Stress control method for plasma surfacing of ultrahigh-hardness material

Abstract

The invention discloses a stress control method for plasma surfacing of an ultrahigh-hardness material, belongs to the field of welding additive manufacturing, can solve the problem that stress cracking is prone to occurring in the surfacing process of an existing high-hardness material, and particularly relates to a self-heating device for surfacing of rod and shaft parts and a surfacing process control strategy. The self-heat-supplementing devices are distributed on the two sides of a surfacing area, the solidification temperature of a welding layer arc stopping section is controlled in a heat transfer mode, the welding layer arc stopping section is slowly cooled after the temperature is homogenized, and the surfacing process control strategy mainly comprises the following steps that 1, cleaning is conducted, specifically, a cleaning agent is used for cleaning, and the cleaning area needs to be 60 mm outwards from a surfacing part; the cleaning agent does not contain elements causing alloy embrittlement; 2, the preheating temperature before welding is at least 350 DEG C or above; 3, the interlayer temperature is controlled to be 350-550 DEG C;

Description

Technical Field

[0001] The present invention proposes a stress control method for plasma surfacing of ultra-high hardness materials, which belongs to the field of welding additive manufacturing. It specifically includes a self-heating device combined with a corresponding process control strategy, which is suitable for the plasma surfacing process of various nickel-based high-hardness alloy powder materials with a hardness exceeding 55HRC. Background Art

[0002] At present, the plasma surfacing technology of nickel-based high-hardness alloy powder materials is a common local performance gradient design method for rod and shaft parts. In order to meet the use requirements of such parts, multi-layer heterogeneous structure plasma surfacing is usually required, that is, the metal powder is melted at high temperature by a plasma beam and stacked layer by layer to form the final physical product. Under normal circumstances, it is usually difficult to achieve the dilution rate and powder melting quality requirements during the plasma surfacing process of high-hardness powder materials. In addition, the high alloying state of high-hardness materials causes the alloy elements to have large thermal stress and grain boundary stress during the surfacing melting and solidification process, resulting in a high scrap rate, which is mainly reflected in post-weld stress cracking. This stress cracking phenomenon is closely related to the stress state during the surfacing process. In the plasma surfacing process of high-hardness powder materials, the first layer of accumulation is the fusion of the welding material and the base material, and the subsequent surfacing process is the fusion of the welding material, the base material and the previous layer of deposited metal, which makes the entire component present a complex stress state. In particular, there is a large temperature difference when the arc is closed in the last layer. Different materials produce large differences in unbalanced thermal shrinkage stress under the huge temperature difference, which leads to direct cracking after welding or cracking during heat treatment / thermal shock testing. The tendency of this type of cracking is very high. Summary of the invention

[0003] In view of the stress cracking problem of plasma surfacing of high-hardness powder materials described in the background technology, the present invention provides a stress control method for plasma surfacing of ultra-high hardness materials, which can effectively overcome the post-weld stress cracking problem of plasma surfacing of high-hardness powder materials that cannot be solved by adjusting the existing process parameters, and realize high-quality plasma surfacing manufacturing of high-hardness rod and shaft parts. Specifically, it includes a self-heating device and a surfacing process control strategy.

[0004] The self-heating device uses a square cross-section coil with rounded corners to form a closed loop when powered on, and achieves temperature uniformity treatment on both sides of the surfacing area through heat transfer on both sides, and controls the surfacing stress during the solidification process of the arc closing section. The device can quickly increase the temperature to the set temperature. The plasma surfacing workpiece is fixed on a chuck fixture, and the chuck fixture is fixed on a turntable. The turntable is driven by gears and has a displacement encoder on it. Heating is started and stopped according to different displacement positions, and the temperature of the heating process is controlled.

[0005] The square cross-section coil with rounded corners is made of conductive material, preferably copper. An insulating protective cover is added to the coil surface to avoid mutual influence between current loops. A cooling device is provided inside the coil to avoid faults such as oxidation and burn-through of the coil.

[0006] The self-heating device controls the solidification temperature of the arc closing section of the welding layer by heat transfer, so that the temperature is uniformed and then slowly cooled, thereby avoiding gradient shrinkage stress caused by rapid temperature changes.

[0007] The described cladding process control strategy is to control the preparation process of rod and shaft parts within the most suitable process range of existing materials, mainly including: 1. Cleaning before welding, using a cleaning agent to clean the area 60mm outward from the cladding area, and the cleaning agent must not contain elements that cause alloy embrittlement; 2. The preheating temperature before welding is at least 350°C; 3. The interlayer temperature is controlled at 350-550°C.

[0008] The present invention is suitable for plasma surfacing of different nickel-based high-hardness alloy powders with a hardness of more than 55HRC, including Colmonoy 56, Colmonoy 6, etc.; different coil sizes can be designed according to different welding groove widths to make the heating effect more uniform and better control the stress generated during the surfacing process. The present invention adopts coil medium-frequency heating, which can quickly control the heating temperature and heating rate. It is convenient, movable, replaceable, low-cost, and high-efficiency, and has a good effect on stress control during the surfacing process of high-hardness materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of self-heating device

[0010] Figure 2 Schematic diagram of the coil position of the self-heating device (top view)

[0011] Figure 3 Workpiece dimensions before welding

[0012] Figure 4 Schematic diagram of cracked workpiece DETAILED DESCRIPTION

[0013] The present invention is described in detail below with reference to the accompanying drawings and specific implementation modes.

