Advances in heat treatment of high speed steel rolls

1. The basic characteristics of high-speed steel rolls are: high carbide hardness; good thermal stability; excellent strength and toughness; good hardenability; strong ability to form oxide film; good thermal cracking resistance; good wear resistance.

The main characteristics of the high-speed steel roll composition are: higher carbon content and vanadium content, the purpose is to obtain more high-hardness MC-type carbides and improve the wear resistance of the roll.

With a higher chromium content, the roll contains a certain amount of M7C3 carbides, which is beneficial to improving the roughness resistance of the roll surface and reducing the rolling force. In addition, the centrifugal casting high-speed steel roll contains less than 5% niobium, which is beneficial to reduce the segregation caused by the large density difference between alloying elements and their carbides in high-speed steel.

High speed steel roll manufacturing technologies are as follows: forged high speed steel roll, cast high speed steel roll, spray deposition forming (OSPREY) high speed steel roll and hot isostatic pressing (HIP) to manufacture high speed steel roll.

Among them, the methods that can be used to cast high-speed steel rolls are: centrifugal casting method (CF), continuous casting outer layer forming method (CPC), electroslag remelting method (ESR) and liquid metal electroslag welding method (ESLLM).

 

2. The main contents of research progress on heat treatment of high-speed steel rolls include the following aspects:

 

The effect of quenching on the structure and performance of high-speed steel rolls In order to accurately formulate the heat treatment process of high-speed steel rolls. According to the analysis of the continuous cooling curve after austenitization at 1050°C, the bainite temperature of the high-speed steel roll is lower than 400°C, and the cooling rate for obtaining bainite is lower than 10°C/s. If the rate exceeds 10°C/s, a quenched martensite matrix with high hardness is obtained.

Austenitizing holding time has certain influence on the microstructure and properties of high-speed steel rolls. The quenching and holding time affects the microstructure of high-speed steel rolls. Baosteel will contain 2.28%C, 4.66%W, 4.79%Mo, 6.05%V, 7.70%Cr, 0.60%Ni, 0.80%Si and 0.50%Mn for high-speed steel rolls After austenitizing at 1000℃, the change of microstructure was studied.

After austenitizing for 2 hours, the carbides in the high-speed steel roll structure are mainly of M7C3 type; after 4 hours of heat preservation, the carbides are mainly of M2C type; after 6 hours of heat preservation, the carbides are mainly of MC type.

The austenitizing holding time also affects the wear resistance of the high-speed steel roll. The austenitizing holding time is 2 hours, and the wear resistance of the high-speed steel is the worst, and the carbide peeling is serious; The thicker M2C carbides peeled off; the holding time was extended to 6h, the M7C3 carbides disappeared, the high hardness MC carbides increased, and no carbides fell off. The high-speed steel rolls had the best wear resistance.

 

3. The effect of tempering on the structure and performance of high-speed steel rolls.

 

Reasonable control of tempering temperature In the actual use of high-speed steel rolls, it is not the best use effect at the place with the highest tempering hardness.

Effect of tempering temperature on hardness, wear resistance and surface roughness resistance of high-speed steel rolls containing 2.0%C, 5.0%V, 3.0%Mo, 1.5%W, 6.5%Cr and 1.0%Ni. When tempered at 540°C, the hardness reaches the highest value, and when it exceeds 540°C, the hardness gradually decreases. In addition, when tempered at 540°C, the high-speed steel roll has the least wear loss and the best wear resistance. As the tempering temperature increases, the wear loss increases and the wear resistance decreases.

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