Steel weld cold crack occurs

Because the tube is low intensity, 400 ℃ following is basically no plastic, when the tensile stress exceeds the tensile strength of steel, weld cold cracking occurs.
When present in the weld seamless, since the shrinkage tube (2.3%) than in seamless shrinkage (1.26%) is large, the more likely the weld cold cracking, especially when the weld strength than the parent metal during cooling of the weld base metal could not contain shrinkage, resulting in the base material is torn junction, a phenomenon known as "peeling."
When welded joints rigid, multi-layer welding, welding metal bulky, so welded joints in high-stress state, such as the weld metal has a higher yield point, it is difficult to relaxation through its plastic deformation of welded joints of high stress, then weld cracking in the heat affected zone is easy white zone or zones produce martensite formed HAZ cold cracking. Prevent cold cracking the most effective way is to be welded pieces complement the overall 550 ~ 700 ℃ preheating, followed by use of heterogeneous weld welding material. Tungsten steel can improve the heat resistance and red hardness and can improve the wear resistance of steel. Chromium can improve the hardenability and wear resistance, can improve the corrosion resistance of steel and antioxidant effects. Vanadium can refine steel grain structure and improve the strength of steel, toughness and wear resistance. When it melt into the austenite at high temperature, the increase of steel hardenability; On the contrary, when it is in carbide forms, it will reduce its hardenability. Molybdenum can significantly improve the steel hardenability and heat resistance, prevent temper brittleness, increased remanence and coercivity. Titanium can refine grains of the steel, thereby improving the strength and toughness of steel. Advanced materials and commercial products of high technology; fine grain high-strength, high toughness, high corrosion resistance steel material production technology; steel materials to improve the cleanliness, uniformity and fineness organization influence the material properties, improve the metallurgical industry resources, energy efficiency, energy-saving, environmental protection, and promote sustainable development in the steel industry related ancillary materials, components manufacturing technology; high strength, high toughness, high conductivity, corrosion resistance, high wear resistance, high (low) temperature, etc. special steel, high temperature alloys, tool and die materials, manufacturing technology; ultra-fine steel material rolling process, advanced micro-alloyed, high homogeneous slab, high purity steel smelting technology, high strength alloy steel and heat-resistant Casting technology and welding technology, high-performance carbon structural steel, high strength low alloy steel, high strength steel, high-grade cold-rolled silicon steel production process; performance copper alloy materials (high strength, high conductivity, lead-free brass, etc.) production technology, the use of metal plastic deformation and cold lateral forcing a molding process to produce a heat exchanger with copper and copper alloy seamless high fin tube technology; through casting, made of alloy pipe wire drawing technology. In order to obtain a better cleanliness and roughness uniform distribution of abrasive particle size and mix design is very important. Roughness too easily lead to corrosion layer thinning at the peak in the anchor lines; same time as the anchor pattern too, in the course of anti-corrosion coating is easy to form bubbles, seriously affect coating performance. Steel in the process, often due to the clamping force of cutting forces and deformation caused by heat, resulting in reduced machining accuracy PIPE main elements of influence of carbon, chromium, nickel, molybdenum, nitrogen, copper, silicon and manganese sometimes in the production of stainless steel cutting, also sulfur as additive elements. Is the formation of carbon in the steel pipe, and the expansion of austenite stabilizing elements.