The Challenge of cast Iron Today and its Future Development trend

Summary of the Development of cast Iron

Cast iron is a kind of casting material which is old and new, traditional and modern. It is recognized in the world that around 600 BC, China first smelted iron ore into molten iron and cast it into iron castings. By the middle and late warring States period at the latest, the division of labor between smelting pig iron and casting iron had begun. For a long time before the Industrial Revolution, China led the world in iron smelting and casting production, and exported to Southeast Asia and other places. Cast iron smelting technology was introduced into Europe between 1200 and 1450 AD. However, until the Industrial Revolution, the development of cast iron technology was very slow, and people's understanding of cast iron was limited to gray iron, white iron and gunned iron judged by the color of fracture. In the early days of Europe and America, it was considered that cast iron was not suitable for tensile test, but only for pressure test.

The pursuit of high mechanical properties has always been the mission of cast iron workers in the world. In 1860, the tensile strength of cast iron recorded in Europe and America was only 60 MPa,. During the first World War, the tensile strength of cast iron was increased to 120 MPa; by adding scrap steel. In 1922, inoculated cast iron was invented, and the tensile strength was increased to 300 MPa. After alloying, the tensile strength of inoculated cast iron is increased to 400 MPa. Although the tensile strength of white-core malleable cast iron and black-heart malleable cast iron invented in 1722 and 1826 respectively has been greatly improved, it can only produce small thin-walled parts. The ductile iron invented in 1948 has a tensile strength of 600MPa, and an elongation of 3%, and the tensile strength of alloy ductile iron can reach 800mm 900 MPa. The tensile strength of ADI developed in the 1970s can reach up to 1 200 MPa, and up to 1 600MPa (ASTM A897M-2003), and the highest recorded tensile strength of ADI reaches 1 700 MPa, elongation of 3%. In the past 140 years, the tensile strength of cast iron has increased nearly 20 times. Figure 1 shows the development of cast iron strength with age and the development of different cast iron and strength with age. The invention of nodular cast iron in 1940s greatly improved the properties of cast iron. The subsequent emergence of vermicular cast iron and ADI, silicon solution strengthened Ferritic ductile iron and various special applications of wear-resistant, heat-resistant and corrosion-resistant cast iron further enriched the cast iron family members, expanded the scope of application of cast iron, and increased the output of iron castings. By the 1990s, the properties of cast iron were 20 times higher than those in the early stage.

The Development of the strength of (a) cast Iron with the years

Development of (b) cast iron (LG low grade and high grade gray cast iron, DI ductile iron, ADI isothermally quenched ductile iron) and strength with age

Fig. 1 Development of cast iron

Not only the properties of cast iron have been significantly improved, but also the global output has increased significantly. Since 1966, under the influence of the world economic development cycle, political climate and unexpected events, the world casting output has increased and decreased, but the overall upward trend. The total output increased from 63,261,475 tons in 1966 to 103,223,514 tons in 2013, to an all-time high of 112,738,168 tons in 2018, an increase of 78 percent. 2019 the output dropped slightly, and affected by the worldwide novel coronavirus epidemic in 2020, the output dropped to 105,505,602 t, figure 2; the global ductile iron output increased nearly 15 times from 1,930,700 t in 1966 to 28128,422 t in 2018, and dropped to 23,593,945 t in 2020, as shown in figure 2.

Total global casting output of (a) 1966-2020

Development of several main material castings of (b)

Fig. 2 Development of global nodular cast iron production

Competition and Challenge of cast Iron

1.1 cast iron and aluminum alloy

Because aluminum alloy has a face-centered cubic crystal structure, light specific gravity, good thermal conductivity, good ductility and low temperature performance, and the continuous improvement of the performance of aluminum alloy, aluminum alloy has grown steadily in automotive and other applications for more than 50 years. The global proportion of castings has increased from 2% in 1966 to 12% in 2000 to about 16% in recent years, as shown in figure 3. The proportion of aluminum alloy in castings in China was very small in 1978 and before, accounting for 7.30% in 2000 and 13.12% in 2020, as shown in figure 4. Because of the ductility of aluminum alloy, the whole frame structure of the car can even be molded at once, and the body will be changed from 70 parts to 1 part, thus greatly reducing the capital expenditure for all robots to assemble these parts.

Fig. 3 steady growth of aluminum alloy application in the world

The global share of castings increased from 2.27% in 1966 to 12.43% in 2000 and about 16% in 2020.

Fig. 4 steady growth of aluminum alloy application in China

The proportion of aluminum alloy in castings in China was very small in 1978 and was not listed separately. It was 7.30% in 2000 and increased to 13.12% in 2020.

