AU2012201390A1

AU2012201390A1 - Method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface

Info

Publication number: AU2012201390A1
Application number: AU2012201390A
Authority: AU
Inventors: Gang Wang; Zhenming Wang; Shengyong Zhou
Original assignee: KING STRONG TOOLS AND MOULDS CO Ltd
Current assignee: King-Strong Material Engineering Ltd
Priority date: 2011-08-04
Filing date: 2012-03-08
Publication date: 2013-02-21
Anticipated expiration: 2032-03-08
Also published as: CN102274923B; AU2012201390B2; CN102274923A

Abstract

Specification Abstract A method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface, belongs to metal based composite material preparation technical field. Adopting vacuum lost foam casting technique, W powder, graphite powder, metal powder are mixed, and agglomerant is added to produce powder coating paste, then the powder coating paste is coated on the surface of EPS foam plastic model or filled in the holes and grooves of the model. In the pouring process, high temperature molten steel induces self-propagating synthesis reaction, that is 3W+2C--*WC+W 2C, to form tungsten carbide based hard alloy phase, and obtain surface or part self-propagating synthesis of tungsten carbide based hard alloy coated castings. The advantages of the present invention are, good surface quality of the castings, solid combination of coating and castings, high abrasive resistance, not falling off of antifriction alloy layer, and simple technique, suitable for industrial production.

