Method for preparing stainless reinforcing steel bar resistant to corrosion of chloride ions

Abstract

This present invention provides a method for preparing a stainless reinforcing steel bar resistant to corrosion of chloride ions, and belongs to the technical field of corrosion-resistant materials. This method particularly comprises the steps of: selecting a reinforcing steel bar blank, and performing oil removing, rust removing, water washing, and drying treatments on the surface of the reinforcing steel bar blank to be treated, or directly performing sand blasting or shot blasting on a reinforcing steel bar blank whose surface is only slightly rusted; placing the reinforcing steel bar blank in a chromium-containing environment, and keeping at a certain temperature for a certain time such that chromium in the environment is capable of diffusing into the surface of the reinforcing steel bar blank to form a chromium-containing diffusion layer, wherein an area in the diffusion layer where the weight content of Cr exceeds 12% meets the basic component requirements for a stainless steel, and this area is the effective diffusion layer described in this invention; and performing cooling treatment on the heat diffusion treated reinforcing steel bar. In this invention, a reinforcing steel bar blank is pre-formed, a heat diffusion technique is optimized, and the corrosion resistance to chloride ions of the stainless reinforcing steel bar of this invention is superior to that of the 316L stainless reinforcing steel bar.

Claims

1. A method for preparing a stainless reinforcing steel bar resistant to corrosion of chloride ions, comprising the following steps of: (a) selecting a reinforcing steel bar blank, and performing oil removing, rust removing, water washing, and drying treatments on the surface of the reinforcing steel bar blank to be treated, or directly performing sand blasting or shot blasting on a reinforcing steel bar blank whose surface is only slightly rusted; wherein the reinforcing steel bar blank has the following chemical ingredients in terms of percentage by weight: C: 0.01-0.08 wt %, Mn: 0.10-0.50 wt %, P: 0.04 wt %, S: 0.03 wt %, Si: 0.2-0.6 wt %, Cr: 2.0-8.0 wt %, Mo: 1.50-2.50 wt %, Cu: 0.08-0.35 wt %, Ti: 0.10-0.40 wt %, and Fe and inevitable impurities as the balance; (b) performing heat diffusion by placing the reinforcing steel bar blank in a chromium-containing environment, and keeping at a certain temperature for a certain time such that chromium in the environment is capable of diffusing into the surface of the reinforcing steel bar blank to form a chromium-containing diffusion layer, in which an effective diffusion layer having a chromium content exceeding 12% has a thickness exceeding 10 m; and (c) performing cooling treatment on the reinforcing steel bar which has been treated by heat diffusion; wherein after the heat diffusion treatment is completed and when a heat diffusion treatment container is cooled to 100 C. or less along with a heat diffusion treatment furnace, the heat diffusion treatment container is withdrawn from the heat diffusion treatment furnace and subjected to air cooling to room temperature continuously, and then the reinforcing steel bar is separated from a heat diffusion powder.

2. The method for preparing the stainless reinforcing steel bar resistant to corrosion of chloride ions as claimed in claim 1, wherein said heat diffusion in step (b) comprises the steps of: charging the surface treated reinforcing steel bar blank and a heat diffusion powder into the heat diffusion container, wherein the total volume of the reinforcing steel bar blank and the heat diffusion powder does not exceed 95% of the volume of the heat diffusion container; placing and heating the heat diffusion container charged with the reinforcing steel bar blank and the heat diffusion powder in a heating furnace, wherein a heating speed is controlled at 4-6 C. per minute; maintaining the temperature constant for 2.0-4.0 hours when the temperature reaches 800-950 C.; and then stopping heating.

3. The method for preparing the stainless reinforcing steel bar resistant to corrosion of chloride ions as claimed in claim 2, wherein the heat diffusion powder is formulated from 45% of a 100-200 mesh aluminum oxide powder, 50% of a 100-200 mesh chromium-iron alloy powder containing 70% of chromium, and 5% of ammonium chloride in terms of percentage by weight.

