A finishing pass system for stainless steel composite threaded rebar, a rolling method and a stainless steel composite threaded rebar

Abstract

The application discloses a finishing groove system of stainless steel composite threaded steel bars, a rolling method and the stainless steel composite threaded steel bars, and belongs to the technical field of metallurgy. According to the process characteristics of the stainless steel composite steel bars, the k1 and k2 finishing grooves for rolling conventional hot-rolled ribbed steel bars are improved and optimized, specifically, the size parameters of the k2 groove are adjusted, and the processing method of the k1 groove is improved, the improved k1 and k2 grooves are used in cooperation, and the stainless steel composite steel bars produced can guarantee that the stainless steel cladding layer fully covers the base body, and the stainless steel cladding layer and the base body are well combined.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a finishing groove system for stainless steel composite threaded steel bars, a rolling method and the stainless steel composite threaded steel bar. BACKGROUND

[0002] The stainless steel composite threaded steel bar is generally obtained by hot rolling of an inner core and a cladding layer on the surface of the inner core, and the two metals can reach a metallurgical bonding state, which can meet the requirement that the stainless steel and the carbon steel are not separated during use, greatly enhancing the corrosion resistance. The weight of the stainless steel accounts for 10%-20% of the total weight, and the cost is only about 25% of that of solid stainless steel bars, which can fully play the corrosion resistance of stainless steel, reduce the cost of using full stainless steel, and greatly prolong the service life of the building. In the construction of seaports, the stainless steel composite threaded steel bar has a very wide application prospect in the sea-mixed and sea-cured reinforced concrete engineering.

[0003] The rolling process of the stainless steel composite threaded steel bar is generally consistent with that of the conventional threaded steel bar, but the opening rolling temperature is about 50-80 DEG C higher than that of the conventional threaded steel bar. Under this condition, due to the difference in rolling temperature and the difference between the dual-phase metal and the single-phase metal, the original groove system cannot be used to obtain the stainless steel composite threaded steel bar with a good cladding layer.

[0004] In view of the above problems, it is necessary to provide a finishing groove system for stainless steel composite threaded steel bars, a rolling method and the stainless steel composite threaded steel bar. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a finishing groove system for stainless steel composite threaded steel bars, a rolling method and the stainless steel composite threaded steel bar.

[0006] The technical problem of the present application is solved by using the following technical scheme.

[0007] The present application provides a finishing groove system for stainless steel composite threaded steel bars, which is composed of a pre-product groove k2 and a finished product groove k1, wherein the pre-product groove k2 is a flat ellipse, and the structural parameters are as follows:

[0008] The notch width B=(1.18-1.2)×b; mm

[0009] The slot bottom straight line width L=(0.13-0.15)×B; mm

[0010] The groove width-height ratio B / H=2.6-2.8;

[0011] The material type width-height ratio b / H=2.0-2.3;

[0012] The chamfering arc radius r is 2-5 mm.

[0013] The hole type cross-sectional area S is (1.18-1.22) * nominal cross-sectional area; mm 2

[0014] Wherein:

[0015] b - incoming width;

[0016] H - hole type height;

[0017] The finished hole type k1 is provided with a transverse rib, and the processing parameters are as follows:

[0018] The angle alpha between the transverse rib side surface and the steel bar surface is not less than 45 degrees.

[0019] The angle beta between the transverse rib and the steel bar axis is not less than 45 degrees.

[0020] The transverse rib height h is 1.2-1.3 times the lower limit value of the standard corresponding specification of the carbon steel threaded steel bar.

[0021] The application also provides a method for rolling the stainless steel composite threaded steel bar by using the above-mentioned finishing hole type system, which comprises: heating and rolling the large round billet obtained by assembling the inner core and the cladding layer to obtain the stainless steel composite threaded steel bar.

[0022] The application also provides a stainless steel composite threaded steel bar rolled according to the above-mentioned rolling method, and the interface between the cladding layer and the inner core of the stainless steel composite threaded steel bar is metallurgically combined, the thickness of the cladding layer is greater than or equal to 0.8 mm, and the diameter of the inner core is 20-40 mm.

