The application of stainless steel, stainless steel structure welding and cutting is inevitable. With the characteristics of the stainless steel itself, compared with carbon steel, stainless steel welding and cutting has its particularity, easier to produce a variety of defects in welded joints and heat affected zone (HAZ). Pay special attention to the physical properties of stainless steel welding. For example, the coefficient of thermal expansion of austenitic stainless steel is low carbon and high chromium stainless steel, 1.5 times; thermal conductivity is about 1/3 of the low carbon steel, high chromium stainless steel thermal conductivity is about 1/2 of the low carbon steel ; specific resistance of low carbon steel, 4 times more than high-chromium stainless steel is three times that of low-carbon steel. These conditions coupled with the metal density, surface tension, magnetic, and other conditions have an impact on the welding conditions.
Martensitic stainless steel are generally represented by the 13% Cr steel. Welding, due to the heat-affected zone is heated to above the phase transition region of the gamma-alpha (M) phase transition, so there is a low-temperature brittleness, low temperature toughness deterioration, along with the hardening ductility decline. Thus need to warm up for the martensitic stainless steel welding, carbon, low nitrogen content and the use of D Department when the welding material without preheating. Weld heat affected zone of the organization are usually hard and brittle.Steel pipe|
For this problem, can be restored by heat treatment after welding so that the toughness and ductility. The addition of carbon, nitrogen content in the lowest grades in the welded condition also has a certain toughness.
Ferritic stainless steel 18% Cr steel. In the case of low carbon content, good weldability, weld crack sensitivity is also low. However, due to the welding heat affected zone grain is heated to above 900 ℃ was significantly thicker, making the lack of ductility and toughness at room temperature, prone to low temperature crack. In other words, it is generally in terms of ferrite body stainless steel 475 ℃ embrittlement ,700-800 ℃ for a long time heating caused by brittle phase inclusions and grain coarsening due to embrittlement, low temperature embrittlement, carbide precipitation decline in corrosion resistance and high alloy steels prone to delayed cracking and other issues. should normally be in the welding preheat and post weld heat treatment, welding and good toughness in the temperature range.
Austenitic stainless steel to 18% Cr-8% Ni steel. In principle, subject to the preheat and post weld heat treatment. Generally have good weldability. Including nickel, molybdenum content of high-alloy stainless steel welding is easy to produce high-temperature crack. Also prone to the σ phase embrittlement, ferrite generated in the ferrite to generate the elements caused by the low temperature embrittlement, as well as the decline of corrosion resistance and stress corrosion cracking and other defects. By welding, the mechanical properties of welded joints is usually good, but when chromium carbides on the grain boundaries in the heat affected zone will easily generate a chromium depletion layer, the chromium depletion layer will be easy to produce in the course of intergranular corrosion. To avoid problems, should adopt low-carbon (C ≤ 0.03%) grade or grades of Titanium and Niobium. In order to prevent the high temperature cracking of weld metal, usually considered to control the austenite in the δ ferrite is certainly valid. Generally advocate with more than 5% of δ ferrite at room temperature. Corrosion resistance of steel as the main purpose should be used in low-carbon and stable steel, and the appropriate welding and heat treatment; structural strength of steel as the main purpose should not be a heat treatment after welding, to prevent deformation and due to the precipitation of carbides and σ phase embrittlement occurs.