4. The method for preparing the stainless reinforcing steel bar resistant to corrosion of chloride ions as claimed in claim 2, wherein the heat diffusion container is rotated at a rotation speed of 5-20 rounds per minute in a process of heating and maintaining the temperature constant so as to perform heat treatment on the reinforcing steel bar within the heat treatment container to allow uniform heating while increasing the possibility of collision between the heat diffusion powder and the reinforcing steel bar blank.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 is a sectional morphology of an Example of this invention.

(2) FIG. 2 is a graph of element line scanning analysis results.

DETAILED DESCRIPTION OF THE INVENTION

(3) The ingredients of the reinforcing steel bar blanks of the Examples and the Comparative Example of this invention can be seen in Table 1.

(4) TABLE-US-00001 TABLE 1 The chemical ingredient analysis results of the main alloy elements in Examples of reinforcing steel bar blanks in this invention and those of the Comparative Example (wt %) Sample No. C Mn Si Cr Mo Cu Ti A (Comparative 0.196 1.57 0.57 0.08 / 0.01 0.002 Example) B 0.031 0.15 0.24 2.11 2.08 0.09 0.27 C 0.055 0.13 0.26 2.08 2.11 0.32 0.26 D 0.039 0.13 0.24 7.9 2.05 0.11 0.28 E 0.062 0.14 0.25 7.8 2.13 0.35 0.26

(5) The Comparative Example was an industrially produced normal HRB400 reinforcing steel bar. The process flow of the reinforcing steel bar blank was: molten iron desulfurization pretreatment, smelting in an electric furnace or a top and bottom combined blown converter, refining outside of furnace, continuous casting, cast blank heating, rolling, and cold bed air cooling.

(6) The surface treated reinforcing steel bar blanks of the Comparative Example and the Examples, as well as a heat diffusion powder, were charged into a heat diffusion container. Here, the heat diffusion powder was formulated from 45% of an aluminum oxide powder (150 mesh), a 50% of a chromium-iron alloy powder (containing about 70% of chromium, 150 mesh), and 5% of ammonium chloride by weight. The heat diffusion container charged with the reinforcing steel bar blank and a diffusion treatment agent were placed and heated in a heating furnace, wherein the heating speed was controlled at about 5 C. per minute, the temperature was maintained constant for 2.0 hours when the temperature reached 930 C., and then the heating was stopped. After the completion of the treatment of heat diffusion, the heat diffusion treatment container was withdrawn from the heat diffusion treatment furnace when the heat diffusion treatment container was cooled to 100 C. or less along with said heat diffusion treatment furnace, air cooling was continued to room temperature, and the reinforcing steel bar was separated from the heat diffusion powder. The main process parameters of the samples of the Examples of this invention and the Comparative Example subjected to the treatment of heat diffusion were as shown in Table 2.

(7) TABLE-US-00002 TABLE 2 The testing results of the effective diffusion layers where the weight content of chromium was above 12% in the Examples and the Comparative Example after heat diffusion treatment. Pitting Resistance Average Average Cr Equivalent Number Thickness Content (PREN = % Cr + Sample No. (m) (wt %) 3.3 % Mo) A (Comparative <3 m / / Sample) B 10 17.51 24.4 C 11 24.76 31.7 D 12 19.63 26.4 E 18 29.12 36.2

(8) The results of the contents of main alloy elements in effective diffusion layers of the Examples of this invention detected by EDS can be seen in Table 3.

(9) TABLE-US-00003 TABLE 3 Results of contents of main alloy elements in the effective diffusion layers of Examples in this invention detected by EDS Example C Mn Si Cr Mo Cu Ti B 0.059 0.14 0.22 19.32 1.96 0.08 0.21 C 0.062 0.11 0.23 25.1 2.05 0.29 0.22 D 0.047 0.13 0.23 20.35 1.82 0.09 0.25 E 0.079 0.12 0.25 29.66 2.11 0.31 0.23

(10) A sectional morphology of an Example of this invention was shown in FIG. 1.

(11) The element line scanning analysis results of an Example of this invention were shown in FIG. 2.