[0023] Preferably, when the material of the inner core is HRB400E, the stainless steel composite threaded steel bar satisfies: the yield strength is 420-450 MPa, the tensile strength is 580-620 MPa, the elongation is greater than or equal to 12%, the maximum force total elongation is greater than or equal to 19%, and the strength yield ratio is greater than or equal to 1.35.

[0024] Preferably, when the material of the inner core is HRB500E, the stainless steel composite threaded steel bar satisfies: the yield strength is 520-550 MPa, the tensile strength is 690-740 MPa, the elongation is greater than or equal to 11%, the maximum force total elongation is greater than or equal to 19%, and the strength yield ratio is greater than or equal to 1.25.

[0025] The application has the following beneficial effects:

[0026] The finishing hole type system, the rolling method and the stainless steel composite threaded steel bar provided by the application improve and optimize the k1 and k2 finishing hole types for rolling conventional hot-rolled ribbed steel bars, improve the shortcoming that the stainless steel cladding layer cannot fully cover the base body when stainless steel composite steel bars are produced, and greatly improve the product quality. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0028] Figure 1 Schematic diagram for structure design of finished product hole k2;

[0029] Figure 2 Schematic diagram for structure design of finished product hole k1;

[0030] Figure 3 Actual photos of the stainless steel composite threaded steel bars prepared in Example 1, wherein the actual photos of products of different batches are shown in a photo and b photo;

[0031] Figure 4 Actual photos of the stainless steel composite threaded steel bars prepared in Example 2;

[0032] Figure 5 Actual photos of the stainless steel composite threaded steel bars prepared in Example 3;

[0033] Figure 6 Metallographic structure photos of the stainless steel composite threaded steel bars prepared in Example 1;

[0034] Figure 7 Actual photos of the stainless steel composite threaded steel bars prepared in Example 1 after pickling, wherein the actual photos of different angles after pickling are shown in a photo and b photo;

[0035] Figure 8 Actual photos of the stainless steel composite threaded steel bars prepared in Comparative Example 1 after pickling, wherein the actual photos of different angles after pickling are shown in a photo and b photo. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not mentioned by the manufacturers are all conventional products that can be purchased in the market.

[0037] The finishing hole system, the rolling method and the stainless steel composite threaded steel bar provided by the embodiments of the present application will be described in detail as follows.

[0038] In a first aspect, embodiments of the present invention provide a precision rolling die system for stainless steel composite threaded steel bars. The precision rolling die system consists of a pre-finished die k2 and a finished die k1, wherein the pre-finished die k2 is a flat ellipse, and its configuration parameters are as follows:

[0039] The slot width B = (1.18 - 1.2) × b; mm

[0040] The width of the straight section at the bottom of the trench is L = (0.13 - 0.15) × B; mm

[0041] The aperture width-to-height ratio B / H = 2.6-2.8;

[0042] The aspect ratio of the material, b / H, is 2.0-2.3.

[0043] Chamfer radius r = 2-5 mm

[0044] The cross-sectional area of ​​the aperture, S, is calculated as (1.18 - 1.22) × nominal cross-sectional area (mm). 2

[0045] in:

[0046] b - Incoming material width;

[0047] H - Hole height;

[0048] The finished hole type k1 has transverse ribs, and the processing parameters are as follows:

[0049] The angle α between the side of the transverse rib and the surface of the reinforcing bar shall not be less than 45°;

[0050] The angle β between the transverse rib and the axis of the reinforcing bar shall not be less than 45°;

[0051] The height h of the transverse rib is 1.2-1.3 times the lower limit of the corresponding specification of carbon steel threaded steel bar.

[0052] According to the process requirements for rolling composite rebar, considering the poor thermal conductivity of the double-layer metal, to ensure sufficient heating of the double-layer metal in the round billet, the billet must be heated in the furnace for at least 180 minutes, and the initial rolling temperature must be above 1050℃. This initial rolling temperature is about 50℃-80℃ higher than that of conventional rebar production. Rolling within this temperature range allows for better utilization of the ductility of the stainless steel cladding, enabling a good metallurgical bond with the matrix during rolling and achieving the required product quality. However, if the original rolling pass, especially the finishing pass, is used during the rolling process, a good bond between the core and the cladding cannot be achieved. In severe cases, the stainless steel cladding may not completely cover the matrix, resulting in "exposed points," which seriously affects product quality.

