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Stainless Steel Pipe Heating Process Improperly Produced Defects

Improper heating defects can be divided into: ① due to the impact of the outer layer of blank structure chemical changes caused by defects such as oxidation, decarbonization, carbon and sulfur, copper and so on. ② by the internal organizational structure of the abnormal changes caused by defects, such as overheating, over burning and not heat and so on. ③ due to the uneven distribution of temperature inside the blank, Stainless steel pipe causing internal stress (such as temperature stress, tissue stress) is too large and the resulting blank cracking and so on. Here are some of the common shortcomings.


Decarburization refers to the metal in the high temperature surface of the carbon is oxidized, making the surface of the carbon content of the phenomenon than the internal significantly reduced.

The depth of the decarburization layer is related to the composition of the steel, the composition of the furnace gas, the temperature and the holding time at this temperature. The use of oxidative atmosphere heating prone to decarburization, Stainless steel pipe high carbon steel decarburization, silicon content of steel is also easy to decarburization.

Decarburization reduces the strength and fatigue properties of the parts, and the wear resistance decreases.

2. Increased carbon

The forging of the oil furnace, often in the surface or part of the surface of the phenomenon of carbon. Sometimes the carbon layer thickness of 1.5 ~ 1.6mm, carbon layer of carbon content of 1% (mass fraction) around the local point of carbon content even more than 2% (mass fraction), the emergence of the body structure.

This is mainly due to the fact that when the position of the blank is close to the oil furnace nozzle or the area where the fuel is injected in the two nozzles, the oil and air are not well mixed and the combustion is incomplete, Stainless steel pipe The surface of the blank forms a reducing carburizing atmosphere, thereby producing the effect of surface addition of carbon.

Increased carbon to make the machinability of forgings deteriorate, easy to fight when cutting.


Overheating refers to the fact that the heating temperature of the metal blank is too high or the residence time is too long in the specified forging and heat treatment temperature range, or the coarse grain is caused by the thermal effect.

Carbon steel (paralysis or hypereutectoid steel) after the overheating often appear Wei organization. Martensitic steel after the overheating, often appear within the fabric texture, die and die steel is often a carbide angle characteristics to determine the superheat organization. Titanium alloy overheating, there is a clear β-phase grain boundary and flat and elongated Wei's organization. Alloy steel overheating after the fracture will appear stone fracture or strip fracture. Overheated tissue, due to coarse grain, Stainless steel pipe will cause mechanical properties to reduce, especially the impact toughness.

Generally overheated structural steel after normal heat treatment (normalizing, quenching), the organization can improve the performance also will be restored, this overheating is often referred to as unstable overheating; and alloy structural steel serious overheating by the normal normalization (Including high temperature normalizing), annealing or quenching, the superheat tissue can not be completely eliminated, this overheating is often referred to as stable overheating.

4. burned

Odor is the heating temperature of the metal blank is too high or the residence time in the high temperature heating zone is too long. Oxygen and other oxidizing gases in the furnace penetrate into the gap between the metal grains and are oxidized with iron, sulfur and carbon. The co-crystal of the fusible oxide destroys the contact between the grains, causing the plasticity of the material to drastically decrease. To burn a serious metal, remove the coarse when the light hit on the crack, pull the long time will appear in the burning cracks.

There is no strict temperature boundary between overheating and overheating. Generally to grain oxidation and melting characteristics to determine the burning. For carbon steel, when the grain boundary melting, severe oxidizing die steel (high speed steel, Cr12 steel, etc.) over the burning, the grain boundary due to melting fish bones. Stainless steel pipe When the aluminum alloy burned grain boundary melting triangle and re-melting ball and so on. Forging after burning, often can not be saved, had to scrapped.

5. Heat the crack

In the high cross-section of the large steel ingot and poor thermal conductivity of high alloy steel and high temperature alloy blank, if the low temperature heating rate is too fast, the blank due to large internal and external temperature difference and produce great thermal stress. In addition, the billet is poor in plasticity due to the low temperature. If the thermal stress value exceeds the strength limit of the blank, a heated crack is radiated from the center to the surroundings, and the entire section is cracked.

6. Copper crisp

The brass is cracked on the surface of the forging. High-power observation, there are light yellow copper (or copper solid solution) along the grain boundary distribution. When the billet is heated, such as the residual copper oxide in the furnace, the oxidized steel is reduced to free copper at high temperature, and the molten steel atoms extend along the austenite grain boundary, weakening the relationship between the grains. In addition, Stainless steel pipe when the amount of copper in the steel is higher [> 2% (mass fraction)], such as heating in an oxidizing atmosphere, forming a copper-rich layer under the iron oxide,