Micro-nano composite powder dedicated for laser repair of tiny cracks in stainless steel surface

Abstract

A micro-nano composite powder dedicated for laser repair of tiny crack on stainless steel surface, includes 3 wt %-7 wt % of nano-WC, 0.5 wt %-2 wt % of nano-Al.sub.2O.sub.3, 0.2 wt %-0.8 wt % of micro-V powder and the balance of micro stainless steel powder. The stainless steel powder includes 0.08 wt % of C, 0.5 wt % of Si, 1.46 wt % of Mn, 0.03 wt % of P, 0.005 wt % of S, 19 wt % of Cr, 9.5 wt % of Ni, 0.5 wt % of Mo and the balance of Fe. The micro and nano powders are mixed through ball milling and mixed with anhydrous ethanol. The composite powder is suitable for laser repair of tiny crack on the surface of stainless steel part with high toughness requirement. After laser repair, the composite powder can be fused with the substrate, the repaired layer and the substrate are metallurgically bonded at the interface, the repaired layer contains fine grains, and therefore the compatibility and fracture property of the repaired layer are improved.

Claims

1. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces, wherein the composite powder comprises 3 wt %-7 wt % of nano-WC, 0.5 wt %-2 wt % of nano-Al.sub.2O.sub.3, 0.2 wt %-0.8 wt % of micro-V powder and the balance of micro stainless steel powder, wherein the micro and nano powders are fully mixed through ball milling and further uniformly mixed after being blended with anhydrous ethanol; the stainless steel powder comprises 0.08 wt % of C, 0.5 wt % of Si, 1.46 wt % of Mn, 0.03 wt % of P, 0.005 wt % of S, 19 wt % of Cr, 9.5 wt % of Ni, 0.5 wt % of Mo and the balance of Fe.

2. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces claim 1, wherein the nano-WC powder has a particle diameter of 50-80 nm and a purity of 99.99%.

3. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 1, wherein the nano-Al.sub.2O.sub.3 powder has a particle diameter of 30-50 nm and a purity of 99.99%.

4. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 1, wherein the stainless steel powder has a particle diameter of 30-50 μm and a purity of 99.9%.

5. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 3, wherein the stainless steel powder has a particle diameter of 30-50 μm and a purity of 99.9%.

6. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 1, wherein the V powder has a particle diameter of 20-50 μm and a purity of 99.9%.

7. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 3, wherein the V powder has a particle diameter of 20-50 μm and a purity of 99.9%.

8. A micro-nano composite powder dedicated for the laser repair of tiny cracks on stainless steel surfaces of claim 4, wherein the V powder has a particle diameter of 20-50 μm and a purity of 99.9%.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a strain contour in Y-direction eyy at the tip of a crack in a laser repaired stainless steel specimen.

(2) FIG. 2 is a strain contour in Y-direction eyy at the tip of a crack in an unrepaired stainless steel specimen.

(3) FIG. 3 is a diagram showing the interface between the laser repaired layer and the substrate of stainless steel.

(4) FIG. 4 is a diagram showing the microstructure in the laser repaired layer of stainless steel.

DETAILED DESCRIPTION

(5) The present invention is described in detail below through specific embodiments. The embodiments are implemented on the premise of the present invention and detailed implementation mode and specific operation procedures are given, but the protection scope of the present invention is not limited to the following embodiments.

(6) Embodiment 1: comprising 5 wt % of nano-WC (50-80 nm), 1 wt % of nano-Al.sub.2O.sub.3 (30-50 nm), 0.5 wt % of micro-V powder (20-50 μm) and the balance of micro stainless steel powder (30-50 μm), wherein the stainless steel powder comprises 0.08 wt % of C, 0.5 wt % of Si, 1.46 wt % of Mn, 0.03 wt % of P, 0.005 wt % of S, 19 wt % of Cr, 9.5 wt % of Ni, 0.5 wt % of Mo and the balance of Fe. With the above formulation, the powders are fully mixed through ball milling and further uniformly mixed after being blended with anhydrous ethanol.

(7) Prior to laser repair process, drying treatment is conducted to the composite powder at a temperature of 150° C. for 2 hours; the area to be repaired is sanded with #400-2000 abrasive papers in sequence, cleaned with anhydrous ethanol, and then dried; proportioned composite powder is uniformly applied to a tiny crack to be repaired with a thickness of about 0.8-1.2 mm to ensure a flat surface and low porosity. When repairing, the processing parameters are laser power of 1.5-3 KW, laser repair duration of 1-2 s, spot diameter of 3.0-5.0 mm, and defocusing amount of 220-240 mm.

(8) After laser repair, the fracture parameters COD of the compact tensile specimen under each load are reduced, wherein the results of Y-direction strain eyy at the tip of a crack in a laser repaired specimen and an unrepaired specimen measured by digital image correlation software under a load of 20 kN are respectively shown in FIG. 1 and FIG. 2. It can be seen from the figures that the Y-direction strain value eyy at the tip of a crack in a laser repaired specimen is smaller than that in an unrepaired specimen. According to the calculation of the digital image correlation software VIC-2D, the fracture parameter COD of the specimen is reduced by 21.9%, indicating that the fracture property of the specimen is improved after repair. In addition, the substrate and the composite powder are metallurgically bonded, as shown in FIG. 3, with no crack or impurity in the bonded area. Meanwhile, as shown in FIG. 4, the grains in the repaired layer at the tip of the crack are refined, and the compactness of the microstructure is significantly improved.

(9) Embodiment 2: comprising 3 wt % of nano-WC (50-80 nm), 2 wt % of nano-Al.sub.2O.sub.3 (30-50 nm), 0.8 wt % of micro-V powder (20-50 μm) and the balance of micro stainless steel powder (30-50 μm), wherein the stainless steel powder comprises 0.08 wt % of C, 0.5 wt % of Si, 1.46 wt % of Mn, 0.03 wt % of P, 0.005 wt % of S, 19 wt % of Cr, 9.5 wt % of Ni, 0.5 wt % of Mo and the balance of Fe. With the above formulation, the powders are fully mixed through ball milling and further uniformly mixed after being blended with anhydrous ethanol. The method for laser repair of crack is the same as that using Embodiment 1. The interface is metallurgically bonded after repair; the grains in the repaired layer are refined, and the compactibility of the microstructure is improved; the fracture parameter COD of the specimen is reduced by 19.3% under a load of 20 kN, and the fracture property is improved.

(10) Embodiment 3: comprising 7 wt % of nano-WC (50-80 nm), 0.5 wt % of nano-Al.sub.2O.sub.3 (30-50 nm), 0.2 wt % of micro-V powder (20-50 μm) and the balance of micro stainless steel powder (30-50 μm), wherein the stainless steel powder comprises 0.08 wt % of C, 0.5 wt % of Si, 1.46 wt % of Mn, 0.03 wt % of P, 0.005 wt % of S, 19 wt % of Cr, 9.5 wt % of Ni, 0.5 wt % of Mo and the balance of Fe. With the above formulation, the powders are fully mixed through ball milling and further uniformly mixed after being blended with anhydrous ethanol. The method for laser repair of crack is the same as that using Embodiment 1. The interface is metallurgically bonded after repair; the grains in the repaired layer are refined, and the compactibility of the microstructure is improved; the fracture parameter COD of the specimen is reduced by 18.6% under a load of 20 kN, and the fracture property is improved.