Method for producing a food contact baking tray steel, food contact baking tray steel and baking tray

Abstract

The application relates to a medium-thickness plate product applied to the food field, in particular to a food contact baking tray steel and a preparation method thereof. The technical problem solved by the application is that, in addition to meeting the mechanical requirements, the baking tray steel product also needs to meet the strict requirements of harmful elements to meet the requirements of food contact. Meanwhile, the narrow hardness fluctuation control is required to realize good hardness matching of the baking tray steel and the contact kitchenware product. The actual application scene of the product requires that the plate shape of the high-strength steel is extremely high under the actual cold and hot cycle working condition, which puts higher requirements on the plate shape of the steel plate. The application relates to a preparation method of the food contact baking tray steel, which comprises the following steps: iron smelting, steel smelting, casting blank heating, rolling, straightening, pit slow cooling, room temperature, temperature control quenching, stack cooling and tempering. The obtained food contact baking tray steel has low harmful element content, moderate hardness and good plate shape stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of steel industry, and in particular to a food-grade medium plate product. BACKGROUND

[0002] The baking tray steel for food processing is a medium plate product directly used in contact with food in the field of frying and baking equipment of the chain catering industry. This kind of food contact baking tray steel is mainly used for medium plate products of standardized back-end frying and baking equipment in large catering enterprises, which usually cooks different semi-finished food materials under standardized process. Its special application scenario requires food contact safety, hardness, flatness, thermal conductivity coefficient fluctuation, etc. in addition to mechanics. Ideally, this kind of food-grade medium plate product should meet the following requirements:

[0003] In addition to the mechanical property requirements, since the food contact baking tray steel is in direct contact with food, it requires strict control of harmful elements such as As, Cd, Pb in the whole production process of the steel plate.

[0004] Compared with conventional steel plates, the food contact baking tray steel applied to the baking tray steel requires strict control of the hardness index within a certain range in addition to the usual tensile strength, yield strength and elongation, in order to match the hardness of the daily contact tools such as spatula during use. It is necessary to ensure a certain hardness level to prevent being scratched by the contact tool, and not to cause excessive wear of the matching tool due to too high hardness, which affects the service life, which requires strict control of the hardness.

[0005] In terms of flatness stability, since the baking tray steel product needs to be continuously cycled in the temperature range of room temperature ~ 170℃, the flatness stability of the steel plate product is required to be high, and the deformation is not allowed during repeated cycling.

[0006] However, the baking tray steel currently in use is all ordinary high-strength steel plates, which cannot meet the special requirements of the above baking tray steel products, and there is a risk in food safety, and the hardness (including the requirement of ultimate strength reduction factor under high temperature service environment) and flatness stability cannot meet the application requirements of high-end kitchen equipment.

[0007] The All-China Federation of Metallurgical Research Institutes Co., Ltd. has proposed "An Alloy and Its Preparation Method and Application" (Patent Application No. 202211581535.3), which has invented an alloy product for food contact utensils, obtained by hot rolling or cold rolling process, with a yield strength of 235 MPa level, and the microstructure is mainly ferrite, and there is no performance requirement on hardness, which is quite different from the overall process route, strength level, microstructure and performance requirements of the baking tray steel of the present patent, and belongs to completely different application conditions and product types.

[0008] Nanjing Iron and Steel Co., Ltd. proposed a "low-cost short production cycle preparation method for wear-resistant steel" (application number: 201711423651.1), Shandong Iron and Steel Co., Ltd. proposed a "low residual stress medium-thick specification wear-resistant steel plate and its preparation method" (application number: 201811511237.0), the overall technical ideas of the two steel enterprises are similar, both propose a short process production and low residual stress control of wear-resistant steel through rolling + offline quenching + straightening. The ideas described in the above two applications are mainly that the wear-resistant steel is rolled and quenched offline, and then straightened by residual heat (low-temperature tempering is cancelled) to finally deliver the goods. Compared with the above two ideas, the present application has obvious differences. The present application mainly ensures the low stress state of the rolled structure by air cooling + slow cooling after rolling, and then realizes the low residual stress state of the steel plate by temperature-controlled quenching + stack cooling + high-temperature tempering in the quenching process.

