阅读说明：本技术 一种适用于低温条件的矿用车架的热处理工艺 (Heat treatment process suitable for mining frame under low-temperature condition ) 是由 高超 闫沛堂 谈安宝 刘林 马宏儒 杨宪军 于 2019-08-24 设计创作，主要内容包括：本发明公开了一种适用于低温条件的矿用车架的热处理工艺,使用高温退火预处理退火方法,实现珠光体转变以及冷却过程中发生与此相反的相变重结晶,形成晶粒较细、组织均匀的珠光体组织。通过正火处理,珠光体发生重结晶,细化晶粒,组织变均匀,提高钢件的塑韧性。通过亚温淬火可以将机械性能达到最佳状态,尤其是可以得到较高的冲击功。冶炼过程合理的控制化学成分,合金元素Cr、Ni、Mo上限控制,增加材料的淬透性,使产品最终获得优良的力学性能和组织形态。本发明通过冶炼过程合理的控制化学成分,采用高温退火、淬火与亚温淬火结合、回火水冷的方式能够使一种低温条件下使用矿用车架获得理想的综合力学性能,尤其是具有很高的冲击功。(The invention discloses a heat treatment process of a mining frame suitable for a low-temperature condition, which uses a high-temperature annealing pretreatment annealing method to realize pearlite transformation and phase transformation recrystallization opposite to the pearlite transformation in a cooling process so as to form a pearlite structure with fine grains and uniform structure. Through normalizing treatment, pearlite is recrystallized, crystal grains are refined, the structure becomes uniform, and the plasticity and toughness of the steel part are improved. The mechanical properties can be optimized by sub-temperature quenching, in particular higher impact energy can be obtained. The smelting process reasonably controls chemical components, the upper limit of alloy elements Cr, Ni and Mo is controlled, and the hardenability of the material is increased, so that the product finally obtains excellent mechanical properties and tissue morphology. The invention can obtain ideal comprehensive mechanical property by using the mining frame under the low temperature condition by reasonably controlling chemical components in the smelting process and adopting the modes of high-temperature annealing, quenching, sub-temperature quenching, tempering and water cooling, and particularly has very high impact energy.)

1. A heat treatment process of a mining frame suitable for low-temperature conditions is characterized by comprising the following steps: the method comprises the following steps:

(1) casting pretreatment: cutting a dead head with temperature after casting and demoulding of the mining frame casting;

(2) charging: the mining frame is charged by using a charging tray and is placed in an effective heating area in the furnace, a flame path is avoided, and flame is prevented from being directly sprayed;

(3) high-temperature annealing: performing high-temperature annealing process of 650 plus material temperature and 680 ℃ step heat preservation and 930 plus material temperature and 950 ℃ heat preservation for 7-8 hours, and after the heat preservation is finished, stopping furnace cooling, and discharging and air cooling the furnace when the furnace cooling is below 300 ℃;

(4) normalizing: and (3) charging in the charging mode in the step (2), in order to avoid deformation caused by too fast heating or influence on tissue uniformity due to too large temperature difference, heating to 910-plus 930 ℃ at a heating speed of 120 ℃/h, and calculating the heat preservation time by using an empirical formula t = alpha × K × D, wherein t: incubation time (min), K: correction coefficient, charging and taking a single piece of pad iron, alpha: heating coefficient (min/mm), gas furnace heating alloy steel gets 1.2, D: is the maximum wall thickness (mm) of the casting; after the heat preservation is finished, cooling is carried out in an air cooling mode, and the furnace temperature uniformity in the normalizing process meets +/-10 ℃;

(5) quenching and quenching cooling: re-charging in the charging mode in the step (2), quenching the casting after normalizing, and heating to 900-920 ℃ for 6 hours; after the heat preservation is finished, the quenching and cooling process is carried out: water cooling is adopted, a thermometer is used for measuring the temperature of a water tank, the temperature is 20-40 ℃, a flow meter of the equipment is used for measuring the flow rate within the range of 25-40mm/s, a discharging machine is used for forking and discharging the water out of a furnace, the water is discharged, the discharging machine is used for swinging after the water is discharged, the swinging is carried out for 20-30min, the cooling is continued, the uniformity of the furnace temperature meets +/-8 ℃, the temperature of a measured casting is lower than 50 ℃, and the;

