Steel for nitriding pot and production method and application thereof

Abstract

The invention provides steel for a nitriding pot as well as a production method and application of the steel. The steel comprises the following components: 0.0015%-0.0035% of C, 0.09%-0.20% of Mn, less than or equal to 0.012% of S, less than or equal to 0.015% of P, less than or equal to 0.030% of Si, 0.020%-0.040% of Al, less than or equal to 0.0030% of N, 0.035%-0.050% of Ti and the balance of Fe and other inevitable impurities. Compared with the prior art, by controlling the content of carbon, manganese, titanium and the like in the steel, it can be guaranteed that the steel has certain strength, the problem of embrittlement of the nitriding pot is solved when the nitriding pot is prepared, and meanwhile it can be guaranteed that the steel has certain strength and also has good formability. By controlling the temperature parameters of the cold rolling process and cooperating with the hot rolling coiling temperature, a metallographic structure with the grain size of 8-10 levels is obtained, the stamping performance of the steel is improved, and the corrosion resistance of the steel is improved to a certain extent.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to steel for a nitriding pot and a production method and application thereof. Background Art

[0002] Since the preparation of the nitriding pot is usually to spin-form the steel plate, then scrub the surface oil, and then enter the pit furnace to heat to 500-550℃ for nitriding, the steel plate is required to have certain stamping properties to ensure that the steel plate can be spin-formed. Too high strength is not conducive to spinning, and too low strength is prone to large grains, which is easy to cause brittle cracks, and rust spots are more likely to appear on the surface after nitriding.

[0003] At present, the strength, plasticity and grain size of steel used for preparing nitriding pots cannot meet its manufacturing requirements at the same time. The patent with the publication number CN 106222570 A published on December 14, 2016 discloses a substrate for nitriding steel with excellent corrosion resistance and a production method, wt% C0.010-0.10%, Mn 0.10-1.00%, Si0.010-0.10%, P≤0.02%, S≤0.01%, Als 0.50-1.50%, N≤0.005%, Cr0.10-1.50%, Cu0.01-1.00%, Ni 0.01-1.00%. Preparation steps: smelting and continuous casting into billets; heating the billets; hot rolling; coiling; cold rolling; annealing; leveling. It is based on the steel used in traditional iron pans. After nitriding treatment, it can effectively avoid rust, and has high surface hardness, excellent corrosion resistance, stable high temperature performance and high fatigue strength. After nitriding treatment, low carbon steel plate can replace stainless steel and functional coated steel plate, and be used in the manufacture of frying pans, corrosion-resistant containers, etc. However, its elongation is low, which affects the processing and forming performance.

[0004] Therefore, it is urgent to propose a steel that meets the requirements of nitriding pot preparation, with high strength, plasticity and grain size to meet market demand. Summary of the invention

[0005] The purpose of the present invention is to provide a steel for nitriding pot and a production method thereof, which can ensure that the steel has a certain strength by controlling the content of carbon, manganese, titanium, etc. in the steel, eliminate the problem of brittle cracking of the nitriding pot when preparing the nitriding pot, and at the same time ensure that the steel has a certain strength and good formability. By controlling the temperature parameters of the cold rolling process and coordinating the hot rolling coiling temperature, a metallographic structure with a grain size of 8-10 is obtained, the stamping performance of the steel is improved, and the corrosion resistance of the steel is improved to a certain extent.

[0006] Another object of the present invention is to provide an application of steel for nitriding pots for manufacturing nitriding pots.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A steel for a nitriding pot, comprising the following components in percentage by mass:

[0009] C: 0.0015%~0.0035%, Mn: 0.09%~0.20%, S: ≤0.012%, P: ≤0.015%, Si: ≤0.030%, Al: 0.020%~0.040%, N: ≤0.0030%, Ti: 0.035%~0.050%, and the rest are Fe and other inevitable impurities.

[0010] Preferably, the steel for nitriding pot comprises the following components in mass percentage:

[0011] C: 0.0018%~0.0028%, Mn: 0.09%~0.15%, S: ≤0.012%, P: ≤0.015%, Si: ≤0.030%, Al: 0.020%~0.035%, N: ≤0.0030%, Ti: 0.035%~0.045%, and the rest are Fe and other inevitable impurities.

[0012] The metallographic structure of the steel for nitriding pot includes ferrite and cementite, wherein the volume proportion of the ferrite is 95-99%, the volume proportion of the cementite is 1-5%, and the grain size of the ferrite is 8.0-10;

[0013] The yield strength of the steel for the nitriding pot is 140-175 MPa, the tensile strength is 290-310 MPa, and the elongation is A 80 ≥44%, surface roughness Ra is 0.70~1.60μm.

