1 Foreword A reservoir maintenance gate door slot main rail design using the structure is a section of 40 × 60mm 1Cr13 stainless steel welded fixed in the thickness of 50mm Q235 steel plate. As the thermal conductivity and linear expansion coefficient of the two materials are very different, in order to ensure the quality of welding, careful analysis of the welding performance of the two materials and the existence of problems, and accordingly developed specific welding process measures.
2 welding performance analysis
1Cr13 stainless steel and Q235 carbon steel chemical composition and physical properties as shown in Table 1, 2.
1Cr13 stainless steel Cr content in 11.5% to 13.5%, while matching no more than 0.15% C, Cr itself can increase the austenitic stability of the steel, the addition of carbon after solidification and then air cooling will occur martensitic transformation, so 1Cr13 stainless steel weld and heat affected zone after welding state organization for hard and brittle martensitic organization. In addition, the carbon equivalent of 1Cr13 is about 2.76%, so its weldability is poor. As 1Cr13 stainless steel thermal conductivity than Q235 carbon steel is poor, welding residual stress, coupled with the main rail of this gate stiffness, so from high temperature directly cooled to 100 ~ 120 ℃ below is easy to produce cold cracking. Due to the role of welding thermal cycle, 1Cr13 stainless steel has a greater tendency to overheat, the grain is easy to coarsen, the heat affected zone will appear coarse ferrite and carbide organization, plasticity is reduced, cooling can cause embrittlement, if the role of hydrogen, the tendency of cold cracking is more obvious.
3 The main problems in welding
As 1Cr13 stainless steel and Q235 carbon steel chemical composition is very different, so their welding is a heterogeneous steel welding, to obtain a reliable welded joint under the conditions of fusion welding there are many problems.
3.1 The difference in thermal conductivity and specific heat capacity
The thermal conductivity and specific heat capacity of the metal strongly affects the melting of the welded material, the formation of the melt pool, as well as the temperature field of the weld area and the solidification of the weld crystallization. 1Cr13 stainless steel thermal conductivity of about half of the Q235 carbon steel, such a large difference can make the melting of the two is not synchronized, the formation of the melt pool and poor metal bonding, resulting in bad crystallization of the weld conditions, weld performance and poor forming.
3.2 Difference in the coefficient of linear expansion
Due to the 1Cr13 stainless steel and Q235 carbon steel, the coefficient of linear expansion is different, causing them to form a welded joint after the cooling process, the amount of shrinkage on both sides of the weld is different, resulting in a complex high stress state in the welded joint, which in turn accelerates the generation of cracks.
3.3 1Cr13 stainless steel and Q235 carbon steel welding the same problem of weld dilution and the formation of the transition layer, resulting in Q235 carbon steel side of the weld formation decarburization layer and 1Cr13 stainless steel side of the formation of carbon layer, with the persistence of diffusion, so that the carbon content of Q235 carbon steel side of the reduction into a ferrite organization, and the welded joint weld organization into austenite plus ferrite.
4 Welding process measures
In order to obtain crack-free welded joints, should try to avoid welding joints fusion line organization and inconsistency of the weld metal, so that the 1Cr13 stainless steel side without significant dilution phenomenon, the following measures taken in the process.
4.1 Correct choice of welding materials
1Cr13 stainless steel and Q235 carbon steel welded joints of the weld metal chemical composition depends mainly on the filler metal. In order to ensure that the structure using the performance requirements, the composition of the weld metal should strive to be close to the composition of one of the steel. In order to minimize the welding deformation of the component, two electric welders symmetrical welding manual arc welding method, electrode selection E5015 (or E309), the Cr equivalent of the weld metal is 5% to 6%, after tempering treatment has good mechanical properties.
4.2 Preheating temperature and interlayer temperature
The preheating and interlayer temperature control before welding has a certain influence on reducing the formation of cracks. Preheating temperature is too high, will lead to slow cooling of the weld, may cause the welded joint grain boundary carbide precipitation and the formation of ferrite organization, greatly reducing the impact toughness of the joint. 1Cr13 stainless steel and Q235 carbon steel welding preheating temperature and interlayer temperature should be controlled at 150 ~ 300 ℃.
4.3 Post-welding temperature control and tempering heat treatment
After welding must be slowly cooled to 100 ~ 150 ℃, insulation 0.5 ~ 1h, so that the organization of the welded joints all transformed into martensite, followed by a temperature tempering, heat treatment. Tempering temperature should be controlled in the range of 700 ~ 730 ℃, holding time in 4 ~ 5h.
4.4 Operation process
To prevent the stainless steel welding side of the crystal coarse, brittle and cracking, but also to take the following process measures: 1 choose a small heat input, small welding current, faster welding speed. 2 using short arc welding, the arc is slightly biased towards the carbon steel base material side, so that the two base metals are uniformly heated. 3 as the need for multi-layer welding, the first layer of weld cooling to 200 ~ 300 ℃ after welding the next weld. 4 welding after slow cooling. Specific welding process parameters are selected as in Table 3.
For 1Cr13 stainless steel and Q235 carbon steel dissimilar steel welding, using manual arc welding, electrode selection E5015 or E309, choose the appropriate preheating temperature before welding, welding current and speed and other welding process parameters and appropriate post-welding heat treatment, you can get good welding results to meet the requirements of the use of welded structures.
The project due to the use of reasonable welding materials and welding technology, welded joints are well formed and no cracks are seen.