A rolling process for refining the grain size of medium carbon steel
By controlling process parameters such as rolling temperature and reduction, the grain size of medium carbon steel is refined, solving the problems of increased costs and environmental pollution caused by the quenching and tempering process of medium carbon steel, and achieving low-cost and efficient grain size improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BENGANG STEEL PLATES CO LTD
- Filing Date
- 2026-06-30
- Publication Date
- 2026-07-31
AI Technical Summary
Existing medium carbon steel processing technology requires quenching and tempering, which increases costs and environmental pollution. Adding alloying elements to refine the grain also presents cost issues, making it difficult to apply in large-scale production.
By controlling the rolling process, such as rolling temperature and reduction, the grain size of medium carbon steel is refined, and the addition of alloying elements such as Cr, Ni, Mo, Nb, V, and Ti is avoided. A walking beam furnace and rapid cooling treatment are used to control the grain growth rate.
It has achieved significant refinement of the grain size of medium carbon steel, reduced costs and energy consumption, reduced environmental pollution, and improved the mechanical properties of steel.
Smart Images
Figure CN122480106A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal material rolling technology, specifically relating to a rolling process for refining the grain size of medium carbon steel. Background Technology
[0002] Medium carbon steel possesses excellent hot working and machinability. Compared to low carbon steel, it exhibits higher strength and hardness, but lower plasticity and toughness. This steel can be used directly as hot-rolled or cold-drawn stock, or after heat treatment. After quenching and tempering, medium carbon steel exhibits good comprehensive mechanical properties, with a maximum hardness of 55 HRC and a tensile strength of 600~1100 MPa, making it widely used in medium-strength applications. Besides being used as a building material, it is also widely used in the manufacture of various mechanical parts, especially high-strength moving parts, such as pistons in air compressors and pumps, impellers in steam turbines, shafts, worm gears, and gears in heavy machinery, as well as wear-resistant parts such as crankshafts, machine tool spindles, rollers, and fitter's tools.
[0003] In the past, medium carbon steel parts typically underwent quenching and tempering to achieve a microstructure with high strength and good plasticity, resulting in excellent overall mechanical properties before being used in various mechanical equipment. While quenching and tempering improves the mechanical properties of medium carbon steel, it also incurs additional heat treatment costs. Surface oxidation and decarburization reduce the yield of the steel, directly or indirectly increasing the cost of use. Furthermore, using gas furnaces and quenching oil for quenching and tempering increases the emission of harmful gases, polluting the environment.
[0004] With the increasing urgency of cost reduction and emission reduction, more and more companies are choosing to abandon the quenching and tempering heat treatment process for medium carbon steel, and instead refine the grain size by appropriately adding alloying elements such as Cr, Ni, Mo, Nb, V, and Ti. This grain refinement aims to improve the mechanical properties of the steel, allowing it to be directly applied to certain parts and equipment in a less demanding state after rolling. However, adding alloying elements also increases costs and is not suitable for large-scale production. Therefore, developing a low-cost, pollution-free rolling process for refining the grain size of medium carbon steel is of great significance. Summary of the Invention
[0005] In view of this, the present invention proposes a rolling process for refining the grain size of medium carbon steel. Without adding alloying elements such as Cr, Ni, Mo, Nb, V, and Ti, the grain size of medium carbon steel is refined by controlling the rolling process, such as rolling temperature and reduction, thereby improving the mechanical properties of the steel and ultimately achieving the goals of reducing costs, saving energy, and protecting the environment.
[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a rolling process for refining the grain size of medium carbon steel, comprising the following process flow: billet heating, initial rolling, continuous rolling, and steel cooling; the heating process is crucial for refining the grain size of medium carbon steel. The higher the heating temperature and the longer the heating time, the faster the grain growth rate, and the billet will form coarse primary austenite grains, which will eventually be inherited by the steel to produce coarse grains. Therefore, the heating temperature and heating time should be reduced as much as possible, but they cannot be reduced indefinitely. Excessively low heating temperature and heating time will also lead to uneven heating of the billet surface and core, affecting the quality of the steel. Therefore, a reasonable heating regime needs to be established; the billet heating preheating section temperature is <700℃, the second heating section temperature is 790℃~830℃, the first heating section temperature is 1090℃~1150℃, the soaking section temperature is 1080℃~1180℃, and the total heating time is ≤450 min.