[0009] Fujian Province Sanming Steel (Group) Co., Ltd. proposed a "preparation method of low residual stress Q355B low alloy steel plate" (application number: 202111508779.4), mainly through rolling to obtain a medium-low stress Q355B steel plate. Compared with the technical content of the above application, there are significant differences in the process route (rolling + quenching) and strength level.

[0010] Handan Iron and Steel Group Co., Ltd. proposed a "low residual stress cold forming high strength steel S700MC and its production method" (application number: 202111363619.5), which is mainly for the production technology of a cold forming high strength steel, and realizes the steel plate production through a process route of hot continuous rolling + coiling + cold rolling. The present application is mainly a hot rolling + quenching process of plate production line to obtain the final plate product, and there is a big difference in the technical route.

[0011] Shougang Group Co., Ltd. proposed a "preparation method of low residual stress low alloy high strength steel plate" (application number: 201910521148.2), which proposes a technical idea of hot continuous rolling production of high strength steel, and the overall route is: smelting, continuous casting, heating, rough rolling, finish rolling, laminar cooling, coiling, flattening, straightening, tempering, and a series of hot continuous rolling technical routes, and is directly tempered without offline heating, which is essentially different from the technical route of the present application (rolling + offline quenching process).

[0012] The steel materials involved in the above patents cannot meet the requirements of high-end kitchen equipment for food safety, hardness, and plate shape stability. SUMMARY

[0013] The embodiment of the present application provides a preparation method of food contact baking tray steel, a food grade medium plate product and a baking tray, so as to solve the problem that the conventional high-strength steel cannot meet the application requirements of the baking tray steel product.

[0014] In a first aspect, the embodiment of the present application provides a preparation method of food contact baking tray steel, which comprises: iron smelting-steel smelting-cast blank heating-rolling-straightening-pit slow cooling-room temperature-temperature control quenching-pile cooling-tempering, and specifically comprises the following steps:

[0015] Iron smelting is performed to obtain molten iron with low arsenic content, and after steel smelting, a cast blank is obtained;

[0016] The cast blank is heated and rolled, wherein the opening rolling temperature in the finish rolling process is 860-890 DEG C, and the final rolling temperature is 800-830 DEG C;

[0017] The steel plate to be cooled is straightened and then transferred to a slow cooling pit to be cooled to not higher than 80 DEG C, and a rolled steel plate is obtained after the pit, wherein the temperature of the steel plate to be cooled when entering the slow cooling pit is not lower than 400 DEG C;

[0018] The rolled steel plate is heated to 905-915 DEG C for austenitizing and holding, and then quenched, and the final cooling temperature of the quenching is 120-180 DEG C;

[0019] The steel plate after quenching is pile cooled and tempered, wherein the temperature of the tempering is 640-655 DEG C, and the food contact baking tray steel is obtained.

[0020] In some embodiments of the present application, the heating of the cast blank is 1150-1170 DEG C; and / or,

[0021] The heating coefficient of the heating of the cast blank is 1 min / mm-2 min / mm; and / or,

[0022] The straightening is performed at 680-730 DEG C.

[0023] In some embodiments of the present application, the molten iron contains As≤10ppm.

[0024] In some embodiments of the present application, the steel smelting process comprises primary smelting and refining,

[0025] The primary smelting comprises smelting by a converter, and the scrap steel used in the process of smelting by the converter is low-arsenic scrap steel generated in the steel smelting process;

[0026] In the refining process, the basicity of the slag is controlled to be 15-25, the arsenic content of the molten steel is controlled to be less than 10 ppm, and the arsenic content of the final cast blank is controlled to be less than 20 ppm.

[0027] In a second aspect, the embodiments of the present application provide a food contact baking tray steel, which is prepared by the method for preparing the food contact baking tray steel according to any one of the embodiments of the first aspect.

[0028] In some embodiments of the present application, the metallographic structure of the food contact baking tray steel comprises at least one of tempered martensite and precipitated metal compounds.

