Abstract: This article provides a comprehensive overview of wear-resistant steel casting, focusing on their characteristics, types, application status, and development trends. It introduces typical wear-resistant steel casting and their production processes, and elaborates on the main standards related to wear-resistant steel. By analyzing the current status and future trends, this article aims to provide valuable insights and suggestions for the development of the wear-resistant steel casting industry.
Introduction
The wear-resistant steel casting industry in China is renowned for its large production scale and diverse product range. From austenitic manganese wear-resistant steel to non-manganese wear-resistant alloy steel, China boasts a wide variety of wear-resistant materials that cater to the needs of various heavy industries such as metallurgy, construction materials, power generation, machinery, national defense, shipping, railways, coal, chemicals, and petrochemicals. According to statistics, China requires approximately 5 million tons of wear-resistant steel casting annually. The large-scale production of these materials and the corresponding engineering and industrialization technologies provide solid technical support for the development of China’s heavy industry.
Wear-resistant steel casting is major category within wear-resistant castings and are commonly used in large-scale heavy industrial production due to their excellent wear resistance and strength-toughness properties. In China, wear-resistant steels are primarily divided into two categories: austenitic manganese steel and non-manganese wear-resistant alloy steel. Although most products belong to traditional categories, rapid advancements in steel smelting technology and independent innovations by domestic universities, research institutes, and wear-resistant material enterprises have led to the continuous development and production of economical and high-performance wear-resistant steels with independent intellectual property rights. These developments have significantly promoted technological progress in the wear-resistant material industry.
This article, combining national standards for wear-resistant steel casting and recent advancements in domestic technology, focuses on the development and innovation of industrialization technologies to introduce wear-resistant steel casting and their development trends. By exploring technical fields and analyzing development trends, we aim to provide useful insights and suggestions for the future development of China’s wear-resistant material industry.
1. Cast Wear-resistant Manganese Steel
The Englishman R.A. Hadfield invented high-manganese steel (ZGMn13) in September 1882 and obtained a patent for it in the UK the following year. This material exhibits high surface hardness while maintaining high toughness in the core, offering superior wear resistance compared to other materials in resisting high pressure and impact. It is widely used in various mechanical equipment such as bucket teeth, liners, and jaw plates of ball mills, railway turnouts, tractor track plates, and jaw crushers. Depending on alloy content and carbon content, wear-resistant steels are classified differently. Currently, the most commonly used engineering applications include three series: high-manganese steel (Mn13 series), medium-manganese steel (Mn7), and ultra-high-manganese steel (Mn18 series).
(1) High-manganese Steel (Mn13 Series)
Standard Mn13 high-manganese steel, also known as Hadfield steel, was invented by Hadfield in 1882. The primary composition of currently mass-produced high-manganese steel has not changed significantly, with a carbon content of 0.7% to 1.4% and a manganese content of 10% to 14%. Carbon in high-manganese steel serves two main purposes: facilitating the formation of a single-phase austenitic structure and enhancing solid solution strengthening. Generally, as carbon content increases, the strength and hardness of high-manganese steel increase, while plasticity and impact absorption energy decrease. For every 0.1% increase in carbon mass fraction, the impact absorption energy (KU2) at room temperature decreases by approximately 32 J. High carbon content improves casting fluidity but tends to promote the precipitation of carbides, reducing toughness. Therefore, higher heat treatment temperatures or longer holding times are required to fully dissolve carbides and uniformly solid-solute carbon elements. Manganese is the primary element stabilizing austenite in high-manganese steel. When the manganese content is less than 14%, the strength, plasticity, and impact absorption energy of high-manganese steel increase with increasing manganese content. A Mn/C mass ratio of approximately 10 provides a good balance of strength and toughness. When Mn/C < 10, the wear resistance of high-manganese steel improves. Depending on working conditions, elements such as chromium, molybdenum, nickel, and tungsten can be added to the ordinary high-manganese steel, typically in amounts not exceeding 4%.