[0007] Based on the above technical solution, the billet heating is further described using a walking beam furnace.
[0008] Based on the above technical solution, the billet is further defined as a continuously cast rectangular billet with a cross-sectional dimension of 300~400 mm × 450~500 mm.
[0009] Based on the above technical solution, further, the initial rolling process adopts a 7-pass reduction process, with reductions of 55 mm~65 mm, 95 mm~105 mm, 80 mm~90 mm, 55 mm~60 mm, 60 mm~70 mm, 70 mm~75 mm, and 70 mm~76 mm for the 1st to 7th passes, respectively; the 2nd and 3rd passes are large reduction passes, and the steel turning operation is performed in the 1st, 3rd, 5th, and 7th passes; a Φ1150 mm BD initial rolling mill is used. The initial rolling is to reciprocate the continuous casting billet on the initial rolling mill to form a pre-formed billet that enters the continuous rolling mill. Under the condition that the total deformation remains unchanged, increasing the reduction of certain passes is beneficial to breaking the grains and improving the grain size level.
[0010] Based on the above technical solution, further, in the initial rolling process, the billet temperature is 1000℃~1050℃ when it enters the initial rolling mill and 950℃~1000℃ when it exits the initial rolling mill. Controlling the billet temperature at a lower level during the initial rolling process is also beneficial to suppress grain growth and improve the grain size level.
[0011] Based on the above technical solution, the continuous rolling start temperature is 930℃~980℃ and the final rolling temperature is 800℃~850℃ to control the grain growth rate.
[0012] Based on the above technical solution, the billet is further subjected to rapid cooling treatment by a water cooling device after final rolling, and the temperature of the upper cooling bed is controlled at 650℃~750℃ to control the grain growth rate.
[0013] Based on the above technical solution, the steel is further subjected to air cooling treatment on the cooling bed to control the cooling rate. The air cooling rate is ≥20℃ / min. When the steel temperature is ≤200℃, the air cooling is stopped, and the steel is collected and bundled.
[0014] Secondly, the present invention provides a medium carbon steel produced by the aforementioned rolling process for refining the grain size of medium carbon steel, wherein the grain size of the medium carbon steel is grade 8.0 to 9.0.
[0015] Based on the above technical solution, the chemical composition of the medium carbon steel is further specified as follows: C: 0.30%~0.60%, Si: 0.17%~0.37%, Mn: 0.50%~0.80%, P≤0.035%, S≤0.035%, with the balance being iron and unavoidable impurities; the specification is ≤Φ80mm, as larger specifications would make it difficult to control the steel temperature and cooling rate.
[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The rolling process for refining the grain size of medium carbon steel described in this invention can partially replace ordinary medium carbon steel quenched and tempered steel, saving heat treatment costs and reducing carbon emissions.
[0017] (2) The rolling process proposed in this invention does not add alloying elements such as Cr, Ni, Mo, Nb, V, Ti, etc. It only refines the grains of medium carbon steel by controlling the rolling process such as rolling temperature and reduction, so as to achieve mechanical properties similar to those of adding alloying elements. This can reduce alloy costs and increase benefits for enterprises.
[0018] (3) Rolling is carried out according to the rolling process described in this invention, and the grain size of the medium carbon steel is 8.0~9.0. Compared with the grain size of 3.5~4.0 of the conventional rolling process, the grain refinement effect is very obvious. Attached Figure Description
[0019] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.
[0020] Figure 1 The microscopic results of grain size detection of medium carbon steel prepared in Example 2 of the present invention are shown.
[0021] Figure 2 The microscopic results of grain size detection of medium carbon steel prepared in Comparative Example 1 of this invention are shown. Detailed Implementation
[0022] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.
