galvanized steel coil Test conditions
Galvanized steel coil
When measuring bake hardening value, in accordance with the provisions of GB / T228, the first on the specimen elongation of 2% of the total pre-stretch, while the measured Rt2.0. When the pre-stretched two percent of the sample to complete the required heat treatment, tensile test specimens again measured ReL or Rp0.2.
In order to better maintain the consistency of the test results, we should adopt the displacement or strain controlled stretching speed, and recommended a rate of 5% of the sample parallel to the length / min speed setting stretch, stretching from the beginning until the measure these indicators process, not the speed switch.
R = Ft2t2.0 / A0
Rp0.2 = Fp0.2 / A1
ReL = FeL / A1
Ft2.0 - specimen elongation to the total elongation of 2% of the tensile strength (N);
Fp0.2 - non-proportional sample after heat treatment tensile strength extension of 0.2% (no significant yield) (N);
FeL - sample after heat treatment under tensile force occurs at yield (N);
A0 - the original specimen cross-sectional area (mm2);
A1 - 2% cross-sectional area of the specimen after pre-strain (mm2).
D.3 heat treatment conditions
After heating device temperature reached 170 ℃ has been placed in pre-strain of 2% of the sample, a heating device to be re reach 170 ℃, insulation (20 ± 0.5) minutes. Temperature control to maintain the accuracy ± 2 ℃, the maximum resolution of a temperature measuring device does not exceed 1 ℃. After heating the sample was cooled to room temperature in air.
D.4 value bake hardening (BH2) Calculation
The value of bake hardening (BH2) is (when no significant yield) or a non-proportional extension strength after baking the sample at a yield of 0.2% corresponding to yield strength before and bake with a sample of the total extension of 2% of the corresponding yield strength difference. BH2 computing diagram shown in Figure D.1, calculated as follows:
BH2 = ReL (or Rp0.2) (after baking) - Rt2.0 (before baking)