[0053] The inventors propose a method for improving the finishing pass shape in view of the above problems, which is to optimize and improve the parameters of the pre-finished pass k2 and the finished pass k1, and to determine the accurate pass shape of the k2 pass through the above standard control of the finishing pass system. The pass shape composed of the structure and the proportion can ensure that k2 is rolled in k1 to achieve a suitable reduction, ensure that the finished cross rib and longitudinal rib can meet the requirements of the national standard, and at the same time, minimize the wear of the k1 pass, improve the service life of the finished pass, and facilitate the full coverage of the stainless steel material composite layer on the cross rib and the longitudinal rib. In order to ensure that the cross rib and the longitudinal rib of the threaded steel bar can be fully covered, after the k1 pass is optimized and designed, the k1 pass and the k2 pass are used in combination to improve the disadvantage that the stainless steel coating cannot fully cover the base body when producing stainless steel composite steel bars, so that the stainless steel composite steel bars can ensure that the stainless steel coating fully covers the base body, and the combination of the stainless steel coating and the base body is good, which greatly improves the product quality.

[0054] In an optional embodiment, the nominal cross-sectional area of the pre-finished pass k2 is obtained according to the corresponding nominal cross-sectional area of the specified size in the GBT 1499.2-2018 Hot-Rolled Ribbed Steel Bars for Reinforced Concrete Part 2.

[0055] The following is the nominal cross-sectional area according to the corresponding nominal cross-sectional area of the specified size in the GBT 1499.2-2018 Hot-Rolled Ribbed Steel Bars for Reinforced Concrete Part 2:

[0056] GB / T 1499.2-2018

[0057]

[0058] In an optional embodiment, the size of the side wall arc R of the pre-finished pass k2 is automatically obtained according to the tangency of the side wall arc, the straight line segment of the groove bottom and the chamfer arc when drawing.

[0059] In an optional embodiment, the angle a between the cross rib side surface of the finished pass k1 and the surface of the steel bar is 46°-50°; and the angle β between the cross rib and the axis of the steel bar is 60°-65°.

[0060] In an optional embodiment, the top of the cross rib of the finished pass k1 of the stainless steel composite threaded steel bar is a circular arc angle, preferably a 0.3-0.5 mm chamfered circular arc angle.

[0061] In a second aspect, the embodiments of the present application also provide a method for rolling a stainless steel composite threaded steel bar by using the above-mentioned finishing pass system for the stainless steel composite threaded steel bar, which comprises: heating and rolling a large round billet obtained by assembling an inner core and a cladding layer to obtain a stainless steel composite threaded steel bar.

[0062] In an optional embodiment, the method comprises the following steps: vacuumizing and welding the coating layer and the inner core to form a composite large round blank; and heating the composite large round blank and then rough rolling, intermediate rolling and finish rolling to obtain a Ф12mm-Ф40mm stainless steel composite threaded steel bar, wherein the pass system of the finish rolling mill used for finish rolling is the above-mentioned finish rolling pass system.

[0063] In an optional embodiment, the material of the coating layer is stainless steel and the material of the inner core is carbon steel. The material of the inner core includes but is not limited to carbon steel, vessel steel and pipeline steel, and the material of the coating layer includes but is not limited to 304 or 316.

[0064] In an optional embodiment, the rough rolling temperature is 1030-1095℃ and the finish rolling temperature is 950-1055℃.

[0065] In an optional embodiment, the heating comprises a preheating section, a heating section and a soaking section, the temperature of the preheating section is below 700℃, the temperature of the heating section is 1100-1230℃, the temperature of the soaking section is 1150-1200℃, and the total heating time is above 100min.

