A high-temperature fast-firing based steel plate normalizing heat treatment production method

Abstract

This application discloses a production method for normalizing heat treatment of steel plates based on high-temperature rapid heating. The conventional normalizing heat treatment temperature for steel plates is the austenitizing temperature +30~50℃. This patent is an enhanced improvement of the traditional normalizing process, increasing the heating rate and shortening the heating and holding time at a temperature higher than the conventional normalizing temperature (austenitizing temperature +60~100℃). This allows the steel plate to quickly reach the austenitizing state, followed by cooling in still or slightly flowing air. Without reducing strength, a more uniform microstructure is obtained, improving impact toughness, resulting in better impact resistance and finer grain size.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, specifically to a normalizing heat treatment production method based on high-temperature rapid firing. Background Technology

[0002] Traditional normalizing processes typically operate at temperatures between 860 and 880°C. The furnace time varies depending on the thickness of the steel plate being normalized in a conventional heat treatment furnace. Medium-thick plates can achieve complete austenitization at 1.8 times their thickness. For steel plates thicker than 50mm, the furnace time for complete austenitization is longer, requiring at least twice the thickness, and the normalizing heating rate is relatively slow (2-8°C / min). For E-grade plates or steel plates with higher impact requirements, the performance cannot be met. Adding grain-refining alloys can be used, but this increases costs. Therefore, there is an urgent need to optimize current heat treatment processes without altering the composition to meet higher performance requirements. Summary of the Invention

[0003] Based on the above-mentioned existing technologies, the present invention aims to provide a novel high-strength, high-toughness, and wear-resistant steel based on QP treatment. This method is used to improve the low-temperature toughness of low-alloy wear-resistant steel while reducing the hardness by a small amount.

[0004] The technical solution of the present invention: A method for producing steel plates using high-temperature rapid firing heat treatment includes the following steps: preparing the steel plate to be normalized; calculating the theoretical austenitizing temperature based on the composition; determining the conventional normalizing temperature (austenitizing temperature + 30~50℃) based on the austenitizing temperature; and specifying the furnace time (1.8~2.2 times the plate thickness) based on the thickness and heat treatment capacity. The high-temperature rapid firing normalizing temperature (austenitizing temperature + 60~100℃), higher than the conventional normalizing temperature, results in a furnace time 10~50 min shorter and a holding time 5~10 min shorter than the conventional normalizing holding time. After normalizing in the furnace, the strength, impact resistance, and microstructure properties are compared between the two heat treatment processes.

[0005] Compared with existing technologies, the present invention achieves the following technical effects: optimizing the heat treatment process without changing the steel plate composition; improving the impact toughness of the steel plate without a significant decrease in strength, and achieving finer grain size. Attached Figure Description

[0006] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0007] Figure 1 This is a comparison diagram of the metallographic structures of the examples and the control examples.

[0008] Figure 2 This is a comparison diagram of the metallographic structures of the examples and the control examples.

[0009] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0011] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0012] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0013] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0014] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0015] 1. Composition: The alloy composition of the steel, by mass percentage, is C=0.16%~0.18%, Si=0.3%~0.4%, Mn=1.2%~1.7%, P≤0.02%, S≤0.01%, Nb≤0.05%, V≤0.05%, Ti≤0.03%, Cr≤0.3%, Mo≤0.08%, Ni≤0.3%, Cu≤0.3%, with the remainder being Fe and unavoidable impurities. The actual composition is C=0.17%, Si=0.35%, Mn=1.56%, P≤0.0157%, S≤0.0011%, Nb≤0.0468%, V≤0.0267%, Ti≤0.0179%, Cr≤0.2006%, Mo≤0.0074%, Ni≤0.0146%.

[0016] 2. Rolling process: The furnace tapping temperature is 1160-1250℃. The initial rolling temperature for roughing is ≥1050℃, and the final rolling temperature is ≥980℃. The roughing reduction must be at least three passes of ≥30mm, and the intermediate slab thickness must be ≥1.5 times the finished product thickness. The initial rolling temperature for finishing is ≥890℃, and the final rolling temperature is 670-700℃.

[0017]

[0018] 3. Normalizing process: The calculated austenitizing temperature of the steel plate is 845.2℃.

[0019]

[0020] Total furnace time calculation method: heating coefficient Order thickness + insulation time.

[0021] 4. Performance data: (Sampling location for steel plates: sampling at the tail 1 / 4 position; processing location for strength and impact samples: 1 / 4 position in the thickness direction.) Delivery condition strength standards: yield strength ≥305MPa, tensile strength 490-620MPa, elongation ≥20%. Minimum transverse impact at -20℃: 29J, average impact: 41J.

[0022] Maximum mold-welded strength standards: Yield strength ≥ 305 MPa, tensile strength 490-620 MPa, elongation ≥ 20%. Minimum transverse impact strength at -20℃: 29 J; average impact strength: 41 J. (Mold welding process: 606-620℃, heating rate 80℃ / s, holding time 600 min, air cooling after removal from the furnace.)

[0023] As shown in the table above: Example 55927689100, produced using the high-temperature rapid-firing normalizing heat treatment method of this patent, has an average impact performance of 130~155J in both the delivered and mold-welded states. Steel plate 55928026100, produced using a conventional normalizing heat treatment process, has an impact performance ≤100J and a mold-welded state impact performance ≤50J. Therefore, the impact performance of the steel plate produced using the high-temperature rapid-firing normalizing heat treatment method of this patent is significantly better than that of steel plates produced using conventional heat treatment processes. Example 55927689100 has better strength in the delivered state than steel plate 55928026100 produced using a normal normalizing heat treatment process, while the strength difference between the two in the mold-welded state is not significant. Both heat treatment methods produce steel plates with a ferrite + pearlite microstructure. The steel plate produced by the high-temperature rapid normalizing heat treatment method of this patent has a grain size of 8-8.5 grade, which is higher than the grain size of 9 grade steel plate produced by conventional normalizing heat treatment process. The grains are finer and more uniform in size.

[0024] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing steel plates using high-temperature rapid firing normalizing heat treatment, characterized in that: By increasing the heating rate and shortening the heating and holding time at temperatures higher than conventional normalizing temperatures, the steel sheet can be rapidly brought to an austenitic state. It is then cooled in still or slightly flowing air to obtain a finer, more uniform microstructure, thus improving impact toughness. The process includes the following steps: preparing the steel plate to be normalized, calculating the theoretical austenitizing temperature based on the composition, and determining the conventional normalizing temperature and time, and the high-temperature rapid-fired normalizing temperature and time based on the austenitizing temperature. After normalizing in the furnace, comparing the strength, impact, and microstructure properties under the two heat treatment processes.

2. The method for producing steel plates based on high-temperature rapid firing normalizing heat treatment according to claim 1, characterized in that: Normalizing temperature = austenitizing temperature + 60~100℃, which is higher than conventional normalizing temperature. The furnace time for high-temperature rapid normalizing is 10~50 minutes shorter than that for conventional normalizing, and the holding time is 5~10 minutes shorter than that for conventional normalizing.

3. The method for producing steel plates based on high-temperature rapid firing normalizing heat treatment according to claim 1, characterized in that: High-temperature fast-heating steel plates do not lose strength compared to conventional normalizing, have better impact resistance, and produce finer grains.

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