(Source: China Automotive News, Zhao Lingling)
Among steel, aluminum and plastic, the three major materials for car making, steel is a highly cost-effective material primarily used for the car body. In recent years, advanced high strength steel (AHSS), an excellent lightweight material for cars, has seen rapid development.
China aims at reaching peak emission in CO2 by 2030 and realizing carbon neutrality by 2060. In this context, massive development and application of AHSS will not only remarkably reduce car weight, but also significantly contribute to reaching the strategic carbon peak and neutrality goals.
Rapid Development of AHSS
Advanced High Strength Steel (AHSS) generally refers to automotive steel over 500MPa in strength with good plasticity, such as Dual-Phase (DP) Steel, Transformation-Induced Plasticity (TRIP) Steel, Martensitic Steel (MS), Complex Phase (CP) Steel, Press Hardening Steel (PHS), Twin-Induced Plasticity (TWIP) Steel, Quenching and Partitioning (Q&P) Steel, and Medium Manganese Steel (MMnS). AHSS and the highly efficient stamping technology have been widely applied in the automotive industry, primarily to structural, safety and reinforcing components.
According to senior expert Wu Hao from CATARC (Tianjin) Automotive Engineering Research Institute Co. Ltd., with the development of the steel industry, advanced automotive steel is continuously improving in both production and strength, and the production capacity and technical reserve of HSS are also creating more potentials for the lightweight trend.
Currently, automotive steel has entered a profoundly changing new development phase. Most steel makers have developed and started the mass production of the 3rd generation HSS to address the increasing needs of higher strength, improved formability and better usability.
“With the 3rd generation cold-stamping and hot-stamping AHSS now available on the market thanks to the constant innovation and development of new steel grades, the automotive industry no longer needs to turn to more expensive aluminum and composite materials.” A relevant person from ArcelorMittal (AM) pointed it out that, the R&D of hot-stamping AHSS is much more complex than that of the traditional steel grades, because such steel grades cannot provide the desired high performance right after production. Their optimum performance capacity can be brought to full play only after high-precision processing. For this reason, during the R&D of hot-stamping materials, a processing technology from steel material to final components was also developed by AM and shared with AM’s customers.
According to Mr. Jurgen Cobbaut, CMO of VAMA, as ArcelorMittal’s branch in China, VAMA remains committed to bringing world-leading AHSS products and technologies to Chinese customers since SOP in 2014, gradually filling the gap in the domestic high strength automotive steel market. After the completion of Phase II Project, VAMA will introduce and produce the 3rd generation cold stamping ultra high strength steel (UHSS) and Zn-Al-Mg coated products to further meet the requirements of domestic OEMs on UHSS and highly corrosion-resistant exposed parts.
Longer Range and Better Safety Performance of NEVs
NEVs’ driving range, which is highly impacted by vehicle weight, remains a concern of the industry. To lower battery cost and extend range, weight reduction is imperative. Lightweight technologies will not only reduce energy consumption of NEVs, but also influence future auto design concept, thus become a major drive for technological upgrading of NEVs.
HSS can be used to make not only car bumpers, door beams, safety structural parts, chassis parts, expansion system parts and seats, but also protective structures to improve the safety performance of NEVs.
According to Jurgen Cobbaut, in as early as 2015, ArcelorMittal launched the S-in motion® BEV SUV lightweight solution, and has been making innovative improvements with the technological upgrading of NEVs, including the brand-new lightweight steel battery pack solution which may potentially reduce the overall weight of vehicles compared with the benchmark models on the market. The solution involves the application of many new materials and new processes. Among them, the second-generation AS-coated hot-stamping steel products, Usibor®2000 and Ductibor®1000, compared with the first-generation Usibor®1500 and Ductibor®500 products, further reduce vehicle weight by 10% to 15% and improves the lightweight factor, dynamic safety performance and comfort of vehicles. At present, both Usibor®2000 and Ductibor®1000 have been put into mass production in China, and applied to models on the market.
To adapt to the NEV trend, advanced technologies has been developed for HSS and will soon be implemented. Wu Hao continued that, CATARC has carried out a lot of research with many universities and research institutes in integrated high strength car body forming technology, composite connection technology for HSS and aluminum alloy/CFRP materials, and HSS anti-corrosion and protection technology, etc. Relevant technological achievements have drawn great attention from the industry and realized good value in application.
Cost Bottleneck to be Addressed
With continuously improved laws and regulations and the increasingly harsh market competition environment, carmakers and their suppliers are faced with huge challenges in weight reduction, safety performance and cost control of passenger vehicles. Nowadays, OEMs and parts suppliers take cost control as a key focus. AHSS and its outstanding design undoubtedly provide an excellent overall cost control solution from design to the entire car mass production.
“For carmakers, not only is higher proportion of UHSS needed for weight reduction and safety performance purposes, but the material should also have good processability and connectability, as well as good compatibility with other materials. Apart from meeting the performance requirements, it should also realize good cost efficiency, lower energy consumption in production and recycling of the material and parts, and a full lifecycle green supply chain. Therefore, lower cost, including raw material cost and parts manufacturing cost, is a major development trend for the automotive steel industry,” said Wu Hao.
Mr. Jurgen Cobbaut pointed out that AHSS is indeed more expensive than traditional steel grades considering merely the price per unit weight, because on the one hand, the alloying and production cost is higher, and on the other hand, more resources are required for its R&D. However, considering the cost of parts, it is the other way round: since AHSS has much higher strength, component weight can be reduced to balance off the unit price of the material. “More importantly, we have also introduced advanced steel solutions for our customers, such as the optimized nesting and blanking to reduce scrap during parts production, the combination of multiple parts into one to reduce the weight of each single piece as well as the cost of processing, etc.”
Researcher Luo Yan from China Auto Lightweight Technology Innovation Strategic Alliance highlighted that, through years of development, China has made many international leading achievements in HSS development and application, with HSS application in passenger vehicle body leading international level. China has the capacity of developing and producing HSS ranging from 340MPa to 2GPa in strength. HSS proportion in domestic leading passenger vehicles has reached 50%, and even 73% in some models. 2GPa hot-stamping steel has also taken the lead in realizing industrial application internationally.
“With further maturing of technologies in product design, formability and connectability, a development pattern featuring the coexistence of multiple technologies and multiple technological routes will emerge, and ‘rational lightweight solutions’ will become a core need of future enterprises. For assembly plant, before determining which lightweight technological route to follow, they consider more comprehensively by balancing market positioning of the vehicle, user needs, performance and cost, product profit and supply chain, etc.,” added Luo Yan.