| The steel 30CrMnSiNi2A is a kind of low-alloyed and ultra-strength steel which is used extensively in China. It is applied to many fields, such as the aviation, spaceflight, naval vessel, transportation and national defense. It is important to study its mechanical behavior under dynamic loadings and mathematical model-dynamic constitutive equation. In this paper, heat treatment, static experiments were first carried out by using heat treatment sets and MTS. The effects of heat treatment on hardness and yield strength of 30CrMnSiNi2A were studied. Then, by using SHPB apparatus, dynamic properties under different heat treatment were systematically studied. The main contents were as follows:1) Six specimens were intercepted from steel 30CrMnSiNi2A projectile body that was extrusion forming. One did not apply any heat treatment. The other applied quenching at 860℃and oil cooling with cabinet-type electrical resistance furnace, then tempering drawing at 200℃, 300℃, 400℃, 500℃, 600℃and oil cooling were carried out. After heat treating, the hardness values of steels with different heat treatment were measured with Rockwell hardometer. The results showed that hardness value of steel by normalizing treatment was the lowest. The hardness value of the others steels incremented with the degradation of tempering temperature. The organization changes of steel under the system of different heat treatment were analyzed through the metallographic picture.2) Three groups of materials were selected to carry out static and dynamic experiments. The first group was applied normalizing treatment. The second group was applied quenching at 860℃and oil cooling, then tempering drawing at 200℃. The third group was tempering drawing at 600℃. They were made into small specimens with dimensionΦ4×6mm. The static experiments with strain rates 10-1/s and 10-3/s were carried out by using universal material test machine. Static stress-strain curves were obtained under various strain rates. Static strain-stress curves of specimens under different strain rates were compared. Conclusions were drawn: yield strength of specimens showed certain strain rate sensitiveness. Yield strength of the same group under various strain rates increased with strain rate rising. Under the same strain rate, yield strength of the first group was the lowest and other groups incremented with decreasing of tempering drawing temperature. 3) The dynamic compression experiments of the above three groups of steel30CrMnSiNi2A were carried out by using SHPB apparatus. The specimens were cylindrical with dimensionΦ4×4mm,Φ3×2mm andΦ1×1mm. The mean strain rate were individually 1000/s, 3000/s, 5000/s, 10000/s, 12000/s. The dynamic yield strength under various strain rates was obtained. It could be concluded from dynamic stress-strain curve that yield strength incremented with increasing of strain rate under the same heat treatment condition. Under the same strain rate that yield strength of the first group was the lowest and the other groups still incremented with decreasing of tempering drawing temperature under the same strain rate.4) The relationship of yield strength to strain rate of 30CrMnSiNi2A were obtained according to the static and dynamic experimental results and the formula presented by Perzyna:Normalizing treatment:Quenching at 860℃and tempering drawing at 200℃:Quenching at 860℃and tempering drawing at 600℃:The results showed excellent agreement between theory and experiments. The Perzyna model could express the relationship of yield strength to strain rate of 30CrMnSiNi2A.Constitutive equations of 30CrMnSiNi2A which were studied in this paper were fitted by using static and dynamic experiment results and Johnson-Cook model:Normalizing treatment: Quenching at 860℃and tempering drawing at 200℃: Quenching at 860℃and tempering drawing at 600℃:The theory results showed good agreement with experimental results.5) Based on the above experimental results, on condition that considering strain rate, employing the analytic approach of finite element, the thesis carried out the simulation to the SHPB dynamic compressive test technology, and has carried out the finite element analysis result and the test result the comparison. |
PDF Full Text Request