(6) sub-temperature quenching and cooling: re-charging in the charging mode in the step (2), performing sub-temperature quenching treatment on the casting after quenching, and keeping the temperature at 860-880 ℃ for 6 hours; after the heat preservation is finished, entering a sub-temperature quenching cooling process: water cooling is adopted, a thermometer is used for measuring the temperature of a water tank, the temperature is 20-40 ℃, the flow rate is measured by a self-provided flowmeter of equipment within the range of 25-40mm/s, a discharging machine is used for forking and discharging out of a furnace for fast water discharging, the discharging machine is used for swinging and swinging for 20-30min after water discharging, cooling is continued, the uniformity of the furnace temperature is +/-8 ℃, the temperature of a measured casting is lower than 50 ℃, and cooling is finished;

(7) tempering: re-charging in the charging mode in the step (2), heating the casting to 570-590 ℃, and preserving heat for 8 hours, and cooling with water until the temperature of the casting is lower than 100 ℃ to avoid temper brittleness;

(8) stress relief treatment: charging at low temperature by adopting the charging mode in the step (2), keeping the temperature at 220 ℃ at 180 ℃ for 10-12 hours when the uniformity of the furnace temperature meets +/-8 ℃, and discharging and air cooling;

(9) and (3) mechanical property detection: and (4) preparing the heat-treated sample into a standard tensile sample for detecting various mechanical properties.

2. The heat treatment process for the mining vehicle frame suitable for the low-temperature condition according to claim 1, wherein the mining vehicle frame casting is subjected to chemical composition control in a smelting process, and the control chemical composition comprises the following chemical components in percentage by mass: c: 0.20 to 0.25%, Si: 0.40-0.60%, Mn: 0.80-1.20%, Ni: 0.40-0.80%, Mo: 0.15-0.30%, P is less than or equal to 0.035%, S is less than or equal to 0.025%, the total residual elements is not more than 0.50%, and the carbon equivalent calculation formula CE = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.55 according to the International society for welding.

3. The heat treatment process for the mining vehicle frame suitable for the low-temperature condition as claimed in claim 1, wherein the mining vehicle frame casting in the step (1) adopts a thermal cutting riser with the temperature of 200 ℃ and 250 ℃.

4. The heat treatment process of the mining vehicle frame suitable for the low-temperature condition according to claim 1, wherein the high-temperature annealing treatment in the step (3) is implemented by performing heat preservation for 3 hours at 650 ℃, then performing heat preservation for 8 hours at 950 ℃, then stopping the fire, performing furnace cooling, and discharging and air cooling the furnace to below 300 ℃.

5. The heat treatment process for the mining vehicle frame suitable for the low-temperature condition, according to claim 1, is characterized in that the maximum wall thickness of the cast example in the step (4) is 260mm, and the calculated available holding time t =364 min; and controlling the temperature rise speed of the normalizing treatment at 110 ℃/h, raising the temperature to 920 ℃, preserving the heat for 6 hours, and cooling in an air cooling mode after heat preservation is received.

6. The heat treatment process for the mining vehicle frame suitable for the low-temperature condition according to claim 1, wherein the specific process flow of the quenching treatment in the step (5) is as follows: raising the temperature to 910 ℃ and preserving the temperature for 6 hours, and cooling the mixture to room temperature by water.

7. The heat treatment process of the mining vehicle frame suitable for the low-temperature condition according to claim 1, wherein the specific process flow of the sub-temperature quenching treatment in the step (6) is as follows: heating to 870 deg.c, maintaining for 6 hr and cooling to room temperature.

8. The heat treatment process for the mining vehicle frame suitable for the low-temperature condition according to claim 1, wherein the specific process flow of the tempering treatment in the step (7) is as follows: heating to 580 deg.C, keeping the temp. for 8 hr, and cooling with water until the temp. of casting is lower than 100 deg.C.

