What is silicon chromium alloy?
A ferroalloy is mainly composed of silicon, chromium, and iron. Also known as silicon-chromium alloy. It is mainly used as a master alloy for the production of medium, low and micro carbon iron by electrosilicothermal method. Used as deoxidizer (replacing ferrosilicon) and chromium additive in steelmaking. Generally, it contains Cr>30%, Si>35%, and the balance is iron and a small amount of impurities. Classified according to carbon content, such as carbon content ≤0.06%, ≤0.10%, ≤1.0%, etc.
The source of silicon in the alloy is mainly SiO2 in silica, and the sources of chromium are chromium ore and carbon ferrochrome. They are all produced by smelting in ferroalloy submerged arc furnaces. It is mainly used as a reducing agent for the production of medium-low carbon ferrochrome and micro-carbon ferrochrome and as an intermediate alloy agent for steelmaking.
Properties of silicon chromium
Chromium and silicon produce two stable compounds at high temperatures: CrSi and CrSi2. Because chromium silicide is more stable than its carbide when silicon is present, part of the carbon will be replaced by silicon to form a carbon-silicon composite chromide until silicide is formed.
When Si<20% in the alloy, it is basically composed of one phase (Cr, Fe)3(C, Si)2. It can be considered that part of Cr in Cr3C2 is replaced by Fe and part of C is replaced by Si. When the silicon content increases to >20%~29%, a new composite phase (Cr, Fe) (Si, C) is formed. Excess Cr and Fe form the intermetallic compound FeCr, which is the σ phase. Containing Si between 29% and 34%, a new phase (Cr, Fe)Si is added. When Si exceeds 34%, chromium, iron, and silicon form silicide. Due to the increase in silicon content, CrSi2 and SiC phases appear. The affinity between chromium and silicon is greater than that between iron and silicon, so CrSi2 is generated first. However, CrSi2 and FeSi2 have different crystal structures and cannot form solid solutions with each other. When the Si content is 44% to 51%, Cr and Si form CrSi2, and part of FeSi and Si form FeSi2. When Si is 51%~60%, the alloy is composed of Cr-Si2, FeSi2, SiC, and Si. From the above results, it can be seen that the chromium-silicon ferroalloy with high silicon content is composed of chromium and iron silicides, SiC and Si, that is, carbon exists in the SiC phase. The structural analysis of industrially produced silicon-chromium ferroalloys is basically consistent with this. Carbon exists in the SiC phase and is insoluble in the liquid ferrosilicon.
Silicon chromium production process
There are two processes for producing silicon-chromium ferroalloy from chromium ore: the one-step method and the two-step method.
The one-step method is to directly smelt chromium ore, silica, coke, etc. into ferrosilicon alloy in a submerged arc reduction electric furnace. Therefore, it is also called the direct method or the slag method. Due to the large amount of slag in this method, more chromium is lost in the slag. MgO, Al2O3, and CaO were partially reduced and volatilized, which increased production energy consumption. Therefore, a two-step method was developed, that is, chromium ore, coke, and part of silica were used as fluxes to refine high-carbon chromium in a submerged arc reduction electric furnace. Iron is then granulated or broken into granules; then the high-carbon ferrochromium particles, silica, and coke are smelted into ferrosilicon alloy in another submerged arc reduction electric furnace. Because the product contains high carbon content, carbon reduction treatment is required outside the furnace to obtain silicon-chromium ferroalloy with qualified carbon content. Because the chromium ore is refined into an alloy in two steps, it is called the two-step method. Also known as the indirect method or the slag-free method. After long-term improvement and operation, compared with the two-step method, the one-step method uses one less electric furnace and reduces investment; low-carbon products can be obtained directly; and the process flow is short. After recovering metal through slag, the recovery rate of chromium is higher and the total smelting power consumption is lower; but the process is difficult to master. The main reason is that the slag is sticky and the problem of smooth discharge of slag from the furnace is difficult to solve. In addition, there are the shaking package decarburization method and the slag washing decarburization method.
Silicon Chromium Price Trend
Recently, silicon-chromium alloys have turned from falling to stable operation. The current mainstream transaction price in the silicon-chromium market of 72 grades is 9200-9300 yuan/ton (cash including tax ex-factory).
Reasons for the price to stop falling and stabilize:
1. The price decline period of silicon-chromium alloy lasted for two months in the early stage, with a cumulative decline of 650 yuan/ton, far exceeding the decline of raw material high-carbon ferrochromium. The profit of the silicon-chromium factory was almost squeezed out, and it is temporarily difficult to There is room for continued concessions.
2. The price of downstream products has increased slightly. Low-carbon ferrochrome factories in Shanxi, Jiangsu, and other places have recently been actively replenishing raw materials. The consumption of silicon-chromium alloy has improved. In addition, some high-quality silicon-chromium alloys are exported, sharing a certain shipment pressure. Therefore, silicon-chromium Alloy factory quotations gradually stabilized.