[0029] In some embodiments of the present application, the precipitated metal compounds comprise at least one of Ti-containing carbonitride, V-containing carbonitride and Cu-containing carbonitride.

[0030] In some embodiments of the present application, the precipitated metal compounds comprise Cu-containing carbonitride, and the Cu-containing carbonitride is at least one of cementite and epsilon carbide.

[0031] In some embodiments of the present application, in the metallographic structure of the food contact baking tray steel, the width of the tempered martensite lath is 600-900 nm, and the average diameter of the original austenite grain is 10-20 μm.

[0032] In some embodiments of the present application, the food contact baking tray steel has the following properties:

[0033] the surface Rockwell hardness is HRC 42-48,

[0034] the yield strength is greater than or equal to 750 MPa,

[0035] the tensile strength is 800-920 MPa,

[0036] the elongation A 50 is greater than or equal to 25%, and the reduction of area is greater than or equal to 45%,

[0037] the carbon equivalent is 0.48-0.53,

[0038] the unevenness is less than or equal to 2 mm / m,

[0039] the content of harmful elements is less than or equal to 0.001 mg / kg after soaking in a citric acid solution, wherein the harmful elements comprise As, Cd and Pb,

[0040] the ultimate strength reduction factor at 250 DEG C is greater than or equal to 0.98.

[0041] In a third aspect, the embodiments of the present application provide a baking tray, wherein the material of the baking tray is the food contact baking tray steel according to any one of the embodiments of the second aspect.

[0042] Compared with the prior art, the above technical solutions provided by the embodiments of the present application have the following advantages:

[0043] The preparation method of the food contact baking tray steel provided by the embodiment of the application avoids the high residual stress state or even the shape problem of the steel plate caused by the post-rolling water cooling and the conventional quenching to room temperature, guarantees that the steel plate has good uniformity, suitable hardness and low residual stress state, and guarantees that the baking tray steel product is suitable for high-end standardized kitchen frying and baking equipment. BRIEF DESCRIPTION OF DRAWINGS

[0044] The drawings incorporated in the specification and forming a part thereof illustrate embodiments consistent with the present application and together with the description are used to explain the principles of the application.

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, for those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative labor.

[0046] Figure 1 The SEM photo of the food contact baking tray steel provided by the embodiment 1 of the application;

[0047] Figure 2 The TEM photo of the food contact baking tray steel provided by the embodiment 1 of the application;

[0048] Figure 3 The SEM photo of the food contact baking tray steel provided by the comparative example 1 of the application;

[0049] Figure 4 The TEM photo of the food contact baking tray steel provided by the comparative example 1 of the application;

[0050] Figure 5 The SEM photo of the food contact baking tray steel provided by the comparative example 3 of the application;

[0051] Figure 6 The TEM photo of the food contact baking tray steel provided by the comparative example 3 of the application. DETAILED DESCRIPTION

[0052] In order to make the objects, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the application.

[0053] Unless otherwise defined, all terms used in the present application are to be interpreted as in common usage by one of ordinary skill in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of conflict, the present specification will control.

[0054] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0055] The existing currently applied baking tray steel still has the technical problem that the hardness and plate shape stability are not ideal.

[0056] The technical scheme provided by the embodiments of the present application solves the above technical problems, and the general idea is as follows:

[0057] In a first aspect, the embodiments of the present application provide a preparation method of food contact baking tray steel, which comprises: ironmaking-steelmaking-casting blank heating-rolling-straightening-pit slow cooling-room temperature-temperature controlled quenching-pile cooling-tempering, and specifically comprises the following steps:

[0058] S1: ironmaking to obtain molten iron with low arsenic content, and steelmaking to obtain a casting blank;

[0059] S2: heating and rolling the casting blank, wherein the opening rolling temperature in the finishing rolling process is 860-890℃, and the final rolling temperature is 800-830℃;

[0060] S3: after the steel plate to be cooled is straightened, it is transferred to a slow cooling pit to be cooled to not higher than 80℃, and a rolled steel plate is obtained after leaving the pit, wherein the temperature of the steel plate to be cooled when entering the slow cooling pit is not lower than 400℃;

[0061] S4: the rolled steel plate is heated to 905-915℃ for austenitizing and holding, and then quenched, and the final cooling temperature of the quenching is 120-180℃;

[0062] S5: pile cooling and tempering the quenched steel plate, wherein the tempering temperature is 640-655℃, and the food contact baking tray steel is obtained.