Chromium-added high-manganese steel typically contains 1.5% to 2.5% chromium by mass. Chromium causes the dispersion and precipitation of fine carbides in the austenitic matrix, achieving second-phase strengthening. Compared to ordinary high-manganese steel, chromium-added high-manganese steel exhibits higher yield strength and initial hardness but lower plasticity and impact absorption energy. Under conditions of strong impact abrasive wear, chromium-added high-manganese steel exhibits better work-hardening performance and improved wear resistance. Molybdenum content in high-manganese steel is usually less than 2%. Molybdenum enhances the yield strength of high-manganese steel without reducing impact toughness or even improving it. Molybdenum delays or inhibits the precipitation of carbides, which is beneficial for the water-toughening treatment of thick high-manganese steel parts and reduces the tendency for cracking during casting, welding, cutting, and high-temperature use (>275°C). Some studies suggest that adding molybdenum promotes the dispersion and precipitation of fine carbides in the austenitic matrix, achieving second-phase strengthening. The distribution of these carbides has little impact on the toughness of high-manganese steel but can impede dislocation movement, thereby significantly enhancing its work-hardening ability. Nickel content in high-manganese steel ranges from 3% to 4%. Nickel dissolved in the austenite of high-manganese steel significantly increases its stability. Nickel inhibits carbide precipitation between 300°C and 550°C, reducing the sensitivity of high-manganese steel to cracking during welding, cutting, and high-temperature use. Nickel has minimal impact on the yield strength of high-manganese steel but decreases its tensile strength. It does not affect the work-hardening performance or wear resistance of the steel. Tungsten content in austenitic manganese steel ranges from 0.9% to 1.2%. Tungsten alters the distribution of carbon in medium-manganese steel, refining the grain structure and effectively enhancing the tensile strength, impact toughness, and wear resistance of austenitic manganese steel. Additionally, trace amounts of vanadium, titanium, niobium, boron, and rare earth elements can be added to refine the microstructure and achieve fine-grain strengthening. Research and practice show that adding multiple alloy elements has a greater impact on improving properties than adding a single alloy element.
Due to high manganese and carbon contents, the as-cast microstructure of high-manganese steel consists of austenite and carbides. After heating to approximately 1050°C followed by water-toughening treatment, most of the carbides dissolve into the austenite, resulting in a microstructure of single-phase austenite or austenite with a small amount of carbides. Therefore, high-manganese steel exhibits good plasticity and toughness with a low crack propagation rate, ensuring safe and reliable use. Another key characteristic of high-manganese steel is that under large impact loads or contact stresses, the surface layer rapidly work-hardens, causing a sharp increase in surface hardness (up to 500-700 HBW), thus providing excellent wear resistance while the interior maintains good toughness, enabling it to withstand impact loads without fracturing. To improve initial hardness, mechanical or explosive methods can be used to induce surface work-hardening (>450 HBW) before use.
High-manganese steel is particularly suitable for impact abrasive wear and high-stress crushing abrasive wear conditions. It is commonly used to manufacture ball mill liners, hammer crusher hammers, jaw crusher jaw plates, cone crusher mantles and concaves, excavator bucket teeth and walls, railway turnouts, and tractor and tank track plates, among other impact-resistant and wear-resistant castings.
(2) Medium-manganese Steel (Mn7)
Medium-manganese wear-resistant steel has a carbon content of 1.05% to 1.40% and a manganese content of 5% to 9%. After water-toughening treatment, its microstructure consists of an austenitic matrix containing relatively more carbides. Compared to Mn13 steel, medium-manganese steel has a lower manganese content and reduced austenitic stability, making it more wear-resistant than standard Mn13 high-manganese steel under non-severe impact conditions. Medium-manganese steel often contains 0.9% to 1.2% molybdenum to inhibit the precipitation of carbides in the as-cast microstructure. The tensile strength and yield strength of molybdenum-containing medium-manganese steel are comparable to or slightly better than those of standard Mn13 steel, but its elongation after fracture and impact toughness are lower. Therefore, from a fracture resistance perspective, medium-manganese steel is suitable for wear conditions with moderate impact.
Additionally, some medium-manganese steels contain a certain amount of chromium. Chromium-containing medium-manganese steel generally has a composition of 0.8% to 1.2% carbon, 6.0% to 9.5% manganese, and 1.5% to 3.0% chromium. After water-toughening treatment, it still obtains a single-phase austenitic structure. Deformation at room temperature can induce martensitic transformation, thereby enhancing work-hardening ability. Even under low impact and stress conditions, it significantly hardens due to deformation-induced phase transformation, improving wear resistance. Compared to high-manganese steel, chromium-containing medium-manganese steel exhibits lower toughness but significantly higher wear resistance.
