Uncertainty Evaluation of Vickers Hardness Measurement for Resistance Welding Joint of DP780 High Strength Steel

The Vickers hardness of base metal, heat affected zone and weld zone of resistance welding joint of DP780 high strength steel was tested by direct evaluation method with 430SVD digital microhardness tester. The influences of different factors on the measurement results were analyzed, and the uncertainty of Vickers hardness measurement results was evaluated. The results show that the uncertainty of Vickers hardness measurement of base metal, heat affected zone and weld zone of resistance welding joint of DP780 high strength steel is 9, 9, 10 HV respectively, which meets the maximum allowable error of hardness tester in table 5 of GB/T 4340.2—2012, and the Vickers hardness testing method and testing level can meet the requirements of national standard. Compared with the hardware facility error of hardness tester, the measurement of indentation diagonal length has a greater impact on the evaluation result of combined uncertainty.