[0014] The invention provides a production method for nitriding pot steel, which comprises hot rolling of continuous casting billet, pickling and cold continuous rolling, annealing, leveling and straightening.

[0015] The hot rolling includes rough rolling, and the thickness of the intermediate billet obtained by the rough rolling is 15-20% of the thickness of the continuous casting billet, preferably 16-18%;

[0016] The process also includes heating the continuous casting billet before the rough rolling, wherein the heating temperature is 1200-1240°C.

[0017] Preferably, the rough rolling horizontal rolling mill comprises a first horizontal rolling mill and a second horizontal rolling mill, the first horizontal rolling mill has three rolling passes, and the second horizontal rolling mill has three or five rolling passes;

[0018] Preferably, the reduction parameters of the first horizontal rolling mill include: a first pass reduction rate of 20-24%, a second pass reduction rate of 18-22%, and a third pass reduction rate of 15-18%;

[0019] Preferably, the outlet temperature of the rolled piece at the first horizontal rolling mill is 1030-1080°C.

[0020] Preferably, the rolled piece includes a descaling operation when entering and leaving the first horizontal rolling mill;

[0021] Preferably, the reduction parameters of the second horizontal rolling mill when the rolling passes are 3 passes include: the first pass reduction rate is 29-35%, the second pass reduction rate is 32-38%, and the third pass reduction rate is 16-20%;

[0022] Preferably, the reduction parameters of the second horizontal rolling mill when the rolling passes are 5 passes include: a first pass reduction rate of 20-24%, a second pass reduction rate of 20-25%, a third pass reduction rate of 20-25%, a fourth pass reduction rate of 20-24%, and a fifth pass reduction rate of 10-15%;

[0023] Preferably, when the rolling width of the rolled piece is greater than 1300 mm and / or the width reduction of the rolled piece is greater than 50 mm, the second horizontal rolling mill performs 5 rolling passes;

[0024] Preferably, the outlet temperature of the rolled piece at the second horizontal rolling mill is 1000-1030°C;

[0025] Preferably, the rolled product includes a descaling operation before entering the second horizontal rolling mill.

[0026] The hot rolling also includes finish rolling, and the finish rolling includes rolling the intermediate billet obtained by the rough rolling. The final rolling temperature of the rolled piece during the finish rolling is 860-900°C, preferably 865-895°C.

[0027] Preferably, the finish rolling further includes laminar cooling of the rolled piece, the laminar cooling method is front-stage cooling, and the opening degrees of the upper and lower headers of the front-stage cooling are both 80-100%, more preferably 100%.

[0028] Preferably, the laminar cooling further includes coiling the rolled piece, and the coiling temperature is 660-700°C, preferably 665-695°C.

[0029] The pickling cold rolling comprises pickling the rolled piece obtained after hot rolling and then rolling it;

[0030] Preferably, the parameters of the pickling cold rolling process include: pickling temperature 75-85°C, stretching and leveling machine elongation 1.5-2.5%, cold rolling reduction rate 70-80%, pickling S5 stand roll roughness 3.5-4.5 μm, and pickling S5 stand roll unit rolling force 5-7 MN / m.

[0031] The annealing soaking zone temperature is 780-820°C;

[0032] Preferably, the rolled piece after pickling and cold continuous rolling is placed in a vertical continuous annealing furnace for continuous annealing;

[0033] Preferably, the annealing is continuous annealing, including a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an over-aging section and a final cooling section;

[0034] More preferably, the preheating section temperature is 140-160°C, the heating section temperature is 805-820°C, the soaking section temperature is 810-820°C, the slow cooling section temperature is 640-660°C, the fast cooling section temperature is 390-440°C, the over-aging section temperature is 300-400°C, and the final cooling section temperature is 150-180°C.

[0035] The production method further comprises leveling and straightening the annealed rolled piece, wherein the leveled working roll has a roughness of 3.0 to 3.50 μm and a leveled elongation of 0.3 to 0.5%;

[0036] The elongation of the tension-correction is 0.03-0.1%.

