Mechanism Of Crack Sealing Surface Welding Stainless Steel Cast Iron Valves

It is required to apply anti-corrosive coatings to the interior that is osculatory liquidto improve the corrosion resistance of the valve when functioning in the corrosivemedium. However, the sliding working surface of the brake valve cannot be coated,which calls for welding an anti-corrosive stainless steel coating to enhance thecorrosive resistance of the valve surface. Cast iron tends to generate welding cracks asit performs badly on welding. Thus that cracks come into being in welding heataffected zone and transition layer results in scrapped welding layer when welding theanti-corrosive stainless steel coating. Moreover, cast iron being with high carboncontent comes with the phenomenon that the hard phase that showing up on thewelding layer is hard to process. This paper is about welding A102、A402stainlesssteel electrode on samples with materials Q450-10、 HT250based onspheroidal graphite cast iron and gray pig iron valve welding stainless steel. Cast ironwelding stainless steel formation mechanism is concluded by observation and analysison microstructure of the welding joint and simulation of temperature field and postwelding residual stress distribution during the welding process with the help ofsoftware of infinite element analysis ANSYS. The conclusions can be arrived at asbelow:（1）Carbide and acicular Martensite arise in the high temperature and melt zonesof the welding heat affected area when welding monolayer austenitic stainless steelA402on QT450-10. Carbide structure comes into being in the weld zone as thecarbon in cast iron dissolves and distributes into the weld joint. The residual stressarrived at the maximum value260Mpa in the fuse zone after welding via infiniteelement simulation analysis on weld stress field of the welding zone. The combinedaction of fragility and residual stress is the primary reason for cracks’ appearing of thepost welding spheroidal graphite cast iron welding stainless steel monolayer.（2）Ferro-nickel welding rod is adopted to bead weld Z408, a thinner transitionlayer and then A102. The results show that carbide reduces apparently in the heataffected zone as lesser welding current is applied and that the Ferro-nickel bufferfunction cuts down the carbon distribution in the cast iron to weld joint which leads tothe obvious reduction of the carbide in the joint. The residual stress is lowered afterwelding as the weld heat input is comparatively lower when welding Z408transition layer and ferro-nickel narrows down the shrinking percentage effectively between thecast iron and stainless steel. Therefore, compared with QT450-10monolayer welding,QT450-10double–layer welding reduces the sensitivity to welding cracks.（3）Carbide and acicular Martensite arise in the high temperature and melt zonesof the welding heat affected area when welding monolayer austenitic stainless steelA402on material HT250, along with iron phosphide eutectic phenomenon in the fusezone. Meanwhile cracks tend to come into being when welding monolayeraustenitic stainless steel A402on HT250due to the existence of welding residualstress.（4）The simulation results show that the residual stress is large of the post weldingsamples joint and fuse zones and it reaches the maximum value260Mpa based onANSYS infinite element platform. As for the deal,welding current does not havemuch effect on residual stress peak value and it only shows that the larger the weldingenergy input, the wider of the relevant welding pulling stress area. The residual stressafter welding decreases along with the preheat increasing.