Technical Field
The shield machine is a construction machine widely applied to underground engineering and tunnel driving in recent years, a shield cutter is a key part for breaking rocks of the shield machine, is a tooth of the shield machine and is also a part of the shield machine directly contacted with a tunnel face, the working condition is severe, the stress is complex, the loss is extremely large, and the performance and the service life directly influence the construction effect and the construction efficiency of the underground engineering. Therefore, the tool steel material is required to have sufficient strength, high hardness, and good toughness.
The conventional shield cutter steel in China is 5Cr5MoSiV1, the material has the advantages of relatively good hardness and strength, and the main defect is that the toughness and the hardness cannot be well considered, and the toughness is just one of key performance indexes influencing the quality and the service life of the cutter, so that the cutter is easy to crack and lose in the working process, and the stability and the efficiency of production are severely restricted. In addition, at present, domestic high-end shield cutter steel mainly depends on import, such as German Vilter steel type X50CrVMo5-1 steel, American Robbins cutter steel and the like, and huge cost is brought.
Therefore, the research and development work of matching the cutter material with good hardness and toughness is actively carried out, which is beneficial to breaking the monopoly abroad, and the method makes a strong contribution to accelerating the construction of subways and railway tunnels in China, improving the technical level in China, reducing the construction cost and making key parts of the development machine into the localization.
Chinese patent application CN 108486499A discloses 'steel for shield machine cutter and manufacturing method thereof', which comprises the following components by mass percent: 0.40-0.60% of C, 0.80-1.20% of Si, 0.20-0.60% of Mn, 4.00-6.00% of Cr, 1.10-1.30% of Mo, 0.45-1.0% of V, 0.30% of Ni, 0.1-0.6% of Ti, less than or equal to 0.020% of P, less than or equal to 0.005% of S, less than or equal to 0.01% of B, and the balance of Fe and inevitable impurities. The production process flow of the shield machine cutter steel is as follows: smelting, casting, electroslag remelting, three-dimensional refining uniformity and FM method forging, annealing and superfine treatment, and finally preparing the shield machine cutter steel with good toughness, rigidity and wear resistance. The mechanical property of the product is similar to that of the product, but the process is simple, the cycle is shortened, the energy is saved, and the cost is reduced.
Disclosure of Invention
Aiming at the problems, the invention provides the high-hardness steel for the shield cutter and the preparation process thereof by reasonably adjusting and optimizing chemical components and proportion and designing a reasonable heat treatment process. Specifically, the invention aims to increase the impact toughness of the shield steel and change the final phase composition of the material. After forging, a quenching-partitioning heat treatment process is adopted to partition carbon from supersaturated martensite to residual austenite, so that the toughness of the shield cutter steel is greatly improved. A titanium-containing shield cutter steel is developed, and a preparation method of the steel is provided.
The invention is realized by the following technical scheme:
the high-hardness steel for the shield cutter is characterized by comprising the following raw materials in percentage by mass: 0.40-0.60% of C, 0.80-1.20% of Si, 0.20-0.60% of Mn, 4.00-6.00% of Cr, 1.10-1.30% of Mo, 0.45-1.0% of V, 0.30% of Ni, 0.10-0.60% of Ti, and the balance of Fe and inevitable impurity elements, wherein the content of the impurity elements S is less than or equal to 0.005%, and the content of P is less than or equal to 0.020%.
The manufacturing method of the steel for the high-hardness shield cutter is characterized by comprising the following steps of:
step 1, steel making: putting the raw materials into an electric furnace for smelting, refining and vacuum degassing, and then casting into ingots;
step 2, high-temperature diffusion annealing: carrying out high-temperature diffusion annealing on the cast ingot; (ii) a
Step 3, forging: forging the ingot subjected to high-temperature diffusion annealing to form a forging stock;
step 4, heat treatment: the forged billet is austenitized in an electric resistance furnace, then salt-bath quenched to a temperature between the martensite start temperature (Ms) and the martensite finish temperature (Mf), and held at a quench stop Temperature (TQ) or slightly higher partitioning Temperature (TP) for a suitable time to partition carbon from supersaturated martensite into retained austenite, thereby stabilizing to room temperature.