[0023] Example 1 In this embodiment, the steel composition by mass percentage is C: 0.45%, Si: 0.25%, Mn: 0.68%, P: 0.013%, S: 0.008%, with the balance being iron and unavoidable impurities.
[0024] The heating process involves a preheating section temperature of 630℃, a second heating section temperature of 790℃, a first heating section temperature of 1090℃, a soaking section temperature of 1100℃, and a total heating time of 320 minutes.
[0025] The reduction amounts for the first to seventh passes of the primary rolling mill are 58 mm, 103 mm, 89 mm, 56 mm, 63 mm, 73 mm, and 75 mm, respectively. The billet temperature entering the primary rolling mill is 1030℃, and the temperature exiting the primary rolling mill is 950℃.
[0026] The rolling specification is Φ40 mm. After the initial rolling mill, the continuous rolling temperature is 970℃ and the final rolling temperature is 840℃. After the final rolling, it is subjected to rapid cooling treatment by water cooling equipment, and the upper cooling bed temperature is 650℃.
[0027] The steel is cooled by air on the cooling bed at a rate of 25°C / min. When the steel temperature reaches 200°C, the air cooling is stopped, and the steel is collected and bundled.
[0028] Grain size was tested on the rolled steel samples and graded according to the ferrite mesh method in GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", and the grade was 9.0.
[0029] Example 2 In this embodiment, the steel composition by mass percentage is C: 0.55%, Si: 0.28%, Mn: 0.71%, P: 0.011%, S: 0.006%, with the balance being iron and unavoidable impurities.
[0030] The heating process involves a preheating section temperature of 650℃, a second heating section temperature of 800℃, a first heating section temperature of 1100℃, a soaking section temperature of 1100℃, and a total heating time of 300 minutes.
[0031] The reduction amounts for the first to seventh passes of the primary rolling mill are 63 mm, 100 mm, 90 mm, 56 mm, 62 mm, 73 mm, and 71 mm, respectively. The billet temperature entering the primary rolling mill is 1020℃, and the temperature exiting the primary rolling mill is 980℃.
[0032] The rolling specification is Φ60 mm. After the initial rolling mill, the continuous rolling temperature is 960℃ and the final rolling temperature is 830℃. After the final rolling, it is subjected to rapid cooling treatment by water cooling equipment, and the upper cooling bed temperature is 690℃.
[0033] The steel is cooled by air on the cooling bed at a rate of 30°C / min. When the steel temperature reaches 180°C, the air cooling is stopped, and the steel is collected and bundled.
[0034] Grain size was tested on samples of the rolled steel and graded according to the ferrite mesh method in GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The grade was 8.5. The microscopic results are as follows: Figure 1 As shown.
[0035] Example 3 In this embodiment, the steel composition by mass percentage is C: 0.48%, Si: 0.35%, Mn: 0.66%, P: 0.010%, S: 0.003%, with the balance being iron and unavoidable impurities.
[0036] The heating process involves a preheating section temperature of 600℃, a second heating section temperature of 810℃, a first heating section temperature of 1150℃, a soaking section temperature of 1180℃, and a total heating time of 290 min.
[0037] The reduction amounts for the first to seventh passes of the primary rolling mill are 58 mm, 98 mm, 88 mm, 55 mm, 68 mm, 74 mm, and 75 mm, respectively. The billet temperature entering the primary rolling mill is 1010℃, and the temperature exiting the primary rolling mill is 970℃.
[0038] The rolling specification is Φ80 mm. After the initial rolling mill, the continuous rolling temperature is 950℃ and the final rolling temperature is 820℃. After the final rolling, it is subjected to rapid cooling treatment by water cooling equipment, and the upper cooling bed temperature is 680℃.
[0039] The steel is cooled by air on the cooling bed at a rate of 28°C / min. When the steel temperature reaches 190°C, the air cooling is stopped, and the steel is collected and bundled.
[0040] Grain size was tested on the rolled steel samples and graded according to the ferrite mesh method in GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", and the grade was 8.0.
