Tool steel belt for measuring tape and preparation method of tool steel belt

Abstract

The invention discloses a tool steel strip for a measuring tape and a preparation method thereof, belongs to the technical field of metallurgy, and realizes that high-carbon steel forms a uniform and fine sorbite structure in a hot rolling state by accurately controlling hot rolling deformation and a cooling system, so that the strength, the elastic limit and the fatigue life of a material are improved, meanwhile, good plasticity is kept, the technological process is simplified, and the production cost is reduced. The production cost is reduced.

Description

Technical Field

[0001] This invention relates to a steel strip, specifically a tool steel strip for measuring tapes and its preparation method, belonging to the field of metallurgical technology. Background Technology

[0002] As a portable measuring tool widely used in construction, engineering, and home decoration, the core functional component of a measuring tape is a flexible tape that can be repeatedly stretched and retracted. This tape must withstand high-frequency bending, stretching, and rewinding stresses during use. With the increasing demands for accuracy and durability in measuring tools from fields such as construction, home decoration, and industrial measurement, the market demand for high-strength, highly elastic, and long-life measuring tapes continues to grow.

[0003] Currently, high-carbon, high-quality carbon tool steel is widely used as the base material for mid-to-high-end measuring tapes both domestically and internationally. Typical grades include SK5 and SK4 steels in the Japanese standard JIS G4401, with carbon contents ranging from 0.85% to 0.95% and 0.90% to 1.00%, respectively. These are eutectoid or hypereutectoid components, and with appropriate treatment, they can achieve high strength and wear resistance. However, in practical applications, the traditional process for producing SK4 / SK5 hot-rolled narrow strip steel suffers from a lack of effective control over the phase transformation process during hot rolling. This results in the formation of a coarse pearlite + network cementite structure, with large grains and wide interlamellar spacing (>500nm). This makes the material hard and brittle, with low plasticity and toughness. It is prone to cracking, fracture, and unstable springback during cold working. During frequent stretching and rewinding, problems such as "permanent deformation" and "decreased springback force" are likely to occur. The root cause lies in the coarse material structure and the mismatch between strength and toughness.

[0004] Therefore, developing a tool steel strip for measuring tapes that can overcome the above defects and its preparation method has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a tool steel strip for measuring tape and its preparation method. The method optimizes the cooling path in the hot rolling process to realize the transformation of the microstructure of steel into fine lamellar sorbite, which significantly improves the strength, elastic limit and toughness of hot-rolled narrow strip steel. At the same time, it simplifies the subsequent processing flow and meets the requirements of high-end measuring tape for high strength and elasticity, stable springback, long service life and precision forming of materials.

[0006] To solve the above technical problems, the present invention provides a tool steel strip for measuring tapes, which comprises the following components by mass percentage: C: 0.95-1.00%, Si: 0.20-0.30%, Mn: 0.35-0.50%, P≤0.015%, S≤0.010%, Cr: 0.16-0.25%, Ni≤0.20%, Cu≤0.20%, with the balance being Fe and unavoidable impurities, and the sum of the above components being 100%.

[0007] The technical solution further defined in this invention is: Furthermore, the aforementioned steel strip for measuring tape comprises the following components by mass percentage: C: 0.96%, Si: 0.23%, Mn: 0.42%, P: 0.010%, S: 0.005%, Cr: 0.18%, Ni: 0.06%, Cu: 0.08%, with the balance being Fe and unavoidable impurities, and the sum of the above components is 100%.

[0008] This invention also designs a method for preparing tool steel strip for measuring tapes, adjusting the final rolling temperature and optimizing the post-rolling rapid cooling process, specifically including the following steps: (1) Under mill load conditions, roughing is carried out in 10 passes with an initial rolling temperature of 1080-1120℃ and a total reduction of 85%; finishing is carried out in 12 passes with a final rolling temperature of 850-900℃, preferably 880℃, a final rolling speed of 11m / s, and a total reduction of 94%. (2) After rolling, the rolled steel strip is fed onto a flat chain for controlled cooling treatment. The cooling rate is controlled at 50-70℃ / s, the temperature of the flat chain is 700-750℃, preferably 720℃, the speed of the flat chain is 0.53-0.57m / s, preferably 0.55m / s, and the swing frequency is 470-490rpm / min, preferably 480rpm / min. (3) The coiling temperature is 600-650℃. The coil is quickly coiled and placed in a slow cooling pit for slow cooling. The residual temperature is used for low-temperature self-tempering, which softens the material and reduces its hardness while improving the uniformity of the structure. Finally, the coil is packaged and labeled to obtain the final finished steel strip.

[0009] Furthermore, in the aforementioned method for preparing the tool steel strip for measuring tape, the rough rolling process in step (1) specifically consists of 3 passes of vertical rollers and 7 passes of horizontal rollers.