However, cast iron, especially vermicular iron and ductile iron, especially ADI, has higher strength and higher fatigue strength than aluminum alloy because of its low total production cost, good casting performance and mechanical processability, good wear resistance, low notch sensitivity and good recyclability. Cast iron is still widely used and still accounts for more than 70% of the total output of castings, and is still the most important casting material. Figure 5 and figure 6 show the comparison of the properties of ductile iron and aluminum alloy. In addition, the energy content per unit mass of cast iron is low, and the greenhouse gas emission is low. The production of cast iron of the same quality consumes the lowest energy and greenhouse emissions. Figure 7 shows the energy and greenhouse gas emissions per kilogram of mass produced by different materials. The weight of the cylinder block is reduced when aluminum alloy is used, thus saving fuel and reducing emissions, but from life cycle analysis, that is, from mining to road use, a detailed analysis of each step of the manufacturing process shows that when the cast iron cylinder block is changed into an aluminum alloy cylinder block, there is no net benefit between the total manufacturing energy and the fuel savings achieved as a result of weight reduction. If the cast iron engine adopts lightweight design, the total energy consumption and greenhouse gas emissions have more advantages.

Typical stress / cycle (N) Curves of (a) cast Aluminum Alloy and Nodular cast Iron (DI)

Typical specific stress / cycle curve, r, density of (b) cast aluminum alloy and DI

Fig. 5 fatigue curves of cast aluminum alloy and nodular cast iron

Cast aluminum alloy with different solid solution treatment of (a)

Specific fatigue strength of (b) Nodular cast Iron

Fig. 6 comparison of mechanical properties between ductile iron and aluminum alloy

SC- sand casting; DC- die casting; DI- nodular cast iron; F-ferrite; FP- ferrite-pearlite; P-pearlite; T quenching and tempering; AUST- austenite quenching. Effect of temperature on (DI) specific tensile strength of aluminum alloy and nodular cast iron. UTS, ultimate tensile strength, r, density 357=Al7Si0.8Cu.

Fig. 7 Energy and greenhouse gas emissions per kilogram of mass produced by different materials

Energy energy, GHG greenhouse gas emissions, PigIron pig iron, Scrap Iron scrap machine iron, VirginAl primary aluminum, Scrap Al waste aluminum, Ferro-Si ferrosilicon, Mn manganese, Cu copper

1.2 Challenge of complex high performance castings

With the development of industry, the function of modern equipment is becoming more and more powerful, and there is more and more demand for iron castings of various sizes and different wall thickness. as a result of the continuous development of high-quality raw materials and generation methods, the performance of iron castings is getting better and better. as well as the use of a variety of new modeling materials and new modeling methods, all kinds of complex iron castings can be manufactured.

For example, in recent years, driven by the world demand for clean energy and renewable energy, the demand for nuclear power and wind power is increasing, especially for large castings such as nuclear power spent fuel storage tanks in nuclear power plants. In recent years, the rated output power of wind turbines has become larger and larger, and wind turbines have reached 15 MW,. In the future, the power of wind turbines can reach 21 MW or more. Much of the demand for more renewable energy can only be achieved through the supply of castings. Ductile iron and ADI are very suitable for these parts. In recent years, due to the rapid development of wind power industry, wind power castings have developed the fastest. In 2020, the installed capacity of wind power increased by 111.1 gigawatts over the previous year, and the output of wind power ductile iron was about 2.2 million t. The global growth rate of wind power accelerated in 2021, and it is estimated that wind power ductile iron is 2.5 million tons. The most widely used in wind power and nuclear power is low temperature Ferritic ductile iron 400-18LT, and they are both thick and large (see figure 8: 10). The wind power planetary rack has already adopted ADI, and is getting larger and larger (figure 10). Heavy and heavy low temperature Ferritic ductile iron has strict requirements on microstructure, there can be no broken graphite, and the impact properties at low temperature (- 20 or even-30,-40 ℃) must meet the strict requirements. In order to meet these requirements, all stages of production must be strictly controlled, including the selection of pure raw materials. Silicon solid solution strengthened Ferritic ductile iron has been used in wind power and is expected to account for more than 10% of wind power castings. Figure 11 shows the award-winning silicon solid solution enhanced wind power castings of Ningbo Riyue Co., Ltd. With the increase of wind turbine power, these castings may be larger in size, more stringent in structure and higher in performance.

With the development of industry, the function of modern equipment is becoming more and more powerful, and the structure is becoming more and more large and complicated. Especially for large precision machine tools, there is an increasing demand for large machine tool castings. Figure 12 shows a large precision machine bed produced by a machine tool in Beijing.

At present, the transportation industry such as automobile, railway and shipping is at the center of energy saving, environmental protection, carbon reduction and the use of alternative fuels, and it is necessary to develop lighter and more efficient vehicles and means of transportation. casting can provide more efficient parts for the automobile and other transportation industry, such as high-speed rail gearbox, large V-shaped engine block, lighter and more powerful aluminum alloy and vermicular cast iron composite engine. There are also complex control valves and extremely thin ductile iron impellers, figure 13-14.

