Wyniki wyszukiwania - BazTech

1

The microstructure and mechanical properties of FSPed HSLA steel

Aktarer S. M., Küçükömeroğlu T.

Journal of Achievements in Materials and Manufacturing Engineering

|

2016

|

Vol. 75, nr 2

55--60

EN

Purpose: High-strength low-alloy (HSLA) steels have been used in a wide range of applications from automotive to ship building industry due to their low weight, formability and good weld ability. However, especially in the automotive industry, it is still attempted to improve this steel for the better formability and strength properties. Grain refinement is a well-known method to improve mechanical properties of metallic materials without changing their chemical compositions. Friction stir processing (FSP) is a new method of enhancing the properties of metals as a result of grain refinement by severe plastic deformation, which is based on the basic principles of Friction Stir Welding (FSW) technique. The purpose of this study is to investigate microstructural alteration and the main mechanical properties of HSLA after friction stir processing. Design/methodology/approach: HSLA steel sheet with a thickness of 1.5 mm was processed using a tungsten carbide (WC) tool consisting of a cylindrical shoulder and a cylindrical conical pin. The parameters of FSP are kept to a fixed tool rotation speed of 1600 rpm, traverse speed of 170 mm.min-1 and down force of 5 kN. The evaluation after and before FSPed of HSLA steel was performed by optical microscope, scanning electron microscope, tensile test and hardness measurement. Findings: After FSP, refined microstructure brought about a considerable increase in both hardness and strength values. The increase in the yield and tensile strength after FSP was about30% and 34%, respectively. Research limitations/implications: Electron backscatter diffraction (EBSD) mapping could not be done in this study. The EBSD mapping should be performed for detailed microstructural characterization of processed zone such as grain size distribution and misorientation angle distribution. Practical implications: FSP can be applied to other steel to obtain high strength steel without any decrease in their ductility properties by means of grain boundary strengthening mechanism. Originality/value: FSP, as a severe plastically deformation technique, is applied to many aluminium alloys and steels. However, only few studies were reported on FSPed HSLA steels. Moreover, further investigations are needed to identify the microstructural and mechanical properties of the FSPed HSLA steels.

2

The effect of nitrogen and vanadium on hardenability of medium carbon 0.4 %C and 1.8 %Cr steel

Adrian H., Staśko R.

Archives of Materials Science and Engineering

|

2008

|

Vol. 33, nr 2

69-74

EN

Purpose: To investigate the effect of V and N on hardenability of steel containing 0.4 % C and 1.8 % Cr. Design/methodology/approach: Four laboratory melts with different N and V contents were used. Hardenability of steel was investigated using standard Jominy test and Grossmann analytical method. The effect of calculated undissolved carbonitride V(C,N) content on austenite grain size was investigated. Findings: Nitrogen addition without microalloying elements increased the austenite grain size. Very high hardenability was obtained in steel containing 0.004 %N and 0.08 %V at 870°C. Addition of 0.08 %V at elevated nitrogen content significantly decreased the grain size and at 870°C increased the hardenability of steel. Practical implications: Investigated steel showed very high hardenability with ideal critical diameter DiJ approximately 200 mm, at appropriate austenitizing temperature. Higher nitrogen content in steel with vanadium addition retards austenite grain growth in broad austenitizing temperature range. Originality/value: Results of investigations provide valuable information on the effect of vanadium and nitrogen content on the hardenability of quenched and tempered steel with 1.8 % Cr. Thermodynamic calculations enable to select the optimum austenitizing temperature range.

3

Wpływ mikrostruktury stali niskostopowych o wysokiej wytrzymałości na ich spawalność

Ćwiek J., Łabanowski J.

Inżynieria Materiałowa

|

2003

|

R. XXIV, nr 6

709-711

PL

Mikrostruktura stali niskostopowych o wysokiej wytrzymałości wpływa na skłonność do pęknięć zimnych ponieważ ma wpływ na hartowność i twardość maksymalną strefy wpływu ciepła (SWC). Dwa gatunki stali o wysokiej wytrzymałości 18G2AV i 14HNMBCu, w różnych stanach obróbki cieplnej, zostały poddane symulowanym cyklom cieplnym spawania. Maksymalna twardość SWC zależna jest od rodzaju mikrostruktury przed cyklem cieplnym spawania. Najwyższą twardość w SWC obserwowano dla stanu ulepszonego cieplnie w porównaniu ze stanem wyżarzonym zupełnie i przegrzewająco.

EN

Microstructure of steel before welding has influence on the steel's susceptibility to cold cracking because it influences hardenability and maximum hardness of heat affected zone (HAZ). Two high-strength low-alloy (HSLA) steel grades 18G2AV and 14HNMBCu, in various heat treatment conditions, were subjected to simulated welding thermal cycles. It has revealed that maximum HAZ hardness is influenced by microstructure presented before thermal cycle was applied. The higher HAZ hardness was observed for quenched and tempered condition, comparing to full annealed and overheated conditions.