Strengthening and toughening heat treatment production method of 50CrVA steel elastic element for bridge

Abstract

The invention discloses a strengthening and toughening heat treatment production method of a 50CrVA steel elastic element for a bridge, and belongs to the technical field of steel preparation, and the method comprises the steps of blanking, free forging, annealing, rough turning, quenching and tempering. Free forging is conducted, the initial stage temperature is 1200 + / -10 DEG C, and the final forging temperature is 950 + / -10 DEG C; annealing is conducted, the annealing temperature is 860 + / -10 DEG C, heat preservation is conducted for 2.5-3.5 h, furnace cooling is conducted to 400 + / -10 DEG C, and air cooling is conducted; quenching is conducted, the quenching temperature is 915 + / -10 DEG C, the heat preservation time is 20 min, and oil cooling is conducted; the tempering temperature is 500 + / -20 DEG C, the heat preservation time is 3 h, and oil cooling is conducted. The method has the advantages that the cutting performance of the steel is improved through annealing, and deformation and cracking during quenching are reduced. Meanwhile, undissolved carbides and aphanitic martensite structures are obtained, and good wear resistance is guaranteed. And the fracture toughness in a medium-temperature tempering state is improved by quenching at 915 DEG C. And finally, martensite is promoted to start to decompose through medium-temperature tempering, and quenching internal stress gradually disappears. But part of solid solution carbon begins to be separated out in the form of cementite and can be pinned for dislocation, and a certain strengthening effect on a matrix is achieved. Meanwhile, due to the fact that the tempering temperature is slightly low, most alloy elements are still in a matrix, and solid solution strengthening still plays a main role. And when tempering is carried out within the temperature range, the test steel can keep certain hardness. Through quenching and tempering processes after annealing, the 50CrVA steel elastic element for the bridge, which is excellent in strength and hardness and high in toughness, can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of steel manufacturing, and in particular to a method for producing a 50CrVA steel elastic element for a bridge by heat treatment. Background Art

[0002] Due to the working environment and application conditions of elastic elements for bridges, permanent plastic deformation is not allowed, so the material is required to have high elastic limit, yield strength and tensile strength. Therefore, in addition to good strength and hardness, elastic elements should also have good plasticity and toughness properties.

[0003] 50CrVA spring steel has many advantages of chrome-vanadium spring steel, such as high elastic limit and high temperature strength, good hardenability, low thermal sensitivity, etc. It can be used to manufacture high working stress, harsh working conditions and more important occasions. For example, it can be used to manufacture steam turbine gas seal springs, regulating valve springs, condenser support springs, springs with impact loads with heat resistance below 300-350℃, large spiral springs, leaf springs and buffer return springs for mine crushers, etc.

[0004] Domestic research on the heat treatment of 50CrvA spring steel for elastic components of bridges, part of which is to obtain better comprehensive performance through the heat treatment process of quenching at about 870℃ and then tempering, but the research shows that the qualified rate of products of this process is low and it is easy to crack; the other part of the research focuses on the use of isothermal quenching and tempering heat treatment to obtain mixed structures such as bainite, martensite and residual austenite. This mixed structure has better plasticity and toughness than martensite, and the strength and hardness do not decrease too much. However, the research shows that isothermal quenching does not significantly improve the performance of 50CrvA spring steel compared with the traditional quenching process, and isothermal quenching is not suitable for mass production, the production cycle is long, and the energy consumption is higher than that of ordinary quenching.

[0005] In view of this, the present invention is proposed to solve the above technical problems. Summary of the invention

[0005] The first object of the present invention is to provide a heat treatment process for 50CrVA steel elastic elements for bridges, which improves the cutting performance of steel by annealing, reduces deformation and cracking during quenching, and simultaneously obtains undissolved carbides and cryptocrystalline martensite structures to ensure good wear resistance.

[0007] The second object of the present invention is to provide a heat treatment process for 50CrVA steel elastic elements for bridges, which improves the fracture toughness in the medium-temperature tempering state by quenching at 915°C.

[0008] The third object of the present invention is to provide a heat treatment process for 50CrVA steel elastic elements for bridges, which uses 500°C tempering to promote the decomposition of martensite and gradually eliminate the quenching internal stress. However, part of the solid-dissolved carbon begins to precipitate in the form of cementite, which can pin dislocations and have a certain strengthening effect on the matrix. At the same time, since the tempering temperature is slightly lower, most of the alloying elements are still inside the matrix, and solid solution strengthening still plays a major role. Tempering within this temperature range can maintain a certain hardness of the test steel.

