CN111054928A

CN111054928A - Preparation method of hard alloy/steel welding part

Info

Publication number: CN111054928A
Application number: CN201911354985.7A
Authority: CN
Inventors: 万维财; 王杰; 王宗元; 李玉和; 樊坤阳
Original assignee: Xihua University
Current assignee: Xihua University
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2020-04-24
Anticipated expiration: 2039-12-25
Also published as: CN111054928B

Abstract

The invention discloses a preparation method of a hard alloy/steel welding piece, and belongs to the technical field of welding. It includes: preparing a hard alloy material into a green body, and then preparing a gradient hard alloy after vacuum sintering; and sequentially stacking the gradient hard alloy, the metal brazing filler metal and the steel and then brazing the gradient hard alloy, the metal brazing filler metal and the steel. The gradient structure is built in situ on the surface side of the hard alloy/steel welding piece, the controllable gradient structure is built in the alloy preparation process by focusing on the surface of the hard alloy, the process is simplified, the cost is saved, the welding efficiency is improved, the service reliability of a hard alloy workpiece can be greatly improved, and the application of hard alloy materials in wider projects is promoted.

Description

Preparation method of hard alloy/steel welding part

Technical Field

The invention relates to the technical field of welding, in particular to a preparation method of a hard alloy/steel welding piece.

Background

The hard alloy has wide application in the fields of cutters, molds, wear-resistant and corrosion-resistant parts and the like, has higher bending strength and impact toughness, better grindability and thermal conductivity and good cutting performance, and is commonly used for producing cutters such as turning tools, reamers, gear hobs and the like. Because the toughness and the processability of the hard alloy are poor, the hard alloy can exert respective advantages when being connected with metal materials such as steel with higher toughness and large bearable impact load. However, the most widely used brazing method for joining hard metal and steel has major problems of wettability and residual stress, and since the hard metal contains a certain volume of metal phase, the problem of wettability of the brazing material to the substrate is not prominent. However, the physical and mechanical properties of the cemented carbide, such as the thermal expansion coefficient, the elastic modulus, the yield limit, and the poisson's ratio, are greatly different from those of the metal material and the brazing filler metal, so that a large residual thermal stress is easily generated at the brazing interface. The high stress gradient is very unfavorable for the reliability of the joint, which leads to great reduction of the strength of the joint and causes cracks to appear in the joint under the working condition of low stress service even in the brazing cooling process.

At present, the residual stress of hard alloy/steel brazing is relieved by adjusting the structure and components of the brazing filler metal and optimizing the welding process to reduce the mismatching of the physical and mechanical properties of the interface, and the aim of relieving the stress is fulfilled and the stress is relieved by adopting the special brazing filler metal through a special brazing mode and process optimization.

Wherein, adopt special brazing mode and the processing mode of technology optimization: the homogeneous hard alloy, the common brazing filler metal and the steel are subjected to special brazing, such as furnace brazing, vacuum brazing and the like, so that the welding is completed, and the residual stress relieving effect of the treatment mode is common; the dependence of the brazing equipment is large; the welding process parameter is complex to regulate and control; the welding efficiency and the process convenience are not high.

And (3) relieving stress by adopting special brazing filler metal: homogeneous hard alloy and steel are welded in common soldering mode, but the brazing filler metal is special brazing filler metal such as composite brazing filler metal, gradient brazing filler metal and composite intermediate layer. The middle layer is a transition layer which is added into the brazing filler metal and incompletely melted in order to relieve residual stress; the composite solder is prepared by adding hard phase reinforcements such as particles, fibers and whiskers into a softer basic solder, and changing the composition proportion of the basic solder and the reinforcements to adjust the mismatch degree of physical and mechanical properties of a base material by utilizing the good plasticity and toughness of the basic solder and the high-temperature strength and low thermal expansion coefficient of the reinforcements so as to relieve stress; the gradient brazing filler metal is gradient distribution of the brazing filler metal among base materials, and residual stress caused by base material property mismatch can be reduced in aspects of components, tissues and the like. The residual stress relieving effect is good by adopting the special brazing filler metal; in order to improve the continuity degree of the interface, the number of layers of the middle layer or the gradient brazing filler metal is increased, and the preparation process is complex; the distribution controllability of the reinforced phase in the composite brazing filler metal and the alloy phase in the gradient brazing filler metal is poor, and the introduction of the reinforced phase or the alloy phase can increase the elastic modulus of the brazing filler metal while reducing the thermal expansion coefficient of the brazing filler metal, so that the welding stress is influenced; the special brazing filler metal has higher cost; the welding process is complicated.

