A steel belonging to the C67 grade, possessing a bright surface and homogeneous mechanical properties, and a method for obtaining this steel.

Abstract

The invention relates to a high-carbon steel of grade C67 with a bright and oxide-free surface, used in the production of automotive, machinery manufacturing, springs, cutting tools, and various industrial products requiring high strength, and an optimized method for obtaining this steel.

Description

C67 HAS A GLOSSY SURFACE AND HOMOGENEOUS MECHANICAL PROPERTIES. A STEEL BELONGING TO A HIGH-QUALITY CLASS AND THE PROCESS OF OBTAINING THIS STEEL. A METHOD TECHNICAL FIELD The invention has applications in the automotive industry, machine manufacturing, springs, cutting tools, and various other industries requiring high strength. C67, a material used in the production of industrial products, has a bright and oxide-free surface finish. a high-carbon steel included in the quality class and optimization for obtaining this steel. It is related to an established method. PREVIOUS TECHNIQUE C67 steel grade is defined under the EN 10132-4 standard and contains 0.65–0.73% by weight. It is a steel grade containing carbon. The carbon content in the mentioned values ​​is medium-high. While offering a much higher strength potential compared to carbon grades, production processes such as surface oxidation, internal stress formation and deformation hardening This leads to metallurgically challenging problems. These steels are used in springs, saws, etc. blades, chain components, cutting tools and other applications requiring high strength It is commonly used in machine parts. However, its high carbon content, especially During the hot rolling and annealing stages, oxide formation occurs more rapidly and becomes thicker. This leads to it occurring in layers. One of the most common problems in the production of high-carbon steels with current technology is... The thick and compact scale layer that forms is precisely removed with standard pickling baths. It cannot be removed. It leaves microscopic oxide residues on the surface during subsequent rolling. This increases surface roughness in the steps and causes a loss of gloss. Additionally, Oxide residues trigger the formation of microcracks on the surface during rolling, which This negatively affects the mechanical behavior of the final product. The high carbon content of steel... Because it leads to faster hardening during hot working, the low levels in current techniques High concentration HCl solutions ensure complete dissolution of the compact oxide layer. It cannot provide. 2 Another critical issue in the production of C67 steel grade is microstructural homogeneity. The inability to achieve this. The high carbon content makes ferrite-pearlite transformations more delicate. This causes the process to occur within the temperature range. Single-stage annealing processes. It is unable to distribute the carbon diffusion homogeneously enough. Inside and outside of large coils. Due to the different thermal conductivity rates in its layers, the temperature distribution becomes uneven, which This leads to variations in tensile strength and elongation values ​​throughout the length. This can lead to out-of-tolerance mechanical behavior, especially after cold forming processes. This situation can lead to significant waste in production. Deformation hardening in high-carbon steels is much higher compared to low-carbon steels. It happens faster. The high speed used in current rolling lines. Reduction values ​​lead to internal stress concentration and cracking risk in C67 steel grade. It can open. Also, the cooling and lubrication conditions used during rolling. This deficiency leads to irregular surface roughness and thickness tolerance defects. This situation occurs, especially in high-speed reversible rolling mills, where thickness varies. This leads to an increase in deviations. Another significant problem encountered during the annealing stage of C67 steel is grain size. This is due to carbon growth and segregation. Annealing in steels with high carbon content. Even the smallest amount of oxygen in the atmosphere can cause surface dulling and oxide formation. Meanwhile, unsuitable temperature profiles lead to irregular growth of the grain structure, ferrite-pearlite This leads to a disruption of the distribution and damage to the tensile strength-ductility balance. This is the case. Single-stage bright annealing processes are insufficient for improving the quality of C67 steel. This is one of the main reasons why it stays. The forces of 100–150 tons used in the current technique during the tempering rolling stage are: Insufficient in eliminating micro-undulations on the surface of high-carbon C67 steel. Because internal stresses remain and are not completely relieved, cracking occurs during cold forming. This increases the risk. Therefore, the surface gloss of the final product is not homogeneous, and mechanically... Performance does not remain constant throughout the production process. In the current technique, the scale layer that forms on the surface of hot-rolled steel strips There are various approaches to addressing this issue. One of the studies in this technique is... In patent number EP0644276 A1, the pickling of hot-rolled steel strips is described. during its advancement along the pipeline, the effectiveness of the acid bath is increased and the scale layer is removed. a physical effect that facilitates dissolution is used The method is discussed. Similarly, in patent number US5472579 A, ​​hot rolled steel strips in hydrochloric acid-based pickling baths for controlled duration and a method for removing the oxide layer on the surface by processing under flow conditions The process is the subject of discussion. However, these patents concern high carbon content. The thick and compact scale layer encountered in C67 grade steels is completely inability to remove, microscopic oxide residues remaining on the surface after acid etching, cold rapid deformation hardening during rolling, internal stress accumulation along