[0014] refer to Figure 1, the self-heating device in this specific implementation mode is introduced. First, the workpiece 1 is fixed by a tooling. The fixing tooling 6 is fixed on the turntable 7 by clearance fit. The turntable 7 is provided with a displacement encoder 8. The welding gun starts working under the setting of the existing welding process parameters. The welding gun 9 does not rotate. The turntable 7 is rotated to perform welding at the welding groove 3 of the workpiece. The square cross-section coil 2 and the coil 4 with rounded corners are independently controlled to form a closed loop when powered on. The temperature of the two sides of the surfacing area is uniformly treated by heat transfer on both sides. The surfacing stress of the arc closing section solidification process is controlled. The square cross-section coil with rounded corners is provided with a cooling channel 5.

[0015] The specific conditions of the workpiece and the implementation process are described below. This implementation case takes a typical rod and shaft part, namely a marine diesel engine valve, as an example.

[0016] The workpiece base material is 45Cr9Si3 material, the welding material is Colmonoy 56, the workpiece welding groove width is 16.6mm, the disk diameter is φ118mm, the disk circumference is 118π, and a square cross-section coil with a side length of 8mm is selected according to the welding groove width.

[0017] Before welding, factors affecting the process need to be controlled, including 1. Cleaning: Use a cleaning agent to clean the area to be welded and the surrounding area of ​​the workpiece. The cleaning area should be 60mm outward from the surfacing part. The cleaning agent must not contain elements that cause alloy embrittlement; 2. The preheating temperature before welding is 350℃. During the welding process, the temperature between the surfacing layers is controlled at 350-550℃.

[0018] This implementation case uses the traditional surfacing parameter loading scheme as a control, and compares the control effect of the plasma surfacing stress control self-heating device and control method on stress cracking. The same number of layers are surfacing under the same process parameters, including current, welding gun swing, turntable speed, feed weight, shielding gas, etc., and a thermal shock test is carried out after the same processing (that is, the workpiece is placed in a heating furnace at 60°C, and the temperature is raised to 320°C within 4 hours, kept at 320°C for 1 hour, quickly placed in 20-30°C water, and air-cooled to room temperature after 5-8 seconds). After plasma surfacing, the high-hardness welding material has a thermal shock test. Figure 4 The valve surface cracking problem shown is very high, and the qualified rate of the traditional process is usually less than 50%. The main purpose of the present invention is to improve the qualified rate of the product after surfacing to more than 85%.

[0019] In this implementation case, the temperature of the self-heating device is set to 850°C, the time for rapid increase to 850°C is set to 3s, and the heating is stopped 3s after the arc is closed.

[0020] The supplementary heat device achieves temperature uniformity treatment on both sides of the surfacing area by heat transfer on both sides, and controls the surfacing stress during the solidification process of the arc closing section.

[0021] When the last layer of welding material is built up to half the circumference of the gas valve disc, the displacement encoder on the turntable automatically starts the heating device after giving a signal, and heats to the set temperature within 3 seconds.

[0022] When the last layer of welding material is built-up to 3 / 4 of the circumference of rod and shaft parts, the temperature of the heating device is gradually reduced to 500-550℃, and the heating device stops heating 3s after the arc is closed.

Claims

1. A stress control method for plasma surfacing of ultra-high hardness materials, used to solve the stress cracking problem that is prone to occur in the existing high hardness material surfacing process, and its characteristics include: It includes a self-heating device for surfacing welding of rod and shaft parts and a surfacing welding process control strategy. The self-heating device is composed of a square cross-section coil with rounded corners to form a closed loop when energized, and temperature uniformization and arc closing section solidification process control are achieved on both sides of the surfacing area through heat transfer on both sides. The surfacing welding process control strategy includes cleaning area control, preheating temperature control before welding and interlayer temperature control.

2. The stress control method for plasma surfacing of ultra-high hardness materials according to claim 1, characterized in that The self-heating device described above is a device in which the plasma surfacing workpiece is fixed on a chuck fixture, the chuck fixture is fixed on a turntable, the turntable is driven by a gear, and a displacement encoder is provided on the turntable; the side length of the square coil with rounded corners is H = 0.4-0.5h, where h is the width of the welding groove; the parameters of the heat-replenishing device are set according to the melting point of the surfacing material, and are given by the formula T s =ζT f OK, T s is the set temperature, T f is the melting point temperature, ζ is the coefficient, ζ∈[0.8,0.9]; the high hardness alloys suitable for the supplementary heat device include Colmonoy 56, Colmonoy 6 and other nickel-based high hardness alloys with a hardness of more than 55HRC.

3. The stress control method for plasma surfacing of ultra-high hardness materials according to claim 1, characterized in that The control strategy for the cladding process includes three steps:

1. Cleaning: Use a cleaning agent to clean the area 60 mm from the cladding area. The cleaning agent must not contain elements that cause alloy embrittlement.

2. The preheating temperature before welding should be at least 350℃; 3. The interlayer temperature should be controlled at 350-550℃; when the last layer of cladding is carried out to 1 / 2 of the circumference of the rod and shaft parts, the displacement encoder on the turntable receives a signal to automatically start the heating device, and the heating device needs to be heated to the set temperature within 5s; when the last layer of cladding is carried out to 3 / 4 of the circumference of the rod and shaft parts, the temperature of the heating device is gradually and steplessly reduced to 500-550℃, and the heating device stops heating 3s after the arc is closed.

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