In the application of stainless steel in the structure of Stainless Steel Electrode and cutting is inevitable. As the stainless steel itself has the characteristics of stainless steel compared with carbon steel welding and cutting has its particularity, its welded joints and more in the heat affected zone (HAZ) produced a variety of defects. Stainless steel welded to pay attention to the physical properties. For example, austenitic stainless steel is a low coefficient of thermal expansion and high-chromium stainless steel is 1.5 times; thermal conductivity, low-carbon steel is about 1 / 3, and the high thermal conductivity of chromium stainless steel of low carbon steel is about 1 / 2 ; resistance is lower than 4 times higher than steel, and high chromium stainless steel is a low-carbon steel 3 times. These conditions together with the metal density, surface tension, magnetism and other conditions have an impact on the welding conditions.

Martensitic stainless steel 13% Cr steels are generally represented. It for welding, due to the heat-affected zone is heated to above the phase transition point

The region has γ-α (M) phase transition, so there is low-temperature brittleness, low temperature toughness deterioration of ductility decreased with sclerosis and other issues arising. Thus for the average martensitic stainless steel welding preheating is required, but the carbon and nitrogen content is low and use of small systems do not need to preheat when welding materials. HAZ organizations are usually hard and brittle. For this problem, can be post weld heat treatment to recover its toughness and ductility. Also carbon and nitrogen the lowest grades, the welding state has some toughness.

Ferritic stainless steel with 18% Cr steel as the representative. In the case of low carbon content has a good weldability, weld crack sensitivity and lower inner. However, due to be heated to above 900 ℃ grain HAZ significantly thicker, making the lack of extension at room temperature and toughness, high incidence of low-temperature cracking. That is, in general, ferritic stainless steel with 475 ℃ ,700-800 ℃ embrittlement occurs under prolonged heating "phase brittle, inclusions and grain coarsening induced embrittlement, low temperature embrittlement, carbide precipitation caused decreased corrosion resistance and high-alloy steel in the crack prone to delays and other problems usually should be carried out before welding in the welding preheat and post weld heat treatment, and has good toughness in the temperature range for welding.

Austenitic stainless steel with 18% Cr-8% Ni steel as the representative. In principle to carry out welding preheat and post weld heat treatment. Generally have good weldability. But nickel, molybdenum content of high alloy stainless steel is easy to produce high-temperature welding cracks. Also prone to brittle σ phase, generated in the ferrite elements generated under the action of ferrite caused by low-temperature embrittlement, and corrosion resistance and stress corrosion cracking down defects. After welding, the welded joints of the mechanical properties of the general good, but the heat affected zone in the grain boundary chromium carbides have easily generated when the chromium depleted layer, while the chromium depleted layer occurs in the course easy to produce intergranular corrosion. To avoid problems, should be low-carbon (C ≤ 0.03%) grades or add titanium, niobium grades. To prevent weld metal hot cracking, generally considered the control austenite δ ferrite is certainly valid. Generally promoted at room temperature for more than 5% of δ ferrite. For corrosion resistance as the main purpose of the steel should be used in low-carbon and stable steel, and appropriate post-weld heat treatment; and structural strength as the main purpose of the steel, should not be heat treated after welding to prevent distortion and As the precipitation of carbides and σ phase embrittlement occurs.

Duplex stainless steel weld crack sensitivity is low. But in the heat affected zone to increase the ferrite content will increase susceptibility to intergranular corrosion, it can result in reduced corrosion resistance and low temperature toughness degradation.

For precipitation hardening stainless steel have occurred HAZ softening and other issues.

In summary, stainless steel welding performance mainly in the following areas:

(1) high temperature cracking: cracks in the high temperature mentioned here refers to Welding Electrodes. Cracks can be divided into high-temperature solidification cracking, micro-cracks, HAZ (heat affected zone) of the crack and re-heating cracks.

(2) low-temperature cracking: some of the martensitic stainless steel and has a martensite ferritic stainless steel in low-temperature cracks sometimes occur. Since its formation is mainly due to hydrogen diffusion, the constraints of welded joints and hardening of tissue which, so solution is mainly in the welding process to reduce the spread of the hydrogen, suitable to carry out warm-up and weld heat treatment and reducing the level of regulation.