[0037] The production method of steel for nitriding pot provided by the present invention comprises the following steps in sequence: desulfurization of molten iron, converter smelting, argon blowing, LF furnace refining, RH furnace vacuum decarburization; continuous casting of refined molten steel into continuous casting billets; hot rolling of the continuous casting billets, the hot rolling comprising rough rolling and finishing rolling, laminar cooling after finishing rolling and then coiling to obtain hot rolled coils; pickling of the hot rolled coils, pickling cold continuous rolling; leveling and tensioning to obtain steel for nitriding pots.

[0038] The steel for nitriding pot produced by the above method is a steel strip or a steel plate.

[0039] The application of the steel for nitriding pot provided by the present invention is used for manufacturing nitriding pots. The steel has good formability, no brittle cracking problem after nitriding, and no quality problems such as oxidation color and rust spots in smoke test after nitriding.

[0040] Compared with the prior art, the present invention can ensure that the steel has a certain strength by controlling the content of carbon, manganese, titanium, etc. in the steel. When preparing the nitriding pot, the problem of brittle cracking of the nitriding pot is eliminated. At the same time, the steel can have a certain strength and good formability. By controlling the temperature parameters of the cold rolling process and coordinating the hot rolling coiling temperature, a metallographic structure with a grain size of 8-10 is obtained, the stamping performance of the steel is improved, and the anti-rust ability of the steel is improved to a certain extent; there is no brittle cracking problem after nitriding, and no quality problems such as oxidation color and rust spots appear in the smoke test after nitriding. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1The metallographic structure diagram of the steel for nitriding pot provided in Example 1 of the present invention;

[0042] Figure 2 This is the metallographic structure diagram of the steel for nitriding pot provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The present invention provides a nitriding pot steel, comprising the following components in percentage by mass:

[0045] C: 0.0015%~0.0035%, Mn: 0.09%~0.20%, S: ≤0.012%, P: ≤0.015%, Si: ≤0.030%, Al: 0.020%~0.040%, N: ≤0.0030%, Ti: 0.035%~0.050%, and the rest are Fe and other inevitable impurities.

[0046] Preferably, the steel for nitriding pot comprises the following components in mass percentage:

[0047] C: 0.0018%~0.0028%, Mn: 0.09%~0.15%, S: ≤0.012%, P: ≤0.015%, Si: ≤0.030%, Al: 0.020%~0.035%, N: ≤0.0030%, Ti: 0.035%~0.045%, and the rest are Fe and other inevitable impurities.

[0048] The design ideas of the present invention are as follows:

[0049] C: A strengthening element of steel. In order to control the steel to have a certain strength, its content is controlled between 0.0015 and 0.0035%.

[0050] Si: deteriorates the surface properties of steel. As the Si content increases, the iron oxide scale on the steel becomes difficult to remove, which affects the effect of the pickling process. Therefore, the silicon content must be controlled within a low range.

[0051] Mn: Appropriate Mn is to supplement the strength of steel. Mn can also play a deoxidation role, reduce the oxygen content in the product, thereby improving the processability of the product. Mn can also combine with S to form high-melting-point MnS, reduce the low-melting-point FeS content, and avoid hot brittleness of the product. The present invention controls Mn to 0.09% to 0.20%.

[0052] P: P is a harmful element in steel. Although it increases the strength of the material, it also increases the cold brittleness of the steel and reduces the plasticity of the material. Generally, the lower the better. In order to ensure the excellent performance of the product, the P content of the present invention is controlled to ≤0.015%.

[0053] S: S is a harmful element in steel, which will form inclusions and reduce the ductility and toughness of steel. Generally, the lower the better. In order to ensure the excellent performance of the product, the S content of the present invention is controlled to be ≤0.012%.

[0054] Al: Al is a strong deoxidizer and has a strong binding force with N. The AlN generated during the reaction can reduce the aging of the finished product, and AlN can inhibit the growth of grains in the steel. Controlling its proportion within the range of Al: 0.020% to 0.040% in the present invention can refine the grains during the heating and annealing of the steel.

[0055] Ti: Ti has a strong affinity with elements such as N, C, and S, and combines with carbon and nitrogen in steel to form Ti(C,N) compounds, thereby fixing elements such as C and N in the steel, reducing their precipitation along the austenite grain boundaries, and improving the mechanical properties and aging of the steel plate; at the same time, the fine and dispersed Ti(C,N) compounds precipitated at high temperatures can inhibit the growth of high-temperature austenite grains and play a role in refining the grains, but as the Ti content increases, TiN is precipitated at the grain boundaries during the nitriding process, increasing the risk of nitriding cracking. In combination with the present invention, the control of the Ti content in the steel can fix all the C, N, and S elements in the steel, which is calculated to be 0.035% to 0.050%.