the length, and insufficient homogenization of carbon diffusion in single-stage annealing processes It does not offer a holistic solution to interrelated problems such as these. Furthermore, it is brilliant. annealing and temper rolling steps specific to high carbon C67 steel grade There is no technical instruction on how to address this issue along with the parameters. A BRIEF DESCRIPTION OF THE INVENTION During the production of industrial products using high-carbon steels in the C67 grade, surface oxidation, inability to remove compact scale layer, deformation hardening rapid increase, inability to achieve internal structural homogeneity and deterioration in mechanical properties A number of technical problems are encountered, such as irregularities along the measurement. These technical issues... These problems directly and negatively affect the surface appearance and mechanical behavior of the steel. This has an impact, especially for springs, cutting tools, and other applications requiring high strength and elasticity. This limits the quality of steel in applications such as precision machine components. The invention, within this scope, relates to the interaction of process steps in the production of steels belonging to the C67 grade class. It relates to a method that enables its optimization in a compatible manner. Within the scope of the invention, pickling, cold rolling, double-stage bright annealing and temper rolling processes By controlling them in a way that complements each other, the surface oxide-free surface is increased. Carbon diffusion is balanced, and the negative effects of deformation hardening are reduced. and high stability in mechanical properties is ensured throughout the length. The subject of the invention The method addresses surface dulling and oxide deterioration frequently encountered in high-carbon steels. microcrack formation due to layering, thickness deviations, and internal stress accumulation, etc. by eliminating problems, a bright, homogeneous and mechanically stabilized This invention makes it possible to obtain C67 steel in the structure. The invention is high-carbon. Surface quality and mechanical consistency, long-standing unresolved issues in steel production. 4 It offers a systematic solution to their problems, especially in cold forming and high-performance applications. It offers a significant advantage for applications requiring fatigue resistance. DETAILED DESCRIPTION OF THE INVENTION In this detailed description, the subject of the invention is high-carbon steels belonging to the C67 grade class. Surface gloss, lack of oxidation, microstructural homogeneity, and mechanical properties throughout the length are ensured in its production. a way to obtain steels with improved stability properties It is related to the method and has no limiting effects, only contributing to a better understanding of the subject. This is explained with examples that will not create a problem. The chemical composition of the steel that is intended to be obtained within the scope of this invention is high strength. and while maintaining elasticity properties, it will negatively affect surface quality and processability. It has been determined in a way that will prevent negative consequences such as excessive embrittlement or grain enlargement. The carbon content of C67 grade steel is in the range of 0.65%–0.73% by weight. This carbon content gives the steel high tensile strength and hardness. However, this carbon... In terms of value, cold forming and annealing processes become even more critical. The internal structure needs to be controlled to ensure homogeneity. The silicon element in the steel discussed in the invention is 0.15%–0.35% by weight. It is found in this range and, in addition to its deoxidizing function, this element contributes to the elasticity of steel. It has a positive effect on improving the modulus and yield strength of the steel in question. In the invention, the steel in question... The manganese content is selected to be between 0.60% and 0.90% by weight. This weight-based value increases the hardenability of the steel in question, resulting in finer particles within its structure. It contributes to the formation of perlite structures, thereby increasing tensile strength, and Internal structural homogeneity is being improved. However, this is due to the ratio of carbon by weight. By balancing these elements together, care is taken to preserve the toughness of the material. The phosphorus and sulfur alloying elements present in the steel covered by the invention. The total percentage by weight is kept below 0.05%, and the percentage by weight of each is at most... It is limited to 0.025% by weight. These two elements are present at low levels. Preservation reduces the tendency to crack, especially at high temperatures, and improves surface quality. It contributes to its preservation. It also includes secondary alloys such as chromium, nickel, and copper. The elements shall not exceed 0.40%, 0.10%, and 0.40% by weight, respectively. This is how it is limited. The controlled presence of these elements causes mild corrosion to the steel. It provides resistance while also ensuring stability in mechanical properties. The steel covered by this invention has high weight values ​​thanks to its chemical composition. While maintaining the stiffness and strength advantages provided by the carbon content, it offers a low weight advantage. The presence of phosphorus and sulfur in the values ​​affects surface homogeneity and processability. It shows improved performance. In addition, the specified manganese value by weight is thermal. It is possible to obtain a finer-grained and more balanced microstructure after processing. This enables deformation control and surface quality in subsequent processing steps. This facilitates optimization. Therefore, the resulting chemical composition is standard. The chemical properties of C67 grade steels remain within these limits. Specifically designed to provide an optimum balance of strength, ductility, and surface quality. It offers an adapted composition. Furthermore, the chemical composition of the steel discussed here... Its composition is also given in Table 1. Element Weight Ratio (%) C (Carbon) 0.65-0.73 Si (Silicon) 0.15 – 0.35 Mn (Manganese) 0.60 – 0.90 P (Phosphorus) ≤ 0.025 S (Sulfur) ≤ 0.025 Cr (Chromium) ≤ 0.400 Ni (Nickel) ≤ 0.100 Cu (Copper) ≤ 0.400 Other impurities (Al, N, etc.) in trace amounts. Table 1. Chemical composition of the steel described in the invention. 