[0066] The embodiment of the present application also provides a rolling method of the above-mentioned stainless steel composite threaded steel bar. Compared with the traditional rolling method of the stainless steel composite threaded steel bar, the rough rolling temperature is about 50-80℃ higher than that of the conventional threaded steel bar, and the composite large round blank is rough rolled, intermediate rolled and finish rolled by using the above-mentioned finish rolling pass system provided by the embodiment of the present application, so that the composite threaded steel bar with metallurgical bonding between the inner core and the coating layer can be finally obtained, the coating layer can be ensured to fully cover the transverse ribs and the longitudinal ribs, and the stainless steel composite threaded steel bar with good quality can be obtained.

[0067] In a third aspect, the embodiment of the present application also provides a stainless steel composite threaded steel bar rolled by the above-mentioned rolling method, the interface between the coating layer and the inner core of the stainless steel composite threaded steel bar is metallurgically bonded, the thickness of the coating layer is ≥0.8mm, and the diameter of the inner core is 20-40mm.

[0068] Preferably, when the material of the inner core is HRB400E, the stainless steel composite threaded steel bar satisfies: the yield strength is 420-450MPa, the tensile strength is 580-620MPa, the elongation is ≥12%, the maximum total elongation is ≥19%, and the strength-yield ratio is ≥1.35.

[0069] Preferably, when the material of the inner core is HRB500E, the stainless steel composite threaded steel bar satisfies: the yield strength is 520-550MPa, the tensile strength is 690-740MPa, the elongation is ≥11%, the maximum total elongation is ≥19%, and the strength-yield ratio is ≥1.25.

[0070] The features and performances of the present application are further described in detail in combination with the following embodiments.

[0071] Example 1

[0072] The bloom material is rolled into round steel and used as a core material, and the core material is HRB400E, and a 400MPa grade diameter 25mm specification stainless steel composite reinforcing bar is prepared. The core of the composite round steel blank is a round steel blank with a diameter of 160mm and a length of 10m, and a 316 type stainless steel seamless pipe with a wall thickness of 8mm is used as a cladding layer. The remaining gap of the other end face is sealed by ion welding in a vacuum state, and the cladding layer + core is vacuumized and welded to form a composite large round blank.

[0073] The temperature requirements of the composite large round blank are shown in the following table:

[0074] Charging method Preheating zone temperature °C Heating zone temperature °C Soaking zone temperature °C Heating time min Cold charging 700 1180 1200 150

[0075] The rolling temperature requirements are shown in the following table:

[0076] Charging method Start rolling temperature °C Finish rolling temperature °C Temperature on top of the cooling bed °C Cold charging 1080 1030 950

[0077] The rolling process is as follows:

[0078] The rolling mill is configured as 8 rough rolling mill groups, 6 intermediate rolling mill groups and 4 finishing rolling mill groups, the 18th mill is the finished product, the 15th and 16th mills are skipped, and the finishing rolling pass system used is composed of a pre-finished product pass k2 and a finished product pass k1. Among them, the pre-finished product pass k2 is a flat ellipse, see Figure 1 , the Ф25mm specification k2 incoming material width b = 43.7mm; the pass height is H = 20mm, and the pre-finished product pass k2 is designed as follows:

[0079] The pass width B = 1.19 x 43.7 = 52; mm

[0080] The groove bottom straight line segment width L is determined according to the pass width B, height H and groove bottom straight line segment length L values, L = 0.15 x 52 = 7.8; mm

[0081] The pass width-height ratio B / H = 2.6;

[0082] The material pass width-height ratio b / H = 2.2;

[0083] The chamfer arc radius r = 3; mm

[0084] The pass side wall arc R: when drawing, the side wall arc is tangent to the groove bottom straight line segment and the chamfer arc r, according to the "tangent, tangent, tangent", the side wall arc size can be automatically generated value is 16.7; mm.

[0085] Cross-sectional area S: according to the specification and corresponding nominal cross-sectional area specified in "GBT 1499.2-2018 Steel for Reinforced Concrete Part 2 Hot Rolled Ribbed Steel Bar", S = 1.21 x 490.9 = 594 Nominal cross-sectional area; mm 2 .

[0086] Referring to Figure 2 , the processing method of the k1 pass is as follows:

[0087] Adjust the size of the milling machine tool bit, and the sharp corner part of the bit needs to be rounded by 0.3mm;

[0088] The angle a between the transverse rib side surface and the surface of the steel bar is 46°;

[0089] The depth control of the transverse rib when milling the groove is 0.2mm larger than the national standard value of the corresponding specification;

[0090] The angle β between the transverse rib and the axis of the steel bar is 63°.

