【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20190715

Temperature, loading time, initial fit retention time, etc

1. (1) The phenomenon in which the strength of steel increases, while its plasticity and toughness decrease and brittleness rises, as a result of certain factors, is known as hardening. Generally, the elastic limit increases under repeated loading (this occurs after entering the plastic stage). (2) During cold working (such as bending, punching, and shearing at room temperature), the phenomenon in which steel undergoes plastic deformation and thus becomes harder is known as cold work hardening. (3) The formation of carbides and nitrides in steel due to C and N over time and with changes in temperature, which renders the steel more brittle, is known as aging hardening. 2. Influence of temperature: (1) Effect of positive temperatures. The general trend is that as the temperature rises, the strength of steel decreases while its plasticity and toughness increase. When the temperature reaches around 450–600°C, the strength of steel drops to almost zero, whereas its plasticity and toughness are very high, making it easy to perform hot working; this temperature is known as the hot working temperature. It should be noted that at around 250°C, the strength of steel increases while its plasticity and toughness decrease; the surface of the steel turns blue, and this phenomenon is known as blue brittle fracture. Insulation measures should be taken for steel at temperatures above 200°C. (2) Effect of low temperatures: As the temperature drops, the strength of steel increases, while its plasticity and toughness decrease and its brittleness increases; this phenomenon is known as low-temperature cold brittleness. When the temperature reaches a certain value, the brittleness of steel increases sharply, and this temperature is referred to as the transition temperature to brittleness. 3. Influence of the production process (1) The smelting process mainly controls the chemical composition. (2) The main impact of casting lies in the deoxidization method: for boiling steel, Mn is used as a deoxidizer, which results in fast processing times, low costs, but poor quality ； Silicon is used as a deoxidizer for calm steel; the process is slow, the cost is high, but the quality is good. (3) Repeated rolling can reduce the size of steel bars, improve their plasticity, and at the same time weld together defects such as pores, cracks, and porosity in the steel. This results in a denser metal crystal structure, finer grains, and the elimination of fibrous structure defects, thereby enhancing the mechanical properties of the steel. For steel of the same grade, the smaller the thickness or diameter, the higher the strength.

1. (1) The phenomenon in which the strength of steel increases, while its plasticity and toughness decrease and brittleness rises, as a result of certain factors, is known as hardening. Generally, the elastic limit increases under repeated loading (this occurs after entering the plastic stage). (2) During cold working (such as bending, punching, and shearing at room temperature), the phenomenon in which steel undergoes plastic deformation and thus becomes harder is known as cold work hardening. (3) The formation of carbides and nitrides in steel due to C and N over time and with changes in temperature, which renders the steel more brittle, is known as aging hardening. 2. Influence of temperature: (1) Effect of positive temperatures. The general trend is that as the temperature rises, the strength of steel decreases while its plasticity and toughness increase. When the temperature reaches around 450–600°C, the strength of steel drops to almost zero, whereas its plasticity and toughness are very high, making it easy to perform hot working; this temperature is known as the hot working temperature. It should be noted that at around 250°C, the strength of steel increases while its plasticity and toughness decrease; the surface of the steel turns blue, and this phenomenon is known as blue brittle fracture. Insulation measures should be taken for steel at temperatures above 200°C. (2) Effect of low temperatures: As the temperature drops, the strength of steel increases, while its plasticity and toughness decrease and its brittleness increases; this phenomenon is known as low-temperature cold brittleness. When the temperature reaches a certain value, the brittleness of steel increases sharply, and this temperature is referred to as the transition temperature to brittleness. 3. Influence of the production process (1) The smelting process mainly controls the chemical composition. (2) The main impact of casting lies in the deoxidization method: for boiling steel, Mn is used as a deoxidizer, which results in fast processing times, low costs, but poor quality ； Silicon is used as a deoxidizer for calm steel; the process is slow, the cost is high, but the quality is good. (3) Repeated rolling can reduce the size of steel bars, improve their plasticity, and at the same time weld together defects such as pores, cracks, and porosity in the steel. This results in a denser metal crystal structure, finer grains, and the elimination of fibrous structure defects, thereby enhancing the mechanical properties of the steel. For steel of the same grade, the smaller the thickness or diameter, the higher the strength.

Temperature, loading time, initial fit retention time, etc

Alloying elements, heat treatment, repeated loading,

Stabilization treatment, heat treatment method, microalloying method

1. (1) The phenomenon in which the strength of steel increases, while its plasticity and toughness decrease and brittleness rises, as a result of certain factors, is known as hardening. Generally, the elastic limit increases under repeated loading (this occurs after entering the plastic stage). (2) During cold working (such as bending, punching, and shearing at room temperature), the phenomenon in which steel undergoes plastic deformation and thus becomes harder is known as cold work hardening. (3) The formation of carbides and nitrides in steel due to C and N over time and with changes in temperature, which renders the steel more brittle, is known as aging hardening. 2. Influence of temperature: (1) Effect of positive temperatures. The general trend is that as the temperature rises, the strength of steel decreases while its plasticity and toughness increase. When the temperature reaches around 450–600°C, the strength of steel drops to almost zero, whereas its plasticity and toughness are very high, making it easy to perform hot working; this temperature is known as the hot working temperature. It should be noted that at around 250°C, the strength of steel increases while its plasticity and toughness decrease; the surface of the steel turns blue, and this phenomenon is known as blue brittle fracture. Insulation measures should be taken for steel at temperatures above 200°C. (2) Effect of low temperatures: As the temperature drops, the strength of steel increases, while its plasticity and toughness decrease and its brittleness increases; this phenomenon is known as low-temperature cold brittleness. When the temperature reaches a certain value, the brittleness of steel increases sharply, and this temperature is referred to as the transition temperature to brittleness. 3. Influence of the production process (1) The smelting process mainly controls the chemical composition. (2) The main impact of casting lies in the deoxidization method: for boiling steel, Mn is used as a deoxidizer, which results in fast processing times, low costs, but poor quality ； Silicon is used as a deoxidizer for calm steel; the process is slow, the cost is high, but the quality is good. (3) Repeated rolling can reduce the size of steel bars, improve their plasticity, and at the same time weld together defects such as pores, cracks, and porosity in the steel. This results in a denser metal crystal structure, finer grains, and the elimination of fibrous structure defects, thereby enhancing the mechanical properties of the steel. For steel of the same grade, the smaller the thickness or diameter, the higher the strength.