production itself. Testing of automotive steels under dynamic conditions is increasingly important. Changing the hardness HV 1 was performed on the fractured bars on the static and dynamic loading conditions. Tests were made on steel IF and S 460.

IMPACT OF STRAIN RATE ON MICROALLOYED STEEL SHEET BREAKING

Strain rate is a significant external factor and its influence on material behavior in forming process is a function of its internal structure. The contribution is analysis of the impact of loading rate from 1.6 x 10 -4 ms -1 to 24 ms -1 to changes in the fracture of steel sheet used for bodywork components in cars. Experiments were performed on samples taken from HC420LA grade strips produced by cold rolling and hot dip galvanizing. Material strength properties were compared based on measured values, and changes to fracture surface character were observed.

The Effect of Strain Rate on the Mechanical Properties of Automotive Steel Sheets

The automotive industry is currently seeking detailed information about various types of materials and their behavior under dynamic loading. Dynamic tensile testing of sheet steels is growing in importance. The experimental dynamic tensile technique depends on the strain rate. Each type oftest serves for a specific range of strain rates, and provides specific types of information. This workdeals with the influence of the strain rate on the mechanical properties of automotive steel sheets.Three different types of steel: IF steel, DP steel, and micro-alloyed steel (S 460) were used to compare static and dynamic properties.