[0091] The performance and structure of the composite steel bar prepared by the present example meet the requirements, the interface between the cladding layer and the core of the stainless steel composite threaded steel bar is metallurgical bonding, the average thickness of the cladding layer is 0.8mm, and the cladding layer is uniform without dew point defects.

[0092] Example 2

[0093] The square billet is rolled into round steel by blooming and is used as core material billet, the core material is HRB400E, and a 400MPa grade diameter 28mm specification stainless steel composite steel bar is prepared. The core of the composite round steel billet is a round steel billet with a diameter of 160mm and a length of 10m, a 316 type stainless steel seamless pipe with a wall thickness of 10mm is used as a cladding layer, and the remaining gap of the other end face is sealed by ion welding in a vacuum state. The cladding layer + core is vacuumized and welded to form a composite large round billet.

[0094] The temperature requirements for the composite large round billet are shown in the following table:

[0095] Charging method Preheating zone temperature °C Heating zone temperature °C Soaking zone temperature °C Heating time min Cold charging 700 1180 1200 150

[0096] The rolling temperature requirements are shown in the following table:

[0097] Charging method Start rolling temperature °C Finish rolling temperature °C Temperature on top of the cooling bed °C Cold charging 1080 1030 950

[0098] The rolling process is as follows:

[0099] The rolling mill is configured with 8 rough rolling mill groups, 6 medium rolling mill groups and 4 finishing rolling mill groups, the 18th mill is used to form the finished product, the 11th, 12th, 15th and 16th mills are bypassed, and the finishing pass system used is composed of a finished product front pass k2 and a finished product pass k1, wherein the finished product front pass k2 is a flat ellipse, referring to Figure 1, Ф28mm specification k2 incoming width b = 46.5mm; the pass height is H = 22.5mm, and the product front pass k2 is designed as follows:

[0100] The pass width B = 1.19 * 46 = 54.74; mm

[0101] The groove bottom straight segment width L is determined according to the pass width B, the height H and the groove bottom straight segment length L value, L = 0.15 * 55.3 = 8.3; mm

[0102] The pass width-height ratio B / H = 2.5;

[0103] The material type width-height ratio b / H = 2.1;

[0104] The chamfer arc radius r = 4; mm

[0105] The pass side wall arc R: when drawing, the side wall arc is tangent to the groove bottom straight segment and the chamfer arc r, and the side wall arc size is automatically generated as 22; mm.

[0106] The cross-sectional area S: according to the specification and the corresponding nominal cross-sectional area specified in "GBT1499.2-2018 Steel Reinforced Concrete Part 2 Hot Rolled Ribbed Steel", S = 1.21 * 615.8 = 745 Nominal cross-sectional area; mm 2 .

[0107] Referring to Figure 2 , the processing method of the k1 pass is as follows:

[0108] Adjust the size of the milling machine tool bit, and the bit tip corner part needs to be chamfered by 0.4mm arc angle;

[0109] The angle a between the transverse rib side surface and the surface of the steel bar is 46°;

[0110] The depth control of the transverse rib when milling the groove is 0.3mm larger than the national standard value of the corresponding specification;

[0111] The angle β between the transverse rib and the axis of the steel bar is 63°.

[0112] The composite steel bar prepared by the example has the required performance and organization, the interface between the cladding layer and the inner core of the stainless steel composite threaded steel bar is metallurgically combined, the average thickness of the cladding layer is 0.9mm, and the cladding layer is uniform without dew point defects.

[0113] Example 3

[0114] The square billet is rolled into round steel as a core material billet, and the core material is HRB500E, and a 500MPa grade stainless steel composite reinforcing bar with a diameter of 25mm is prepared. The core of the composite round billet is a round billet with a diameter of 160mm and a length of 10m, and a 316 type stainless steel seamless pipe with a wall thickness of 8mm is used as a cladding layer. The remaining gap of the other end face is sealed by ion welding in a vacuum state, and the cladding layer + core is vacuumized and welded to form a composite large round billet.