Description

Specification METHOD FOR IN SITU SYNTHESIS OF TUNGSTEN CARBIDE BASED HARD ALLOY COATING ON CASTING SURFACE Technical Field The present invention belongs to metal based composite material preparation technical field and provides a method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface. Background Art Abrasion is one of the principal forms of part failure, leading to reduced low running efficiency of equipments, workpiece replacement or frequent maintainance, increase of energy consumption, which means huge economic loss. At present, the methods for increasing abrasion resistance of parts mainly are surface modification and coating technology, wherein coating technology uses very little meterial to function better than mass, costly monolith material and greatly lower product cost. Tungsten carbide has high hardness, abrasion resistance and infusibility. Tungsten carbide based hard alloy is applied widely to cutter material , e.g. lathe tool, milling cutter and drill, et al, and to cutting cast iron, non-ferrous metal and common steel, as well to cutting the treatment-resistant material, e.g. heat-resistant steel, stainless steel, tool steel, et al. Besides, Tungsten carbide based hard coating has wide application future in abrasion resistance, corrosion-resistant coating fields. Self-propagating High-temperature Synthesis (abbreviated as SHS) utilizes novel technology of self heat release from chemical reactions to prepare material, whose most outstanding characteristic is making full use of high energy heat-release reactions when elements form compounds. Except a small amount of external energy needed in inducing the synthetic reaction, the whole reaction process mainly depends on the self heat release from material. Self-propagating synthesized Tungsten carbide has the advantages of simple technology, high production efficiency and energy conservation, suitable to high volume production. 1 Specification Summary of the invention The present invention aims to provide a method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface so as to increase the abrasion resistance and corrosion resistance of castings. The present invention provides a method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface, which is characterized in that: (1) The material comprises 20-80 weight percentage of W powder, 1.5-25 graphite powder, 5-68 metal powder, mixing in a ball mill for 1-24 hours to produce powder mixture; (2) Add agglomerant to the powder mixture, wherein the mass ratio of agglomerant to powder mixture is 1:10-1:100, then stir and mix to produce powder coating paste; (3) Coat the surface of EPS foam plastic model with the powder coating paste or fill the powder coating paste into pre-processed holes or grooves of the model; (4) Spread a layer of anti-adhesive sand coating on the prepared casting model, and dry it in the temperature range of 40-50'C for 5-18 hours; (5) Melt molten steel in medium frequency induction furnace, then pour, high temperature molten steel induces self-propagating synthesis reaction, that is 3W+2C--WC+W 2 C, to form tungsten carbide based hard alloy phase; (6) Heat treat the casting or water toughening treat the casting with residual heat, cooling to room temperature and perform surface clearance and polish to obtain surface or part self-propagating synthesis of tungsten carbide based hard alloy coated castings. Preferably, the casting technique is vacuum lost foam casting. Preferably, molten steel may be high manganese steel, plain-carbon steel or alloy steel. Preferably, the weight percentage of the powder metal is, 0-60 percent of Ni, 0-30 percent of Cr, 0-11 percent of Si, 0-8 percent of B, 0-60 percent of Co, with the remaining Fe. Further preferably, the weight percentage of the powder metal is, 0-60 2 Specification percent of Ni, 5-30 percent of Cr, 5-11 percent of Si, 3-8 percent of B, 0-60 percent of Co, with the remaining Fe. Preferably, particle size of W powder is 1-20 [m; particle size of graphite powder, 1-20 [m; particle size of powder metal, 1-100 jm. Preferably, the agglomerant can be 10 weight percent of petrol-rubber solution, or 10 weight percent of polyethylene glycol with molecular weight 6000 in aqueous solution, or 8 weight percent of polyvinyl alcohol in aqueous solution. Preferably, thickness of hard alloy coating on the casting surface is 0.5-60mm; further preferably, thickness of hard alloy coating on the casting surface is 3-8mm. The thickness of hard alloy coating on holes or grooves of part of the casting is 1-100mm, further preferably, and the thickness of hard alloy coating on holes or grooves of part of the casting is 3-40mm. Preferably, hard alloy coating comprises matrix texture (the coating is formed from molten ferroalloy powder bonding with tungsten carbide, matrix texture is binder phase which is formed from molten ferroalloy powder) and WC and W 2 C particles and alloy cementite distributed on the matrix (part of iron atoms of the cementite are replaced by metallic elements, so that the alloy cementite is formed) , wherein the total volume percent of WC and W 2 C particles is 10-60, and the volume percent of alloy cementite is 1-15, with the remaining matrix texture, and the hardness of alloy coating is HRC50-85. The person skilled in the art will understand that, any combinations of the aforementioned schemes will constitute a part of the present invention. The advantages of the present invention are, good surface quality of the castings, solid combination of coating and castings, high abrasive resistance, not falling off of antifriction alloy layer, and simple technique, suitable for industrial production. Mode of Carrying out the Invention Embodiment 1: Step 1: Weigh out 4.0kg of W powder with the average particle size of 3-4.5pjm, 0.5kg of graphite powder with average particle size of 10pjm and 1.5kg of metal 3 Specification powder with average particle size of 40pm(60%wt of Ni, 5%wt of Cr, 5%wt of Si, 3%wt of B, with the remaining Fe), and mix in a ball mill for 5 hours; Step 2: Add 400g polyvinyl alcohol (with the concentration of 8%wt) aqueous solution to the powder mixture, then