6 In order to ensure that the mechanical performance of C67 steel remains stable throughout the production process, it is subjected to tensile testing. tensile strength 600–700 MPa, yield strength 480–560 MPa, elongation value at least 16% and hardness The target value is to be in the range of 180–220 HB. High carbon content... the resulting deformation hardening, internal stress accumulation and carbon Annealing, rolling, and tempering are necessary to prevent segregation. The parameters in each step need to be controlled with extreme precision. Tolerance Throughout Production Mechanical Properties Target Value Range (Within the meter) Tensile Strength 600-700 MPa ±3% Yield Strength 480-560 MPa ±3% Elongation ≥ 16% ±1.5% Hardness 180-220 HB ±5 HB Table 2. Mechanical strength values ​​of the target steel. Surface problems are one of the most common issues encountered in C67 grade steels. In order to remove oxidation and scale residues, the pickling step in the invention is repeated. It is structured. The current production lines use 10–12% HCl by weight. instead of a solution, the invention includes a solution containing HCl in the range of 16–20% by weight. A higher concentration solution is used. This preference is for hot rolling. subsequently, a thick and stable scale layer forms on the steel surface, with a higher profile. It ensures efficient dissolution at high speeds. After this stage, the pickling process begins. This is done after hot rolling in C67 steel. The resulting oxide layer is more compact and resistant to dissolution compared to low-carbon steels. because it is more resistant, the concentration of the acid bath used within the scope of the invention The HCl content was determined to be 16–20% by weight. The pickling process was carried out at a temperature range of 70–80 °C. This process is being carried out, and at this temperature, the oxide layer is chemically completely dissolved. It is optimized to ensure dissolution. After etching, the strip is rinsed with water. It is dried with hot air and a thin layer of protective oil is applied to the surface. This This prepares the step surface for cold rolling and minimizes the risk of oxidation. After the pickling process, the prepared strip is sent for thinning and homogenization of the microstructure. It is subjected to a multi-pass reversible cold rolling process. This process is invention 7. within the scope of 6 to 9 passes and with a total reduction rate of 40%–70%. This is carried out. The reduction rate for each pass is kept between 5% and 10%. Thus, excessive deformation hardening and internal stress observed in high-carbon steels Accumulation is kept under control. The pressing force during cold rolling is 1800–2200. The weight is set at tons, and the rolling speed at 900–1100 m / min. These parameters indicate high performance. Control of steel surface roughness and thickness tolerance even at deformation rates It allows for the use of a boron oil-based emulsion for cooling and lubrication. Its use contributes to the stabilization of surface temperature and improves surface quality. This makes its protection possible. After the cold rolling process, a bright annealing process is carried out on C67 steel. High carbon content increases the likelihood of the steel developing heterogeneous structures during annealing. Since it increases the two-stage bright annealing method within the scope of the invention. It is used. The annealing process is carried out entirely in a 100% hydrogen atmosphere. Hydrogen gas, thanks to its high thermal conductivity and low dew point, can be used on surfaces. It completely prevents oxidation and ensures a glossy surface. The first stage annealing takes 4–7 hours at a temperature range of 480–520 °C, and during this stage the internal Stresses are reduced in a controlled manner. The second stage annealing takes place at a temperature of 720–760 °C. This process takes 12–16 hours and involves the homogenization of carbon diffusion. balancing the ferrite-pearlite structure and minimizing the risk of grain growth. It provides. The annealing process is completed with controlled cooling lasting 3–5 hours, In this way, the surface gloss is preserved and oxidation is completely prevented. After the annealing process, the surface roughness of the steel is reduced and residual particles are eliminated. Tempered rolling is applied to relieve stresses. This process... During this process, the constant compressive force is in the range of 230–270 tons, and the tensile force is in the range of 3000–6000 kgf. The surface roughness of the rollers is maintained and selected at a level of 2.3–2.7 Ra. The parameters ensure the elimination of micro-undulations on the surface and the achievement of a homogeneous shine. This makes it possible to apply 0.8–1.2 g / m² of protective oil to the surface after tempering. A protective layer is applied, thereby protecting the surface against oxidation and during storage. This ensures that the commitment is maintained throughout the process. The C67 steel obtained through the method described in this invention has a bright and oxide-free surface. It has a homogeneous internal structure and stable mechanical properties throughout its length. 