The work-hardening rate of medium-manganese steel is much higher than that of high-manganese steel, compensating for the latter’s shortcomings. It possesses sufficient toughness and good wear resistance, outperforming high-manganese steel under conditions of medium to low stress impact wear. Industrial applications have demonstrated its suitability for ball mill liners, medium and small crusher liners, and crusher hammer plates.
(3) Ultra-high-manganese Steel (Mn18 Series)
For thick and large-section Mn13 series wear-resistant steel casting, internal carbides often appear after water-toughening treatment, reducing toughness. Mn13 series wear-resistant cast steel also exhibits brittle fracture under low-temperature conditions and has issues such as insufficient wear resistance and low yield strength. Ultra-high-manganese steel (Mn18) to some extent addresses these issues and exhibits a longer service life under conditions of severe impact abrasive wear. Typical Mn18 wear-resistant high-manganese steels include ZG120Mn18 and ZG120Mn18Cr2, with carbon contents of 1.05% to 1.35% and manganese contents of 16.0% to 19.0%. This steel increases the manganese content based on Mn13 steel, enhancing austenitic stability and preventing carbide precipitation, which in turn improves strength and plasticity. Increasing the manganese content further expands the austenitic phase region, enhancing the ability of austenite to solid-solute elements such as carbon and chromium, thereby improving work-hardening ability and wear resistance. Data suggests that the service life of ZG120Mn18 railway frogs used in northern regions is 20% to 25% higher than that of ZG120Mn13 frogs. Similarly, the service life of ZG120Mn18Cr2 fan impact plates (S36.50 model) is also longer than that of ZG120Mn13 impact plates.
2. Non-manganese Wear-resistant Alloy Steel
Non-manganese wear-resistant alloy steels are characterized by their high hardness, toughness, and strength, particularly their excellent hard-toughness match. Currently, excavator bucket teeth, cement plant and thermal power plant ball mill liners, medium and small hammer crusher hammers, wear-resistant pipes, and other components widely utilize non-manganese wear-resistant alloy steels. Through alloying, refining, casting processes, and heat treatment processes, their hard-toughness properties can be further improved, expanding their application potential.
Non-manganese wear-resistant alloy steels are primarily divided into low-alloy wear-resistant cast steel, medium-alloy wear-resistant cast steel, and recently developed low-carbon high-alloy wear-resistant steel.
(1) Low-alloy Wear-resistant Cast Steel
Low-alloy cast steel plays an increasingly important role in wear-resistant steel casting. The mechanical properties, particularly hardness and toughness, of low-alloy steels can be adjusted over a wide range. Depending on usage conditions, strength, impact absorption energy, and wear resistance can be comprehensively considered and matched. As long as brittleness does not cause fracture, wear resistance increases with hardness.
Generally, low-alloy wear-resistant cast steel is renowned for its high strength and toughness and hard-toughness combination. Its strength and hardness are higher than those of wear-resistant manganese steel, making it a viable substitute for manganese steel under non-severe impact wear conditions. Its plasticity and toughness are higher than those of wear-resistant cast iron, resulting in longer service life under certain impact load wear conditions. The primary purpose of adding alloying elements to low-alloy wear-resistant cast steel is to improve hardenability, strength, toughness, and wear resistance. The most commonly used additive elements include Mo, Cr, Mn, Ni, and Si. The casting process of low-alloy wear-resistant cast steel is similar to that of other low-alloy steels, but refining during melting is essential. Refining methods such as AOD have been applied in the production of low-alloy wear-resistant cast steel and have yielded good results. The welding performance of low-alloy wear-resistant cast steel is similar to that of other low-alloy steels; however, welding performance decreases with higher carbon content.
Low-alloy steels with a carbon content of 0.2% to 0.35% exhibit high hardness and wear resistance after water quenching and tempering, offering a good hard-toughness combination and resistance to deformation and fracture during use. They are widely used in excavator, loader, and tractor bucket teeth, medium and small jaw plates and hammer plates, and ball mill liners.
Multi-element low-alloy cast steels with a carbon content greater than 0.35% can obtain martensitic steel with good strength and toughness, high hardness, and excellent wear resistance after oil quenching (or air quenching) followed by tempering. However, the toughness of this type of steel is lower than that of martensitic steel subjected to water quenching and tempering. Therefore, its application must consider the impact load of working conditions.
