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Relationship between microstructure and mechanical properties of strips from microalloyed steel after cold rolling and annealing

Janošec M., Schindler I., Vodárek V., Místecký E., Růžička M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2007

Vol. 321, z. 89

105-106

A large testing programme of an HSLA strip steel grade S 500 MC was conducted. The experiment was based on combination of cold rolling, recrystallization annealing, mechanical testing and metallographic examinations. Samples of pickled cuts of hot rolled strip of thickness 4 mm were used for simulation by rolling. Chemical composition of the steel grade was as follows: 0.06 C - 1.38 Mn- 0.24 Si - 0.013 P - 0.005 S - 0.022 Al - 0.03 V - 0.02 Ti - 0.07 Nb (wt %). Samples in the form of strips with dimensions 4 x 25 x 340 mm were rolled in several passes with total height reduction 5 to 75 %. Particular partial strains were realized at room temperature in the housingless, hydraulically pre-stressed laboratory mill QUO (a four-high mill with work rolls of diameter 62 mm) [1]. Afterwards the laboratory mill products were annealed in the vacuum furnace with the protective gas atmosphere consisting of N2+H2. The annealed samples underwent the mechanical testing. The gained results yield stress YS, ultimate tensile strength UTS and their ratio, as well as elongation Ago in %, were summarized in graph (see Fig. 1) in dependence on relative height reduction before annealing - 8 [%]. The found out points were plotted in a coordinate system and the corresponding curves were constructed manually. It was confirmed that by a suitable combination of size of previous cold deformation and parameters of the following recrystallization annealing it is possible to influence a complex of mechanical properties of particular strips. Particular trends of strength and plastic properties correspond to each other. These trends are caused by structure-forming processes (deformation strengthening, recrystallization) which were documented by micrographs (see Fig. 2 for example). Values of strength properties may be influenced by the described way in the range of approximately 100 MPa, which enables - related to applications in practice -to use the obtained results in formation of technological procedures of forming and heat treatment in cold rolling mills.

Influence of cold rolling and annealing on mechanical properties of steel QStE 420

Schindler I., Janošec M., Místecký E., Růžička M., Čížek L., Dobrzański L. A., Rusz S., Suchánek P.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 18, nr 1-2

231--234

Purpose: was to investigate impact of cold reduction size and annealing on mechanical properties of HSLA steel. Design/methodology/approach: Testing of strip steel QStE 420 was based on a combination of cold rolling, recrystallization annealing, mechanical testing and metallographic analyses. Findings: It was confirmed that by a suitable combination of size of previous cold deformation and parameters of the following annealing it is possible to influence considerably a complex of mechanical properties of particular strips. Strength properties were more or less decreasing with the rising annealing temperature, whereas plastic properties were increasing. Research limitations/implications: The experiment should be supplemented by additional modes of soft- and recrystallization annealing. Practical implications: The results may be utilized for optimization of terms of heat treatment in a cold rolling mill, exactly in accordance with specific requirements for a relation between plastic and strength properties of the investigated material. Originality/value: Research possibilities of VSB-TUO in the sphere of cold rolling were introduced for the first time.