9. The heat treatment process suitable for the mining vehicle frame under the low temperature condition according to claim 1, wherein the treatment for eliminating the processing stress in the step (8) is carried out after rough processing is completed, the furnace is charged at a low temperature, the uniformity of the furnace temperature meets +/-8 ℃, the temperature is kept for 11 hours at 220 ℃, and the vehicle is discharged from the furnace and cooled in air.

Technical Field

The invention belongs to the technical field of processing and manufacturing of mining frames, and particularly relates to a heat treatment process of a mining frame suitable for a low-temperature condition.

Background

The mining dump truck is a heavy dump truck used for completing the tasks of rock earthwork stripping and ore transportation in an open mine, and has the working characteristics of short travel and heavy load bearing, and is usually loaded by a large electric shovel or a hydraulic shovel to and fro a mining point and an ore unloading point.

The energy industry which takes mine exploitation as a main source recovers, and the raw materials such as steel, nonferrous metal, coal and the like continuously rise in price, so that the market demand of ores is pulled, and the demand of mining automobiles is increased. The market of the mining dump truck enters a more stable and prosperous period. Therefore, the off-highway mining vehicle is a sunward industry with great development potential, is also an urgent product in the rapid economic development process of China, has wide market and high additional value, and has definite competition in the future.

The technical difficulty is high, and domestic common use is to joint ventures or introduce foreign advanced technology. The frame of the mining truck is used as the main body part of the mining truck, the quality directly influences the normal use of the whole mining truck, foreign accessories are delayed in arrival and high in price, and the development of high-quality mining trucks is urgent. The danger of mine operation is large, the safety of mine constructors is ensured, the safety is one of important qualities of mine products, and high requirements are provided for materials, strength and the like of engineering machinery products.

The mining dumper material belongs to low-carbon low-alloy steel, has better hardenability and temper brittleness due to the action of alloy elements Cr, Ni and Mo, and needs to be subjected to quenching and tempering treatment in order to achieve high strength and low-temperature impact toughness. Tap water is selected as a medium for quenching and tempering treatment in order to increase hardenability and improve the hardening depth.

When quenching, because the heat transfer efficiency is related to the effective thickness of the workpiece, generally, when quenching is carried out conventionally, the cooling speed of the surface of the workpiece is far higher than the speed of the center of the workpiece, a martensite structure is formed on the surface of the workpiece, a semi-martensite or non-martensite structure is generated in the center of the workpiece, and the workpiece is not quenched completely, so that the use effect of the workpiece is influenced. The quenching steam film stage is broken in advance by swinging during quenching, the heat exchange process is accelerated, and the work piece meets the use requirement.

One or more times of sub-temperature quenching with the heating temperature between Ac1 and Ac3 is added between normal quenching and tempering, so that the toughness of the steel can be obviously improved, the brittleness change temperature is reduced, and the high-temperature tempering brittleness is reduced, namely the sub-temperature quenching. The crystal grains are refined by sub-temperature quenching, and compared with the conventional quenching process, the high-toughness steel can obtain higher toughness.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a heat treatment process of a mining frame suitable for low-temperature conditions, which comprises the following steps: smelting, high-temperature annealing, repair welding, normalizing, quenching and tempering (sub-temperature quenching), rough machining and stress relief annealing. The smelting process controls chemical components, ensures that C, Ni and Mo elements are controlled at the upper limit level, and ensures hardenability. The casting is subjected to high-temperature annealing, normalizing, quenching and tempering and stress relief annealing processes, and the method is characterized in that the quenching and tempering adopt a sub-temperature quenching and tempering water cooling mode, so that high comprehensive mechanical properties can be achieved, and particularly low-temperature impact is excellent.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a heat treatment process suitable for a mining vehicle frame under a low-temperature condition comprises the steps of controlling chemical components and the content of Ni elements in a smelting process, cutting a riser with temperature after casting and demoulding of a casting, annealing after cutting of the riser, polishing, cleaning and welding repair after annealing, normalizing after polishing, and quenching and tempering a casting after normalizing, wherein the quenching and tempering mainly comprises quenching, sub-temperature quenching and tempering; and (4) carrying out machining stress relief treatment after rough machining of the final casting.