[0041] Comparative Example 1 For comparison, steel produced by conventional rolling processes is selected and compared with steel produced by the rolling process of this invention.
[0042] The steel composition of Comparative Example 1, by mass percentage, is C: 0.57%, Si: 0.30%, Mn: 0.68%, P: 0.010%, S: 0.005%, with the balance being iron and unavoidable impurities. The measured values of the steel composition in this comparative example differ slightly from those in Example 2 due to smelting fluctuations, but both are within the standard range for the same steel grade, and this difference has no substantial impact on the conclusions of the process comparison.
[0043] The heating process involves a preheating section temperature of 680℃, a second heating section temperature of 850℃, a first heating section temperature of 1200℃, a soaking section temperature of 1200℃, and a total heating time of 300 min.
[0044] The reduction amounts for the first to seventh passes of the primary rolling mill are 62 mm, 70 mm, 65 mm, 58 mm, 63 mm, 71 mm, and 71 mm, respectively. The billet temperature entering the primary rolling mill is 1180℃, and the temperature exiting the primary rolling mill is 1150℃.
[0045] The rolling specification is Φ60 mm. After the initial rolling mill, the continuous rolling temperature is 1100℃ and the final rolling temperature is 950℃. After the final rolling, it is not rapidly cooled by water cooling equipment. The temperature on the cooling bed is 910℃.
[0046] The steel is cooled naturally on a cooling bed at a rate of 10℃ / min. When the steel temperature reaches 180℃, the steel is collected and bundled.
[0047] Grain size was tested on samples of the rolled steel and graded according to the ferrite mesh method in GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The grade was 3.5. The microscopic results are as follows: Figure 2 As shown.
[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A rolling process for refining the grain size of medium carbon steel, characterized in that, The process includes the following steps: billet heating, initial rolling, continuous rolling, and steel cooling; the billet heating preheating section temperature is <700℃, the second heating section temperature is 790℃~830℃, the first heating section temperature is 1090℃~1150℃, the soaking section temperature is 1080℃~1180℃, and the total heating time is ≤450 min.
2. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, The billet is heated using a walking beam furnace.
3. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, The billet is a continuously cast rectangular billet with a cross-sectional dimension of 300~400 mm × 450~500 mm.
4. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, The initial rolling process employs a 7-pass reduction process, with reduction amounts of 55 mm~65 mm, 95 mm~105 mm, 80 mm~90 mm, 55 mm~60 mm, 60 mm~70 mm, 70 mm~75 mm, and 70 mm~76 mm for the 1st to 7th passes, respectively. The 2nd and 3rd passes are large reduction passes, and the steel turning operation is performed in the 1st, 3rd, 5th, and 7th passes.
5. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, In the initial rolling process, the billet enters the initial rolling mill at a temperature of 1000℃~1050℃ and exits the initial rolling mill at a temperature of 950℃~1000℃.
6. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, The continuous rolling temperature is 930℃~980℃ at the start and 800℃~850℃ at the finish.
7. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, After final rolling, the billet undergoes rapid cooling treatment using a water cooling system, with the temperature of the upper cooling bed controlled at 650℃~750℃.
8. The rolling process for refining the grain size of medium carbon steel according to claim 1, characterized in that, The steel is cooled by air cooling on the cooling bed at a rate of ≥20℃ / min. When the steel temperature is ≤200℃, the air cooling is stopped, and the steel is collected and bundled.
9. A medium carbon steel produced by a rolling process for refining the grain size of medium carbon steel as described in any one of claims 1 to 8, characterized in that, The medium carbon steel has a grain size of 8.0 to 9.
0.
10. The medium carbon steel according to claim 9, characterized in that, The medium carbon steel has the following chemical composition by mass percentage: C: 0.30%~0.60%, Si: 0.17%~0.37%, Mn: 0.50%~0.80%, P≤0.035%, S≤0.035%, with the balance being iron and unavoidable impurities; Specifications are ≤Φ80mm.