Research On Welding Residual Stress Testing Technology For Ni-based Alloy

Welding residual stress of Ni-based alloy, typical Inconel 690 welded joints and, with the Hole-Drilling Strain Gage Method and indentation method was investigated. The research results can have a guiding role on welding residual stress test technology for Ni-base alloy.The paper studies the influence factors on measuring residual stress of nickel base alloy with Hole-Drilling Strain Gage Method. Fitting Experiments between hole sizes and strain gauge found that for measuring of residual stress of Inconel 690, the greater of the bit diameter, greater of the cutting strain for the same kind of the strain foil. When, we drill the strain foil of BE 12 0-2CA-B type with bit of 2.4 mm diameter, it was found that the strains in three directions were the most homogeneous. The determined fit between hole sizes and strain gauge is that bit of 2.4mm diameter. and the strain foil of BE120-2CA-B type.The coefficients of A and B of Inconel 690 for stress calculation through the following three methods,the oretical arithmetic, strain-gage method and non-gage method. The experimental results indicated that the residual stress determined with the coefficient by theoretical arithmetic is higher than that with the coefficient by strain-gage method. The difference value is about 200MPa. However, the result of the strain-gage method and non-gage method is close, but the mechanisms are different. We believe that the calibration value is exacter than theoretical value. In this thesis, the calibration method is strain-gage method. The calibrated coefficients of A and B are that A equals -0.3659×10^-6mm²/N, and B equals -0.5579×10^-6mm²/N.The tests of the welding residual stress on butt welding plate and multi-layer cladding of Inconel 690 with the Hole-Drilling Strain Gage Method and indentation method. The stress measuring results with two methods are close. The difference value on butt welding plate is greater, and the value is 33MPa, about 8% of the average. With indentation method, the indentation pattern will become irregular, and it will lead to low results if the indentation device is not vertical to plane onto the test points.The welding residual stress of multi-layer cladding with Ni327 Ni-based alloy electrode was also measured with the calibration coefficient of Inconel 690. The stress measured with Hole-Drilling Strain Gage Method is about twice of the indentation method. The average stress with Hole-Drilling Strain Gage Method is about 0.8σ_s, and the residual stress value of the Weld zone is above 0.7σ_s generally, Hole-Drilling Strain Gage Method is more accurate. The applicability of Hole-Drilling Strain Gage Method calibration coefficient is better than that of the indentation method calibration coefficient.