Further, the chemical components are controlled by the following chemical element percentages: c: 0.20 to 0.25%, Si: 0.40-0.60%, Mn: 0.80-1.20%, Ni: 0.40-0.80%, Mo: 0.15-0.30%, P is less than or equal to 0.035%, S is less than or equal to 0.025%, the total residual elements is not more than 0.50%, and the carbon equivalent calculation formula CE = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.55 according to the International society for welding.

Further, the casting adopts a hot cutting riser with the temperature of 200 ℃ and 250 ℃.

Further, the annealing is carried out by using a high-temperature annealing process of 650 plus sand 680 ℃ step heat preservation and 930 plus sand 950 ℃ heat preservation for 7-8 hours, and after the heat preservation is finished, the furnace is stopped for cooling, and the furnace is discharged for air cooling when the temperature of the furnace is below 300 ℃.

Further, the heat preservation time is calculated by an empirical formula t = α × K × D, where t: incubation time (min), K: correction coefficient, charging and taking a single piece of pad iron, alpha: heating coefficient (min/mm), gas furnace heating alloy steel gets 1.2, D: is the maximum wall thickness (mm) of the casting.

Further, the temperature rise speed of the normalizing treatment is controlled at 120 ℃/h of 100-.

Further, the quenching treatment, namely the casting is re-loaded into the furnace, and the temperature is raised to 900-; after the heat preservation is finished, the quenching and cooling process is carried out: the cooling water temperature is 20-40 ℃, the flow rate is 25-40mm/s, the casting swings after entering water, the swinging time is 20-30min, and the furnace temperature uniformity meets +/-8 ℃.

Further, performing sub-temperature quenching treatment, re-charging the casting, heating to 860-880 ℃, and preserving heat for 6 hours; after the heat preservation is finished, entering a sub-temperature quenching cooling process: the cooling water temperature is 20-40 ℃, the flow rate is 25-40mm/s, the casting swings after entering water, the swinging time is 20-30min, and the furnace temperature uniformity meets +/-8 ℃.

Further, the tempering treatment, the casting is re-loaded, the temperature is raised to 570-590 ℃, the temperature is kept for 8 hours, the uniformity of the furnace temperature meets +/-8 ℃, and a water cooling mode is adopted after the temperature is kept, and the temperature is cooled to be lower than 100 ℃.

Further, the processing stress eliminating treatment is carried out after the rough processing is finished, the furnace is charged at a low temperature, the uniformity of the furnace temperature meets +/-8 ℃, the temperature is kept at 220 ℃ for 10-12 hours at 180 ℃ and the temperature is removed from the furnace for air cooling.

Has the advantages that: by the annealing method of the casting pretreatment using high-temperature annealing, pearlite with fine grains, thick lamella and uniform structure is formed by pearlite transformation into austenite during heating and second-time phase transformation recrystallization opposite to the transformation during cooling, and as a result, as-cast structure defects such as widmannstatten structures, banded structures and the like are eliminated. Through the normalizing treatment after welding repair, the welding stress in the casting is released, the pearlite is recrystallized, the crystal grains are refined again, the structure becomes thin and uniform, the plasticity and the toughness of the steel piece are improved, the hardness is reduced, and the machinability is improved. The martensite transformed from ferrite and eutectoid point by sub-temperature quenching can make the mechanical property reach the optimum state, in particular, can obtain higher impact energy. By reasonably controlling chemical components in the smelting process, the alloy elements Cr, Ni and Mo are controlled to the upper limit, and the hardenability of the material is increased, so that the product finally obtains ideal comprehensive mechanical properties and structure morphology. In summary, by reasonably controlling chemical components in the smelting process, and adopting the modes of high-temperature annealing, quenching, sub-temperature quenching combination and tempering water cooling in the subsequent process, the mining frame can be used under a low-temperature condition to obtain ideal comprehensive mechanical properties, and particularly has very high impact energy.