Disclosure of Invention

The invention aims to provide a preparation method of a hard alloy/steel welding piece, which aims to solve the problems of low residual stress relieving effect, complex process treatment and high brazing filler metal cost in the existing hard alloy/steel welding process.

The technical scheme for solving the technical problems is as follows:

a preparation method of a hard alloy/steel welding piece comprises the following steps: preparing a hard alloy material into a green body, and then preparing a gradient hard alloy after vacuum sintering; and sequentially stacking the gradient hard alloy, the metal brazing filler metal and the steel and then brazing the gradient hard alloy, the metal brazing filler metal and the steel.

According to the invention, the hard alloy with the continuous metal-rich phase gradient layer with the controllable structure and the controllable components on the surface is constructed, so that the continuity of the hard alloy/brazing filler metal interface is realized, the continuity of the microstructure and the physical and mechanical properties of the interface is improved, and the purpose of relieving the welding residual stress is achieved.

Wherein, TiC in the process of vacuum sintering of hard alloy_0.5N_0.5N is decomposed through a dissolution and precipitation process, the nitrogen potential difference between the surface and the inside of the hard alloy is caused by a vacuum denitrification environment, the nitrogen potential inside the hard alloy is higher than that of a surface layer, and N elements migrate from the inside to the outside; the amount of the internal liquid phase is larger than that of the surface layer, so that the volume diffusion of the metal bonding phase from the inside to the surface occurs along with the migration of the N element; elements such as Ti and the like have strong thermodynamic coupling effect with N element and are diffused into the interior for forming stable compounds; finally, a gradient of rich metal phase and poor alloy phase is formed on the surface of the hard alloyAnd (5) structure.

And in the sintering preparation process of the hard alloy, a controllable gradient layer rich in metal phase and poor in alloy phase is formed on the surface of the alloy through the control of a sintering process. The chemical composition, phase composition and physical and mechanical properties of the gradient layer are continuously changed in a gradient manner from the inside to the surface of the hard alloy matrix, and the gradient layer has physical and chemical properties closer to those of the metal brazing filler metal, so that a macroscopic interface between the hard alloy and the metal brazing filler metal layer is eliminated, and the continuity of a microstructure structure and the physical and mechanical properties of the hard alloy/brazing filler metal interface is improved. The existence of the surface gradient layer converts the connection problem of the hard alloy and the metal solder into the connection problem between the metal and the metal, obviously improves the matching of the structure and the performance between the hard alloy and the solder, and further achieves the purpose of relieving the residual stress of the interface.

Further, in a preferred embodiment of the present invention, the cemented carbide material includes: ni 5-15 wt%, Co 5-15 wt%, and TiC_0.5N_0.53-8 wt%, TiC 5-15 wt%, and the balance WC.

The hard alloy material adopted by the invention adopts Ni and Co as composite metal adhesives (the total adhesive content is 10-30 wt%, Ni: Co is 1:1), forms NiCo solid solution to improve the toughness of an adhesive phase, adopts TiC as an additive (the total content is 5-20 wt%) to improve the strength and high-temperature performance of the hard alloy, and adopts TiC_0.5N_0.5The key additive (total content is 3-8 wt%) for forming the surface gradient layer provides N source, N generated by decomposition during high-temperature sintering is utilized to diffuse to the surface of the material, Ti, W and the like diffuse to the inside under the action of thermodynamic coupling, bonding phases Ni and Co migrate to the surface to form the surface gradient layer, and WC (the balance) is used as a main hard phase of the hard alloy material. The invention adopts TiC with higher N content_0.5N_0.5Rather than the mature and stable TiN and TiC performance of the prior preparation process_0.7N_0.3Because the higher N content is easier for Ti (C, N) decomposition and N diffusion to form a surface gradient layer, TiC_0.5N_0.5After partial N is decomposed and lost, the Ti-C-N system can still be formed to be stable, and the sufficient N content of the system and the performance of the material are ensured. If it is burntTiC in the knot System_0.5N_0.5Too high content, or too high content of N in Ti (C, N) component, results in too large sintering deformation and sintering stress of the cemented carbide to be favorable for controlling the stability of material properties.

Further, in a preferred embodiment of the present invention, the step of forming the green compact comprises: after ball milling, filtering the hard alloy material by a 200-mesh and 400-mesh screen, and drying the filtered slurry; sieving the dried powder through a 600-sand 800-mesh screen and granulating; the granulated powder is pressed into a green body under the pressure of 200-500 MPa.