[0010] In the aforementioned method for preparing the tool steel strip for measuring tape, step (1) specifically involves 12 passes of precision rolling, which consists of 2 passes of vertical rolls and 9 passes of horizontal rolls.

[0011] In the aforementioned method for preparing the tool steel strip for measuring tape, in step (2), before production, the flat chain is preheated with ordinary steel strip. Preferably, three Q235 ordinary steel strips are used to preheat the flat chain.

[0012] Technical effect: The present invention uses ordinary steel strip to preheat the flat chain, which can reduce the temperature drop rate of the lower surface of the steel strip, reduce the temperature difference between the upper and lower surfaces, and ensure the uniformity of the temperature of the entire surface of the steel strip.

[0013] In the aforementioned method for preparing the tool steel strip for measuring tape, the temperature in the slow cooling pit in step (3) is ≥250℃.

[0014] In the aforementioned method for preparing steel strip for measuring tape, the matrix structure of the hot-rolled steel strip is sorbite, with an average lamellar spacing of ≤300nm, and the mechanical properties are tensile strength of 900~950Ma, with an average of 925MPa, and elongation of 12~14%, with an average of 13%.

[0015] The beneficial effects of this invention are: This invention aims to solve the problems of coarse microstructure, unstable performance, and reliance on annealing in traditional processes, and provides a high-efficiency, energy-saving, and high-performance tool steel strip for measuring tapes and its preparation technology. By precisely controlling the hot rolling deformation and cooling regime, a uniform and fine sorbitic microstructure is formed in the hot-rolled state of high-carbon steel, which significantly improves the strength, elastic limit, and toughness of hot-rolled narrow strip steel, simplifies the process, reduces production costs, and meets the requirements of high-end measuring tapes for high strength, high elasticity, stable springback, long service life, and precision forming. At the same time, it promotes the localization and high-end development of precision measuring tool materials in my country.

[0016] The method of this invention can be directly applied to existing equipment without requiring upgrades. By adjusting the final rolling temperature and optimizing the post-rolling rapid cooling process, the steel strip achieves a fine lamellar sorbite structure in the hot-rolled state, significantly improving the material's strength, elastic limit, and fatigue life while maintaining good plasticity. Furthermore, it reduces the need for one annealing step in downstream cold rolling, lowering processing costs and further meeting the requirements of downstream users. Specifically, the method is as follows: (1) The matrix structure is sorbite, and the pearlite lamellar spacing is ≤300nm (see Appendix). Figure 2 and appendix Figure 3 ); (2) The tensile strength of the material is increased to over 900 MPa and the elongation is increased to 13%, which improves the strength while maintaining good plasticity; (3) Downstream users can reduce one annealing process, reducing the cost per ton of steel by about 300 yuan. Attached Figure Description

[0017] Figure 1 This is a CCT curve of hypereutectoid steel in an embodiment of the present invention; Figure 2 This is a metallographic diagram of the steel in an embodiment of the present invention; Figure 3 This is an electron microscope image of pearlite tissue in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them; the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example 1

[0019] This embodiment provides an SK4 steel strip for measuring tape tools. It is produced by refining a steel billet using raw materials whose chemical composition by weight percentage includes the following components: C: 0.96%, Si: 0.23%, Mn: 0.42%, P: 0.010%, S: 0.005%, Cr: 0.18%, Ni: 0.06%, Cu: 0.08%, with the balance being Fe and unavoidable impurities. The sum of all components is 100%. The pearlite phase transformation initiation point A1 of the SK4 steel was simulated and determined using existing JMatPro material property simulation software to be 732℃ (see attached figure). Figure 1 As shown in the figure, this provides a theoretical basis for formulating the experimental plan. The raw materials are sequentially subjected to electric furnace smelting, LF refining, RH vacuum and continuous casting to obtain steel billets to be processed. The billet size is 250*300*9800mm. The billet is then sequentially subjected to heating, descaling, controlled rolling, controlled cooling and high-temperature coiling to obtain finished steel strip. The pre-obtained finished steel strip rolling specification is 2.10*380mm.

