Crack classification
Basic characteristics
Sensitive temperature range
Welded material
Location
Crack direction
Thermal cracking
Crystalline cracking
In the late stage of crystallization, cracking occurs due to the formation of a liquid film of low-melting**** crystals that weakens the linkage between grains. p>
In the late stage of crystallization, cracking occurs under tensile stress due to the formation of a liquid film by the low-melting *** crystals that weakens the intergranular bonding
At slightly higher temperatures (solid-liquid state) above the solid-phase line temperature
Carbon steels, low to medium-alloyed steels, austenitic steels, nickel-base alloys, and aluminum
Welding joints on, and to a lesser extent in, the heat-affected zone
along the austenitic grain boundaries
Multilateralized cracks
have solidified at the crystallization front, under the action of high temperature and stress, lattice defects to move and gather, the formation of secondary boundaries, which at high temperatures is in a low-plastic state, the cracks produced under the action of stress
solid state line below the recrystallization temperature
pure metals and single-phase austenitic alloys
On the weld, a small number of cracks in the heat-affected zone
along the austenite grain boundaries
Liquefaction cracks
Cracks produced under stress in the heat-affected zone and between layers of multi-layer welds under the action of the peak temperature of the weld thermal cycle
Slightly lower temperatures below the solid state line
Nickel-chromium high-strength steels, austenitic steels and nickel-based alloys containing a large amount of S, P and C. base alloys
Heat-affected zone and multi-layer welding interlayer
Cracking along the grain boundaries
Reheat cracking
Thick welded structures in the process of stress relieving treatment, in the heat-affected zone of the coarse grain area of the existence of varying degrees of stress concentration, due to the additional deformation arising from the relaxation of the stress is greater than the site of the creep plasticity, then the occurrence of reheat cracking
600 -700℃ tempering treatment
High-strength steels, pearlite steels, austenitic steels, nickel-based alloys, etc. containing precipitation strengthening elements
Heat-affected zone of the coarse grain area
Cracking along the grain boundaries
Cold cracking
Delayed cracking
Delayed cracking in the quenched organization, the hydrogen and the confining stress of the **** the same action and the characteristic of the delayed Cracks
Below the MS point
Medium and high carbon steels, resistive and medium alloy steels, titanium alloys, etc.
Heat-affected zone, a small amount of in the weld
Along the crystal or through the crystal
Hardened embrittlement cracks
Mainly by the hardened tissues of the cracks produced by the action of the welding stresses
Near the MS point
More Carbon-containing NiCrMo steel, martensitic stainless steel
Heat-affected zone, a small amount in the weld
Along the crystal or through the crystal
Low plasticity embrittlement cracks
At lower temperatures, due to the shrinkage strain of the material to be welded, exceeding the material's own plasticity reserves and the cracks
Below 400 ℃
Cast iron, Surfacing carbide
Heat-affected zone and weld
Along the crystal or through the crystal
Laminar tear
Mainly due to the presence of steel plate internal inclusions layered (along the direction of rolling), the perpendicular to the rolling direction of the stress generated in the weld, resulting in heat-affected zone or a little farther away from the production of "steps "-like laminar cracking
Below about 400°C
Low-alloy, high-strength steels containing inclusions
Near the heat-affected zone
Along the crystal or through the crystal
Stress Corrosion Cracking (SCC)
Some welded structures (e.g., pressure vessels and pipelines, etc.), in the corrosive medium and the stresses of the **** Delayed cracking under the same action
Any working temperature
Carbon steel, low alloy steel, stainless steel, aluminum alloys
Welds and heat-affected zones
Along or through the crystal