stir and mix to produce powder coating paste; Step 3: Coat the surface of EPS foam plastic model with the powder coating paste, with coating thickness 3mm on the casting abrasion working surface; Step4: Spread a 2mm layer of magnesite powder anti-adhesive sand coating on the prepared casting model, and dry in the temperature of 50'C for 4 hours; Step5: Assemble the pouring system, fill dry sand and vibrate the mould, melt Mn13 molten high manganese steel, vacuumize and pour, with the pouring temperature 1470'C and vacuum degree of 0.06Mpa. In the pouring process, high temperature molten steel induces self-propagating synthesis reaction, Step6: when the casting is cooled to 1100 C, the casting sand is shaken out and quenched the casting in 25 C water tank. Then water toughening treat the casting with residual heat, cooling to room temperature and perform surface clearance and polish to obtain surface or part self-propagating synthesis of tungsten carbide based hard alloy coated castings. Hard alloy coating and M13 high manganese steel matrix are metallurgical bonding, with excellent surface quality. The alloy coating's thickness is 3.5mm, with the hardness HRC67.8. Embodiment 2: Step 1: Weigh out 5.0kg of W powder with the average particle size of 3-4.5ptm, 0.2kg of graphite powder with average particle size of 15ptm and 2.8kg of metal powder with average particle size of 50ptm(50%wt of Co, 10%wt of Cr, 5%wt of Si, 3%wt percent of B, with the remaining Fe), and mix in a ball mill for 12 hours; Step 2: Add 600g polyethylene glycol aqueous solution with molecular weight 6000 (with the concentration of 10%wt) to the powder mixture, then stir and mix to produce powder coating paste; Step 3: Coat the surface of EPS foam plastic model with the powder coating paste, with coating thickness 53mm on the casting abrasion working surface; 4 Specification Step4: Spread a about 2mm layer of quartz powder anti-sticking coating on the prepared casting model, and dry in the temperature of 4 0 'C for 13 hours; Step5: Assemble the pouring system, fill dry sand and vibrate the mould, melt low alloy 65Mn molten steel, vacuumize and pour, with the pouring temperature 1560-C and vacuum degree of 0.06Mpa. In the pouring process, high temperature molten steel induces self-propagating synthesis reaction; Step6: when the casting is cooled to 500 C, the casting sand is shaken out and the casting is immediately embedded in quartz sand to perform slow cooling treatment. When the casting is cooled to room temperature, perform surface clearance and polish to obtain surface self-propagating synthesized tungsten carbide based hard alloy coated low alloy steel castings. Hard alloy coating and 65Mn steel matrix are metallurgical bonding, with excellent surface quality. The alloy coating's thickness is 55.2mm, with the hardness HRC76.2. Embodiment 3: Step 1: Weigh out 0.4kg of W powder with the average particle size of 3-4.5ptm, 0.05kg of graphite powder with average particle size of 10ptm and 0.15kg of metal powder with average particle size of 40ptm(60%wt of Ni, 5%wt of Cr, 5%wt of Si, 3%wt of B, with the remaining Fe), and mix in a ball mill for 5 hours; Step 2: Add 40g polyvinyl alcohol (with the concentration of 8%wt) aqueous solution to the powder mixture, then stir and mix to produce powder coating paste; Step 3: Coat the pre-processed holes of EPS foam plastic model with the powder coating paste, with the holes diameter (D10mm and filling depth 35mm; Step4: Spread a about 2mm layer of magnesite powder anti-sticking coating on the prepared casting model, and dry in the temperature of 50'C for 4 hours; Step5: Assemble the pouring system, fill dry sand and vibrate the mould, melt Mn13 molten high manganese steel, vacuumize and pour, with the pouring temperature 1470'C and vacuum degree of 0.06Mpa. In the pouring process, high temperature molten steel induces self-propagating synthesis reaction; Step6: when the casting is cooled to 1100 C, the casting sand is shaken out and 5 Specification quenched the casting in 25 C water tank. Then water toughening treat the casting with residual heat, cooling to room temperature and perform surface clearance and polish to obtain surface or part self-propagating synthesis of tungsten carbide based hard alloy coated castings. Hard alloy coating and M13 high manganese steel matrix are metallurgical bonding, with excellent surface quality. The hard alloy coating pole's diameter is 0 10mm, with the thickness 33mm and the hardness HRC61.8. Embodiment 4: Step 1: Weigh out 25kg of W powder with the average particle size of 3-4.5ptm, 1.0kg of graphite powder with average particle size of 15ptm and 14kg of metal powder with average particle size of 50pm(50%wt of Co, 10%wt of Cr, 5%wt of Si, 3%wt of B, with the remaining Fe), and mix in a ball mill for 15 hours; Step 2: Add 3.0kg polyethylene glycol aqueous solution with molecular weight 6000 (with the concentration of 10%wt) to the powder mixture, and stir and mix to produce powder coating paste; Step 3: Coat the pre-processed grooves of EPS foam plastic model with the powder coating paste, with the grooves width 10mm and filling depth 25mm; Step4: Spread a about 2mm layer of quartz powder anti-sticking coating on the prepared casting model, and dry in the temperature of 40'C for 13 hours; Step5: Assemble the pouring system, fill dry sand and vibrate the mould, melt low alloy 65Mn molten steel, vacuumize and pour, with the pouring temperature 1560-C and vacuum degree of 0.06Mpa. In the pouring process, high temperature molten steel induces self-propagating synthesis reaction; Step6: when the casting is cooled to 500 C, the casting sand is shaken out and the casting is immediately imbedded in quartz sand to perform slow cooling treatment. When the casting is cooled to room temperature, perform surface clearance and polish to obtain surface self-propagating synthesized tungsten carbide based hard alloy coated low alloy steel castings. Hard alloy coating and 65Mn steel matrix are metallurgical bonding, with excellent surface quality. The hard alloy coating groove's width is 10mm, with the thickness 24.5mm and the hardness HRC82.2. 6

