On 2018-08-08 14:48:54
Common problems of high frequency quenching
The common defects of high frequency quenching are quenching crack, soft spot and stripping. High frequency quenching is the most taboo heating uneven and produce local overheating phenomenon, such as the workpiece acute Angle parts, keyway parts, around the hole are very easy to cause overheating, and the occurrence of quenching crack, the above situation can be filled by copper sheet to reduce the possibility of quenching crack.
In addition, the non-uniform quenching process of high frequency quenched workpiece will cause the defect of low surface hardness of the workpiece, which is called soft point. This phenomenon is caused by the non-uniform quenching temperature of high frequency quenched workpiece, the blockage of water jets or the improper size and number of holes. The third kind of missing is the phenomenon of surface peeling, the main reason is that the hardness of the section changes greatly or the hardened layer is too shallow, so the way of preheating is often used to deepen the hardened layer, can effectively prevent the peeling phenomenon.
Why can't stainless steel be tempered between 500℃ and 650℃? If most of the stainless steel after solution treatment, in the long time the temperature between 475 ℃ to 500 ℃, can produce the phenomenon of hardness and brittleness surged, this is called a 475 ℃ embrittlement, the main reason there are various, including phase decomposition, on the grain boundary precipitation of chromium carbides and Fe - Cr compounds formation, etc., the real temperature toughness, and corrosion resistance is poor, also hold the heat treatment of stainless steel should avoid often time temperature in the temperature range. In addition, long-term temperature holding between 600℃ and 700℃ will lead to the precipitation of s-phase, which is fe-cr intermetallic compound, which is not only hard and brittle in texture, but also depletes a large amount of chromium inside steel, reducing the corrosion resistance and toughness of stainless steel.