Further, in a preferred embodiment of the present invention, the ball milling conditions are as follows: the ball milling medium is No. 120 solvent gasoline, and 80-150ml of ball milling medium is added into each 100g of hard alloy material; the ball milling speed is 60-120r/min, the grinding alloy balls are WC-8 wt% Co (representing: tungsten carbide containing 8 wt% of cobalt) with the diameter of 6-8mm, the ball-to-material ratio is 5:1-15:1, and paraffin is added, wherein the addition amount of the paraffin is 10-15 wt% of the hard alloy material; the ball milling time is 48-72 h.

Further, in a preferred embodiment of the present invention, the drying conditions are as follows: the drying temperature is 90-120 ℃; the vacuum degree is 10-15 Pa; the drying time is 2-5 h.

Further, in a preferred embodiment of the present invention, the vacuum sintering comprises:

(1) the first stage is as follows: the vacuum degree is 10-20Pa, the sintering temperature is 300-650 ℃, and the heat preservation treatment is carried out for 2-5 h;

(2) and a second stage: the vacuum degree is 1-5Pa, the sintering temperature is 1340-1450 ℃, and the heat preservation treatment is carried out for 1-3 h.

The sintering process of the invention:

the first stage is as follows: the paraffin wax as the forming agent is removed at the temperature of 300-650 ℃, because the density of the hard alloy is lower, the addition amount of the paraffin wax as the forming agent in the hard alloy is slightly more than that of the common hard alloy in order to improve the pressing performance of the hard alloy, so the temperature for removing the forming agent is slightly higher, and the time is slightly longer. Because the paraffin volatilizes gas at high temperature and the oxidation effect is not obvious at lower temperature (less than or equal to 800 ℃), the sintering of the removing forming agent is carried out at lower vacuum degree (more than or equal to 15 Pa).

And a second stage: liquid phase sintering is carried out at the temperature of 1340-1450 ℃, the sintering system is completely densified, the heat preservation time is slightly longer than 1-3h of the common hard alloy sintering, which is 1-2h higher than that of the common hard alloy sintering, which is beneficial to the diffusion of N, Ti atoms and the like, and a gradient layer is formed; in addition, as Ti (C, N) of the sintering system is decomposed, atomic diffusion is obvious, the trends of matrix deformation and sintering stress are large, the temperature is kept for a long time, the temperature rise speed is low (1-3 ℃/min), and the control of sintering deformation and the release of sintering stress are facilitated.

Further, in a preferred embodiment of the present invention, the brazing step includes: the gradient hard alloy, the metal brazing filler metal and the steel are sequentially stacked and then welded through flame brazing, induction brazing, furnace brazing or vacuum brazing.

Further, in a preferred embodiment of the present invention, the metal filler metal includes a Cu-Zn filler metal or a Ag-Cu-Zn filler metal.

Further, in the preferred embodiment of the present invention, the metal solder is Cu-Zn solder, and the welding temperature is 920-.

Further, in the preferred embodiment of the present invention, the metal solder is Ag-Cu-Zn solder, and the soldering temperature is 750-850 ℃.

Further, in the preferred embodiment of the present invention, the above mentioned

The invention has the following beneficial effects:

1. the gradient structure is built in situ on the surface side of the hard alloy/steel welding piece, the controllable gradient structure is built in the alloy preparation process by focusing on the surface of the hard alloy, the process is simplified, the cost is saved, the welding efficiency is improved, the service reliability of a hard alloy workpiece can be greatly improved, and the application of hard alloy materials in wider projects is promoted.

2. According to the invention, the sintering process and the sintering atmosphere are controlled in the preparation process of the hard alloy, the controllable gradient structure is formed on the surface, and the hard alloy is connected with the steel by the common brazing filler metal and the conventional brazing method, so that the aims of effectively relieving stress, improving welding efficiency, saving cost and realizing gradient construction in the alloy production process so as to simplify the process can be achieved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a graph illustrating the morphology and composition distribution of a gradient cemented carbide produced in example 1 of the present invention;

FIG. 2 is a microstructure diagram of a cemented carbide/steel vacuum brazed joint obtained in example 1 of the present invention.

Detailed Description

The principles and features of the present invention are described below in conjunction with the embodiments and the accompanying drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The hard alloy material adopted by the invention is as follows: ni of 1.0-2.5 μm, Co of 1.0-2.5 μm, and TiC_0.5N_0.5The granularity of the titanium alloy is 0.8-2.0 mu m, the granularity of WC is 1.0-2.0 mu m, and the granularity of TiC is 1.0-2.0 mu m.

