Baosteel's Innovations in Wear-Resistant Steel: Advancing Strength and Sustainability

Material wear is a common issue across various industries, with an estimated 2 to 3 million tons of steel materials consumed annually due to wear. Resources and energy constraints are becoming increasingly evident, and environmental protection issues are growing more severe. The global market for top-tier wear-resistant steel has long been dominated by foreign companies such as Sweden's SSAB (including Finland's RUUKI) and Japan's JFE. As China's industry rapidly develops, mechanical equipment is becoming more complex, large-scale, lightweight, and diverse in service environments. There is a surging demand for high-strength, tough, complex-shaped, low-loss, and environmentally friendly wear-resistant steel materials, which are quickly being adopted across various industries. Baosteel, China's largest and most advanced steel mill, is swiftly advancing in the field of wear-resistant steel, consistently introducing products that meet international leading standards.

Technological Innovations

We have overcome the co-control technology of lath martensite substructure refinement and ε-carbide precipitation, developing high-strength wear-resistant steel with precise control over martensite substructure, multi-scale precipitation, and bainite phase. For the first time, we have achieved mass production of the NM600F grade product, which boasts the highest strength of 2000MPa. By leveraging the synergistic effects of micro-alloys and alloying elements, we ensure quenchability while minimizing alloy addition, enhancing strength-toughness matching, and reducing quenching stress. The target steel grade is the 2000MPa wear-resistant steel NM600, characterized by a microstructure of low-carbon lath martensite. The microstructure control units consist of original austenite grains, packets, blocks, and laths. The block width is an effective control unit for strength, while the packet size is for toughness. By controlling the blocks and packets within the martensite microstructure, we can manage the strength and toughness of the martensite wear-resistant steel. Following the industrialization of F-grade wear-resistant steel of varying strengths, the -60°C toughness is well-matched with its strength and wear resistance, marking the first development of 2000MPa ultra-high-strength E and F grade wear-resistant steel. This addresses the toughness control challenges posed by high hardness and surpasses SSAB's -40°C low-temperature impact toughness limit.

Quality Control Technology

We have developed a "medium carbon + boron + niobium + chromium + molybdenum" gigapascal-level martensitic wear-resistant steel casting quality control technology.

(1) We have crafted a dynamic adjustment method for the red billet pressure control of the continuous casting machine to enhance the internal quality of the martensitic wear-resistant steel billet. Utilizing a secondary model of solidification heat transfer to calculate the thickness in each sector of the billet, we achieve dynamic stability with varying thicknesses. Precisely controlling the dynamic adjustment of red billet pressure, we achieve self-adaptive smooth transition under different pouring conditions, thereby enhancing the internal quality of wear-resistant steel billets. After billet quality grading, the proportion of center segregation C0.5 and center porosity 0.5 has increased from 75% to 93.4%, especially for NM500 to NM600 grade products, the proportion has increased from 61% to 93.4%.

(2) We have pioneered a method to reduce surface cracks on the head and tail billets of wear-resistant steel continuous casting by controlling the secondary cooling. By tracking the billet head and tail during the opening and tail stages of high-end wear-resistant steel product continuous casting, we adjust the secondary cooling water in real-time to achieve weak cooling of the billet head and tail, self-adaptively increasing the surface temperature of the head and tail billets, reducing the occurrence of surface transverse cracks, and significantly improving the quality of wear-resistant steel products. This technology is the first of its kind in the continuous casting process of high-end wear-resistant steel billets, breaking through the technical barrier of achieving good internal and surface quality for "medium carbon + boron + niobium + chromium + molybdenum" martensitic wear-resistant steel billets. We have also developed a narrow composition control method and clean steel smelting technology to enhance the stability of finished steel performance.

Heat Treatment Control System

We propose a Nb-V-Mo-Ti composition system and controlled heat treatment process that disperses particles at low temperatures to prevent the occurrence and expansion of cracks during severe wear, as well as to prevent M grain boundary migration in acid-base and high-temperature environments, enhancing martensite stability. Under special conditions such as extreme cold, sandstone permafrost, acid-base, and high temperature, wear resistance is increased by 1.18 to 1.53 times, achieving high wear resistance, low loss, and environmentally friendly development.

(1) In the development of high-temperature wear-resistant steel with good erosion wear performance, we add martensite solid solution strengthening stability elements such as Nb, V, Mo, and Ti to increase the degree of deformation resistance and work hardening, as well as temper stability, achieving high-temperature strengthening. This ensures that the tensile strength and Brinell hardness of martensitic wear-resistant steel does not decrease too much with increasing temperature, meeting the requirements for good wear resistance under high-temperature service conditions. ② By adopting a controlled temperature and speed quenching heat treatment process, we promote the precipitation of fine and dispersed Nb, Mo, V, and other micro-alloy elements' C, N compounds during the quenching cooling process. The fine and dispersed Nb(C,N), Mo(C,N), V(C,N) prevent grain boundary migration and increase the grain growth temperature, achieving a quenched steel plate with fine grain size and dual effects of fine grain strengthening and precipitation strengthening. Ultimately, during service at 100~500°C, the steel plate still maintains dual effects of fine grain strengthening and precipitation strengthening, stabilizing the tensile strength and Brinell hardness of the steel plate at high temperatures, and improving high-temperature wear resistance. The wear resistance of NM500-tuf is 1.7 times higher than that of ordinary NM500.

