Introduction to Steel – Characteristics – Classification: The main components of steel slag are introduced, which are active and can be used to produce steel slag cement, which is used for road construction and other related knowledge points.
(1) production of cement because the steel slag contains and cement similar to tricalcium silicate, dicalcium silicate and iron aluminate and other active minerals, with water hard cementitious, so can become the production of clinker-free and less clinker cement raw materials, but also as a cement mixer. The varieties of slag cement produced now include clinkerless slag slag cement, clinker less slag slag cement, slag zeolite cement, slag slag silicate cement, slag slag high temperature gypsum white cement and slag silicate cement. The above cements are suitable for steam curing and have the characteristics of high late strength, corrosion resistance, micro-expansion, good wear resistance and low heat of hydration, etc. They also have the advantages of easy production, low investment, less equipment, energy saving and low cost. Its disadvantage is the low early strength and unstable performance, thus limiting its promotion and use. The production of steel slag cement in China has developed rapidly in recent years, with a current production capacity of nearly 300,000 tonnes.
In addition, as Steel scrap cement contains 40% to 50% of calcium oxide, using it as raw material to formulate cement raw material is attracting increasing attention. It is reported that the Japanese research on the production of ferrate cement with steel slag, the compressive strength of its cement and other major properties are almost the same as that of silicate cement, the process used in the study is to mix limestone, blast furnace slag and steel slag, as well as a small amount of silica, finely ground in proportion to the diameter of 0.5 ~ 1.5cm small ball, calcined at 1340 ~ 1460 ℃ temperature for 30min. and ordinary silicate cement Compared with ordinary silicate cement, ferrate cement has high early strength and low heat of hydration. The addition of gypsum to the ferrate cement produces a large amount of sulphate of iron, which effectively reduces the dry shrinkage of the cement and improves the resistance to seawater corrosion. The heat of formation of clinker was also measured and the application of steel slag to the manufacture of ferrate cement reduced the heat of formation of clinker by approximately 50% compared to normal silicate cement.
China’s current production of Steel scrap cement mainly has two kinds: one is to gypsum for the excitation of clinker-free Steel scrap slag cement, its ratio of steel slag 40% ~ 45%, blast furnace slag 40% ~ 45%, gypsum 8% ~ 12%, grade 27.5 ~ 32.5, the early strength of such cement is low, only for masonry mortar, wall materials and agricultural water conservancy projects; the other is to cement clinker for the excitation of the agent The ratio of steel slag 35% to 45%, blast furnace slag 35% to 45%, cement clinker 10% to 15%, gypsum 3% to 5%, grade 32.5 or more. Steel slag cement has the advantages of low heat of hydration, high strength, corrosion resistance and wear resistance, etc. It is ideal and dam cement and road cement, and has attracted the attention of the relevant industries.
(2) for road construction and backfill materials Steel scrap gravel has a high density, high strength, rough surface, good stability, good wear resistance and durability, and asphalt bonding firm characteristics, and therefore widely used in railways, highways and engineering backfill. Because of its activity,Steel scrap can be slabbed into large blocks, especially suitable for swamps and beaches for road construction. Steel scrap as road gravel, with a large amount of material and good permeability and drainage properties, for asphalt concrete pavement, wear-resistant and anti-slip. In addition to the aforementioned advantages, steel slag as railway slag does not interfere with the electrical work of the railway system due to its low electrical conductivity. Steel slag instead of gravel there is a volume expansion of this technical problem, foreign generally is sprinkled with water pile for six months before use, to prevent the volume of steel slag expansion, rupture pulverisation. China with steel slag for engineering materials, the basic requirements are: steel slag needs to be aged, the rate of pulverisation can not be higher than 5%, to have a suitable gradation, the maximum block diameter can not exceed 300mm, preferably with the right amount of fly ash, slag or clay mixed use, strictly prohibited to steel slag gravel for concrete aggregate use.
C in heat-resistant steel has the role of strengthening the matrix, w (C) should be controlled as high as possible within the range allowed by the specifications, generally w (C) take the value of 0.44% -0.48%. Heat-resistant steel in Si, has the role of enhancing oxidation resistance, but the content is too high, will make the matrix embrittlement, w (C) should be in the target value should be slightly higher in the middle of the target value, such as 1.5% – 2.0%.
Exhaust manifold are small, thin-walled and complex shape of the casting, the production of these castings, the need for strict quality control, are generally used induction furnace melting, operations should be noted that.
(1) the electric furnace used must be equipped with a furnace cover.
(2) after the furnace charge melting clear, each time after opening the lid operation, should be in the liquid surface sprinkle a small amount of carbon powder and Si-Fe powder mixture, and then the lid cover tight, in order to avoid the steel oxidation.
3）After the furnace charge is melted and cleared, Si-Fe and Mn-Fe are added for pre-DO.
(4) the composition and temperature of the molten steel are in line with the requirements of the steel, it is appropriate to use Al, Ca composite deoxidation O way for the final deoxidation of the molten steel, and strict control of the varieties of composite deoxidizer, adding the amount and adding the way.
Since the flowability of heat-resistant steel is much worse than that of cast iron, the production requires attention to.
(1) cast steel parts production, with bottom injection pouring ladle casting is the commonly used traditional process, heat-resistant steel exhaust manifold, the best use of bottom injection pouring ladle. Since there is no small bottom injection pouring ladle available on site, it must be designed and manufactured according to the specific conditions of the production unit special pouring ladle.
2) The pouring process to keep the cavity in a reduced pressure state, so that the steel filling conditions can be greatly improved, the casting of porosity defects and other surface defects will be significantly reduced.