[0056] N: a strengthening element of steel. In order to improve the strength of steel, a small amount of N may be contained as a supplement. In the present invention, N is controlled to be ≤0.0030%.

[0057] The production method of the steel for nitriding pot comprises hot rolling of continuous casting billet, pickling and cold continuous rolling, annealing, leveling and straightening.

[0058] By controlling the element composition of the continuous casting billet within the above range and combining the temperature control of the annealing process, the steel coil is kept at a temperature of 780-820°C in the soaking section, and the flat elongation is 0.30-0.50%, which can ensure that the steel has a certain strength. When preparing the nitriding pot, the problem of brittle cracking of the nitriding pot is eliminated. At the same time, the steel can have a certain strength and good formability. By controlling the temperature parameters of the cold rolling process and coordinating the hot rolling coiling temperature, a metallographic structure with a grain size of 8-10 is obtained, the stamping performance of the steel is improved, and the corrosion resistance of the steel is improved to a certain extent.

[0059] In an optional embodiment, annealing includes a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an over-aging section and a final cooling section.

[0060] Among them, the preheating section, heating section, soaking section and slow cooling section are the first stage of annealing, and their main function is to recrystallize the ferrite in the steel and grow the ferrite grains. However, as mentioned above, due to the control of the temperature in the soaking section by the present invention, the growth of the grains in the first stage will not grow infinitely, but will be limited and controllable, thereby ensuring the strength of the steel while avoiding brittle fracture.

[0061] The rapid cooling section, over-aging section and final cooling section are the second stage of annealing. Their main function is to determine the distribution of cementite in the organization and the content of supersaturated solid solution carbon, so as to ensure that the quality of the steel meets the manufacturing requirements of the nitriding pot.

[0062] In the present invention, the annealing, the preheating section temperature is 140-160°C, the heating section temperature is 805-820°C, the soaking section temperature is 810-820°C, the slow cooling section temperature is 640-660°C, the fast cooling section temperature is 390-440°C, the over-aging section temperature is 300-400°C, and the final cooling section temperature is 150-180°C.

[0063] In an optional embodiment, the hot rolling includes rough rolling, and the intermediate billet obtained by the rough rolling has a thickness of 15-20%, preferably 16-18%, of the thickness of the continuous casting billet. For example, when the thickness of the continuous casting billet is 230 mm, the intermediate billet obtained by the rough rolling has a thickness of 34.5-46 mm, more preferably 36.8-41.4 mm.

[0064] Preferably, the horizontal rolling mill for rough rolling includes a first horizontal rolling mill and a second horizontal rolling mill, the first horizontal rolling mill has three rolling passes, and the second horizontal rolling mill has three or five rolling passes.

[0065] It can be understood that the rough rolling process of hot rolling is generally composed of a horizontal rolling mill and a vertical rolling mill, wherein the horizontal rolling mill is used to adjust the thickness of the rolled piece, and the vertical rolling mill is used to adjust the width of the rolled piece, and there are two horizontal rolling mills and two vertical rolling mills, which are arranged alternately. During rolling, the rolled piece passes through the first vertical rolling mill, the first horizontal rolling mill, the second vertical rolling mill, and the second horizontal rolling mill in sequence, and then returns in the reverse direction along the above path for multiple rolling to ensure that the specifications of the intermediate billet obtained after rough rolling meet the requirements.

[0066] Preferably, in order to control the plate shape and thickness accuracy of the intermediate billet, the reduction rate of each rough rolling pass is reduced successively, and the reduction parameters of the first horizontal rolling mill include: the first pass reduction rate is 20-24%, the second pass reduction rate is 18-22%, and the third pass reduction rate is 15-18%.

[0067] Preferably, the outlet temperature of the rolled piece at the first horizontal rolling mill is 1030-1080°C.

[0068] Preferably, in order to improve the surface quality of the rolled piece, the rolled piece includes a descaling operation when entering and leaving the first horizontal rolling mill. The descaling operation in the rough rolling can be processed by high-pressure water descaling.

[0069] Preferably, in order to control the plate shape and thickness accuracy of the intermediate billet, the reduction rate of each rough rolling pass is reduced successively. The reduction parameters of the second horizontal rolling mill when the rolling passes are 3 passes include: a reduction rate of 29-35% in the first pass, a reduction rate of 32-38% in the second pass, and a reduction rate of 16-20% in the third pass.