8 One of the most important technical results obtained is the C67 grade with high carbon content. The invention refers to the significant improvement achieved in the surface oxide-free and brightness level of class steel. The acid pickling process, which is carried out within the scope of this, involves a mixture containing 16-20% HCl by weight and is performed at a hot temperature. The thick and compact scale layer formed after rolling is effectively removed. In addition, a two-stage bright annealing process is carried out in a 100% hydrogen atmosphere. Thanks to hydrogen, oxygen and iron oxide residues are completely removed from the surface. The strong reducing effect of gas, oxygen during annealing of high-carbon steels It prevents the metal surface from reacting with the surface, thus preventing surface dulling. This prevents a homogeneous, metallic and reflective coating on the surface of C67 steel. Brightness is obtained and surface roughness remains stable in the range of 2.3–2.7 Ra. is fixed. This surface quality is especially important in coatings, painting, and surface hardening. A significant technical advantage in terms of parts that will undergo secondary surface treatments. It provides. Another important technical result is the microstructural homogeneity and despite the high carbon content. The goal is to ensure mechanical stability. In the double-stage bright annealing process, 480–520 °C Internal stresses resulting from cold rolling are eliminated with the first stage carried out within the temperature range. Carbide formations are reduced in a controlled manner and balanced. Following this... Diffusion of carbon atoms by second-stage annealing applied in the 720–760 °C range. It is becoming fully homogenized, the ferrite-pearlite distribution is regulated, and the grain structure is stabilized. This is done. Thanks to the aforementioned process steps, tensile strength is reduced along the length of C67 steel. The strength and elongation values ​​are stabilized, and tensile strength deviations are corrected. ±3% elongation deviations and ±1.5% elongation deviations can be kept within limits. High carbon Local embrittlement and mechanical imbalances frequently observed in steels can be corrected using this method. This is largely eliminated. Thus, the strength distribution throughout the product is disrupted. It is stabilizing, and its fracture and shaping behaviors are predictable and controllable. It reaches the level. Another technical advantage offered by the invention is in thickness tolerances and surface smoothness. This is the improvement achieved in the multi-pass reversible cold rolling line between 6–9 passes. The rolling process, which is carried out and provides a total reduction of 40–70%, was performed in 1800– It is carried out under controlled compressive forces in the range of 2200 tons. These conditions, This allows the deformation to be distributed evenly throughout each pass, and high Excessive deformation hardening observed in carbon C67 steel is brought under control. 9 The boron oil-based cooling system used during rolling prevents overheating and surface irritation. It prevents fluctuations; thus, thickness deviations are achieved within narrow tolerances such as ±0.02 mm. It can be contained within. This is especially true for springs and cutters that require precise dimensions. It provides high dimensional stability in terms of elements and automotive components. The invention also ensures long-term stability and repeatability in mechanical properties. It provides this. The constant pressure applied during the tempering rolling stage is in the range of 230–270 tons. compressive force and tensile force in the range of 3000–6000 kgf, micro-undulations on the surface While eliminating deformation, it also effectively reduces internal stresses caused by deformation. This prevents cracking that may occur during forming of high-carbon C67 steel. The risk is reduced while the surface gloss is preserved. After tempering The protective lubrication process applied in the range of 0.8–1.2 g / m² prevents the surface from coming into contact with oxygen. By cutting, it prevents oxidation during storage and transportation processes and extends the shelf life of the product. It prolongs it. The C67 grade steel obtained by the method described in the invention has high mechanical strength and stability. It offers both microstructure and bright, oxide-free surface properties. Tensile strength 600– 700 MPa, yield strength 480–560 MPa and elongation of at least 16%. It is fixed; the hardness value is kept under control in the range of 180–220 HB. This Mechanical properties, wear resistance and elasticity expected in high carbon steels. It provides an optimal balance between processability. These obtained values ​​are for C67 quality. This class of steel represents a high and consistent level of quality. The C67 grade steel obtained in this way has high strength, elasticity, and surface properties. Thanks to its quality and internal structural stability, it has a wide range of industrial applications. It has a number of components, particularly in spring production, such as suspension springs, torsion springs, and retaining rings. It is preferred in applications requiring high elasticity and fatigue resistance. Saw blades, industrial knives, and scissor blades in the production of cutting and semi-cutting tools. It offers the advantage of high hardenability and wear resistance in components such as automotive. locking elements, spring clips, chain components and products that operate under vibration in the industry. It is used in the production of functional parts. Features include a bright surface finish and galvanizing. It forms a suitable substrate for coating processes such as phosphating, PVD and CVD, and It reduces the need for surface preparation. It is also used in machinery, agriculture, energy, and defense. 10 fasteners and mechanisms in industries requiring high impact and fatigue resistance It can also be used effectively in its components. The scope of protection of the invention is specified in the claims attached hereto, and these details are strictly adhered to. The explanation cannot be limited to those given for illustrative purposes. Because a technically skilled person... the person, without deviating from the main theme of the invention, in light of what has been described above, similar It is clear that these structures can emerge.