Fig. 8 Ductile iron base and hub of large wind turbine

Fig. 9 100 t nuclear spent fuel storage and transportation tank

(a) is working on the ADI planetary shelf for austenitization in ADItreatments, Birmingham, England.

The 3.2tADI wind power planetary shelf handled by (b) right Shiyan Aobei Technology Co., Ltd.

Fig. 10 ADI wind power planetary shelf

Fig. 11 award-winning silicon solid solution strengthened ductile iron wind power castings of Ningbo Riyue Co., Ltd.

Fig. 12 Nodular cast iron beam LE901013A020 produced by a machine tool in Beijing, casting weight 123t

(a) high-speed rail gearbox

(b) large V-shaped engine cylinder block

(c) Ning Xavier's ductile iron impeller (only 0.2mm at its thinnest point)

Fig. 13 Ball milled iron castings with complex structure

Fig. 14 combined structure of Ford aluminum alloy bracket and CGI cylinder block

It provides optimized strength and stiffness, reduces overall weight, realizes energy saving and emission reduction, and the bracket and cylinder block are mechanically connected through standard washers and bolts.

Development trend of cast Iron in the Future

2.1 production will continue to increase

As shown in figure 2, countries around the world were affected by the novel coronavirus COVID-19 epidemic in 2020. Due to government shutdowns and restrictions, the world casting output dropped to 105,505602 t, 6.4% lower than in 2018; in 2020, ductile iron output dropped to 23,593,945 t, a decrease of 16% compared with 2018. However, the foundry industry is the core industry of the whole manufacturing industry and a vital part of the global industrial value chain. The current production reduction is temporary, and the output of iron castings is bound to increase in the future.

In 2020, China felt novel coronavirus's influence earlier than most countries. however, due to the correct response policy, China's casting production increased by 6% in 2020 after stopping growth for two consecutive years, with a total output of 51.95 million t, including 21.75 million t of gray cast iron and 15.3 million t of nodular cast iron, all of which reached the highest level in history.

Recently, Turner (Turner), Secretary General of the World Foundry Organization, said that in the near future, the impact on casting production is the supply of materials, whether chips have affected the largest casting users in the industry, lack of electricity in foundry enterprises, rising prices of raw materials, and insufficient transport and logistics, but these are all short-term problems, or the normal economic cycle, or some minor problems caused by the impact of the past 12 months. None of them is a systemic long-term problem.

Javier Gonzalez (Javier Gonzalez), elected secretary-general of the World Foundry Organization, said that looking at the production and orders index, the outlook for this year and next suggests that manufacturing levels, including the foundry industry, are expected to recover. We have seen that our foundries around the world actually resumed activities this year and in the second half of 2020; many factories are at high capacity utilization levels, depending on the industries they serve.

Both the American Modern Casting and the European Foundry Association predict that the foundry industry and cast iron will continue to grow. The European Foundry Association reported that the mood in the European foundry industry has been stable at a high level so far due to very good orders from the mechanical engineering sector since June 2021. At the same time, the business climate index remained at a high level in November. The index edged up 0.05 points to 1.80. In particular, sales prices are expected to increase the business climate index in the coming months.

Countries around the world, including some major casting manufacturers and raw and auxiliary material manufacturers in China, have completed or are deploying new plant construction to prepare for future growth.

As predicted by the Secretary General of the World Foundry Organization Turner and the President of the American Foundry Association, the foundry industry will be brilliant again, casting production will grow again, and iron casting production will grow again!

2.2 performance continues to improve

Although the properties of cast iron have been greatly improved, the performance standards of Chinese and international ductile iron, vermicular graphite cast iron and ADI have been improved since 2000. Many Chinese enterprises have produced 900-5 1000-5 ductile iron, which is higher than the existing standard, and the performance of each grade of ADI is also much higher than that of ASTM and international and national current standards. China is considering revising and improving the relevant technical standards of cast iron. At present, the research on the properties of cast iron is extensive and deep to the atomic level. I believe that with the deepening of the research and the improvement of technology, the properties of cast iron will be further improved.

In addition to conventional performance, high-performance and safety-critical structures also require high and stable fatigue performance. The fatigue life of equipment structure is the basic ability to determine the safe and reliable service of equipment. Therefore, improving the fatigue strength of safety key cast iron structures has become an important direction of cast iron development. In order to detect and improve the fatigue strength of cast iron, some advanced foundries in the world, including China, have even built fatigue laboratories.