[0070] Preferably, in order to control the plate shape and thickness accuracy of the intermediate billet, the reduction rate of each rough rolling pass is reduced successively. The reduction parameters of the second horizontal rolling mill when the rolling passes are 5 passes include: a reduction rate of 20-24% in the first pass, a reduction rate of 20-25% in the second pass, a reduction rate of 20-25% in the third pass, a reduction rate of 20-24% in the fourth pass, and a reduction rate of 10-15% in the fifth pass.

[0071] Preferably, the reduction parameters of the second horizontal rolling mill when the rolling passes are 5 passes include: the first pass reduction rate is 20-23%, the second pass reduction rate is 22-25%, the third pass reduction rate is 21-24%, the fourth pass reduction rate is 21-23%, and the fifth pass reduction rate is 12-15%.

[0072] Preferably, in order to ensure that the thickness of the intermediate billet obtained is within the aforementioned range, when the width of the continuous casting billet is large or the width reduction is large, it is necessary to increase the rolling passes. In some embodiments of the present invention, the above problem is solved by increasing the rolling passes of the second horizontal roller. Specifically, when the rolling width of the rolled piece is greater than 1300mm and / or the width reduction of the rolled piece is greater than 50mm, the rolling passes of the second horizontal roller mill are 5 passes.

[0073] Preferably, the outlet temperature of the rolled piece at the second horizontal rolling mill is 1000-1030°C.

[0074] Preferably, in order to ensure the rolling temperature and the final rolling temperature of the second horizontal rolling mill, the rolled piece is only descaled before entering the second horizontal rolling mill.

[0075] Since the strength of the steel used for the nitriding pot is relatively high, the rough rolling adopts a 3+3 or 3+5 mode, that is, the first horizontal roll is rolled for 3 passes, and the second horizontal roll is rolled for 3 or 5 passes, which can ensure that the obtained steel has a higher strength. The present invention controls the parameters of the rough rolling within the above range because the temperature of the rolled piece is high during the rough rolling, the deformation resistance is small, the plasticity is good, and the total reduction rate of the rough rolling mill is large, so as to reduce the load of the finishing mill.

[0076] In an optional embodiment, since rough rolling is hot rolling, the continuous casting billet needs to be heated before rough rolling to ensure effective deformation of the continuous casting billet to the rolled piece. The heating is carried out in a heating furnace with a heating temperature of 1200-1240°C.

[0077] In an optional embodiment, the hot rolling further comprises finishing rolling, and the finishing rolling comprises rolling the intermediate billet obtained by the rough rolling, and the final rolling temperature of the rolled piece during the finishing rolling is 860-900° C., preferably 865-895° C. Controlling the final rolling temperature within the above range can make the ferrite recrystallize more fully and make the ferrite grains grow to a suitable grain size.

[0078] Preferably, the finished rolling also includes laminar cooling of the rolled piece, the laminar cooling method is front-end cooling, and the opening of the upper and lower headers of the front-end cooling is 80-100%, more preferably 100%. Controlling the opening of the upper and lower headers of the cold flow cooling within the above range can effectively refine the grains.

[0079] Preferably, after laminar cooling, the rolled piece is also coiled to obtain a hot-rolled coil. In order to meet the high strength requirements of the steel for the nitriding pot, it is necessary to control the grain growth during the coiling process to prevent the coiling temperature from being too high, which causes the grain growth to affect the performance of the steel. Therefore, the coiling temperature is 660-700°C, preferably 665-695°C.

[0080] In an optional embodiment, the pickling cold rolling comprises pickling the rolled piece obtained after hot rolling and then placing it in a pickling combined rolling unit for rolling.

[0081] Preferably, the parameters of the pickling cold rolling process include: pickling temperature 75-85°C, stretch leveler elongation 1.5-2.5%, cold rolling reduction rate 70-80%, pickling S5 stand roll roughness 3.5-4.5 μm, and pickling S5 stand roll unit rolling force 5-7 MN / m.

[0082] In an optional embodiment, the annealed rolled piece is further flattened and straightened, the roughness of the flattened working roll is 3.0-3.50 μm, the elongation of the flattened work piece is 0.30-0.50%, and the elongation of the straightened work piece is 0.03-0.1%.

[0083] In an optional embodiment, the preparation of the continuous casting billet includes, in sequence, desulfurization of molten iron, converter smelting, blowing argon into the smelted molten steel, refining through an RH furnace, and then continuously casting the molten steel into a continuous casting billet. The above preparation process can obtain purer molten steel, eliminate problems such as inclusions and sand holes on the steel surface, and the above preparation process can be prepared using an existing smelting method, as long as the element composition of the continuous casting billet is within the range described in the present invention.