[0020] The method for preparing the tool steel strip for the measuring tape mentioned above specifically includes the following steps: (1) During the controlled rolling stage, the furnace exit temperature is reasonably controlled and the rolling is carried out under the rolling mill load. The initial rolling temperature is controlled at 1080-1120℃. The roughing rolling is carried out in 10 passes (3 vertical rolls + 7 horizontal rolls), with a total reduction rate of 85% and a billet thickness of about 37.5mm after roughing. At the same time, the rolling process is optimized, the final rolling temperature is controlled at 880℃, the final rolling speed is increased from 9m / s to 11m / s, the rolling time is shortened, and the temperature drop is reduced. The finishing rolling is carried out in 12 passes (2 vertical rolls + 9 horizontal rolls), with a total reduction rate of 94% and a finished product thickness of 2.1mm. (2) After the controlled rolling stage, the rolled semi-finished steel strip is sent to the flat chain for controlled cooling treatment. Before the controlled cooling stage, three Q235 ordinary strips are used to preheat the flat chain to reduce the temperature difference between the upper and lower surfaces. The cooling rate is controlled at 70℃ / s, the target temperature of the upper flat chain is controlled at 720℃, the speed of the flat chain is 0.55m / s, and the swing frequency is 480rpm / min. (3) The material is wound in the temperature range of 600 to 650℃ for 90 seconds. Then it is placed in a slow cooling pit for slow cooling. The temperature in the slow cooling pit is ≥250℃. The material is tempered at low temperature by relying on the residual temperature. This softens the material and reduces its hardness while improving the uniformity of the structure. Finally, the material is packaged and labeled to obtain the final finished steel strip.

[0021] The products obtained from the examples were sampled, tested, and analyzed. Compared to the original process, which involved high-temperature final rolling at 920-950℃ followed by slow cooling at a controlled cooling rate of 20-40℃ / s, the steel strip produced under this invention has a matrix structure of pearlite + network cementite, with an average lamellar spacing >500nm, tensile strength of 800-880MPa (average 840MPa), and elongation of 10-12% (average 11%). The hot-rolled steel strip produced under this invention has a matrix structure of sorbite, with an average lamellar spacing ≤300nm (see appendix). Figure 2 and appendix Figure 3 The mechanical properties include a tensile strength of 900-950 MPa (average 925 MPa) and an elongation of 12-14% (average 13%). The product performance has been significantly improved, exhibiting good strength and toughness, and can meet the user's requirement for direct cold rolling without annealing.

[0022] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A steel strip for measuring tapes, characterized in that: The steel strip comprises the following components by mass percentage: C: 0.95-1.00%, Si: 0.20-0.30%, Mn: 0.35-0.50%, P≤0.015%, S≤0.010%, Cr: 0.16-0.25%, Ni≤0.20%, Cu≤0.20%, with the balance being Fe and unavoidable impurities, and the sum of the above components is 100%.

2. The steel strip for measuring tapes according to claim 1, characterized in that: The steel strip comprises the following components by mass percentage: C: 0.96%, Si: 0.23%, Mn: 0.42%, P: 0.010%, S: 0.005%, Cr: 0.18%, Ni: 0.06%, Cu: 0.08%, with the balance being Fe and unavoidable impurities, and the sum of the above components is 100%.

3. A method for preparing a tool steel strip for measuring tapes as described in claim 1 or 2, characterized in that: Adjusting the final rolling temperature and optimizing the post-rolling rapid cooling process includes the following steps: (1) Under the rolling mill load conditions, the roughing mill is rolled in 10 passes with an initial rolling temperature of 1080-1120℃ and a total roughing reduction of 85%; the finishing mill is rolled in 12 passes with a final rolling temperature of 850-900℃ and a final rolling speed of 11m / s and a total finishing reduction of 94%. (2) After rolling, the rolled steel strip is sent to a flat chain for controlled cooling treatment. The cooling rate is controlled at 50-70℃ / s, the temperature of the flat chain is 700-750℃, the speed of the flat chain is 0.53-0.57m / s, and the swing frequency is 470-490rpm / min. (3) The coiling temperature is 600-650℃. The coil is quickly coiled and placed in a slow cooling pit for slow cooling. It is then tempered at low temperature by relying on the residual temperature. Finally, it is packaged and labeled to obtain the final finished steel strip.

4. The method for preparing the tool steel strip for measuring tape according to claim 3, characterized in that: In step (1), the roughing process of 10 passes specifically consists of 3 passes of vertical rolls and 7 passes of horizontal rolls.

5. The method for preparing the tool steel strip for measuring tape according to claim 3, characterized in that: In step (1), the 12-pass finishing rolling specifically consists of 2 passes of vertical rolls and 9 passes of horizontal rolls.

6. The method for preparing the tool steel strip for measuring tape according to claim 3, characterized in that: Before production in step (2), the flat chain is preheated using ordinary strip steel.

7. The method for preparing the tool steel strip for measuring tape according to claim 3, characterized in that: In step (3), the temperature inside the slow cooling pit is ≥250℃.

8. The method for preparing the tool steel strip for measuring tape according to claim 3, characterized in that: The matrix structure of the prepared hot-rolled steel strip is sorbite with an average lamellar spacing of ≤300nm. The mechanical properties include a tensile strength of 900-950 MPa (average 925 MPa) and an elongation of 12-14% (average 13%).

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