(2) In the core technology research and development of low loss and high wear resistance steel plate, during the quenching heating process of the steel plate, the original fine deformed organization and a large number of finely dispersed precipitates in the Ti or V wear-resistant steel plate accelerate the uniform diffusion process of Ti or V's carbon and nitrogen compounds, shortening the heating and holding time. During the quenching cooling process, the uniform precipitation of Ti or V's carbon and nitrogen compounds is instantaneously frozen, avoiding the aggregation of carbides and micro-alloys and other strengthening phases, resulting in a uniform Brinell hardness, good wear resistance, and excellent matching of strength and toughness of high-grade wear-resistant steel.

Using this process, the microstructure of the wear-resistant steel is fine lath martensite, with the percentage of martensite "lath bundle" ranging from 60% to 90% and an average size of 0.6021 to 1.7453μm, and the percentage of martensite "lath block" ranging from 10% to 40%. This achieves flexible control of the martensite morphology in high-grade wear-resistant steel, with wear resistance 1.18 to 1.53 times higher than that of wear-resistant steel of the same hardness level.

Special Wear-Resistant Steel

We have innovatively introduced nano TiC and residual austenite into high-strength and tough lath martensite wear-resistant steel, successfully developing a series of complex-shaped wear-resistant steel plates. For the first time internationally, we have achieved 180° post-weld forming and large load fatigue without crack propagation in the weld, applied to ultra-large hard rock surface compactors and other extreme equipment manufacturing. The indicators of steel plate welding, forming, and fatigue wear have reached an internationally leading level. A new approach to pre-precipitating the second phase particles and controlling their growth, introducing ultra-hard nano TiC particles into the martensite matrix, and controlling the heat treatment process to retain and disperse them in the martensite matrix, achieving 5% to 15% of the film-like metastable residual austenite organization, thus increasing the welding performance and toughness of the steel plate without increasing the carbon content and alloy elements. The first 1100MPa high-strength, 360-degree roll-forming compactor wheel wear-resistant NM360-YLJ was launched, solving the uniform dispersion control problem of nano TiC and metastable austenite on the martensite matrix, and for the first time internationally, achieving wear-resistant steel plate post-weld 180° bending forming and large load fatigue without crack propagation in the weld, applied to ultra-large hard rock surface compactors and other extreme equipment manufacturing. The indicators of steel plate welding, forming, and fatigue wear have reached an internationally leading level.

We pioneered the "constrained temperature quenching + hot air circulation high-precision ultra-low temperature tempering" wear-resistant steel plate low internal stress control technology, solving the international problem of low residual stress and high uniformity control for 1100~2000MPa ultra-high-strength wide and thick wear-resistant steel plates, meeting the requirements for long welding, stamping, deep stamping, large angle multi-stage bending, roll pressing, and roll pressing circle forming. We have successfully developed the world's first set of steel plate-constrained temperature quenching, steel plate roll pressing quenching equipment, and high flatness quenching technology, with a thickness of 4mm and a width of 3000mm steel plate whole plate quenching unevenness ≤3mm/2m, and for the first time internationally, batch quenching production has been achieved. We have successfully developed a series of wear-resistant steel plate-constrained quenching deformation mechanisms and low residual stress quenching methods, invented multi-stand high rigidity servo control roll system, array jet water knife, plate shape intelligent detection and self-learning, etc. core systems, and developed high torque large speed ratio transmission control technology, hydraulic multi-cylinder synchronous control technology, differential stretching quenching technology, asymmetric quenching technology, multi-stand roll gap optimization control technology, head and tail plate shape control technology, etc. complete set of ultra-thin steel plate roll pressing quenching technology, steel plate quenching without head and tail knock/翘, middle/edge wave and other plate shape defects, laying the equipment technology foundation for the production and research and development of high-quality wear-resistant steel plates.

We have successfully developed 150~750°C high-precision, hot air forced convection circulation tempering technology, with uniformity of ±3°C during tempering, and low-temperature uniformity reaching an internationally leading level. We have studied the interaction mechanism of combustion field-temperature field-flow field under multi-source pulse jet heating, analyzed the control mechanism of non-steady-state convection-radiation-conduction coupled heat transfer, and clarified the influencing factors and laws of temperature field and flow field. Based on the旋流 array orderly control to improve the uniformity of furnace temperature, we have developed high-precision heating and high uniformity heat transfer control technology based on high-strength circulation hot air jet.

‍

Baosteel Group and Baohui Steel Limited

Baosteel's continuous innovation and breakthroughs in the field of wear-resistant steel have led to the development of new materials such as NM500 tuf and NM600, with excellent performance in hardness, wear resistance, and low-temperature impact resistance. These products have been recognized by industries at home and abroad, including world-renowned enterprises such as SANY and China Shipbuilding. Baohui Steel Limited, as a steel dealer deeply involved with Baosteel for over twenty years, has a comprehensive understanding of Baosteel's products and maintains a long-term sufficient stock. At the same time, it is deeply involved in the development of Baosteel's wear-resistant steel series of new products, possesses a rich technical reserve, and can provide customers with the latest wear-resistant steel products, as well as full technical support. If you have any questions related to products and technology, please contact us, and we will have professional steel experts to answer for you.