Process analysis of heat treatment of 9Cr18 steel granulating rotary knife using high-frequency induction quenching machine

The pelletizing rotary knife is an important component in petrochemical industry equipment. Its function is to pelletize plastic wire rods continuously and at high speed. This knife has long been dependent on imports, because it is easy to wear, has a large demand, and consumes a lot of foreign exchange. In order to localize the granulating rotary knife, some domestic units have conducted exploratory research and finally selected it to be made of 9Cr18 steel. Its various performance indicators have reached and exceeded the level of Japanese original products. The heat treatment process is introduced as follows.

1) Pretreatment-spheroidizing annealing. 9Cr18 steel is a ledeburite steel. In order to improve its processing performance and prepare the structure for final heat treatment, a high-frequency induction quenching machine is used for spheroidizing annealing heat treatment. The hardness after annealing is 260HBW, and the metallographic structure is fine spherical carbides and granular pearlite. Such a pretreatment structure can not only reduce the quenching deformation of the tool, but also make the quenched carbides evenly distributed in a fine granular shape, which can improve the toughness and wear resistance.。

2)Quenching process.

①Quenching temperature. If the conventional quenching temperature (1050°C) is used for quenching, there will be a large amount of retained austenite in the quenched structure, which will reduce the sharpness of the tool. Therefore, a lower quenching temperature (980-1000°C) can be used to ensure that carbides And the basic dissolution of alloy elements, and there is an appropriate amount of undissolved carbides to obtain the ideal quenching structure.

②Sectional heating. First, keep the temperature at about 850°C for a period of time to make the temperature of all parts of the workpiece uniform, and then raise it to the quenching temperature (or move it to a furnace at the quenching temperature for heating) and keep it warm.

③Isothermal quenching. At a temperature slightly higher than Ms (145°C), the bainite structure is obtained (to reduce deformation and improve toughness). The isothermal temperature is controlled within the range of 150-180°C. If the isothermal temperature exceeds 180°C, firstly, it will increase the retained austenite and affect the sharpness of the blade; secondly, it will affect the consistency of dimensional changes. The volume should be large enough so that the medium temperature does not rise suddenly after the workpiece is quenched.

④Tempering. According to the relationship between its mechanical properties and tempering temperature, a high-frequency induction quenching machine is often used for tempering heat treatment at 210-220℃x4h or tempering heat treatment at 210-220℃x2hx2 times.

The granulating rotary knife is mainly used for granulation. Therefore, it needs to withstand huge friction during the working process. For this reason, we often use high-frequency induction quenching machine for heat treatment to improve its hardness, wear resistance and service life. . This article briefly introduces the high-frequency heat treatment process of the granulating rotary knife. After many manufacturers adopt the above process, the hardness is 55-56HRC (the edge is sharper after grinding), so that the actual service life of the granulating rotary knife reaches 60 years after one sharpening. The lead time is 30 days, while the lead time for importers from Japan is 45 days, an increase of 30%.