Electron beam welding of D6A ultra high strength steel

D6A steel has a high carbon equivalent of about 1.04%, and its welding hot crack and cold crack sensitivity are quite high, and the weldability is very poor. If no effective measures are taken, the weld is prone to cracking. A series of process tests were carried out on the D6A steel hollow cylinder docking structure by electron beam welding, in an effort to achieve equal strength welding of D6A steel.

The test piece has a step ring and a docking ring. Initially find the parameters with the step ring to grasp the correspondence between the electron beam current and the depth of the weld, and use the docking ring to determine the exact specification to reach the predetermined weld depth. The test is carried out on a high-pressure high-vacuum electron beam welder, which mainly optimizes parameter matching, takes effective and feasible measures to prevent weld cracks, pores and other defects; develops a suitable post-weld heat treatment process to ensure the strength, plasticity, toughness, etc. of the welded joint. The indicator is as close as possible to the base metal.

To prevent the occurrence of cracks, the parameters should be optimized to achieve the deep-welding effect of electron beam welding, and the "I"-shaped welds with deep and narrow widths and nearly parallel widths can be obtained to reduce joint stress, deformation and stress concentration. To this end, the process mainly takes the following steps: First, increase the accelerating voltage, use a lower welding speed, and a smaller current to obtain a deep welding effect. The second is to focus at 40% to 50% of the predetermined depth of the weld under the surface, and the focus is deep into the workpiece.

To prevent the generation of air holes, the following measures are taken: the weldment is strictly cleaned before welding and dried to remove the oil and sewage; the appropriate parameters are selected so that the root of the weld is not too narrow and too narrow; the ∞ deflection function is used to select the appropriate frequency to make the electron The beam is agitated against the weld to facilitate gas escape and improve weld formation. Test piece after welding

X-ray inspection, the internal quality of the weld reached the GB3323–87 secondary standard. After quenching at 840 °C, tempering and tempering at 620 °C, micro-shear test and performance analysis of welded joints, the performance gradient curve is shown in Figure 1. The mechanical properties of the welded joints were as follows: tensile strength sb = 1190 MPa, deformation rate y = 22%, ak = 42.6 J/cm2, bending test (centre diameter f 5 mm) to 20 ° cracking, 30 ° fracture. The tensile specimen was taken from the base metal and the data was average.

Figure 1 performance gradient curve Figure 2 Weld Forming

The analysis shows that the weld zone and the base metal are basically equal in performance, and the yield strength and plasticity are slightly decreased. The fusion zone and the heat-affected zone have no sharp performance changes, the strength is slightly increased, the plasticity is slightly decreased, and the joint performance is excellent. The welded specimens were examined by dissection of the metallographic phase, and no defects such as microcracks or excessive pores were found. The welding depth is controlled within a predetermined range, the shape of the weld is reasonable, the section is deep and narrow, and the upper and lower sides are parallel, showing an "I" shape, as shown in Fig. 2. The microstructure of each part of the welded joint is tempered sorbite, and the structure is uniform and small.

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