【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20190723
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Question: What are the reasons for the thermal brittleness of metal materials? There was no update regarding the gathering yesterday; I hope my fellow forum members can understand. This series of posts does not require answers – members are free to share their own opinions and simply state what they understand. Replies earn rewards ranging from 5 to 15 points; all forum members are welcome to participate actively and support the development of the forum! ! ! Chemical Equipment and Machinery
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
Thermal brittleness: When certain steels are held at temperatures between 400 and 500°C for an extended period before being cooled to room temperature, their impact strength decreases significantly. Steel that exhibits thermal brittleness is not actually brittle at high temperatures; it only shows brittleness when cooled to room temperature. At this time, the impact value of the steel is very low. -It can generally drop by 50-60% compared to its normal value, or even by 80-90%. Steel with thermal brittleness does not show significant changes in its microstructure, and its other properties remain essentially unchanged as well. The main steam pipes and high-temperature bolts in thermal power plants exhibit a tendency to become heat-sensitive; improper handling during maintenance can easily damage the equipment components. Factors: (1) Chemical composition including carbon content, chromium, manganese, molybdenum, phosphorus, etc. (2) The holding time required for steel to develop thermal brittleness varies depending on the holding time. (3) Heat treatment and quenching and tempering can prevent the occurrence of thermal brittleness.
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
Under high-temperature and short-duration loading, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
When steel is hot-worked (forging, rolling), the heating temperature is often above 1000°C; at this temperature, the FeS+Fe eutectic on the grain boundaries melts, leading to cracking of the steel during hot working. Sulfur has an extremely low solubility in solid iron; it can form FeS with iron, which has a low melting point of 1190°C. The melting point of the FeS+Fe eutectic is lower (989°C). This low-melting eutectic generally distributes at the grain boundaries in the form of separated eutectics.
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.
Thermal brittleness: When certain steels are held at temperatures between 400 and 500°C for an extended period before being cooled to room temperature, their impact strength decreases significantly. Steel that exhibits thermal brittleness is not actually brittle at high temperatures; it only shows brittleness when cooled to room temperature. At this time, the impact value of the steel is very low. -It can generally drop by 50-60% compared to its normal value, or even by 80-90%. Steel with thermal brittleness does not show significant changes in its microstructure, and its other properties remain essentially unchanged as well. The main steam pipes and high-temperature bolts in thermal power plants exhibit a tendency to become heat-sensitive; improper handling during maintenance can easily damage the equipment components. Factors: (1) Chemical composition including carbon content, chromium, manganese, molybdenum, phosphorus, etc. (2) The holding time required for steel to develop thermal brittleness varies depending on the holding time. (3) Heat treatment and quenching and tempering can prevent the occurrence of thermal brittleness.
Under high-temperature and short-load conditions, the plasticity of metal materials increases； However, after cooling under high-temperature and prolonged loading conditions, the plasticity of metal materials decreases significantly, their sensitivity to notches increases, and they tend to undergo brittle fracture. This property of metallic materials is known as thermal brittleness.