[0063] It is easy to understand that, in order to control the low arsenic content of the molten iron, the iron ore used for smelting the molten iron should be an iron ore with low arsenic content.

[0064] The overall control range of the quenching and tempering temperature is relatively narrow, which is also to ensure the narrow hardness fluctuation space of the baking tray steel to meet the service requirements of the subsequent product hardness matching.

[0065] The steel plate is sent into the slow cooling pit for slow cooling when the temperature of the steel plate is above 400 DEG C, which is beneficial to make the microstructure of the food-grade baking tray steel product more uniform, lower residual stress and good plate shape unevenness, so as to ensure the material unevenness of the rolled steel plate in the subsequent quenching process and then ensure the plate shape of the quenched steel plate.

[0066] The quenching final cooling temperature of the conventional quenched and tempered steel plate is generally about room temperature 20 DEG C. The final cooling temperature of the quenching is controlled to be 120-180 DEG C in the application, which is beneficial to eliminate the residual stress of the food contact baking tray steel and make the plate shape of the food contact baking tray steel keep stable for a long time.

[0067] The tempering temperature is 640-655 DEG C in the application, which is beneficial to control the hardness of the food contact baking tray steel in the target range to meet the good hardness matching.

[0068] The preparation method of the food contact baking tray steel provided in the application avoids the high residual stress state and even the plate shape problem of the steel plate caused by the processes such as water cooling after rolling and conventional quenching to room temperature, ensures that the steel plate has good uniformity, narrow hardness interval control and low residual stress state, and ensures that the baking tray steel can meet the application requirements.

[0069] In some embodiments of the application, the heating of the casting blank is at 1150-1170 DEG C.

[0070] The positive effect of the heating temperature of 1150-1170 DEG C is that the heating of the steel blank is sufficient for rolling reduction, and the austenite grain is not too large to affect the performance of the subsequent steel plate.

[0071] Lower than 1150 DEG C is easy to cause the rolling reduction process to be limited due to excessive rolling force, and then affect the performance. Higher than 1170 DEG C is easy to cause the austenite grain to be large, and then cause the performance of the steel plate to be unstable.

[0072] In some embodiments of the application, the heating of the casting blank is at a heating coefficient of 1-2 min / mm.

[0073] In some embodiments of the application, the straightening is performed at 680-730 DEG C.

[0074] The straightening temperature is controlled to be the above value, and the straightening temperature range can ensure that the steel plate obtains good plate shape and low residual stress state.

[0075] Higher than the straightening temperature is easy to cause the temperature of the subsequent processes to change, and cannot ensure that the target microstructure is obtained.

[0076] Lower than the straightening temperature range can easily lead to an increase in residual stress, and the straightening effect decreases.

[0077] In some embodiments of the present application, the molten iron As content is ≤10ppm.

[0078] In some embodiments of the present application, the steelmaking process includes primary refining and refining,

[0079] The primary refining includes smelting in a converter, and the scrap used in the converter smelting process is low-arsenic scrap produced in the steelmaking process.

[0080] In the refining process, the basicity of the slag is controlled to be 15-25, the arsenic content of the molten steel is controlled to be <10ppm, and the arsenic content of the final casting blank is controlled to be less than 20ppm.

[0081] It is easy to understand that in the case of low arsenic content of the molten iron, the scrap produced in the steelmaking process is also low-arsenic scrap.

[0082] In a second aspect, the embodiments of the present application provide a food contact baking tray steel prepared by the preparation method of the food contact baking tray steel of any one of the embodiments of the first aspect.

