（1） Excessive carbon concentration

1. Causes and hazards: If the carburizing process is rapidly heated and the temperature is too high, or if a new carburizing agent is used for solid carburizing, or if too much strong carburizing agent is used, it will cause the phenomenon of high carburizing concentration. As the carbon concentration becomes too high, block like coarse carbides or network like carbides appear on the surface of the workpiece. Due to the formation of this hard and brittle structure, the toughness of the carburized layer sharply decreases. And high carbon martensite is formed during quenching, which is prone to grinding cracks during grinding.

2. Methods of prevention

① It is not advisable to heat rapidly, and an appropriate heating temperature should be used to prevent the growth of steel grains. If the grain size is coarse during carburizing, it should be refined by normalizing or quenching twice after carburizing.

② Strictly control the uniformity of furnace temperature and avoid excessive fluctuations. Special attention should be paid when solid carburizing in the reflector furnace.

③ When solid carburizing, the carburizing agent should be used in a ratio of new and old. The infiltration agent uses 4-7% BaCO3 and does not use Na2CO3 as the infiltration agent.

（2） Low carbon concentration

1. Causes and hazards: Large temperature fluctuations or insufficient infiltration agents can cause insufficient carbon concentration on the surface. The ideal carbon concentration is between 0.9-1.0%, below 0.8% C, the parts are prone to wear.

2. Methods of prevention:

① The carburizing temperature is generally between 920-940 ℃. If the carburizing temperature is too low, it will cause a low carbon concentration and prolong the carburizing time; Excessive carburizing temperature can cause coarse grains.

② The dosage of BaCO3 should not be less than 4%.

（3） Localized carbon depletion on the surface after carburizing:

1. Causes and hazards: During solid carburizing, charcoal particles that are too large or contain impurities such as stones, or uneven mixing of the carburizing agent and charcoal, or contact with the workpiece, can cause local carbon deficiency or depletion. Dirt on the surface of the workpiece can also cause carbon depletion.

2. Methods of prevention

① Solid carburizing agent must be prepared in proportion and stirred evenly.

② Be careful not to come into contact with the workpiece being loaded into the furnace. When solid carburizing, the carburizing agent should be compacted to prevent the carburizing from collapsing and causing the workpiece to come into contact.

③ Remove surface dirt.

（4） The carburizing concentration intensifies the transition

1. Causes and hazards: The sudden transition of carburizing concentration refers to the intensified change in carbon concentration between the surface and the center, rather than a uniform transition from high to low, but a sudden transition. The reason for this defect is that the carburizing agent has a strong effect (such as newly formulated charcoal with very little old carburizing agent added), and at the same time, the presence of alloying elements such as Cr, Mn, Mo in the steel promotes the strong formation of carbides, resulting in high surface concentration, low center concentration, and no transition layer. After the occurrence of this defect, it causes significant internal stress both inside and outside, resulting in cracks or peeling during quenching or grinding processes.

2. Prevention method: Prepare the new and old carburizing agents according to the prescribed ratio to make the carburizing process smoother. It is better to use BaCO3 as a penetrating agent because Na2CO3 is more rapid.

（5） Tempering and cracking occur during grinding and processing

1. Reason for occurrence: The phenomenon of softening on the surface of the carburized layer after grinding is called tempering caused by grinding. This is because the machining feed rate is too fast during grinding, improper selection of grinding wheel hardness and particle size or speed, or insufficient cooling during the grinding process can all easily lead to such defects. This is because the heat generated during grinding softens the surface. The occurrence of tempering defects during grinding reduces the wear resistance of the parts.

Hexagonal cracks appear on the surface. This is because the surface of the hard grinding wheel is subjected to excessive grinding, resulting in heat generation. It is also related to insufficient heat treatment tempering and excessive residual internal stress. After acid etching, any defective areas appear black and can be distinguished from areas without defects. This is the heat generated during grinding and tempering. The reason for transforming the horse's body into the Qu's body tissue. In fact, cracks can be seen with the naked eye after grinding.

2. Methods of prevention:

① After quenching, it must undergo sufficient tempering or multiple tempering to eliminate internal stress.

② Using soft or medium alumina grinding wheels with a particle size of 40-60, the grinding feed rate is not too large.

③ When grinding, first turn on the coolant and pay attention to sufficient cooling during the grinding process.