| Low carbon boron cold heading steel is mainly used for fasteners on the automotive, machinery and so on. Trace boron elements is adding to improve the high temperature mechanical properties of materials, and save precious metals and other elements, which is an important direction of the application of cold heading steel. In this paper, the influence of boron content and strain rate on low carbon boron cold heading steel is studied by hot tensile test, and analytical tools such as SEM, TEM. Qualified 10B06 slab is produced by a process test on a Concast contiuous casting machine. Single pass hot compression tests was taken out to do reseasch on the hot flow behavior of 10B06, and the constitutive equation is also derivated; finite element simulation was used to study the effect of rolling temperature on the deformation principle in the process of rough rolling, and process tests is carried out on tape roll production line. The main research results are as follows:(1) High temperature tensile deformation behavior of 10B06 and 10B15 is carried out on a Gleeble 1500 thermal simulation testing machine at the temperature range of 750℃~950℃. In comparison with deformed at strain rate 1×10-3 s-1, the elongation after rupture of 10B06 with boron content 17 ppm deformed at 5×10-4 s-1 is improved by 5% at all the temperature range. Hot brittle zone of 10B15 at range from 850℃to 900℃is shallowed and narrowed, and the elongation is raised by about 5%.(2) Process tests were carried on a Concast contiuous casting machine for 10B06 cold heading steel. A good surface quality of 10B06 can be produced by controlling the boron content, lowering casting speed and water intensity for increasing the second cold slab surface temperature to avoid the brittle temperature range, and the proper boron content and production process for the steel after adjustment is: boron content 5~35ppm, casting speed 2.6~2.7m/min, water intensity 0.97.(3) Hot flow behavior of 10B06 is studied by single pass hot compression tests on a MMT200 machine on the strain rate of 0.01~20 s-1, and temperature range of 750~1100℃. Flow softening behavior of 10B06 steel is the result of combined effects of dynamic recrystallization, dynamic recovery and work hardening. Soften effect is dominated by dynamic recrystallization under lower deformation temperature and smaller strain rate, and by dynamic recovery under higher deformation temperature and larger strain rate. The thermal activation energy of this steel is 220.1323 kJ·mol-1, and the constitutive equation is:ε& = 7. 86×108 sinh(0.007423σ) 5.2724exp( ?220132.3 8 .3 14T )(4) Deformation principle during rough rolling of 10B06 was simulated by finite element analysis software DEFORM, and the strain, deformation zone equivalent stress, temperature, rolling force and rolling moment is obtained. The cross-section shape and size of the billet after rolling is almost consistent at rolling temperature 1020, 1050, 1080℃. When the rolling temperature is 1050℃, temperature distribution on surface and cross-section of the billet is the most uniform, the change of rolling force is small, the inner damage is the smallest.(5) Process tests of 10B06 cold heading steel wire rod is carried out on tape roll production line. When the tapping temperature is 1050±20℃, after the high wire rod rolling, the surface quality is improved, scarring and other defects is disappeared, good performance of cold heading is acquired, and cold forging pass rate is increased from 60% to 100%. |
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