Claims

1. Preparation of the chemical composition of the steel, slab or by continuous casting method. Solidified in bloom form, then flattened into strip form by hot rolling. the process of bringing in and loosening the scale layer by mechanical surface breaking including steps, with a dimensionally homogeneous mechanical structure and a non-oxidizing and bright surface. a method for obtaining C67 grade steels with stability Its distinguishing feature is that it includes the following steps: - steel strip with a relaxed surface coil, 16% to 20% by weight immersed in an acid bath containing hydrochloric acid in a range of 70 to Applying the pickling process step at a temperature range of 80 °C, - the thickness of the steel strip coil prepared after the pickling process by reducing and internally refining the particles. between 6 and 9 passes to ensure homogenization. The application of the multi-pass reversible cold rolling process and a total thickness reduction ratio between 40% and 70% to be carried out, - internal structural homogeneity of the steel strip coil after the cold rolling process. and in order to obtain an oxide-free surface, in a 100% hydrogen atmosphere, 480 to Temperature range of 520 °C for 4 to 7 hours and 720 to 760 °C Two levels of brightness that will last for 12 to 16 hours. subjected to annealing process, - surface smoothness and residue of the steel strip coil after annealing process To relieve stresses, a compressive force between 230 and 270 tons is required. It undergoes a tempering and rolling process underneath.

2. A method that conforms to Claim 1, characterized by the fact that it is applied after the pickling process and cold. The rinsing process is carried out sequentially with deionized water and then with hot air before the rolling process. This includes drying and applying protective oil to the surfaces.

3. A method that conforms to one of the previous requirements, characterized by its cold rolling process. The step is performed between 6–9 passes, and the reduction ratio is given for each pass. It should be in the range of 5-10%. 12 4. A method suitable for one of the previous requirements, characterized by cold rolling. The pressure force in these operations should be between 1800 and 2200 tons.

5. A method suitable for one of the previous requirements, characterized by cold rolling. the rolling speed in the processes is between 900 and 1100 m / min It is the fact that.

6. A method suitable for one of the previous requirements, characterized by its temper rolling process. In these processes, the surface roughness of the rollers is in the range of 2.3 to 2.7 Ra. It is the fact that.

7. A method suitable for one of the previous requirements, characterized by its temper rolling process. In these processes, the tension force of the rollers is between 3000 and 6000 kgf. It is the fact that.

8. A method that conforms to one of the previous requirements, characterized by its temper rolling process. 2 Afterwards, a protective oil is applied to the surface of the steel at a concentration ranging from 0.8 to 1.2 g / m³. It is the implementation.

9. Obtained by a method conforming to one of the requirements 1-8 and belonging to quality class C67. It is made of steel, and its characteristic feature is that it contains... Carbon (C) 0.65% to 0.73% by weight, silicon (Si) contains 0.15% to 0.35% by weight. manganese (Mn) 0.60% to 0.90% by weight, Phosphorus (P) maximum 0.025% by weight, Sulfur (S) maximum 0.025% by weight, Chromium (Cr) maximum 0.40% by weight, nickel (Ni) maximum 0.10% by weight, It is characterized by containing a maximum of 0.40% copper (Cu) by weight.

10. A steel conforming to Claim 9, with a tensile strength of 600 to 700 MPa. within the range of 480 to 560 MPa yield strength and at least elongation rate The percentage is 16%, and the hardness value is between 180 and 220 HB on the Brinell scale. 35 13 11. A steel conforming to Claim 9 or 10 for automotive, machinery, spring, cutting tool, mold, In the energy, defense, and agricultural machinery industries; especially engine components, springs, chain shafts, components requiring high fatigue resistance, saw teeth, cutting parts, blades, shafts, press components, and high impact resistance. It is used in applications.