[0084] The following are several specific embodiments of the present invention:

[0085] Example 1

[0086] A method for producing steel for a nitriding pot comprises the following steps:

[0087] S01. Preparation of continuous casting billet

[0088] The existing smelting method is used to sequentially carry out molten iron desulfurization, converter smelting, argon blowing of the smelted molten steel, refining through LF furnace, decarburization through RH furnace, and then continuous casting of the molten steel into continuous casting billets. The composition of the continuous casting billet is C: 0.0027%, Mn: 0.16%, S: 0.010%, P: 0.012%, Si: 0.021%, Al: 0.035%, N: 0.0022%, Ti: 0.045%, and the rest is Fe and other inevitable impurities.

[0089] S02, hot rolling:

[0090] S021. Heating: placing the continuous casting billet in a heating furnace and heating it to 1226°C.

[0091] S022, rough rolling: the heated continuous casting billet is placed in the rough rolling unit for rolling to obtain the intermediate billet. The thickness of the continuous casting billet is 230mm, the thickness of the intermediate billet is 40mm, and the specific rough rolling process parameters are as follows:

[0092] The horizontal rolling mill for rough rolling includes a first horizontal rolling mill and a second horizontal rolling mill.

[0093] The first horizontal rolling mill has three rolling passes, with a reduction rate of 24% in the first pass, 21% in the second pass, and 16% in the third pass. The outlet temperature of the rolled piece at the first horizontal rolling mill is 1040°C. In order to improve the surface quality of the rolled piece, high-pressure water is used to descale the rolled piece when it enters and leaves the first horizontal rolling mill.

[0094] Since the rolling width of the rolled piece is 1250 mm, the second horizontal rolling mill adopts three-pass rolling, with a first-pass reduction rate of 34%, a second-pass reduction rate of 36%, and a third-pass reduction rate of 18.37%.

[0095] The outlet temperature of the rolled piece at the second horizontal rolling mill is 1000°C. In order to ensure the rolling temperature and final rolling temperature of the second horizontal rolling mill, the rolled piece is only descaled before entering the second horizontal rolling mill.

[0096] S023, finishing rolling, laminar cooling and coiling: The intermediate billet obtained by rough rolling is rolled, and the thickness of the rolled piece after finishing rolling is 5.4 mm. The final rolling temperature of the rolled piece during finishing rolling is 880°C. After finishing rolling, the rolled piece is laminar cooled, and the laminar cooling method is front-stage cooling. The opening degrees of the upper and lower headers of the front-stage cooling are both 100%. After laminar cooling, the rolled piece is coiled, and the coiling temperature is 680°C to obtain a hot rolled coil.

[0097] S03, Pickling and Cold Rolling

[0098] The hot-rolled coil obtained after hot rolling is pickled and then placed in a pickling combined rolling unit for rolling. The rolling parameters include: the hydrochloric acid concentration of the pickling is 182g / L, the pickling temperature is 81°C, the elongation of the tension leveler is 1.50%, the cold rolling reduction rate is 77.63%, the roughness of the pickling S5 stand roll is 4.0μm, the unit rolling force of the pickling S5 stand roll is 5MN / m, and the pickling thickness is 1.208mm.

[0099] S04, Annealing

[0100] Annealing is carried out in a vertical continuous annealing furnace. The workpiece after pickling and cold rolling is placed in a vertical continuous annealing furnace and sequentially passes through a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an aging section and a final cooling section.

[0101] Among them, the temperature of the preheating section is 150℃, the temperature of the heating section is 810℃, the temperature of the soaking section is 815℃, the temperature of the slow cooling section is 650℃, the temperature of the fast cooling section is 430℃, the temperature of the aging section is 380℃, and the temperature of the final cooling section is 160℃.

[0102] S05, leveling, straightening

[0103] The parameters of leveling and tension leveling include: the roughness of the leveling working roll is 3.0 μm, the elongation of leveling is 0.35%, and the elongation of tension leveling is 0.1%.

[0104] The steel strip for nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip is 1.125 μm as measured by a roughness meter. The steel strip is placed under a scanning electron microscope for observation. Figure 1The results shown by Figure 1 It can be known that the structure of the steel strip provided in the embodiment of the present invention is ferrite and cementite, and the content of ferrite is 97.4%, the content of cementite is 2.6%, and the grain size of ferrite is 8.0.