Further, in the step 2, the high-temperature diffusion annealing temperature is 1250-1280 ℃, the heat preservation time is at least D/50+8 hours, and D is the numerical value of the diameter of the ingot measured by millimeters.
Further, in the step 3, the preheating temperature of the anvil for forging is 200-250 ℃, and the ingot is subjected to multidirectional forging processing within the temperature range of 1100-1200 ℃; the final forging temperature is more than or equal to 900 ℃.
Further, in the step 4, the austenitizing temperature is 1000-1100 ℃, then the salt bath quenching is carried out to 200-300 ℃ for 25-35s, and then the distribution and heat preservation are carried out for 25-35min at 350-450 ℃.
In the prior art, the shield cutter steel 5Cr5MoSiV1 comprises, by mass, 0.48-0.52% of C, 4.50-5.00% of Cr, 1.10-1.30% of Mo, 0.80-1.20% of V, 0.90-1.10% of Si and 0.30-0.50% of Mn. The main preparation process is forging, spheroidizing annealing, quenching and tempering. The invention aims to invent shield cutter steel with higher obdurability to replace 5Cr5MoSiV1, and the invention takes the advantages of each element, avoids the shortages thereof, reasonably adjusts and optimizes chemical components and mixture ratio to obtain a new good alloy mixture ratio, and the following are considered in important points:
(1) the function of the C element: carbon element is one of the main elements of the steel for the high-hardness shield cutter, is the most effective element for improving the hardness and the strength of the steel, also influences the component segregation and the structural uniformity of the steel, and simultaneously, various carbides such as chromium, molybdenum, vanadium and the like which are separated out during tempering and play a role in dispersion strengthening are the basic standards for reaching indexes of the performance of the steel for the shield cutter. Meanwhile, the proper reduction of the content can prevent the steel from generating segregation structure in the solidification process, thereby causing the non-uniformity of the hardness of the steel and the toughness of impact.
(2) Function of Mn element: mn is a weak deoxidizer, and a proper amount of Mn can effectively improve the strength of steel, eliminate the influence of sulfur and oxygen on the hot brittleness of the steel, improve the hot workability of the steel, improve the cold brittleness tendency of the steel, and not obviously reduce the plasticity and impact toughness of the steel. However, an excessively high Mn content (up to 1.0 to 1.5% or more) makes the steel brittle and hard, and reduces the rust resistance and weldability of the steel.
(3) Function of Si element: the element is used as a non-carbide forming element, the strengthening effect of a matrix is not obvious under a complex working environment requiring high hardness and wear resistance, and meanwhile, the silicon element can reduce the toughness of the material and is not particularly added as an alloy element; therefore, the content of silicon element is properly reduced in the present invention.
(4) The content of Cr element: the chromium element can strongly delay the pearlite transformation and is beneficial to improving the hardenability of the material and the tempering stability of martensite, but because the carbide of the chromium element is easy to coarsen and has a certain harmful effect on the toughness, the content of the chromium element is properly controlled in the invention, and the range is controlled to be the lower limit of 5Cr5MoSiV 1.
(5) The function of the V element: as a deoxidizer for steel, the deoxidizer can obviously refine structure grains when reaching more than 0.5 percent, improve the strength and toughness of the steel, and improve the corrosion capability (H corrosion) of the steel at high temperature by forming carbide with C.
(6) Function of Ti element: a small amount of Ti element is added, so that the effects of precipitation strengthening and fine grain strengthening can be achieved, the growth of crystal grains is inhibited, and the strength of the steel is improved. Meanwhile, a certain amount of Ti element is added into the steel, so that the corrosion resistance can be improved.
(7) Function of Ni element: ni can refine ferrite grains, improve ductility and toughness of steel, enhance hardening performance of steel, and reduce quenching temperature during heat treatment, so that deformation is small during heat treatment.