2.3 develop castings with stronger function, more complex structure, more energy saving and emission reduction

The development of iron castings is the development of cast iron. Foundry and foundry technicians have been at the forefront of the development of energy, transportation and other equipment for many years, and the development of any new equipment is inseparable from castings. With the demand of energy saving, environmental protection, sustainable, clean energy, reducing CO2 emissions and carbon neutrality, the demand for the performance of new equipment with high requirements is higher and higher, and the number is more and more.

Foundry is the industry that provides spare parts for these equipment. Wind power and nuclear power equipment in new energy, high-speed rail in transportation, and many parts of cars are cast iron. On September 16, according to media reports, Weichai developed the diesel engine with the highest thermal efficiency in the world, with a thermal efficiency of 50.26%, which is a revolutionary breakthrough in the history of internal combustion engine development. There are many demanding iron castings in the internal combustion engine.

The challenge of the transition to a zero-carbon industry and the transition to electric vehicles is both a challenge and a new opportunity for cast iron. Although the electric vehicle has no internal combustion engine, there are still many control, transmission and braking parts. Cast iron mills need to work closely with equipment manufacturers, raw material suppliers and designers to develop more integrated, efficient, energy-saving and functional castings. Due to 3D printing, computer technology, any previously unimaginable metal castings of complex shapes can be developed and manufactured, not only to replace steel castings, forged steel parts, weldments, and some even replace plastic parts.

In addition, as the gray iron castings with the largest share of cast iron, due to its low price, good castability and machinability, good wear resistance and low notch sensitivity, its properties can meet many applications, including engine castings, brackets, shells and so on. will continue to develop steadily and retain its largest share of the position. The redesigned integrated high-grade gray iron 300 can even replace 36 pieces of steel welded parts, reducing cost and delivery time. In addition, with the improvement of people's living standards, the demand for high-quality daily cast iron cooking utensils is increasing, and high-quality daily cast iron cooking utensils with extremely low content of harmful elements, safety, health, beauty and easy to use are becoming more and more popular and sell well at home and abroad.

2.4 Transformation of cast Iron Plant to Green, High efficiency, Energy Saving Digitalization and intellectualization

The development of iron foundry is the development of cast iron. The casting factory is no longer the kind of manual operation, high labor intensity and poor environment in the past. But mechanization and improving the working environment are far from enough.

In order to maintain its competitiveness, cast iron mills must have a comprehensive and accurate control of the production process. It is understood that a foundry has 137 variables to be controlled (based on the assessment of an iron foundry in Mexico). In order to be competitive, the process parameters must be controlled within the standard range of these 137 variables.

Patricio Gil, former president of the American Foundry Association, believes that cast iron mills not only passively fulfill customers' orders, but also provide customers with more service and value. A foundry that can achieve perfect quality, delivery and operation is considered a reliable supplier; a flexible and cost-effective foundry can be seen as a competitive supplier; and a foundry that is willing to share costs and opportunities is a reliable supplier. Foundries that provide fully finished parts are suppliers with value-added space; suppliers that can support parts optimization are considered to be foundries with technical capabilities; and finally, suppliers who can provide parts integration are considered suppliers that can help customers optimize the supply chain.

Cast iron plants should not only provide castings for new demanding equipment with energy conservation, environmental protection, sustainability, clean energy, reduction of CO2 emissions and carbon neutrality, but also develop towards more energy saving, environmental protection, sustainability, reduction of CO2 emissions and carbon neutrality.

Most cast iron plants use electric furnace smelting, but electricity does not necessarily come from renewable energy. Although the demand for more renewable energy can only be achieved through the supply of castings, casting production still needs a lot of energy, which is a dilemma. It needs the cooperation of all aspects of the country to solve the problem.

Another challenge facing the cast iron plant is to gradually develop digitally and intelligently while maintaining its competitiveness, allowing raw material supply, casting quality, customer feedback demand, new product development, etc., through advanced equipment, infrastructure, automation and other technologies to connect and "intelligent", so as to win the competition in the new reality. It is gratifying that some foundries in China have achieved partial intelligence, and are moving towards a higher level of digitalization and intelligence.

Conclusion

Although cast iron, which has experienced thousands of years of development, has temporarily stagnated and declined recently due to the influence of some political economy and the epidemic situation of novel coronavirus, due to the unique physical properties of cast iron and a wide range of continuously improving mechanical properties, and can cast a variety of complex castings, as well as competitive price advantages, the foundry industry is the core industry of the entire manufacturing industry. Is a vital part of the global industrial value chain. Cast iron is still the most important casting alloy at present and in the future. With the progress and development of technology, the performance of cast iron will be further improved, the production of iron castings will increase, and there will be more and more castings with stronger functions, more complex structure, more energy saving and emission reduction. At present, if cast steel is added, cast iron-based alloys will account for more than 81% of the world's foundry production. As far as casting materials are concerned, as Professor Stefanescu said, we are still in the Iron Age.