[0115] The temperature requirements of the composite large round billet are shown in the following table:

[0116] Charging method Preheating zone temperature °C Heating zone temperature °C Soaking zone temperature °C Heating time min Cold charging 700 1180 1200 150

[0117] The rolling temperature requirements are shown in the following table:

[0118] Charging method Start rolling temperature °C Finish rolling temperature °C Temperature on top of the cooling bed °C Cold charging 1080 1030 950

[0119] The rolling process is as follows:

[0120] The rolling mill is configured as 8 rough rolling mill groups, 6 medium rolling mill groups and 4 finishing rolling mill groups, the 18th mill is used to form the finished product, the 15th and 16th mills are bypassed, and the finishing rolling pass system used is composed of a finished product front pass k2 and a finished product pass k1, wherein the finished product front pass k2 is a flat ellipse, see Figure 1 , the Ф25mm specification k2 incoming material width b = 43.7mm; the pass height is H = 20mm, and the finished product front pass k2 is designed as follows:

[0121] The pass width B = 1.19 x 43.7 = 52; mm

[0122] The groove bottom straight line segment width L is determined according to the pass width B, height H and groove bottom straight line segment length L values, L = 0.15 x 52 = 7.8; mm

[0123] The pass width-height ratio B / H = 2.6;

[0124] The material pass width-height ratio b / H = 2.2;

[0125] The chamfer arc radius r = 3; mm

[0126] The pass side wall arc R: when drawing, the side wall arc is tangent to the groove bottom straight line segment and the chamfer arc r, according to the "tangent, tangent, tangent", the side wall arc size is automatically generated as 16.7; mm.

[0127] The cross-sectional area S: according to the specification and corresponding nominal cross-sectional area specified in "GBT1499.2-2018 Steel Reinforced Concrete Steel Part 2 Hot Rolled Ribbed Steel", S = 1.21 x 490.9 = 594 nominal cross-sectional area; mm 2

[0128] Referring to Figure 2 The processing method of the k1 pass diagram is as follows:

[0129] The size of the milling machine tool bit is adjusted, and the tip corner part needs to be reversed by 0.3mm arc angle;

[0130] The included angle a between the transverse rib side surface and the steel bar surface is 46°;

[0131] The depth control of the transverse rib when milling the groove is 0.2mm larger than the national standard value of the corresponding specification;

[0132] The included angle b between the transverse rib and the steel bar axis is 63°.

[0133] The composite steel bars prepared by the example meet the performance and structure requirements, the interface between the cladding layer and the inner core of the stainless steel composite threaded steel bar is metallurgical bonding, the average thickness of the cladding layer is 1mm, and the cladding layer is uniform without dew point defects.

[0134] The mechanical properties of the 25mm and 28mm specifications of HRB400E and HRB500E stainless steel composite steel bars prepared in the above examples 1 to 3 are shown in the following table.

[0135]

[0136] As can be seen from the above table, the performance of the products obtained in examples 1 to 3 can meet the requirements of the national standard, the average thickness of the cladding layer is 0.8-1mm, the cladding layer is uniform without dew point defects, the quality is good, and the appearance of the product obtained in example 1 is shown in Figure 3 , wherein, a figure and b figure are the physical pictures of products of different batches, the appearance of the product obtained in example 2 is shown in Figure 4 , and the appearance of the product obtained in example 3 is shown in Figure 5 It can be seen that the overall appearance quality of the cladding stainless steel products prepared in different batches is good, the cladding stainless steel is uniformly distributed without defects such as pits and holes, further observation of the cross section of the composite threaded steel shows that the cladding layer and the inner core of carbon steel are well combined, which indicates that the combination strength of the two is high, the carbon steel-stainless steel composite threaded steel product obtained in example 1 is observed by metallographic microscope, and the result is shown in Figure 6 , the left side is the carbon steel inner core, and the right side is the stainless steel cladding layer, it can be seen that the thickness of the stainless steel cladding layer on the surface of the carbon steel is 1.05mm and 1.00mm respectively, which indicates that the stainless steel cladding layer on the surface of the carbon steel is very uniform, at the same time, the edge of the combination of carbon steel and stainless steel is clear and defect-free, and the two are well combined, that is, the carbon steel / stainless steel composite threaded steel product with strong metallurgical bonding can be obtained by the method of the example. The pickling detection of the carbon steel-stainless steel composite threaded steel product obtained in example 1 is carried out, and the appearance of the product after pickling process is shown in Figure 7It can be seen that the product has a stainless steel silver appearance without corrosion points, which again shows that the stainless steel coating on the surface of the carbon steel is evenly distributed, and the appearance and quality of the product are good.