Compared with the prior art, the invention has the following beneficial technical effects:
(1) through reasonable component design and process control, the hardness of the shield cutter steel is more than or equal to 55HRC, and the impact toughness is more than or equal to 28J/cm2The tensile strength is more than or equal to 1800 MPa.
(2) The structure type of the shield cutter steel manufactured by the invention mainly comprises martensite and retained austenite, and composite phase precipitates containing Cr, Mo, V, Ti and the like, so that the shield cutter steel plays a role in precipitation strengthening, does not deteriorate plasticity and toughness while improving the hardness, has good comprehensive mechanical properties, and meets complex geological working environments.
(3) The method utilizes the quenching-distribution process to prepare the shield machine cutter steel, introduces the residual austenite phase, improves the toughness of the material, and increases the fatigue resistance of the material. Has excellent combination of strength and toughness, and the shield cutter steel has small deformation after heat treatment. The method can be popularized in certain steel enterprises with heat treatment lines, and lays a foundation for realizing the conversion of shield cutter steel products of the enterprises to the directions of higher hardness and high toughness.
Detailed Description
Example 1:
smelting, casting and forging are carried out according to the component ranges, and then the components of the forging stock are detected, wherein the components are shown in the table 1.
TABLE 1 composition of the forgings (wt.%)
The forging adopts the following process: preheating the anvil for forging at 200-250 ℃, and carrying out multidirectional forging processing on the cast ingot at the temperature of 1100-1200 ℃; the final forging temperature is more than or equal to 900 ℃, and the tissue types are ferrite and pearlite at the time, as shown in figure 1 (a). And (3) heat treatment: heating the test steel to 1050 ℃ and preserving heat for 30min, then quenching the test steel to 200 ℃ in a salt bath, then putting the test steel into a 350 ℃ resistance furnace for preserving heat for 30min, discharging the test steel out of the furnace and air cooling, wherein the structure type is martensite and retained austenite at the moment as shown in figure 1 (b).
TABLE 2 mechanical Properties of Shield steels
Example 2: smelting, casting and forging are carried out according to the component ranges, then the components of the forging stock are detected, and the component 2 is shown in the table 3.
TABLE 3 composition of the forged stocks (wt.%)
The steel was produced in the same manner as in example 1, and the heat-treated structure is shown in FIG. 2.
TABLE 4 mechanical Properties of Shield steels
Example 3: the steel composition of this example was the same as that of example 1. The manufacturing method of the steel comprises the following steps:
the forging adopts the following process: preheating the anvil for forging at 200-250 ℃, and carrying out multidirectional forging processing on the cast ingot at the temperature of 1100-1200 ℃; the final forging temperature is more than or equal to 900 ℃. And (3) heat treatment: heating the test steel to 1050 ℃ and preserving heat for 30min, then quenching the test steel to 150 ℃ in a salt bath, then putting the test steel into a 350 ℃ resistance furnace for preserving heat for 30min, discharging the test steel out of the furnace and air cooling, wherein the structure type is martensite and retained austenite, and the structure is shown in figure 3.
TABLE 5 mechanical Properties of Shield steels
Example 4: the steel composition of this example was the same as that of example 1. The manufacturing method of the steel comprises the following steps:
the forging adopts the following process: preheating the anvil for forging at 200-250 ℃, and carrying out multidirectional forging processing on the cast ingot at the temperature of 1100-1200 ℃; the final forging temperature is more than or equal to 900 ℃. And (3) heat treatment: heating the test steel to 1050 ℃ and preserving heat for 30min, then quenching the test steel to 200 ℃ in a salt bath, then putting the test steel into a 400 ℃ resistance furnace to preserve heat for 30min, discharging the test steel out of the furnace and air cooling, wherein the structure type is martensite and retained austenite, and the structure is shown in figure 4.
TABLE 6 mechanical Properties of Shield steels
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.