(3) the toughness of welded joints: in austenitic stainless steel in order to reduce cracking susceptibility of high temperature, usually in the design of components to make them remaining 5% -10% of the ferrite. However, the presence of these ferrite led to a decline in low-temperature toughness. In the duplex stainless steel welding, the welded joints of austenitic region to reduced impact on the toughness. Also with the ferrite which increases the toughness of a significant downward trend.

Body confirmed the high purity ferritic stainless steel welded joints significantly decreased the toughness is due to mixing of carbon, nitrogen, oxygen's sake. Some steel welded joints in the oxygen content increased epigenetic into oxide type inclusions, these inclusions as crack generator or crack of transmission makes the toughness decreased. And there are some steel is due to the protective gas mixed with the air, which increases the nitrogen content in the matrix {100} cleavage plane surface produced lath Cr2N, the matrix hardens and makes the toughness decreased.

(4) σ-phase embrittlement: austenitic stainless steel, ferritic and duplex stainless steels prone to brittle σ phase. As the organization a few percent of the precipitation of α phase, toughness decreased significantly. "Phase is generally in the range of 600 ~ 900 ℃ precipitation, especially in the most vulnerable to precipitation of about 75 ℃ as to prevent the" phase generated by preventive measures, austenitic stainless steel should be to minimize the ferrite content.

(5) 475 ℃ embrittlement at 475 ℃ in the vicinity (370-540 ℃) long heat, the decomposition of the Fe-Cr alloys for low concentrations of α-solid solution of chromium and high chromium concentrations of α 'solid solution. When α 'solid solution in chromium concentration is higher than 75% deformation by the slip deformation into the twin deformation, which occurred in 475 ℃ embrittlement.

Double-sided spot welding and spot welding is usually divided into two major categories of single-sided Welding Electrode. Double-sided spot welding, the electrode from the workpiece to the welding of both sides of the feed. A typical two-sided spot welding as shown in Figure 11-5. Figure A is a most common way, when both sides of the workpiece electrode indentation. Figure b with a large welding area that the conductivity of the electrode plate to do next, so you can eliminate or reduce the following parts of the indentation. Commonly used in the decorative panel spot. Figure c is the same spot welding two or more double-sided spot welding, use a transformer to the electrodes in parallel, then, all of the current path impedance must be basically the same, and each welded parts of the surface state, material thickness of the electrodes are subject to the same pressure, in order to ensure that the current through the various joints are basically the same. Figure d is more than double the use of multiple transformers little welding, to avoid c deficiency.

Single-sided spot welding, electrode welding by the workpiece at the same side feed, a typical single-sided spot welding as shown in Figure 11-6, Figure A is a single-sided single little welding, the electrode is not used to form solder joints large diameter and large contact surface to reduce the current density. Figure b is the non-diversion of dual-sided little welding, the welding current at this time all through the welding zone. Figure C has little diversion of dual-sided welding, the current does not flow through the top of the workpiece through the Stainless Steel Electrode, the formation of romantic. In order to provide low resistance welding current path, the workpiece underneath the copper plate. Figure d is the distance l when two large joints, such as during re-board the frame components and welding, in order to avoid undue heating caused by board warpage and reduce re-resistance between two electrodes, using a special copper bridge A, with the electrode at the same time pressed in the workpiece.

In mass production, the single multi-point welding is widely available. At this time can be powered by a transformer, the turns of the electrode to suppress the workpiece type (Figure 11-7a), also can be used by each of the electrodes separate transformer power supply, all the electrodes simultaneously press and hold the workpiece type (Figure 11-7b). the latter type has a number of advantages, applications are more widely used. Its advantages are: the transformer can be placed as close to the joint electrode recently, so.

Its power and size can significantly reduce; various joints of the process parameters can be adjusted individually; can weld all the joints, high productivity; all electrodes simultaneously press and hold the workpiece, to reduce distortion; more than one power transformer at the same time, to ensure the three-phase load balancing.