[0083] The food contact baking tray steel is realized by the preparation method of the food contact baking tray steel of the first aspect. Since the food contact baking tray steel adopts all the technical solutions of the embodiments of the first aspect, it at least has all the beneficial effects brought by the technical solutions of the embodiments of the first aspect, which will not be repeated here.

[0084] In some embodiments of the present application, the metallographic structure of the food contact baking tray steel includes at least one of tempered martensite and precipitated metal compounds, and does not include austenite.

[0085] Tempered martensite ensures the overall hardness level and deformation resistance of the steel plate.

[0086] In some embodiments of the present application, the precipitated metal compounds include at least one of Ti-containing carbonitride, V-containing carbonitride, and Cu-containing carbonitride.

[0087] The pinning effect of the precipitated metal compound has an inhibitory effect on the dislocation migration during the cold-heat cycle, thereby also being conducive to improving the deformation resistance of the steel plate.

[0088] In some embodiments of the present application, the precipitated metal compound includes Cu-containing carbonitride, and the Cu-containing carbonitride is at least one of cementite and ε-carbide.

[0089] Various precipitated metal compounds, especially Cu-containing carbonitrides, are mainly beneficial to improve the thermal stability of the baking tray steel and improve the deformation resistance of the steel plate in a cold and hot cycle environment.

[0090] In some embodiments of the present application, the width of the tempered martensite lath in the metallographic structure of the food contact baking tray steel is 600-900 nm, and the average diameter of the prior austenite grain is 10-20 μm.

[0091] The fine tempered martensite lath is beneficial to improve the strength and plasticity of the baking tray steel, and the fine prior austenite grain plays a positive role in optimizing the performance and uniformity of the steel plate.

[0092] In some embodiments of the present application, the food contact baking tray steel has the following properties:

[0093] The surface Rockwell hardness is HRC 42-48,

[0094] The yield strength is ≥ 750 MPa,

[0095] The tensile strength is 800-920 MPa,

[0096] The elongation A 50 ≥ 25%, the reduction of area ≥ 45%,

[0097] The carbon equivalent is 0.48-0.53,

[0098] The unevenness is ≤ 2 mm / m,

[0099] The content of harmful elements is ≤ 0.001 mg / kg after soaking in a citric acid solution, wherein the harmful elements include As, Cd, and Pb,

[0100] The ultimate strength reduction factor at 250°C is ≥ 0.98.

[0101] In a third aspect, the embodiments of the present application provide a baking tray, wherein the material of the baking tray is the food contact baking tray steel according to any one of the embodiments of the second aspect.

[0102] The baking tray is realized by the food contact baking tray steel according to the second aspect, and the specific embodiments of the baking tray can refer to the embodiments of the second aspect and the common knowledge in the baking tray manufacturing field. Since the baking tray adopts all the technical solutions of the embodiments of the second aspect, it at least has all the beneficial effects brought by the technical solutions of the embodiments of the second aspect, which will not be repeated here.

[0103] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. The experimental methods in the following examples, if no specific conditions are noted, are generally determined according to the national standards. If there is no corresponding national standard, the methods are determined according to the general international standards, the conventional conditions, or the conditions suggested by the manufacturers.

[0104] Example 1

[0105] The present example provides a method for preparing a food contact baking tray steel, which comprises the following steps:

[0106] The molten iron with an arsenic content of 8 ppm is obtained by iron smelting, and the casting blank is obtained after steel smelting;

[0107] The casting blank is heated and rolled, wherein the rough rolling temperature is selected from Table 1, and the finish rolling temperature is selected from Table 1;

[0108] The steel plate to be cooled is straightened and then transferred to a slow cooling pit to be cooled to 80°C, and the rolled steel plate is obtained after the pit is discharged, wherein the temperature of the steel plate to be cooled when entering the slow cooling pit is 400°C;

[0109] The rolled steel plate is heated to a predetermined temperature shown in Table 1 for austenitizing and holding, and then quenched, and the final cooling temperature of the quenching is shown in Table 1;

[0110] The quenched steel plate is stack cooled and tempered, wherein the tempering temperature is shown in Table 1, and the food contact baking tray steel is obtained.