[0105] Example 2

[0106] This embodiment provides a method for producing steel for a nitriding pot, and the specific steps are similar to those of Embodiment 1, except that:

[0107] The heating temperature of the heating furnace in step S021 is 1230°C.

[0108] In step S023, the final rolling temperature of the rolled piece during finish rolling is 890°C, and the coiling temperature is 690°C.

[0109] The temperature of the soaking section in step S04 is 812°C.

[0110] The flattening elongation in step S05 is 0.45%.

[0111] The steel for the nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip measured by a roughness meter is 1.08 μm.

[0112] Example 3

[0113] This embodiment provides a method for producing steel for a nitriding pot, and the specific steps are similar to those of Embodiment 1, except that:

[0114] The heating temperature of the heating furnace in step S021 is 1228°C.

[0115] In step S023, the final rolling temperature of the rolled piece during finish rolling is 880°C, and the coiling temperature is 665°C.

[0116] The temperature of the soaking section in step S04 is 814°C.

[0117] The elongation rate of flattening in step S05 is 0.40%.

[0118] The steel for the nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip measured by a roughness meter is 1.093 μm.

[0119] Example 4

[0120] This embodiment provides a method for producing steel for a nitriding pot, comprising the following steps:

[0121] S01. Preparation of continuous casting billet

[0122] The existing smelting method is used to sequentially carry out molten iron desulfurization, converter smelting, argon blowing, and then refining through LF furnace, vacuum decarburization in RH furnace, and then the molten steel is continuously cast into continuous casting billets. Among them, the composition of the continuous casting billet is C: 0.0032%, Mn: 0.18%, S: 0.009%, P: 0.013%, Si: 0.023%, Al: 0.030%, Ti: 0.042%, N: 0.0025%, and the rest is Fe and other inevitable impurities.

[0123] S02, hot rolling:

[0124] S021. Heating: placing the continuous casting billet in a heating furnace and heating it to 1232°C.

[0125] S022, rough rolling: the heated continuous casting billet is placed in the rough rolling unit for rolling to obtain the intermediate billet. The thickness of the continuous casting billet is 230mm, the thickness of the intermediate billet is 42mm, and the specific rough rolling process parameters are as follows:

[0126] The horizontal rolling mill for rough rolling includes a first horizontal rolling mill and a second horizontal rolling mill.

[0127] The first horizontal rolling mill has three rolling passes, with a reduction of 21% in the first pass, 19% in the second pass, and 17% in the third pass. The outlet temperature of the rolled piece at the first horizontal rolling mill is 1050°C. In order to improve the surface quality of the rolled piece, high-pressure water is used to descale the rolled piece when it enters and leaves the first horizontal rolling mill.

[0128] Since the rolling width of the rolled piece is 1350mm, the second horizontal rolling mill adopts five-pass rolling, with a first pass reduction rate of 21%, a second pass reduction rate of 22%, a third pass reduction rate of 21%, a fourth pass reduction rate of 21%, and a fifth pass reduction rate of 10.60%. The outlet temperature of the rolled piece at the second horizontal rolling mill is 1020℃. In order to ensure the rolling temperature and final rolling temperature of the second horizontal rolling mill, the rolled piece is only descaled before entering the second horizontal rolling mill.

[0129] S023, finishing rolling, laminar cooling and coiling: The intermediate billet obtained by rough rolling is rolled, and the thickness of the rolled piece after finishing rolling is 4.75 mm, and the final rolling temperature of the rolled piece during finishing rolling is 880°C. After finishing rolling, the rolled piece is laminar cooled, and the laminar cooling method is front-stage cooling, and the opening degrees of the upper and lower headers of the front-stage cooling are both 100%.

[0130] After laminar cooling, the rolled piece is coiled at a coiling temperature of 680° C. to obtain a hot rolled coil.

[0131] S03, Pickling and Cold Rolling

[0132] The hot-rolled coil obtained after hot rolling is pickled and then placed in a pickling combined rolling unit for rolling. The rolling parameters include: the hydrochloric acid concentration of the pickling is 165g / L, the pickling temperature is 84°C, the elongation of the tension leveler is 1.5%, the cold rolling reduction rate is 79.01%, the roughness of the pickling S5 stand roll is 3.5μm, the unit rolling force of the pickling S5 stand roll is 5.5MN / m, and the pickling thickness is 0.997mm.

