Year1
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- 齐全
Carbon tool steel
Characteristics and scope of application
Steel has higher hardness and wear resistance after quenching and tempering, but has low thermal hardness, poor hardenability, easy deformation, low plasticity and strength. . Carbon tool steel is used for various tools that require higher hardness and wear resistance, such as simple molds and punches, metal cutting tools, drilling tools, woodworking milling cutters, countersunk drills, axes, chisels, longitudinal Hand saws, as well as benchwork assembly tools, rivet dies and other secondary tools.
Chemical composition
Carbon:.~
Silicon:
Manganese:
Sulfur:
Phosphorus:
Chromium allows residual content. (Production of lead When bath quenching steel wire)
Nickel: Allowable residual content. (When manufacturing lead bath quenching steel wire)
Copper: Allowable residual content. (When manufacturing lead bath quenching steel wire)
General heat treatment process of steel Post-structural structure and properties
Normalizing
Normalizing the steel is to eliminate the secondary cementite network and prepare the structure for spheroidizing annealing. The steel is heated to above the transformation point ~ ℃ to completely austenitize. The holding time is determined according to the effective thickness of the workpiece and the form of the heating furnace, and then cooled in the air after being held for a period of time. The rapid cooling rate during normalizing prevents the secondary cementite from having time to precipitate in a network structure along the austenite grain boundaries, thus eliminating the secondary cementite network. After normalizing treatment, the structural structure of steel changes to a structural structure dominated by finer pearlite. The organizational structure is pearlite and lamellar cementite. The hardness of steel after normalizing increases to about 10%, the wear resistance increases, the toughness and plasticity decrease.
Annealing
The spheroidizing annealing treatment of steel causes the lamellar cementite in the pearlite in the steel to spheroidize into spherical cementite to prepare the structure for quenching. The steel is heated to above ~℃ and kept for a period of time and then slowly cooled to below ℃ before being released from the furnace for air cooling. In the spheroidizing annealing treatment, when the heating temperature exceeds a little, the cementite begins to dissolve, but it is not completely dissolved to form many fine chain or point-like cementites that are dispersed and distributed on the austenite matrix. At the same time, short-term heating at low temperature also makes the austenite Body composition is uneven. In the subsequent slow cooling process, granular cementite is uniformly formed with the original fine cementite as the core or a new core generated in the place where carbon atoms are enriched in the austenite. Due to the minimum spherical surface energy, cementite aggregates and grows to form larger granular shapes during slow cooling. Pearlite and granular cementite are obtained at room temperature. After spheroidizing annealing, the hardness of the steel is reduced to no more than the wear resistance, which also reduces the toughness and increases the plasticity.
Quenching
The quenching treatment of steel is to prepare the structure for tempering. The steel is heated to a temperature above ~℃ and kept for a period of time to austenitize it and then rapidly cooled with water. When the steel is heated to the above temperature, the structure of the steel is austenite and a part of undissolved fine-grained cementite. After quenching, the austenite changes to martensite and undissolved fine-grained cementite remains, leaving some residual austenite in the structure. After quenching, the hardness of the steel has increased to no less than r, the wear resistance has increased, and the toughness and plasticity have decreased.
Tempering
The purpose of low temperature tempering is to stabilize the structure and reduce quenching stress. The steel is heated to ~°C, held for a certain period of time and then cooled to room temperature. During the low-temperature tempering process, some supersaturated carbon atoms in martensite precipitate in the form of carbides. The precipitated carbides are associated with the precipitated supersaturated solid solution lattice and maintain a coherent relationship to form a new organizational structure of tempered martensite. The retained austenite is also transformed into tempered martensite carbide and remains in the form of cementite. The structure of steel after low temperature tempering is tempered martensite and cementite. The steel after low temperature tempering maintains the high hardness and high wear resistance of the quenched steel, and the external toughness and plasticity are also enhanced while reducing the internal stress and brittleness after quenching. The hardness of tempered steel is ~ where the hardness of the working part is ~
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