[0137] Comparative Example 1

[0138] Similar to the steps of Example 1, the only difference is that the notch width B = 1.3 x b and the groove bottom straight line width L = 0.25 x B in the parameters of the k2 pass before the finished product, the pass width height ratio B / H = 2.4, the finished pass k1 has a transverse rib, the angle a between the transverse rib side and the surface of the steel bar is 55°, the angle b between the transverse rib and the axis of the steel bar is 70°, and the rolling method is the same as that of Example 1. After detection, the average thickness of the stainless steel composite threaded steel bar surface coating is 0.3-1 mm, and the coating thickness fluctuates greatly. After pickling the stainless steel coating, some of the steel bars have immersion corrosion points on the surface, and the coating has local dew point defects, as shown in Figure 8 , which shows that the finishing pass is not suitable, causing the stainless steel coating on the surface to be uneven, and in severe cases, the stainless steel coating cannot completely wrap the base body, resulting in a "dew point" situation, which seriously affects the product quality and cannot meet the use requirements.

[0139] Comparative Example 2

[0140] Similar to the steps of Example 2, the only difference is that the notch width B = 1.3 x b and the pass width height ratio B / H = 2.85 in the parameters of the k2 pass before the finished product, the finished pass k1 has a transverse rib, the angle a between the transverse rib side and the surface of the steel bar is 50°, the angle b between the transverse rib and the axis of the steel bar is 55°, and the rolling method is the same as that of Example 2. The results are as follows: the average thickness of the stainless steel composite threaded steel bar surface coating is 0.2-0.8 mm, and the coating thickness fluctuates greatly, and the coating also has local dew point defects.

[0141] Comparative Example 3

[0142] Similar to the steps of Example 3, the only difference is that the notch width B = 1.1 x b and the pass width height ratio B / H = 2.3 in the parameters of the k2 pass before the finished product, the finished pass k1 has a transverse rib, the angle a between the transverse rib side and the surface of the steel bar is 48°, the angle b between the transverse rib and the axis of the steel bar is 50°, and the rolling method is the same as that of Example 3. After detection, the average thickness of the stainless steel composite threaded steel bar surface coating is 0.2-1 mm, and the coating thickness fluctuates greatly, and the coating also has local dew point defects.

[0143] From the experimental results of the above examples and comparative examples, it can be seen that the properties of the stainless steel composite threaded steel bars prepared in the examples can meet the requirements of the national standard, the average thickness of the coating is 0.8-1mm, the coating is uniform and free of dew point defects, and the quality is good. When the parameters of the pre-product hole and the finished product hole in the comparative examples change, the thickness of the surface coating of the stainless steel composite threaded steel bar changes greatly, that is, dew point defects may occur in the local coating, which seriously affects the product quality and causes great economic loss.

[0144] In conclusion, the embodiment of the present application provides a finishing hole system, a rolling method and a stainless steel composite threaded steel bar. By optimizing the finishing hole system and the processing parameters of k1 and k2, the rolling is performed by using the optimized finishing hole system, which improves the defect that the stainless steel coating cannot fully cover the base body during the production of the stainless steel composite steel bar, and greatly improves the product quality. The continuous large-scale production of carbon steel-stainless steel composite threaded steel bars can be performed.

[0145] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A precision rolling die system for stainless steel composite threaded steel bars, characterized in that, The finishing rolling pass system consists of a pre-finishing pass k2 and a finished product pass k1, wherein the pre-finishing pass k2 is a flat ellipse, and its parameters are as follows: The slot width B = (1.18 - 1.2) × b; mm The width of the straight section at the bottom of the trench is L = (0.13 - 0.15) × B; mm The aperture width-to-height ratio B / H = 2.6-2.8; The aspect ratio (b / H) of the material is 2.0-2.

