Key points of 304 stainless steel structure welding: Due to the characteristics of stainless steel, the welding of stainless steel has its particularity compared with ordinary carbon steel, and various defects are more likely to occur in its welded joints and heat affected zones (HAZ). Pay special attention to the physical properties of stainless steel when welding. For example, the thermal expansion coefficient of 304 stainless steel is 1.5 times that of low carbon steel and high chromium stainless steel; The thermal conductivity is about 1/3 of low carbon steel, and high chromium stainless steel is about 1/2 of low carbon steel. The specific resistance is more than 4 times that of low carbon steel, and the high chromium stainless steel is 3 times that of low carbon steel. These conditions, together with metal density, surface tension, magnetism and other conditions, have an impact on welding conditions.
Electric welding:
In principle, the welding of 304 stainless steel does not need preheating before welding and heat treatment after welding. Generally, it has good welding performance. But sometimes it is easy to produce high temperature cracks. In addition, б phase embrittlement is easy to occur, and ferrite generated under the action of ferrite generating elements causes low-temperature embrittlement, as well as corrosion resistance decline and stress corrosion cracking. After welding, the mechanical properties of welded joints are generally good, but when there is chromium carbide on the grain boundary of heat affected zone, it is easy to form a chromium-poor layer, which is easy to lead to intergranular corrosion during use. In order to avoid problems, low carbon (C≤0.03%) grade or grade with titanium and niobium added should be adopted. In order to prevent welding metal from cracking at high temperature, it is generally considered that it is effective to control δ ferrite in austenite. Generally speaking, it is recommended to contain more than 5% δ ferrite at room temperature and carry out appropriate post-weld heat treatment.
Argon arc welding:
TIG welding or MIG welding can be used. I want to know what kind is used in your factory?
Preparation before welding: the thickness less than 4mm need not be broken, and it can be directly welded, penetrating one side at a time. Butt welds with a thickness of 4 to 6 mm can be welded on both sides of the joint without breaking. More than 6 mm, generally open V-shaped or U, X-shaped groove.
Secondly, degreasing and derusting are carried out on the welding wire filled in the welding position. So as to ensure the welding quality.
Welding parameters: including welding current, tungsten electrode diameter, arc length, arc voltage, welding speed, shielding gas flow, nozzle diameter, etc.
1, welding current is the key factor to determine weld formation. It is usually determined by the material, thickness and groove shape of the weldment.
2. The electrode diameter is determined according to the welding current, and the larger the current, the larger the diameter.
3, welding arc and arc film, arc length range is about 0.5 ~ 3mm, the corresponding arc voltage is 8~ 10V.
4. Welding speed: Current, sensitivity of weldment material, welding position and operation mode should be considered when selecting.
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