Low alloy steel has a wide application prospect because of its low content of alloying elements, low cost and excellent comprehensive properties. Low alloy steel is generally used to make hydraulic bucket teeth. Si, Mn and Cr are the main added elements, and a small amount of Mo, Ni, B and other trace elements are the auxiliary added elements. The typical alloy systems are Mn Cr, Cr Mo, Si Mn Cr Mo, among which Mn CR low alloy steel is widely used.
Low alloy steel and low-carbon alloy steel can be used for bucket teeth. Si improves the strength and tempering resistance of the steel, increases the amount of retained austenite in the steel and the stability of austenite, and prevents carbide precipitation during heat treatment. Mn, Ni and Cr are beneficial to improve the strength and hardenability of steel. At the same time, Mn and Ni elements can expand the austenite phase zone and help to obtain the residual austenite structure.
Different structures can be obtained by different heat treatment methods to adapt to the corresponding working conditions. When the high-temperature solution spheroidizing annealing is used for pre heat treatment, the defects such as uneven composition and structure of cast steel can be reduced, and then the strip martensite with good strength, toughness and hardness can be obtained by extreme cold quenching after high-temperature austenitizing, and then the internal stress can be removed by low-temperature tempering. The bucket teeth made of zg30cr2mnsivre can be observed under the microscope that the martensitic laths are parallel to each other, the main body of the lath is composed of thin and long crystals, and there are no twins in the lath. The toughness of this kind of martensitic steel is higher than that of alloy white cast iron, and the wear resistance is better than that of austenitic steel. It can be used in high and medium impact wear conditions. Carbide free bainitic steel can be obtained by isothermal quenching and tempering in the bainitic region. It is composed of bainitic ferrite (BF) and retained austenite (AR). It has a good combination of strength and toughness and can be used in high impact conditions.
High carbon low alloy steel bucket teeth 75mncr2moni (composition: 0.70% ~ 0.80% C, 0.40% ~ 0.50% Si, 0.80% ~ 1.00% Mn, 2.00% ~ 2.50% Cr, 0.30% ~ 0.40% Mo, 0.60% ~ 0.80% Ni) are annealed first, and then quenched, tempered and tempered to obtain troostite and carbide.
In China, the service life of bucket teeth of large excavator cast with carbide free bainitic steel (mainly composed of 0.2% ~ 0.35% C, 0.80% ~ 1.0% Mn, 1.4% ~ 1.6% Si, 1.6% ~ 2.0% Ni, 0.2% ~ 0.4% Mo, re and other trace elements) can reach 780h when excavating river pebbles, The service life of bucket teeth of imported original excavator is 720h. The service life of zg38mn2siv bucket teeth produced by Jiangxi casting and forging plant is 160% longer than that of high manganese steel when excavating iron ore with F = 18 ~ 20. The composition (mass fraction) is 0.4% ~ 0.6% C, 1.9% ~ 2.3% Cr, 0.25% ~ 0.35% Mo, 0.25% ~ 0.35% Ni, 0.3% ~ 0.5% Si, 1.6% ~ 1.9% Mn, 0.3% ~ 1.0% Cu, 0.07% ~ 0.30% v, 0.15% ~ 0.20% RE, After special air cooling and sand embedding heat treatment, the medium carbon low alloy steel bucket teeth with P content less than 0.035% and s content less than 0.035% obtain the multiphase structure of martensite or martensite plus bainite, so that the tooth tip and tooth body have different mechanical properties, and its wear resistance is more than 1.5 times that of ordinary high manganese steel.
The components (mass fraction) of low alloy steel bucket teeth abroad are generally c (0.25% ~ 0.30%), Mn (0.6% ~ 1.5%), Si (0.2% ~ 2.5%), Cr (0.5% ~ 2.2%), Mo (0.1% ~ 0.6%), Ni (0.15% ~ 2.0%), P content less than 0.03% and s content less than 0.03%, For example, the chemical composition (mass fraction) of bucket teeth for 280b excavator of American B-E company is 0.28% C, 0.69% Mn, 0.2% Si, 1.43% Cr, 0.51% Mo, 0.15% Ni, 0.015% P and 0.021% s. after quenching and reheating heat treatment, the hardness value is 36hrc. The chemical composition of schrs1500 / 5-305 bucket teeth in West Germany is 0.25% ~ 0.30% C, 0.80% ~ 1.00% Mn, 1.40% ~ 1.60% Si, 2.0% ~ 2.2% Cr and 0.35% ~ 0.45% mo. after quenching and tempering, the hardness is 495hb.
Quenched and tempered multi-element low alloy steel can realize the matching of high hardness and high toughness through composition adjustment and casting and heat treatment process optimization. At present, small and medium-sized bucket teeth (such as common hydraulic bucket teeth) are often made of wear-resistant low alloy steel with high strength and high hardness and toughness. Under the condition of continuous cracking, the wear resistance can be improved by improving the initial hardness and wear hardening hardness.