High-carbon chromium-manganese-molybdenum steels with a carbon content of 0.55% to 0.9% can obtain a pearlitic matrix after normalization and tempering. This type of steel exhibits good toughness and impact fatigue resistance, high work-hardening ability, and low production costs due to the use of fewer expensive alloy elements and the absence of complex heat treatment processes. High-carbon chromium-manganese-molybdenum pearlitic wear-resistant cast steel is used under impact load abrasive wear conditions, such as in the hollow balls and liners of E-type coal mills.
(2) Medium-alloy Wear-resistant Cast Steel
Medium-chromium wear-resistant cast steel is a type of medium-carbon martensitic or cast steel containing a certain amount of bainite. Chromium significantly influences the austenite transformation curve of medium-carbon steel. Increasing chromium not only significantly improves the hardenability of medium-carbon steel, making it suitable for air quenching, but also separates the pearlitic and austenitic regions. During quenching, a martensitic matrix may be obtained along with a certain amount of bainitic matrix, enhancing the strength and toughness of the steel. Adding a small amount of molybdenum can further improve hardenability. These factors contribute to the development and widespread application of medium-chromium wear-resistant cast steel.
Medium-chromium alloy wear-resistant cast steel parts are typically subjected to a heat treatment process of high-temperature air quenching followed by low-temperature tempering. Air quenching of cast steel parts results in lower stress and reduced susceptibility to quenching cracks, ensuring higher safety and resistance to fracture during use. The hardness of medium-chromium cast steel increases while toughness decreases with increasing carbon content, which is determined by specific working conditions. Medium-chromium cast steel is primarily used in ball mill liners, hammer crusher hammers, and wear-resistant pipes under non-severe impact wear conditions. The service life of medium-chromium cast steel liners used in medium and small cement ball mills and thermal power plant coal mills can reach approximately twice that of ordinary high-manganese steel liners.
Represented by ZG30Cr5Mo and ZG40Cr5Mo, medium-alloy wear-resistant cast steels are characterized by good hardenability, allowing for lower-stress quenching processes such as oil quenching and air quenching. Recent research indicates that the impact wear work-hardening ability and wear resistance of medium-alloy wear-resistant cast steels with initially not very high hardness are superior to those of medium-carbon multi-element low-alloy steels, thereby expanding their application in ball mill liners for cement plants and thermal power plants.
(3) Low-carbon High-alloy Wear-resistant Steel
One of the recent achievements in non-manganese wear-resistant alloy steels is the development and application of liner materials for wet ball mills in metallurgical mines. Previously, alloy steel liners with a carbon content of 0.16% to 0.28%, chromium content of 7.0% to 10%, nickel content of 1.5% to 2.2%, and molybdenum content of 0.5% to 0.8% were subjected to quenching and tempering heat treatment, achieving a hardness of HRC 45 to 52 and an impact toughness of ≥50 J/cm². These liners demonstrated certain application effects during industrial trials on iron ore ball mills. Recently, a newly developed wear-resistant and corrosion-resistant alloy steel with a carbon content of 0.20% to 0.28%, chromium content of 8.0% to 13%, nickel content of ≤1.0%, and molybdenum content of ≤0.8% has been achieved, with a hardness of HRC 52 to 57 and a V-notch impact absorption energy of greater than 25 J.
This type of low-carbon high-alloy wear-resistant steel exhibits excellent hardness and impact toughness, making it particularly suitable for applications in harsh environments with high abrasion and corrosion, such as wet ball mills in metallurgical mines. The alloy composition is carefully designed to balance hardness, wear resistance, and impact toughness, ensuring that the material can withstand both high abrasive forces and occasional impact loads.
Moreover, the advanced heat treatment processes employed, such as quenching and tempering, contribute to the fine microstructure and excellent mechanical properties of the steel. These developments in low-carbon high-alloy wear-resistant steels not only enhance the performance of mining equipment but also extend their service life, reducing maintenance costs and improving operational efficiency.
In summary, the progress in low-carbon high-alloy wear-resistant steels, represented by the new liner materials for wet ball mills, highlights the importance of alloy design and heat treatment in achieving optimal mechanical properties for specific applications. These advancements are crucial for meeting the increasing demands of the mining industry and other sectors that require high-performance wear-resistant materials.