Different heat treatment processes (quenching, annealing, tempering, etc.) have significant differences in temperature range, atmosphere, cooling method and workpiece state, so the performance requirements for the tray/frame also have different emphases. The following are the special requirements of the main processes for the tray/frame:
一. Quenching process: resistance to sudden changes and impact
Quenching is a process in which the workpiece is heated to above the critical temperature and then rapidly cooled (such as water cooling, oil cooling) to obtain high strength. The core requirements for the tray/frame are thermal shock resistance and structural stability.
Temperature characteristics: The heating temperature is high (usually 800-1200℃), and the temperature drops sharply during the cooling stage (the temperature difference can reach hundreds of degrees Celsius).
Special requirements:
Strong thermal shock resistance: It is necessary to withstand the thermal stress caused by rapid cooling to avoid cracking (such as ceramic trays are brittle and not suitable for quenching; metal trays need to be made of heat-resistant steel such as 310S, which has a stable thermal expansion coefficient and good resistance to sudden changes).
Strong structure: The workpiece may impact the tray due to collision or deadweight during cooling, and the tray must have sufficient mechanical strength (such as the grid structure needs to be welded firmly to avoid deformation).
Resistant to medium corrosion: If oil cooling is used, the tray must be resistant to oil stains and high-temperature oil erosion (metal materials are better than ceramics, and ceramics are easily affected by oil stains and their lifespan is affected).
二. Annealing process: high temperature resistance and creep resistance
Annealing is to slowly heat the workpiece to a certain temperature, keep it warm for a period of time and then slowly cool it down. The purpose is to eliminate internal stress and soften the workpiece. The core requirements for the tray/frame are long-term high temperature resistance and dimensional stability.
Temperature characteristics: The heating temperature is medium (600-1000℃), but the insulation time is long (several hours to dozens of hours), and the cooling rate is slow.
Special requirements:
High temperature creep resistance: Under long-term high temperature, the tray needs to resist slow deformation (creep) to avoid bending or collapse due to load-bearing (high nickel-chromium heat-resistant steel such as 310S has better creep resistance than ordinary heat-resistant steel and is suitable for long-term insulation).
Uniform heat conduction: The tray material needs to have good thermal conductivity to avoid uneven heating of the workpiece due to local overheating (metal trays have better thermal conductivity than ceramics and are more suitable for annealing).
Oxidation resistance: Annealing is mostly carried out in air atmosphere, and the tray needs to resist long-term high temperature oxidation (such as the formation of an oxide film on the surface of heat-resistant steel to protect the substrate).
三. Tempering process: medium temperature stability, low deformation
Tempering is to heat the workpiece to a lower temperature (usually 150-650℃) after quenching, and cool it after insulation to eliminate brittleness. The requirements for the tray/frame are relatively loose, but medium temperature stability is required.
Temperature characteristics: low temperature and small fluctuation, medium insulation time.
Special requirements:
Dimensional stability: no need to withstand extreme high temperatures, but slight deformation caused by repeated use must be avoided (such as cast iron trays below 600℃ can meet the requirements and have lower costs).
Easy to clean: After tempering, the surface of the workpiece may have oxide scale falling off, and the tray needs to be easy to clean (such as metal trays with smooth surfaces are better than porous ceramics to reduce residue accumulation).
四. Carburizing/nitriding process: corrosion resistance, no impurity pollution
Carburizing (900-1100℃) and nitriding (500-600℃) are processes for infiltrating carbon or nitrogen elements into the surface of the workpiece to increase the hardness. The core requirements for the tray/frame are chemical corrosion resistance and no secondary pollution.
Atmosphere characteristics: There may be corrosive gases (such as CO, H₂S) produced by the decomposition of the penetrant (such as kerosene, ammonia) in the furnace, and it is necessary to avoid the reaction between the tray material and the penetrant to contaminate the workpiece.
Special requirements:
Strong corrosion resistance: It is necessary to resist the erosion of the penetrant (such as heat-resistant alloys Inconel and Hastelloy are resistant to sulfide corrosion, which is better than ordinary heat-resistant steel; ceramic materials have good chemical stability and can also be used).
Low impurity release: The components of the tray itself cannot diffuse to the surface of the workpiece (such as cast iron with a high carbon content, which may cause excessive carburization of the workpiece and should be avoided).
Structural permeability: Carburizing/nitriding requires that the gas evenly contact the workpiece, and the material tray should adopt a grid or porous structure (metal welded grid is better than closed ceramic tray to facilitate gas circulation).
五. High-temperature sintering process (such as powder metallurgy): ultra-high temperature resistance, low pollution
High-temperature sintering is a process of heating the powder body to below the melting temperature to make it dense (the temperature often reaches 1000-1700℃). The core requirements for the tray are ultra-high temperature resistance and cleanliness.
Temperature characteristics: extremely high temperature (partly exceeding 1500℃), and may be carried out in vacuum or inert gas.
Special requirements:
Ultra-high temperature resistance: Need to withstand high temperatures above 1600℃ (such as silicon carbide ceramics, graphite trays, graphite needs to be combined with inert gas to prevent oxidation).
No adhesion: The workpiece (such as powder metallurgy parts) is easy to adhere to the tray at high temperature, and the tray surface needs to be smooth or coated with an isolation layer (ceramic material is better than metal and is not easy to metallurgically bond).
Low volatility: In a vacuum environment, the tray material needs to be free of volatiles (such as alloy elements in metal trays may volatilize and pollute the workpiece, ceramics are more suitable).