Drawings

FIG. 1 is a schematic view showing the charging method of an example of the product of the present invention.

FIG. 2 is a graph showing the value of the charging correction factor K of the product example of the present invention.

Detailed Description

The invention is illustrated below with reference to specific examples. It will be understood by those skilled in the art that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention in any way.

A heat treatment process of a mining vehicle frame suitable for low-temperature conditions comprises the following steps:

(1) casting pretreatment: after casting and demoulding of the mining frame casting, cutting a dead head by adopting heat with the temperature of 220 ℃;

(2) charging: referring to fig. 1, the mining carriage is loaded with a loading tray and placed in an effective heating area in the furnace, so as to avoid a flame path and prevent flame from being directly sprayed;

(3) high-temperature annealing: using a step heating mode, keeping the temperature at 650 ℃ for 3 hours, then heating to 950 ℃ and keeping the temperature for 8 hours, then stopping the furnace for cooling, and discharging the furnace for air cooling when the furnace is cooled to below 300 ℃;

(4) normalizing: charging in the charging mode in the step (2), in order to avoid deformation caused by too fast heating or influence on tissue uniformity due to too large temperature difference, heating to 920 ℃ at a heating speed of 110 ℃/h, and calculating the heat preservation time by selecting an empirical formula t = alpha × K × D to obtain 6 hours; wherein t is the heat preservation time (min), K: correction factor, charging single-piece shim iron, see fig. 2, α: heating coefficient (min/mm), gas furnace heating alloy steel gets 1.2, D: is the maximum wall thickness (mm) of the casting, which is 260mm for this example product, calculated holding time t =364min, which is equal to about 6 hours, see table 1; cooling in an air cooling mode after the heat preservation is finished;

TABLE 1

(5) Quenching: charging in the charging mode in the step (2), and keeping the temperature at 910 ℃ for 6 hours by the calculation method of the heating rate and the heat preservation time in the step (4), and entering a quenching and cooling process;

(6) quenching and cooling: measuring the temperature of the water tank by using a thermometer, wherein the temperature of the water tank meets 20-40 ℃, measuring the flow rate by using a self-provided flowmeter of equipment within the range of 25-40mm/s, forking the water out of the furnace by using a discharging machine, quickly discharging the water, swinging the discharging machine after discharging the water, swinging for 30min, continuously cooling, measuring the temperature of the casting to be lower than 50 ℃ in 1 hour, and finishing the cooling;

(7) and (3) sub-temperature quenching: charging in the charging mode in the step (2), keeping the temperature at 870 ℃ for 6 hours at the heating speed and the heat preservation time in the step (4), and performing a sub-temperature quenching cooling process;

(8) cooling by sub-temperature quenching: the same as the content described in the step (6);

(9) tempering: charging in the charging mode in the step (2), heating to 580 ℃ at the heating speed in the step (4), and keeping the temperature for 8 hours, wherein in order to avoid temper brittleness, water is cooled until the temperature of the casting is lower than 100 ℃;

(10) stress relief treatment: charging at low temperature by adopting the charging mode in the step (2), keeping the temperature at 200 ℃ for 11 hours when the furnace temperature uniformity meets +/-8 ℃, discharging and air cooling;

(11) and (3) mechanical property detection: the sample after heat treatment is made into a standard tensile sample to carry out various mechanical property detection; the results of the mechanical property measurements and the mechanical property measurements of the product examples are shown in Table 2.

TABLE 2

Item

Rm/Mpa

Rel/Mpa

A%

Z%

-40℃ AKV/J

HBW

Standard value

≥690

≥585

≥20

≥40

≥27

207-255

Measured value

725

620

22.5

58

45 55 62

247

Through detection and chemical component control, the heat treatment process can enable a mining frame to obtain ideal comprehensive mechanical properties under a low-temperature condition, and particularly has high impact energy.