Method for preparing steel strand for prestressed concrete

Abstract

A method for preparing a steel strand for prestressed concrete. The phosphating and liquid nitrogen cryogenic treatment described herein effectively improves the fatigue life of the prestressed steel strand. When the cryogenic treatment lasts for 176 minutes, the fatigue life of the material reaches an optimal level. However, prolonged cryogenic treatment can adversely affect the fatigue strength of the steel strand. Therefore, in practice, the cryogenic treatment should be limited to 30-210 minutes.

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 cable consisting of multiple high-strength steel wires that has been stress-relieved. It is suitable for use in prestressed concrete and similar applications. Prestressed steel strand features high strength, good relaxation properties, and maintains a straight position when extended.

[0003] A prestressed concrete steel strand was produced using the process steps of pickling, phosphating, drawing, die drawing, stabilization, and winding described in CN114147083A. The strand achieved a tensile strength exceeding 1700 MPa and a cross-sectional area density exceeding 87.8%. However, the strand's fatigue strength was poor, significantly limiting its service life. Consequently, there is a need to design a prestressed concrete steel strand with superior 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 solutions of the present invention are as follows:

[0006] 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;

[0007] The pickling step comprises: 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;

[0008] The phosphating step is as follows: 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;

[0009] 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.

[0010] Preferably, the concentration of the hydrochloric acid solution is 15 wt %.

[0011] Preferably, the pickling temperature is 40°C.

[0012] Preferably, the pickling time is 50 minutes.

[0013] Preferably, the liquid nitrogen cryogenic treatment time is 176 minutes.

[0014] Preferably, the pH value of the phosphating solution is 1.65.

[0015] Preferably, the total acidity is 55 points.

[0016] The phosphating and liquid nitrogen cryogenic treatment of the present invention can effectively improve the fatigue life of prestressed steel strands. When the liquid nitrogen cryogenic treatment lasts for 176 minutes, the fatigue life of the material reaches the optimal level. At the same time, excessively long liquid nitrogen cryogenic treatments can adversely affect the fatigue strength of the steel strands. Therefore, in actual operation, the liquid nitrogen cryogenic treatment time should be controlled within 30-210 minutes. DETAILED DESCRIPTION

[0017] The technical effects of the present invention are verified below through specific examples, but the embodiments of the present invention are not limited thereto.

[0018] The present invention's method for preparing prestressed concrete steel strand comprises the following steps: pickling, phosphating, liquid nitrogen cryogenic treatment, drawing, die drawing, stabilization, and winding. Drawing, die drawing, stabilization, and winding are conventional operations in the prior art, and details can be found in the patent documents mentioned in the background. The present invention's improvement lies in the organic combination of phosphating and liquid nitrogen cryogenic treatment.

[0019] Example 1

[0020] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0021] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0022] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 30 minutes;

[0023] Example 2

[0024] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0025] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0026] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 60 minutes.

[0027] Example 3

[0028] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0029] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0030] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 120 minutes.

[0031] Example 4

[0032] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0033] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0034] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 176 minutes.

[0035] Example 5

[0036] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0037] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0038] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 210 minutes.

[0039] Comparative Example 1

[0040] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0041] Phosphating: duplex stainless steel was phosphated. 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 min.

[0042] Comparative Example 2

[0043] Pickling: Place the duplex stainless steel in a 15wt% hydrochloric acid solution for pickling for 50 minutes at a temperature of 40°C.

[0044] Phosphating: duplex stainless steel was phosphated with a phosphating solution consisting of 45 g / L zinc dihydrogen phosphate, 35 mL / L phosphoric acid, 5.8 g / L sodium fluoride, and 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 min.

[0045] Liquid nitrogen cryogenic treatment: After the phosphating layer solidifies, the duplex stainless steel is placed in liquid nitrogen for cryogenic treatment for 300 minutes.

[0046] Next, we subjected the experimental samples of Examples 1-5 and Comparative Examples 1-2 to drawing, die drawing, and stabilization treatments, and evaluated their fatigue life. Specifically, we applied an alternating force of 10,000 N to each test sample and recorded the number of times the force was applied until cracks occurred.

[0047] To ensure comparability among the test samples, the drawing, die drawing, and stabilization steps for each group of samples were performed under exactly the same process parameters. The experimental results are shown in Table 1.

[0048] Table 1 Test data of each sample

[0049]

[0050] As can be seen from Table 1, the phosphating and liquid nitrogen cryogenic treatment of the present invention effectively improves the fatigue life of prestressed steel strands. When the liquid nitrogen cryogenic treatment lasts for 176 minutes, the fatigue life of the material reaches the optimal level. However, excessively long liquid nitrogen cryogenic treatments can adversely affect the fatigue strength of the steel strands. Therefore, in practice, the liquid nitrogen cryogenic treatment time should be controlled within 30-210 minutes.

[0051] 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 - winding; The pickling step comprises: 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 as follows: 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 120-210 minutes; When an alternating force of 10,000 N is applied to the prestressed concrete steel strand obtained by the preparation method, the force applied more than 3,000 times to generate cracks.

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

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.

Images