Email: cast@ebcastings.com
Different heat treatment processes (quenching, annealing, tempering, etc.) have significant differences in temperature range, atmosphere, cooling method and workpiece state, so the performance requirements for the tray/frame also have different emphases. The following are the special requirements of the main processes for the tray/frame:
一. Quenching process: resistance to sudden changes and impact
Quenching is a process in which the workpiece is heated to above the critical temperature and then rapidly cooled (such as water cooling, oil cooling) to obtain high strength. The core requirements for the tray/frame are thermal shock resistance and structural stability.
Temperature characteristics: The heating temperature is high (usually 800-1200℃), and the temperature drops sharply during the cooling stage (the temperature difference can reach hundreds of degrees Celsius).
Special requirements:
Strong thermal shock resistance: It is necessary to withstand the thermal stress caused by rapid cooling to avoid cracking (such as ceramic trays are brittle and not suitable for quenching; metal trays need to be made of heat-resistant steel such as 310S, which has a stable thermal expansion coefficient and good resistance to sudden changes).
Strong structure: The workpiece may impact the tray due to collision or deadweight during cooling, and the tray must have sufficient mechanical strength (such as the grid structure needs to be welded firmly to avoid deformation).
Resistant to medium corrosion: If oil cooling is used, the tray must be resistant to oil stains and high-temperature oil erosion (metal materials are better than ceramics, and ceramics are easily affected by oil stains and their lifespan is affected).
二. Annealing process: high temperature resistance and creep resistance
Annealing is to slowly heat the workpiece to a certain temperature, keep it warm for a period of time and then slowly cool it down. The purpose is to eliminate internal stress and soften the workpiece. The core requirements for the tray/frame are long-term high temperature resistance and dimensional stability.
Temperature characteristics: The heating temperature is medium (600-1000℃), but the insulation time is long (several hours to dozens of hours), and the cooling rate is slow.
Special requirements:
High temperature creep resistance: Under long-term high temperature, the tray needs to resist slow deformation (creep) to avoid bending or collapse due to load-bearing (high nickel-chromium heat-resistant steel such as 310S has better creep resistance than ordinary heat-resistant steel and is suitable for long-term insulation).
Uniform heat conduction: The tray material needs to have good thermal conductivity to avoid uneven heating of the workpiece due to local overheating (metal trays have better thermal conductivity than ceramics and are more suitable for annealing).
Oxidation resistance: Annealing is mostly carried out in air atmosphere, and the tray needs to resist long-term high temperature oxidation (such as the formation of an oxide film on the surface of heat-resistant steel to protect the substrate).
三. Tempering process: medium temperature stability, low deformation
Tempering is to heat the workpiece to a lower temperature (usually 150-650℃) after quenching, and cool it after insulation to eliminate brittleness. The requirements for the tray/frame are relatively loose, but medium temperature stability is required.
Temperature characteristics: low temperature and small fluctuation, medium insulation time.
Special requirements:
Dimensional stability: no need to withstand extreme high temperatures, but slight deformation caused by repeated use must be avoided (such as cast iron trays below 600℃ can meet the requirements and have lower costs).
Easy to clean: After tempering, the surface of the workpiece may have oxide scale falling off, and the tray needs to be easy to clean (such as metal trays with smooth surfaces are better than porous ceramics to reduce residue accumulation).
四. Carburizing/nitriding process: corrosion resistance, no impurity pollution
Carburizing (900-1100℃) and nitriding (500-600℃) are processes for infiltrating carbon or nitrogen elements into the surface of the workpiece to increase the hardness. The core requirements for the tray/frame are chemical corrosion resistance and no secondary pollution.
Atmosphere characteristics: There may be corrosive gases (such as CO, H₂S) produced by the decomposition of the penetrant (such as kerosene, ammonia) in the furnace, and it is necessary to avoid the reaction between the tray material and the penetrant to contaminate the workpiece.
Special requirements:
Strong corrosion resistance: It is necessary to resist the erosion of the penetrant (such as heat-resistant alloys Inconel and Hastelloy are resistant to sulfide corrosion, which is better than ordinary heat-resistant steel; ceramic materials have good chemical stability and can also be used).
Low impurity release: The components of the tray itself cannot diffuse to the surface of the workpiece (such as cast iron with a high carbon content, which may cause excessive carburization of the workpiece and should be avoided).
Structural permeability: Carburizing/nitriding requires that the gas evenly contact the workpiece, and the material tray should adopt a grid or porous structure (metal welded grid is better than closed ceramic tray to facilitate gas circulation).
五. High-temperature sintering process (such as powder metallurgy): ultra-high temperature resistance, low pollution
High-temperature sintering is a process of heating the powder body to below the melting temperature to make it dense (the temperature often reaches 1000-1700℃). The core requirements for the tray are ultra-high temperature resistance and cleanliness.
Temperature characteristics: extremely high temperature (partly exceeding 1500℃), and may be carried out in vacuum or inert gas.
Special requirements:
Ultra-high temperature resistance: Need to withstand high temperatures above 1600℃ (such as silicon carbide ceramics, graphite trays, graphite needs to be combined with inert gas to prevent oxidation).
No adhesion: The workpiece (such as powder metallurgy parts) is easy to adhere to the tray at high temperature, and the tray surface needs to be smooth or coated with an isolation layer (ceramic material is better than metal and is not easy to metallurgically bond).
Low volatility: In a vacuum environment, the tray material needs to be free of volatiles (such as alloy elements in metal trays may volatilize and pollute the workpiece, ceramics are more suitable).
Email: cast@ebcastings.com
