Comparative Study on Impact Fracture Behaviors of Domestic 4Cr5Mo2SiV Modified Steel and Similar Imported Hot Work Die Steel
Hot work die steel requires good toughness ratio, impact toughness has always been a more important reference index, to improve the impact toughness of the material has been the focus of research in this area.
Domestic 4Cr5Mo2SiV modified steel is 4Cr5MoSiV1 based on the appropriate reduction of Si, V content, increase the content of Mo obtained high-performance hot work die steel, which has good resistance to thermal fatigue cracking, thermal shock cracking, thermal wear, plastic deformation The performance, and become the best die casting, hot forging, hot extrusion die steel. The same type of imported steel is also a high-performance hot-work die steel containing chromium, molybdenum and vanadium. It is made from the pure hot metal by adding the necessary pure alloying elements and is all ESR-treated so that it has a very high degree of purity and is comparable High temperature wear resistance and high temperature toughness and high resistance to thermal mutation, it is suitable for the manufacture of complex large-scale precision die-casting mold. To this end, some researchers compared the metallurgical structure and impact toughness of the domestic 4Cr5Mo2SiV modified steel with that of the imported steel, and analyzed the gap between domestic materials and imported materials at the quality control level.
4Cr5Mo2SiV improved steel samples taken from a domestic steel mill, the manufacturing process is as follows: induction melting → electrode rod annealing → ESR → ESR annealing → high temperature homogenization → multi-forging → annealing. The imported steel samples were taken from the annealed materials produced by a steel mill abroad. The samples were quenched with vacuum oil at 1030 ° C, then subjected to stress annealing in a 101A-1 oven, and then annealed in a S2-5-12 box heat treatment furnace Heat at 600 ℃ for 2h, air cooled and then heated to 605 ℃ for 2h, the final hardness of the sample is controlled at 44 ~ 46HRC range.
The optical microscope was used to detect the inclusion, segregation and spheroidization of the annealed metallographic samples of the two materials. The grain size is graded by comparison with NADCA # 207-2006 and GB / T 6394-2002 standards. According to GB / T 229-2007 test material impact toughness. The impact test after the sample fixture using clips, the first observation of the fracture surface morphology with a scanning electron microscope, and then cut the sample longitudinally, and then using optical microscopy and scanning electron microscopy microstructure. According to GB / T 4340 standard test specimen near the impact of the hardness. The results showed that:
(1) Although the quality of the domestic 4Cr5Mo2SiV improved steel is well controlled and reaches a high level of quality, the uniformity of its structure and the control of banded segregation are slightly inferior to that of imported steel compared with the imported steel. That domestic steel heat treatment process is still room for further improvement.
(2) The brittle oxide inclusions existing in the dimples of 4Cr5Mo2SiV steel become the formation of micro-cracks during fracture, resulting in the decrease of material toughness, thus improving the purity of materials and controlling the inclusions at a higher level to increase the material impact toughness.
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