Claims

1. A method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface, uses W powder, graphite powder, metal powder as composite material, which is characterized in adopting the following steps: (1) The material comprises 20-80 weight percentage of W powder, 1.5-25 graphite powder, 5-68 metal powder, mixing in a ball mill for 1-24 hours to produce powder mixture; ( 2 ) Add agglomerant to the powder mixture, wherein the mass ratio of agglomerant to powder mixture is 1:10-1:100, then stir and mix to produce powder coating paste; (3) Coat the surface of EPS foam plastic model with the powder coating paste or fill the powder coating paste into pre-processed holes and grooves of the model; (4) Spread a layer of anti-adhesive sand coating on the prepared casting model, and dry it in the temperature range of 40-50'C for 5-18 hours; (5) Melt molten steel in medium frequency induction furnace, and pour, high temperature molten steel induces self-propagating synthesis reaction, that is 3W+2C--WC+W 2 C, to form tungsten carbide based hard alloy phase; (6) Heat treat or water toughening treat the casting with residual heat, cooling to room temperature and perform surface clearance and polish to obtain surface or part self-propagating synthesis of tungsten carbide based hard alloy coated castings.

2. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, the casting technique is vacuum lost foam casting.

3. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, molten steel may be high manganese steel, plain-carbon steel or alloy steel.

4. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, the weight percentage of the powder metal is, 0-60 percent of Ni, 0-30 percent of Cr, 0-11 percent of Si, 0-8 percent of B, 0-60 percent of Co, with the remaining Fe.

5. The method for in situ synthesis of tungsten carbide based hard alloy coating 7 Claims on casting surface according to of in claim 4, characterizes in that, the weight percentage of the powder metal is, 0-60 percent of Ni, 5-30 percent of Cr, 5-11 percent of Si, 3-8 percent of B, 0-60 percent of Co, with the remaining Fe.

6. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, particle size of W powder is 1-20 [m; particle size of graphite powder, 1-20ptm; particle size of powder metal, 1-100 [m.

7. The method for in situ synthesis ofg tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, agglomerant can be 10 weight percent of petrol-rubber solution, or 10 weight percent of polyethylene glycol with molecular weight 6000 in aqueous solution, or 8 weight percent of polyvinyl alcohol in aqueous solution.

8. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, hard alloy coating thickness on the casting surface is 0.5-60mm, and the thickness of hard alloy coating on holes or grooves is 1-100mm.

9. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 8, characterizes in that, thickness of hard alloy coating on the casting surface is 3-8mm, and the thickness of hard alloy coating on holes or grooves is 3-40mm.

10. The method for in situ synthesis of tungsten carbide based hard alloy coating on casting surface according to of in claim 1, characterizes in that, hard alloy coating comprises matrix texture and WC and W 2 C particles and alloy cementite distributed on the matrix, wherein the total volume percent of WC and W 2 C particles is 10-60, and the volume percent of alloy cementite is 1-15, with the remaining matrix texture, and the hardness of alloy coating is HRC50-85. 8