[0009] A method for strengthening and toughening heat treatment of 50CrVA steel elastic elements for bridges, characterized in that the 50CrVA steel comprises components and mass percentages of 0.46% to 0.54% C, 0.17% to 0.37% Si, 0.50% to 0.80% Mn, 0.03% P, 0.03% S, 0.25% Cu, 0.80% to 1.10% Cr, 0.35% Ni, 0.10% to 0.20% V, and the balance is Fe;

[0010] The method specifically comprises the following steps:

[0011] Step 1. According to the composition of 50CrVA steel, smelt and cast into ingots, heat and keep the 50CrVA steel ingots, forge them on a press, the initial temperature is 1200±10℃, the final forging temperature is 950±10℃, and air cool them after forging;

[0012] Step 2. Anneal the 50CrVA steel forging at 860±10°C for 2.5-3.5h, cool the furnace to 400±10°C, and air cool.

[0013] Step 3. After annealing, quenching is performed, the quenching temperature is 915±10℃, the holding time is 20min, and oil cooling is performed;

[0014] Step 4. After quenching, tempering is performed at a temperature of 500±20℃, a holding time of 3h, and oil cooling.

[0015] The beneficial effects of the present invention are:

[0016] Compared with tempering heat treatment after austempering, the process flow is simplified and the production cost is reduced. Compared with the traditional quenching heat treatment process, the addition of annealing process improves the cutting performance of steel and reduces deformation and cracking during quenching. At the same time, undissolved carbides and cryptocrystalline martensite structures are obtained to ensure good wear resistance. In addition, the increase in quenching temperature increases the hardness of the material and increases the proportion of lath martensite in the quenched structure to improve the toughness in the tempered state. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a tempered metallographic structure diagram of 50CrVA steel according to the present invention. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with specific implementation modes.

[0018] Implementation Example

[0019] The heat treatment process of the 50CrVA steel elastic element for bridges in this embodiment includes the following steps:

[0020] Step 1. According to the composition of 50CrV steel, 0.50% C, 0.20% Si, 0.60% Mn, 0.03% P, 0.03% S, 0.25% Cu, 1.10% Cr, 0.35% Ni, 0.15% V, and the balance Fe, smelting and casting into ingots, heating and keeping the 50CrVA steel ingots, forging on a press, the initial stage temperature is 1200° C., the final forging temperature is 950° C., and air cooling is performed after forging and forming;

[0021] Step 2. Anneal the 50CrVA steel forging at 860°C for 3 hours, furnace cool to 400°C, and air cool.

[0022] Step 3. After annealing, quenching is performed at a temperature of 915°C, a holding time of 20 minutes, and oil cooling;

[0023] Step 4. After quenching, tempering is performed at a temperature of 500°C, a holding time of 3 hours, and oil cooling.

[0024] The tensile test results of the steel obtained in this example are shown in the following table: Table 1

[0025] All technical indicators of the 50CrVA steel after the heat treatment meet the product requirements and have stable performance. In addition, the heat treatment of the present invention has the characteristics of high production efficiency, low requirements for equipment and operating skills, low production cost, good heat treatment performance, etc., and is easy to promote.

Claims

1. A method for strengthening and toughening heat treatment of 50CrVA steel elastic elements for bridges, characterized in that: The 50CrVA steel comprises components and mass percentages of 0.46% to 0.54% C, 0.17% to 0.37% Si, 0.50% to 0.80% Mn, 0.03% P, 0.03% S, 0.25% Cu, 0.80% to 1.10% Cr, 0.35% Ni, 0.10% to 0.20% V, and the balance is Fe; The method specifically comprises the following steps: Step 1. According to the composition of 50CrVA steel, smelt and cast into ingots, heat and keep the 50CrVA steel ingots, forge them on a press, the initial temperature is 1200±10℃, the final forging temperature is 950±10℃, and air cool them after forging; Step 2. Anneal the 50CrVA steel forging at 860±10°C for 2.5-3.5h, cool the furnace to 400±10°C, and air cool. Step 3. After annealing, quenching is performed, the quenching temperature is 915±10℃, the holding time is 20min, and oil cooling is performed; Step 4. After quenching, tempering is performed at a temperature of 500±20℃, a holding time of 3h, and oil cooling.

2. The method for strengthening and toughening heat treatment of 50CrVA steel elastic elements for bridges according to claim 1 is characterized in that: The 50CrVA steel comprises components and mass percentages of 0.50% C, 0.20% Si, 0.60% Mn, 0.03% P, 0.03% S, 0.25% Cu, 1.10% Cr, 0.35% Ni, 0.15% V, and the balance is Fe.

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