At Baoshan Iron ＆ Steel Co., Ltd., comer cracks of boron containing LCAK steel slabs had caused remarkable quality loss and mass flow disorder. With the help of fractography and thermodynamics analysis, the embrittle...At Baoshan Iron ＆ Steel Co., Ltd., comer cracks of boron containing LCAK steel slabs had caused remarkable quality loss and mass flow disorder. With the help of fractography and thermodynamics analysis, the embrittlement mechanism of this steel grade was studied and the results are as follows： 1 The transformation from 3＇ to a starts at the austenite grain boundaries and a layer of thin ferrite film gradually forms around the austenite grains. Strain concentration will preferentially start inside the ferrite phase when the stress accumulates to a certain level. 2 The coarse BN particles acceleratedly precipitated at the γ/α interfaces further deteriorate the ductility of the ferrite film, and brittleness results in strain concentration and microvoid coalescence inside the ferrite film. Therefore the austenite grain boundaries are prone to intergranular failure. 3 The stoichiometry among Al, N and B is a very important factor influencing the hot ductility of this steel grade. By controling the B-to-N atomic ratio to above 1, all N can be fixed by B instead of A1. Thus coarsegrained steel is available and fewer grain boundaries and higher ductility can reduce the risk of comer cracks. （4） By adjusting the B-to-N atomic ratio,Baoshan Iron ＆ Steel Co.,Ltd. successfully reduced the number of cracks to nearly one tenth of that in the past and the hot tensile tests confirmed remarkable improvement in the hot ductility of this steel.展开更多
The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing...The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing the formation of the internal cracks was established, in which the strains at the solidifying front caused by' bulging, straightening or unbending, and roll misalignment were calculated and compared with a critical strain value to estimate whether the internal cracks form. Moreover, the established model was appliedto a real slab caster to reveal the distribution of the strains in casting direction and its effect on the internal cracks. It was proved that themodel was reliable and useful for optimizing the operation of continuous casting.展开更多
An antiplane crack problem concerning a pair of coplanar cracks in a finite transversely isotropic elastic slab is considered. Using Fourier integral transform together with singular integral equation which can be sol...An antiplane crack problem concerning a pair of coplanar cracks in a finite transversely isotropic elastic slab is considered. Using Fourier integral transform together with singular integral equation which can be solvel numerically by suing a collocation technique. Once the integral equation is solved, the relevant crack energy and stress intensity factors of the problem are given. The analysis present can be easily extended to include cases where there are two or more pairs of coplanar cracks in the slab.展开更多
The problem of a transversely isotropic elastic slab containing two coplanar cracks subjected to an antiplane deformation is considered. With the aid of an integral transform technique, we formulate the problem in ter...The problem of a transversely isotropic elastic slab containing two coplanar cracks subjected to an antiplane deformation is considered. With the aid of an integral transform technique, we formulate the problem in terms of a finite-part singular integral equation which can be solved numerically, Once the integral equation is solved, relevant quantities such as the crack energy can be readily computed.展开更多
文摘At Baoshan Iron ＆ Steel Co., Ltd., comer cracks of boron containing LCAK steel slabs had caused remarkable quality loss and mass flow disorder. With the help of fractography and thermodynamics analysis, the embrittlement mechanism of this steel grade was studied and the results are as follows： 1 The transformation from 3＇ to a starts at the austenite grain boundaries and a layer of thin ferrite film gradually forms around the austenite grains. Strain concentration will preferentially start inside the ferrite phase when the stress accumulates to a certain level. 2 The coarse BN particles acceleratedly precipitated at the γ/α interfaces further deteriorate the ductility of the ferrite film, and brittleness results in strain concentration and microvoid coalescence inside the ferrite film. Therefore the austenite grain boundaries are prone to intergranular failure. 3 The stoichiometry among Al, N and B is a very important factor influencing the hot ductility of this steel grade. By controling the B-to-N atomic ratio to above 1, all N can be fixed by B instead of A1. Thus coarsegrained steel is available and fewer grain boundaries and higher ductility can reduce the risk of comer cracks. （4） By adjusting the B-to-N atomic ratio,Baoshan Iron ＆ Steel Co.,Ltd. successfully reduced the number of cracks to nearly one tenth of that in the past and the hot tensile tests confirmed remarkable improvement in the hot ductility of this steel.
文摘The internal cracks in continuously cast slabs are attributed to the excessive tensile strain occurring at the solidifying frontduring the continuous casting process. Based on the understanding, a model for diagnosing the formation of the internal cracks was established, in which the strains at the solidifying front caused by' bulging, straightening or unbending, and roll misalignment were calculated and compared with a critical strain value to estimate whether the internal cracks form. Moreover, the established model was appliedto a real slab caster to reveal the distribution of the strains in casting direction and its effect on the internal cracks. It was proved that themodel was reliable and useful for optimizing the operation of continuous casting.
文摘An antiplane crack problem concerning a pair of coplanar cracks in a finite transversely isotropic elastic slab is considered. Using Fourier integral transform together with singular integral equation which can be solvel numerically by suing a collocation technique. Once the integral equation is solved, the relevant crack energy and stress intensity factors of the problem are given. The analysis present can be easily extended to include cases where there are two or more pairs of coplanar cracks in the slab.
文摘The problem of a transversely isotropic elastic slab containing two coplanar cracks subjected to an antiplane deformation is considered. With the aid of an integral transform technique, we formulate the problem in terms of a finite-part singular integral equation which can be solved numerically, Once the integral equation is solved, relevant quantities such as the crack energy can be readily computed.
