Preparation method of steel strand for prestressed concrete

Abstract

The invention discloses a preparation method of a steel strand for prestressed concrete. By means of phosphorization and liquid nitrogen subzero treatment, the fatigue life of the prestressed steel strand can be effectively prolonged, and when the time of liquid nitrogen subzero treatment is 176 min, the fatigue life of the material reaches the optimal level. Meanwhile, the fatigue strength of the steel strand can be affected by overlong-time liquid nitrogen subzero treatment, so that the time of the liquid nitrogen subzero treatment is controlled to be 30-210 minutes during actual operation.

Description

Technical Field

[0001] The present invention relates to the field of phosphating treatment of metal materials (C23C22 / 07), and in particular to a method for preparing a steel strand for prestressed concrete. Background Art

[0002] Prestressed steel strand is a twisted steel cable consisting of multiple high-strength steel wires, which has been stress-relieved and is suitable for prestressed concrete and similar fields. Prestressed steel strand has the characteristics of high strength, good relaxation performance, and straightness when unfolded.

[0003] A prestressed concrete steel strand is prepared by using the process steps of pickling-phosphating-drawing-die drawing-stabilization treatment-winding in CN114147083A. The tensile strength of the steel strand reaches more than 1700MPa, and the density of the cross-sectional area reaches more than 87.8%. However, the fatigue strength of the above steel strand is poor, which greatly limits the service life of the steel strand. In view of this, it is necessary to design a prestressed concrete steel strand with excellent fatigue strength. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a prestressed concrete steel strand, wherein the prestressed concrete steel strand prepared by the method has an excellent fatigue life.

[0005] The technical solution of the present invention is as follows: A method for preparing a steel strand for prestressed concrete, the method comprising the following steps: pickling - phosphating - liquid nitrogen cryogenic treatment - drawing - die drawing - stabilization treatment - winding; The pickling step is as follows: placing the duplex stainless steel in a 15-20wt% hydrochloric acid solution for pickling for 50-70 minutes at a pickling temperature of 35-40°C; The phosphating step is: phosphating the duplex stainless steel, the composition of the phosphating solution is: 45-50 g / L zinc dihydrogen phosphate, 35-40 mL / L phosphoric acid, 5.8-7.2 g / L sodium fluoride, 1.6-2.5 g / L nickel nitrate, the phosphating temperature is 52-55°C, the total acidity is 55-60 points, the pH value of the phosphating solution is 1.65-1.72, and the phosphating time is 6-8 minutes; The liquid nitrogen cryogenic treatment steps are as follows: after the phosphating layer is solidified, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 30-210 minutes.

[0006] Preferably, the concentration of the hydrochloric acid solution is 15wt%.

[0007] Preferably, the pickling temperature is 40°C.

[0008] Preferably, the pickling time is 50 minutes.

[0009] Preferably, the liquid nitrogen cryogenic treatment time is 176 minutes.

[0010] Preferably, the pH value of the phosphating solution is 1.65.

[0011] Preferably, the total acidity is 55 points.

[0012] The phosphating and liquid nitrogen cryogenic treatment of the present invention can effectively improve the fatigue life of the prestressed steel strand. When the liquid nitrogen cryogenic treatment time is 176 minutes, the fatigue life of the material reaches an optimal level. At the same time, too long a liquid nitrogen cryogenic treatment will have an adverse effect on the fatigue strength of the steel strand. Therefore, in actual operation, the liquid nitrogen cryogenic treatment time should be controlled within 30-210 minutes. DETAILED DESCRIPTION

[0013] The technical effects of the present invention are verified below through specific examples, but the embodiments of the present invention are not limited thereto.

[0014] The preparation method of the prestressed concrete steel strand of the present invention comprises: pickling - phosphating - liquid nitrogen cryogenic treatment - drawing - die drawing - stabilization treatment - wire winding, wherein drawing, die drawing, stabilization treatment and wire winding are all conventional operations in the prior art, and the details can be referred to the patent documents mentioned in the background technology. The improvement of the present invention lies in the organic combination of phosphating treatment and liquid nitrogen cryogenic treatment.