[0111] The preheating temperature is selected from Table 1,

[0112] The rolled steel plate is heated to an austenitizing temperature shown in Table 1, and the heating coefficient of the heating is 1 min / mm,

[0113] The straightening is performed at 700°C,

[0114] The holding temperature of the quenching is shown in Table 1.

[0115] The arsenic content of the casting blank is 17 ppm.

[0116] The food contact baking tray steel obtained in the present example is a plate material, and the thickness is shown in Table 1. After the finish rolling step in the present example is completed, the cooling method is shown in Table 1.

[0117] Examples 2-6

[0118] The differences between Examples 2-6 and Example 1 are shown in Table 1.

[0119] Comparative Examples 1-3

[0120] The differences between Comparative Examples 1-3 and Example 1 are shown in Table 1.

[0121] Table 1 shows the conditions involved in Examples 1-6 and Comparative Examples 1-3. Table 1 is as follows:

[0122]

[0123]

[0124] Table 1

[0125] Relevant experiments and effect data:

[0126] The components of the food contact baking tray steel obtained in Examples 1-6 were tested, and the results are shown in Table 2.

[0127]

[0128] Table 2

[0129] Table 2 shows that the components of Examples 1-6 are relatively close, and do not contain harmful elements such as As, Cd, Pb, etc., which shows that the preparation method of the present application can obtain food contact baking tray steel with stable components.

[0130] The food contact baking tray steel obtained in Examples 1-6 and Comparative Examples 1-3 was tested for yield strength, tensile strength, elongation after fracture, surface HRC, unevenness, and residual austenite content, and the results are shown in Table 3.

[0131]

[0132] Table 3 shows the results of SEM and TEM tests on Examples 1, Comparative Example 1, and Comparative Example 3, respectively. Figures 1-6 .

[0133] It is found that there are great differences in the corresponding microstructure, properties and sheet shape under different processes.

[0134] As can be seen from the property results of Examples 1-6 and Comparative Examples 1-3 in Table 3, the processes in Examples 1-6 all meet the process requirements, and the overall properties, sheet shape and residual austenite all meet the technical requirements of the baking tray steel product in the present application.

[0135] Taking the microstructure of Example 1 as an example, Figure 1 and Figure 2 ), the overall tempered martensite is fully tempered, and the overall carbide is dispersedly distributed, which can meet the performance requirements and ensure good sheet shape stability under service conditions.

[0136] The performance results of the comparative examples are analyzed as follows:

[0137] In the comparative example 1, the post-rolling water cooling and no slow cooling measures were used, which led to large rolling residual stress. In addition, the quenched and tempered state of the comparative example 1 was directly quenched to room temperature, which led to large residual stress and further led to the problem that the plate shape was difficult to meet the requirements, and the hardness was higher than the standard requirement, which led to the fact that the steel plate in this state was difficult to meet the requirements. As shown in the microstructure of Figure 3 and Figure 4 , the overall carbide precipitation was insufficient, the dislocation density in the tempered martensite lath was high, and at the same time the strength and hardness were too high, which was not conducive to the plate shape stability of the baking tray steel during service.

[0138] In the comparative example 2, the final cooling temperature under the quenching process reached 350°C, which led to insufficient martensite transformation and retained part of residual austenite, which finally affected the microstructure state and hardness level, and also was difficult to meet the product requirements.

[0139] In the comparative example 3, the microstructure was softened due to the too high tempering temperature, which led to the decrease of strength and hardness, and finally led to the fact that the steel plate was difficult to meet the requirements. As can be seen from Figure 5 and Figure 6 , the overall carbide precipitation size was large, the dislocation density in the lath decreased significantly and the lath merged obviously, which affected the overall strength and hardness.

[0140] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the described range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in this text, it means that any quoted number (fraction or integer) within the indicated range is included.