Example 1:

the preparation method of the hard alloy/steel welding piece comprises the following steps:

(1) making into green body

The hard alloy material comprises: ni 5 wt%, Co 5 wt%, TiC_0.5N_0.53 wt%, TiC5 wt%, and the balance WC.

Ball-milling the hard alloy material, filtering the hard alloy material by a 200-mesh screen, and drying the filtered slurry; sieving the dried powder through a 600-mesh screen and granulating; the granulated powder is pressed into a green body under the pressure of 2000 MPa.

Wherein, the ball milling conditions are as follows: the ball milling medium is No. 120 solvent gasoline, and 80-ml of ball milling medium is added into each 100g of hard alloy material; the ball milling speed is 60r/min, the grinding alloy balls are WC-8 wt% Co with the diameter of 6mm, the ball-to-material ratio is 5:1, and paraffin is added, wherein the addition amount of the paraffin is 10 wt% of the hard alloy material; the ball milling time is 48 h.

The conditions of the drying treatment were: the drying temperature is 90 ℃; the vacuum degree is 10 Pa; the drying time was 2 h.

(2) And (3) vacuum sintering: and sintering the prepared green body in vacuum to prepare the gradient hard alloy.

Wherein, the vacuum sintering step is as follows:

(21) the first stage is as follows: the vacuum degree is 15Pa, the sintering temperature is 300 ℃, and the heat preservation treatment is carried out for 5 hours;

(22) and a second stage: the vacuum degree is 1Pa, the sintering temperature is 1340 ℃, and the heat preservation treatment is carried out for 3 hours.

(3) Brazing: and (3) sequentially stacking the gradient hard alloy, the Cu-Zn solder and the steel under the vacuum degree of 1Pa, and then carrying out vacuum brazing on the gradient hard alloy, the Cu-Zn solder and the steel, wherein the welding temperature is 920 ℃.

In other embodiments of this embodiment, the soldering temperature is 950 ℃ or 970 ℃.

Example 2:

(1) making into green body

The hard alloy material comprises: ni 10 wt%, Co 10 wt%, TiC_0.5N_0.55 wt%, TiC10 wt%, and the balance WC.

Ball-milling the hard alloy material, filtering the hard alloy material by a 300-mesh screen, and drying the filtered slurry; sieving the dried powder through a 700-mesh screen and granulating; the granulated powder is pressed into a green body under the pressure of 350 MPa.

Wherein, the ball milling conditions are as follows: the ball milling medium is No. 120 solvent gasoline, and 110ml of ball milling medium is added into each 100g of hard alloy material; the ball milling speed is 90r/min, the grinding alloy balls are WC-8 wt% Co with the diameter of 7mm, the ball-to-material ratio is 10:1, and paraffin is added, wherein the addition amount of the paraffin is 12 wt% of the hard alloy material; the ball milling time is 60 h.

The conditions of the drying treatment were: the drying temperature is 100 ℃; the vacuum degree is 12 Pa; the drying time was 3.5 h.

Wherein, the vacuum sintering step is as follows:

(21) the first stage is as follows: the vacuum degree is 17Pa, the sintering temperature is 500 ℃, and the heat preservation treatment is carried out for 3.5 h;

(22) and a second stage: the vacuum degree is 3Pa, the sintering temperature is 1400 ℃, and the heat preservation treatment is carried out for 2 h.

(3) Brazing: the gradient hard alloy, the Cu-Zn brazing filler metal and the steel are sequentially stacked and then subjected to induction brazing, and the welding temperature is 920 ℃.

Example 3:

(1) making into green body

The hard alloy material comprises: according to weight percentage, Ni 15 wt%, Co 15 wt%, TiC_0.5N_0.58 wt%, TiC15 wt%, and the balance WC.

Ball-milling the hard alloy material, filtering the hard alloy material by a 400-mesh screen, and drying the filtered slurry; sieving the dried powder through a 800-mesh screen and granulating; pressing the granulated powder into a green body under the pressure of 500 MPa.

Wherein, the ball milling conditions are as follows: the ball milling medium is No. 120 solvent gasoline, and 150ml of ball milling medium is added into each 100g of hard alloy material; the ball milling speed is 120r/min, the grinding alloy balls are WC-8 wt% Co with the diameter of 8mm, the ball-to-material ratio is 15:1, and paraffin is added, wherein the addition amount of the paraffin is 15 wt% of the hard alloy material; the ball milling time is 72 h.

The conditions of the drying treatment were: the drying temperature is 120 ℃; the vacuum degree is 15 Pa; the drying time was 2 h.

