High-speed steel rolls are a new type of roll material developed on the basis of high-speed tool steel by increasing the carbon and vanadium content to increase the number of high-hardness MC carbides. This type of roll has good thermal stability, high-temperature resistance and wear resistance, and has good use effects in steel rolling production. However, high-speed steel rolls often need to add a large number of alloying elements, such as chromium, vanadium, tungsten, cobalt, and niobium. These elements are expensive and will increase manufacturing costs during the production process, which is not conducive to large-scale production and manufacturing. This article mainly focuses on the study of the structure and properties of boron-containing high-speed steel rolls, and studies the possibility of using boron elements to partially replace noble alloy elements, thereby reducing manufacturing costs.
1. Test materials and methods
The high-speed steel roll material is smelted using a medium-frequency induction furnace. The main ingredients include scrap steel and pig iron. After all the raw materials are melted into molten steel, ferrochromium, ferrotungsten, ferromolybdenum and ferronickel are added. Ferrovanadium, ferrotitanium and ferrotitanium are added before the molten steel is released. Ferroboron, and perform deoxidation treatment. After all the component ratios are adjusted to the design requirements, control the exit temperature and pouring temperature of the molten steel. The exit temperature should be controlled between 1570℃~1590℃, and the pouring temperature should be controlled between 1450℃~ Between 1470°C and 1470°C, the deterioration is carried out by punching with molten steel and then cast into rolls of ψ350x600x1530. 20x20x120mm samples were poured before and after the deterioration, and then the test blocks were cut into two types of 20x20x20mm and 10x10x55mm samples using a cutting machine. A total of 4 types of samples were produced to explore their structures and properties respectively.
The main test methods are as follows: the hardness of all samples is measured using the HR-150A Rockwell hardness tester, and the test load option is adjusted to 1470N. During the test process, the samples need to be marked at 7 points in different places. When calculating the sample hardness, remove one of the maximum and minimum values, and then average the other five items. The microhardness of the sample was measured using a MICROMET-5103 digital microhardness tester. When selecting the load, adjust it to 50g and the load duration is 15s. The calculation method of the microhardness value is the same as above, or the average value is calculated. The initial radius of the specimen used in the wear experiment was determined to be 13 mm. The radius after the test was determined to be 103mm, the stroke of the grinding disc during the entire experimental stage was 16.4m, and the load was 4.0kg.
2. Experimental results
1) The organizational form of boron-containing high-speed steel rolls
The 1# and 2# samples in the sample are boron-containing high-speed steel roll samples that have not been modified. The microstructure of the boron-containing high-speed steel roll was observed using a metallographic microscope and a scanning electron microscope. By observing the organizational form, the boron-containing high-speed steel roll The structure in the cast state mainly includes carbon boron compounds, α-Fe and a small proportion of retained austenite. The carbon boron compounds are mainly distributed in a continuous network in the form of a structure, but they will show a network shape in some parts. of fracture.
It can be seen from the Fe-B binary alloy phase diagram that the maximum solid solubility of boron in the y phase is 0.02%, and excess boron atoms will aggregate and crystallize. After XRD analysis of samples 1# and 2#, the physical phase of the roll material without deterioration can be determined. The basic composition of the roll material is mainly austenite and α-Fe. In these two structures, the amount of austenite decreases. , The increase in the number of martensites helps to improve the wear resistance of the material.
Samples 3# and 4# adopted a modification treatment process. The metallography and scanning electron microscope photos after modification showed that compared with the 1# boron-containing high-speed steel roll sample without modification, the carbide morphology in its structure was better. There was a network break. By adding a modifier for modification treatment, the spacing between dendrites of the eutectic structure can be reduced, the eutectic structure and austenite grains in the structure can be refined, and the distribution can be made more uniform. The titanium element in the modifier is formed by strong carbon compounds. Element, titanium reacts with carbon to form a high hardness and wear-resistant phase. After the boron-containing high-speed steel roll undergoes modification treatment, the austenite grains are significantly refined; the eutectic tissue clusters are reduced and distributed more evenly; the boron-carbon compound becomes finer; the microstructure network shape is obvious, but it shows disconnected and discontinuous phenomenon.
2) Hardness and wear test of boron-containing high-speed steel rolls
Conduct a hardness test on the produced roll materials. From the macro hardness and microhardness diagrams of the boron-containing high-speed steel rolls, it can be seen that compared with several other materials, the strength of the 1# material is the lowest. This is because the carbon content of the 1# specimen is significantly lower than that of the other groups of specimens. A higher carbon content will form a large amount of carbides, thereby making the material have a higher hardness. However, the structure of type 4# is fine and uniform, and its wear resistance and toughness are better.
Through the analysis of the above experimental data, the following conclusions are drawn:
(1) The cast structure of boron-containing high-speed steel rolls includes martensite, austenite and other carbon-boron compounds.
(2) After the modification treatment, the sample has an obvious network shape in the structure, but it shows disconnection and discontinuity. The structure is refined. The tempering temperature affects the mechanical properties of boron-containing high-speed steel rolls. It is smaller and has less impact on its wear resistance. However, as the tempering temperature increases, the hardness of the material shows a downward trend;
(3) After modification treatment, sample #4 has high wear resistance, toughness, and more stable hardness, and is stronger than the other specimens in terms of resistance to cutting and fatigue wear.
Boron-containing high-speed steel roll alloy materials partially replace expensive alloy materials with cheap boron elements, which reduces the manufacturing cost of high-speed steel rolls. It also has high wear resistance, toughness and high hardness, which is the development trend of high-performance rolls. and direction.