[0141] In this application, the positional words such as "upper" and "lower" are specifically the directions of the drawing surface in the drawings unless otherwise stated. In addition, in the description of the specification, the terms "comprise", "include" and the like mean "including but not limited to". Moreover, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or devices including a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such processes, methods, articles or devices. Without more limitations, the elements defined by the statement "comprise" do not exclude the presence of other identical elements in the processes, methods, articles or devices including the elements. In this text, the relationship terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In this text, the "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the following cases: A exists alone, A and B exist together, and B exists alone. For the association relationship of more than three associated objects described by "and / or", it means that any one of the three associated objects can exist alone, or any at least two of them exist together, for example, for A, and / or B, and / or C, it means that any one of A, B and C exists alone, or any two of them exist together, or all three of them exist together. In this text, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b and c can be single or multiple.

[0142] The above description is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications of these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A method of making a food contact baking pan steel, the method comprising: Iron smelting-steel smelting-billet heating-rolling-straightening-into pit slow cooling-room temperature-temperature controlled quenching-pile cooling-tempering, characterized in that, specifically comprising the following steps: Carrying out iron smelting to obtain molten iron with low arsenic content, and obtaining billets after steel smelting, wherein the As content of the molten iron is ≤10 ppm; Heating and rolling the billets to obtain a steel plate to be cooled, wherein the heating temperature is 1150-1170℃, the opening rolling temperature in the process of finish rolling is 860-890℃, and the final rolling temperature is 800-830℃; After the steel plate to be cooled is straightened, it is transferred to a slow cooling pit to be cooled to not higher than 80℃, and a rolled steel plate is obtained after being taken out of the pit, wherein the temperature of the steel plate to be cooled when entering the slow cooling pit is not lower than 400℃, and the straightening temperature is 680-730℃; The rolled steel plate is heated to 905-915℃ for austenitizing and holding, and then quenched, and the final cooling temperature of the quenching is 120-180℃; The quenched steel plate is pile cooled and tempered, wherein the tempering temperature is 640-655℃, and the food contact baking tray steel is obtained; The steel smelting process comprises preliminary smelting and refining, The preliminary smelting comprises smelting by a converter, and the scrap steel used in the process of smelting by the converter is low-arsenic scrap steel generated in the steel smelting process; In the process of refining, the basicity of the slag is controlled to be 15-25, the arsenic content of the molten steel is controlled to be <10 ppm, and the arsenic content of the final billet is controlled to be less than 20 ppm; The food contact baking tray steel has the following properties: a surface Rockwell hardness of HRC 42-48, a yield strength of > 750 MPa, a tensile strength of 800-920 MPa, an elongation A 50 ≥ 25%, a reduction of area of > 45%, a carbon equivalent of 0.48-0.53, unevenness of < 2 mm / m, a harmful element content of < 0.001 mg / kg after immersion in a citric acid solution, wherein the harmful elements include As, Cd, Pb, a limit strength reduction factor at 250°C of > 0.

98.

2. The preparation method of the food contact baking tray steel according to claim 1, characterized in that, The heating coefficient of the heating of the billets is 1 min / mm-2 min / mm.

3. A food contact baking tray steel characterized in that, The food contact baking tray steel is prepared by the preparation method of the food contact baking tray steel according to any one of claims 1-2.

4. The food contact pan steel according to claim 3, characterized in that The metallographic structure of the food contact baking tray steel comprises at least one of tempered martensite and precipitated metal compounds.

5. The food contact pan steel according to claim 4, characterized in that The precipitated metal compounds comprise at least one of Ti-containing carbonitride, V-containing carbonitride and Cu-containing carbonitride.

6. The food contact pan steel according to claim 5, characterized in that The precipitated metal compounds comprise Cu-containing carbonitride, and the Cu-containing carbonitride is at least one of cementite and ε-carbide.

7. The food contact pan steel according to claim 3, characterized in that, In the metallographic structure of the food contact baking tray steel, the width of the tempered martensite lath is 600-900 nm, and the average diameter of the original austenite grains is 10-20 μm.

8. A baking tray characterised in that, The material of the baking tray is the food contact baking tray steel according to any one of claims 3-7.

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