Wherein, the vacuum sintering step is as follows:

(21) the first stage is as follows: the vacuum degree is 20Pa, the sintering temperature is 650 ℃, and the heat preservation treatment is carried out for 2 hours;

(22) a fourth stage: the vacuum degree is 5Pa, the sintering temperature is 1450 ℃, and the heat preservation treatment is carried out for 1 h.

(3) Brazing: the gradient hard alloy, the Ag-Cu-Zn brazing filler metal and the steel are sequentially stacked and then brazed in a furnace, and the welding temperature is 750 ℃.

In other embodiments of this embodiment, the soldering temperature is 800 ℃ or 850 ℃.

Analysis of results

The morphology and composition distribution of the gradient cemented carbide obtained in example 1 were analyzed, and the results are shown in fig. 1.

As can be seen from FIG. 1, the surface of the gradient cemented carbide prepared in example 1 forms a surface gradient layer rich in metal phase and poor in alloy phase, and the chemical composition, phase composition and physical and mechanical properties of the surface gradient layer continuously change from the inside of the cemented carbide substrate to the surface.

The microstructure of the cemented carbide/steel vacuum brazed joint obtained in example 1 was examined, and the results are shown in fig. 2.

As can be seen from fig. 2, the surface gradient layer formed on the surface of the gradient hard alloy has physical and chemical properties closer to those of the metal brazing filler metal.

The cemented carbide/steel braze joints produced in examples 1-2 and the prior art stress relief measures/welding methods were tested for performance and the results are shown in the following table.

TABLE 1 hard alloy/steel braze welding joint performance test table

It can be seen from table 1 that the bending strength and the shearing strength of the gradient cemented carbide/steel braze joint manufactured by the stress relief method of the present invention are significantly higher than those of the homogeneous cemented carbide/steel braze joint and better than those of the homogeneous cemented carbide/steel braze joint using the gradient brazing filler metal in the same brazing manner and with the same brazing filler metal.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A preparation method of a hard alloy/steel welding piece is characterized by comprising the following steps: preparing a hard alloy material into a green body, and then preparing a gradient hard alloy after vacuum sintering; and sequentially stacking the gradient hard alloy, the metal brazing filler metal and the steel and then brazing the gradient hard alloy, the metal brazing filler metal and the steel.

2. The method of making a cemented carbide/steel weldment according to claim 1 wherein the cemented carbide material comprises: ni 5-15 wt%, Co 5-15 wt%, and TiC_0.5N_0.53-8 wt%, TiC 5-15 wt%, and the balance WC.

3. The method of making a cemented carbide/steel weldment according to claim 2 wherein the step of forming a green compact comprises: ball-milling the hard alloy material, filtering the hard alloy material by a 200-mesh and 400-mesh screen, and drying the filtered slurry; sieving the dried powder through a 600-sand 800-mesh screen and granulating; the granulated powder is pressed into a green body under the pressure of 200-500 MPa.

4. A method of making a cemented carbide/steel weldment as claimed in claim 3 wherein the ball milling conditions are: the ball milling medium is No. 120 solvent gasoline, and 80-150ml of ball milling medium is added into each 100g of hard alloy material; the ball milling speed is 60-120r/min, the grinding alloy balls are WC-8 wt% Co with the diameter of 6-8mm, the ball-material ratio is 5:1-15:1, and paraffin is added, wherein the addition amount of the paraffin is 10-15 wt% of the hard alloy material; the ball milling time is 48-72 h.

5. The method of producing a cemented carbide/steel weldment according to claim 4 wherein the conditions of the drying process are: the drying temperature is 90-120 ℃; the vacuum degree is 10-15 Pa; the drying time is 2-5 h.

6. A method of making a cemented carbide/steel weldment as claimed in claim 3 wherein the step of vacuum sintering is:

7. A method of making a cemented carbide/steel weld according to any one of claims 1 to 6, characterized in that the brazing step comprises: the gradient hard alloy, the metal brazing filler metal and the steel are sequentially stacked and then welded through flame brazing, induction brazing, furnace brazing or vacuum brazing.

8. The method of making a cemented carbide/steel weld according to claim 7, characterized in that the metal braze comprises a Cu-Zn braze or a Ag-Cu-Zn braze.

9. The method as claimed in claim 8, wherein the brazing filler metal is Cu-Zn brazing filler metal, and the welding temperature is 920-.

10. The method of claim 8 wherein the brazing filler metal is Ag-Cu-Zn brazing filler metal and the brazing temperature is 750-850 ℃.