3. Chamfer radius r = 2-5 mm The cross-sectional area of ​​the aperture, S, is calculated as (1.18 - 1.22) × nominal cross-sectional area (mm). 2 in: b - Incoming material width; H - Hole height; The finished hole type k1 has transverse ribs, and the processing parameters are as follows: The angle α between the side of the transverse rib and the surface of the reinforcing bar shall not be less than 45°; The angle β between the transverse rib and the axis of the reinforcing bar shall not be less than 45°; The height h of the transverse rib is 1.2-1.3 times the lower limit of the corresponding specification of carbon steel threaded steel bar; The nominal cross-sectional area of ​​the pre-drilled hole type k2 is obtained according to the specifications and corresponding nominal cross-sectional area specified in "GBT1499.2-2018 Steel for Reinforced Concrete - Part 2: Hot-rolled Ribbed Steel Bars".

2. The finishing rolling pass system according to claim 1, characterized in that, The dimension of the side wall arc R of the finished front hole type k2 is automatically generated during the drawing process based on the fact that the side wall arc is tangent to the straight line segment of the groove bottom and the chamfer arc respectively.

3. The finishing rolling pass system according to claim 1, characterized in that, The angle α between the side of the transverse rib of the finished front hole type k1 and the surface of the reinforcing bar is 46°-50°; the angle β between the transverse rib and the axis of the reinforcing bar is 60°-65°.

4. The finishing rolling pass system according to claim 1, characterized in that, The top of the transverse rib of the finished stainless steel composite threaded steel bar hole type k1 is a rounded corner.

5. The finishing rolling pass system according to claim 4, characterized in that, The top of the transverse rib of the finished stainless steel composite threaded steel bar with hole type k1 is rounded with a radius of 0.3-0.5mm.

6. A method for rolling stainless steel composite threaded steel bars using the precision rolling pass system according to any one of claims 1-5, characterized in that, It includes: The large round billet obtained by assembling the inner core and the cladding is heated and rolled to obtain stainless steel composite threaded steel bars.

7. The method according to claim 6, characterized in that, Includes the following steps: The cladding and inner core are vacuum-sealed and welded to form a composite large round billet; the composite large round billet is then heated and subjected to rough rolling, intermediate rolling and finish rolling to prepare stainless steel composite threaded steel bars with diameters of Ф12mm-Ф40mm, wherein the die system of the finish rolling mill used for finish rolling is the finish rolling die system as described in any one of claims 1-5.

8. The method according to claim 7, characterized in that, The inner core is made of carbon steel, and the cladding is made of stainless steel.

9. The method according to claim 7, characterized in that, The heating process includes a preheating section, a heating section, and a homogenizing section. The temperature of the preheating section is below 700℃, the temperature of the heating section is between 1100-1230℃, the temperature of the homogenizing section is between 1150-1200℃, and the total heating time is between 100-120 minutes.

10. The method according to claim 9, characterized in that, The initial rolling temperature is 1030-1095℃, and the final rolling temperature is 950-1055℃.

11. A stainless steel composite threaded steel bar rolled using the method described in any one of claims 6-10, characterized in that, The interface between the cladding and the core is metallurgically bonded, the thickness of the cladding is ≥0.8mm, and the diameter of the core is 20-40mm.

12. The stainless steel composite threaded steel bar according to claim 11, characterized in that, When the inner core material is HRB400E, the stainless steel composite threaded steel bar meets the following requirements: yield strength of 420-450MPa, tensile strength of 580-620MPa, elongation ≥12%, total elongation at maximum force ≥19%, and strength-to-yield ratio ≥1.

35.

13. The stainless steel composite threaded steel bar according to claim 11, characterized in that, When the inner core material is HRB500E, the stainless steel composite threaded steel bar meets the following requirements: yield strength of 520-550MPa, tensile strength of 690-740MPa, elongation ≥11%, total elongation at maximum force ≥19%, and strength-to-yield ratio ≥1.25.

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