In wear-resistant alloy steels, the total amount of alloying elements (Fe, C, and harmful and hidden elements) must not be less than 5% to be classified as low-alloy steel (5-10% for medium-alloy steel, 10-15% for high-manganese steel). The mechanical properties of low-alloy steel, especially hardness and toughness, can be adjusted within a wide range. Strength, impact toughness, and wear resistance can be comprehensively considered and matched according to different usage conditions. As long as fracture does not occur due to brittleness, its wear resistance increases with increasing hardness.
Low-alloy wear-resistant steels are generally known for their high strength and toughness, and high hardness and toughness. Their strength and hardness are higher than wear-resistant manganese steel, and they can replace manganese steel in non-high-impact wear conditions; their plasticity and toughness are higher than wear-resistant cast iron, and under certain impact load wear conditions, their service life is longer than that of wear-resistant cast iron.
The main purpose of adding alloying elements to wear-resistant steel is to improve hardenability, strength, toughness, and wear resistance. The most commonly used added elements are Mo, Cr, Mn, Ni, and Si.
The casting and welding properties of wear-resistant low-alloy steel are similar to other low-alloy steels, but welding performance is poor when the carbon content is high. Low-alloy wear-resistant steel can be classified according to heat treatment and carbon content.
Water-quenched heat-treated alloy martensitic wear-resistant steel: Multi-element low-alloy steel with W(C) = 0.2%-0.35%, after water quenching and tempering, has high hardness, good wear resistance, and a good balance of strength and toughness. It is not easily deformed or broken during use and is widely used in excavator, loader, and tractor bucket teeth, track plates, small and medium-sized jaw plates, hammers, hammerheads, ball mill liners, etc.
Oil-quenched and air-quenched heat-treated low-alloy martensitic wear-resistant steel: Multi-element low-alloy steel with W(C) > 0.35%, after oil quenching (or air quenching) heat treatment and tempering, can obtain martensitic steel with good strength and toughness, high hardness, and good wear resistance. It is used for ball mill liners, small and medium-sized jaw plates, hammerheads, hammerheads, etc. However, the toughness of this type of steel is lower than that of the aforementioned low-alloy martensitic steel with W(C) = 0.20%-0.35% water quenching heat treatment. Therefore, the impact load of the working conditions must be considered when applying it.
The chemical cost, hardness, characteristics, and mechanical properties of several oil-quenched or air-quenched high-strength martensitic cast steels are compared. The chemical cost of typical oil-quenched high-strength chromium-molybdenum martensitic wear-resistant steels from abroad is almost the same as the former.
Normalized heat-treated low-alloy pearlitic wear-resistant steel
High-carbon chromium-manganese-molybdenum steel with W(C) = 0.55%-0.9% can obtain a pearlitic matrix through normalizing and tempering heat treatment. Chromium-manganese pearlitic wear-resistant steel has good toughness and impact fatigue resistance, high work hardening ability; and has a lower production cost because it contains only a small amount of inexpensive alloying elements and does not require complex heat treatment.
High-carbon chromium-manganese-molybdenum pearlitic wear-resistant cast steel is used in abrasive wear conditions with certain impact loads, such as the hollow magic balls of E-type coal mills and ball mill liners. A representative example is high-carbon chromium-manganese-molybdenum pearlitic wear-resistant cast steel.
Comparative tests on the wear resistance of chromium-molybdenum pearlitic wear-resistant steel liners with high-manganese steel and chromium-molybdenum martensitic wear-resistant steel liners in a φ2.7m molybdenum ore ball mill show that the service life of the chromium-molybdenum pearlitic wear-resistant steel liner is longer than that of high-manganese steel, but shorter than that of the 555-601HBW chromium-molybdenum martensitic wear-resistant steel liner; even though the pearlitic steel liner has lower hardness, its service life is longer than that of the martensitic wear-resistant steel liner tempered at 480℃.
Wear-resistant carbon steel: The wear resistance of carbon steel is mainly achieved through surface hardening. Carbon steel with W(C) > 0.35% is usually surface induction hardening or flame hardening; low-carbon steel can have its wear resistance improved by carburizing, nitriding, or carbonitriding processes. As the hardness increases, its wear resistance also increases accordingly.
In wear-resistant carbon steels, carbon steel with a W(C) content of 0.4%-0.70% plays a crucial role. For example, cast steel train wheels in the United States are made using carbon steel with a W(C) content of 0.4%-0.70%.
Cast graphite steel is an ultra-high carbon eutectoid steel. After appropriate heat treatment, some carbon precipitates as graphite, thus possessing the combined properties of cast steel and cast iron. Due to the presence of free graphite, this steel is a structural material resistant to friction and wear. Currently, graphite steel is mostly used to manufacture metallurgical rolls, such as rolls for primary or rough rolling operations, because a small amount of graphite can improve the roll's resistance to hot cracking and the adhesion of iron oxide scale.
