The Effect Of Pre Deformation And Annealing For Ultra Low Carbon Bake Hardening Steel

For the ultra low carbon steel, mainly studied the affect of annealing process,numbers of continuous annealing and predeformation stretching rate. Use drawing machine test determination of BH values under different process conditions. under different conditions using internal friction instrument analysis internal friction temperature line. Under the metallurgical microscope and transmission electron microscopy observation the grain size and dislocation configuration. By using electron probe test the distribution of elements in steel. The research contents and main conclusions as follows:(1) Experimental steel water treatment at 750 ℃ 780 ℃ 810 ℃ temperature insulation 2min 5min 8min. With the increase of annealing temperature and holding time grains size increase gradually. The carbon content of interstitial solid solution increase. Samples through baking processing after 2% pre deformation and 170 ℃heat preservation 20 min. BH values increase gradually with the increase of annealing temperature and holding time. Grain boundary internal friction peaks reduce gradually with the annealing temperature increase, relaxation widths decrease and peaks temperature gradually move to the high temperature. Grain boundary internal friction peaks decrease gradually with the increase of annealing holding time, relaxation widths decrease, grain boundary internal friction peaks temperature move gradually toward to the low temperature. The pre deformation gradually increases, the value of BH decreases first and then increase slightly, the grain boundary internal friction peaks decrease gradually first and then increase a little.(2) Sample from room temperature uniform heate to 700 ℃ in the internal friction furnace uder the pre deformation of 2% 4% 6%. To determine the internal friction grain boundary peaks. SKK peaks decrease with the increase of heating time,grain boundary internal friction peaks decrease fist and then increase, the temperature of internal friction peaks move to the high temperature, relaxation widths decrease fist and then increase. Measurement the BH values use the same heating mode of the grain boundary internal friction peaks. BH values decrease with the increase of heating times.(3) Within 2%-6% pre deformation, the experimental steel using five different tensile rates to uniaxial tensile pre deformation and under 170℃ heat preservation bake 20 min. BH values first increase then decrease as the pre deformation increase at the same velocity tensile. Sneok peaks rise gradually, SKK peaks reduce gradually,BH values decrease, yield platform lengths decrease with the increase of stretch rate.