With the general improvement of roll production technology and the increasingly perfect roll use technology of hot rolled strip production enterprises, high chromium cast iron rolls have gradually become routine products in several major roll manufacturers in China. However, with the fierce market competition and the increase of production cost pressure, roll manufacturers have gradually compressed the cost of each stage, resulting in roll quality fluctuations. In order to ensure the performance of the roll, it mainly relies on the continuous optimization of the heat treatment process in the later stage.
1. Technical characteristics of high chromium iron roll production
The casting method of high chromium iron roll is centrifugal composite casting, which is generally the outer layer, the middle layer and the core part, wherein the outer component is high chromium iron, the middle layer is graphite steel or ductile iron, and the core part is ductile iron.
Due to the addition of a large number of Gr elements to the outer layer of this kind of roll, the matrix is martensite + pearlite + Residuum, and a large number of Gr7C3 carbides +Gr23C6 carbides + chrysanthemum carbides are distributed in the matrix. The ratio of carbides varies according to the different Gr/C ratio, and the microhardness can reach 1600-1800HV.
2. There are currently three heat treatment methods for high chromium iron rolls
At present, there are two main forms of heat treatment of high chromium cast iron rolls, one is subcritical heat treatment below the critical transition temperature, and the other is high temperature heat treatment above the critical point (differential temperature treatment and overall treatment). The research results show that the performance of high chromium cast iron rolls can be significantly improved after high temperature heat treatment. In order to further improve the performance of high chromium cast iron rolls, The effects of quenching temperature, cooling method and tempering temperature on the structure and properties of high chromium cast iron rolls were studied in order to improve the properties of high chromium cast iron rolls.
2.1 High temperature heat treatment method
In the austenitizing stage, a large number of pearlite and eutectic carbides in the as-cast structure are transformed into austenite, and the structure is transformed into sortenite through quenching to improve its hardness value and wear resistance.
2.2 Differential heat treatment
At present, the domestic differential thermal treatment technology is gradually mature, and the cost of differential thermal treatment is lower than the above heat treatment methods, which has been gradually expanded from the casting hot rolled plate with support rolls, high chromium steel, etc., to the high chromium iron roll, and the current large roll foundry gradually began to test production.
2.3 Low temperature tempering treatment
With the increase of production cost pressure, the production plant has gradually adopted the secondary tempering heat treatment method, the first stage of tempering heat treatment mainly reduces the residual austenite volume, the second stage of tempering heat treatment mainly eliminates the internal stress and ensures the service performance of the roll.
