The industrial level production of ultrafine grained （or ultrafine ferrite） ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced c...The industrial level production of ultrafine grained （or ultrafine ferrite） ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced con- trolled hot rolling techniques. The steel samples were tension tested and chemically analyzed, and the microstructure was evaluated through quantitative metallographic techniques to determine parameters such as yield stress, amount of microalloying elements, strain hardening coefficient, grain size, and grain size distribution. These steels were micro- alloyed with Ti, Nb, and Mn with ASTM grain sizes of approximately 13--15. The careful control of chemical com- position and deformation during production, giving a specific attention to the deformation sequences, austenite non- reerystallization temperatures and allotropic transformations during cooling, are indispensable to obtain steels with an adequate strain hardening coefficient that allows cold working operations such as bending, stretching or drawing.展开更多
Steels with ultrafine grains （lower than 5 μm）, which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fr...Steels with ultrafine grains （lower than 5 μm）, which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fracture toughness they may reach compared to conventional steels （with grain sizes above this value）. It is shown that the forenamed steels designated in the Euronorm EN 10149-2, which are manufactured by advanced techniques of controlled rolling and mainly used in automotive industry, have an ultrafine grain size in the range of 2.5 to 3.5 μm, and with elastic yield stresses higher than 400 MPa. Based on the Morrison-Miller criterion, it is shown that values of the strain-hardening coefficient lower than 0.08 would make the industrial application of these steels unfeasible.展开更多
文摘The industrial level production of ultrafine grained （or ultrafine ferrite） ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced con- trolled hot rolling techniques. The steel samples were tension tested and chemically analyzed, and the microstructure was evaluated through quantitative metallographic techniques to determine parameters such as yield stress, amount of microalloying elements, strain hardening coefficient, grain size, and grain size distribution. These steels were micro- alloyed with Ti, Nb, and Mn with ASTM grain sizes of approximately 13--15. The careful control of chemical com- position and deformation during production, giving a specific attention to the deformation sequences, austenite non- reerystallization temperatures and allotropic transformations during cooling, are indispensable to obtain steels with an adequate strain hardening coefficient that allows cold working operations such as bending, stretching or drawing.
文摘Steels with ultrafine grains （lower than 5 μm）, which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fracture toughness they may reach compared to conventional steels （with grain sizes above this value）. It is shown that the forenamed steels designated in the Euronorm EN 10149-2, which are manufactured by advanced techniques of controlled rolling and mainly used in automotive industry, have an ultrafine grain size in the range of 2.5 to 3.5 μm, and with elastic yield stresses higher than 400 MPa. Based on the Morrison-Miller criterion, it is shown that values of the strain-hardening coefficient lower than 0.08 would make the industrial application of these steels unfeasible.