[0015] Example 1 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 30 minutes;

[0016] Example 2 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 60 minutes.

[0017] Example 3 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 120 minutes.

[0018] Example 4 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 176 minutes.

[0019] Example 5 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 210 minutes.

[0020] Comparative Example 1 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: The duplex stainless steel was phosphated, and the composition of the phosphating solution was: 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, 1.6 g / L nickel nitrate, the phosphating temperature was 52 ° C, the total acidity was 60 points, the pH value of the phosphating solution was 1.65, and the phosphating time was 8 minutes.

[0021] Comparative Example 2 Pickling: put the duplex stainless steel into 15wt% hydrochloric acid solution for pickling for 50min at a temperature of 40℃; Phosphating: Phosphating treatment of duplex stainless steel, the composition of phosphating solution is: 45g / L zinc dihydrogen phosphate, 35mL / L phosphoric acid, 5.8g / L sodium fluoride, 1.6g / L nickel nitrate, phosphating temperature is 52℃, total acidity is 60 points, pH value of phosphating solution is 1.65, phosphating time is 8min; Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 300 minutes.

[0022] Next, we performed drawing, die drawing, and stabilization treatment on the experimental samples in Examples 1-5 and Comparative Examples 1-2, and evaluated their fatigue life. The specific method is: applying an alternating force of 10000N to each test sample, and recording the number of times the force was applied until the sample cracked.

[0023] In order to ensure the comparability of each test sample, the drawing, die drawing, stabilization treatment and other steps of each group of samples must be carried out under exactly the same process parameters. The experimental results are shown in Table 1.

[0024] Table 1 Test data of each sample

[0025] It can be seen from Table 1 that the fatigue life of the prestressed steel strand can be effectively improved by the phosphating and liquid nitrogen cryogenic treatment of the present invention. When the liquid nitrogen cryogenic treatment time is 176 minutes, the fatigue life of the material reaches the optimal level. At the same time, too long a liquid nitrogen cryogenic treatment will have an adverse effect on the fatigue strength of the steel strand. Therefore, in actual operation, the liquid nitrogen cryogenic treatment time should be controlled within 30-210 minutes.

[0026] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a steel strand for prestressed concrete, characterized in that: The preparation method comprises the following steps: pickling - phosphating - liquid nitrogen cryogenic treatment - drawing - die drawing - stabilization treatment - wire winding; The pickling step is as follows: placing the duplex stainless steel in a 15-20wt% hydrochloric acid solution for pickling for 50-70 minutes at a pickling temperature of 35-40°C; The phosphating step is: phosphating the duplex stainless steel, the composition of the phosphating solution is: 45-50 g / L zinc dihydrogen phosphate, 35-40 mL / L phosphoric acid, 5.8-7.2 g / L sodium fluoride, 1.6-2.5 g / L nickel nitrate, the phosphating temperature is 52-55°C, the total acidity is 55-60 points, the pH value of the phosphating solution is 1.65-1.72, and the phosphating time is 6-8 minutes; The liquid nitrogen cryogenic treatment steps are as follows: after the phosphating layer is solidified, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 30-210 minutes.

2. A preparation method according to claim 1, characterized in that: The concentration of the hydrochloric acid solution is 15wt%.

3. A preparation method according to claim 1, characterized in that: The pickling temperature is 40°C.

4. A preparation method according to claim 1, characterized in that: The pickling time is 50 minutes.

5. A preparation method according to claim 1, characterized in that: The liquid nitrogen cryogenic treatment time is 176 minutes.

6. A preparation method according to claim 1, characterized in that: The pH value of the phosphating solution is 1.

65.

7. A preparation method according to claim 1, characterized in that: The total acidity is 55 points.

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