[0133] S04, Annealing

[0134] Annealing is carried out in a vertical continuous annealing furnace. The workpiece after pickling and cold rolling is placed in a vertical continuous annealing furnace and sequentially passes through a preheating section, a heating section, a soaking section, a slow cooling section, a fast cooling section, an aging section and a final cooling section.

[0135] Among them, the temperature of the preheating section is 155°C, the temperature of the heating section is 809°C, the temperature of the soaking section is 810°C, the temperature of the slow cooling section is 660°C, the temperature of the fast cooling section is 435°C, the temperature of the over-aging section is 380°C, and the temperature of the final cooling section is 160°C.

[0136] S05, leveling, straightening

[0137] The parameters of leveling and tension leveling include: the roughness of the leveling working roll is 3.5μm, the elongation of leveling is 0.40%, and the elongation of tension leveling is 0.1%.

[0138] The steel strip for nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip is 1.03 μm as measured by a roughness meter. The steel strip is placed under a scanning electron microscope for observation. Figure 2 The results shown by Figure 2 It can be seen that the structure of the steel strip provided in the embodiment of the present invention is ferrite and cementite, and the volume content of ferrite is 98.42%, the volume content of cementite is 1.58%, and the grain size of ferrite is 8.5.

[0139] Example 5

[0140] This embodiment provides a method for producing steel for a nitriding pot, and the specific steps are similar to those of Embodiment 1, except that:

[0141] The heating temperature of the heating furnace in step S021 is 1226°C.

[0142] In step S023, the final rolling temperature of the rolled piece during finish rolling is 885°C, and the coiling temperature is 685°C.

[0143] The temperature of the soaking section in step S04 is 812°C.

[0144] The steel for the nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip measured by a roughness meter is 1.06 μm.

[0145] Example 6

[0146] This embodiment provides a method for preparing steel for a nitriding pot, and the specific steps are similar to those of Embodiment 1, except that:

[0147] The heating temperature of the heating furnace in step S021 is 1231°C.

[0148] In step S023, the final rolling temperature of the rolled piece during finish rolling is 870°C, and the coiling temperature is 682°C.

[0149] The temperature of the soaking section in step S04 is 809°C.

[0150] The elongation rate of flattening in step S05 is 0.40%.

[0151] The steel for the nitriding pot prepared through the above steps in this embodiment is a steel strip. The surface roughness of the steel strip measured by a roughness meter is 1.103 μm.

[0152] Comparative Example 1

[0153] This comparative example provides a method for producing steel for a nitriding pot, and the specific steps are the same as those in Example 1, except that the annealing soaking temperature in step S04 includes: 760℃。

[0154] Comparative Example 2

[0155] This comparative example provides a method for producing steel for a nitriding pot, and the specific steps are the same as those in Example 1, except that the annealing soaking temperature in step S04 includes: 835℃。

[0156] Comparative Example 3

[0157] This comparative example provides a method for producing steel for a nitriding pot. The specific steps are the same as those in Example 1, except that the final rolling temperature in step S023 is 850℃。

[0158] Comparative Example 4

[0159] This comparative example provides a method for producing steel for a nitriding pot. The specific steps are the same as those in Example 1, except that the final rolling temperature in step S023 is 945℃。

[0160] Comparative Example 5

[0161] This comparative example provides a method for preparing steel for a nitriding pot. The specific steps are the same as those in Example 1, except that the coiling temperature in step S023 is 620℃。

[0162] Comparative Example 6

[0163] This comparative example provides a method for preparing steel for a nitriding pot. The specific steps are the same as those in Example 1, except that the coiling temperature in step S023 is 740℃。

[0164] Test Example 1

[0165] The mechanical properties of the steel for nitriding pots prepared by the methods of Examples 1 to 6 and Comparative Examples 1 to 6 were tested according to GB / T228, wherein the yield strength, tensile strength and elongation A can be obtained through the tensile test. 80 The results are shown in Table 1.

[0166] Table 1 Mechanical properties of steel for nitriding pot

[0167]

[0168]

[0169] As can be seen from Table 1, the embodiment of the present invention controls the composition and production method of the steel for the nitriding pot, and the obtained steel for the nitriding pot has good mechanical properties and can fully meet the requirements of the nitriding pot for steel. It is used to prepare the nitriding pot, first spin it into a pot shape, then clean the surface, and enter the pit furnace for gas nitriding. The temperature is generally between 500 and 550 ° C. After nitriding, its formability is good, there is no brittle cracking problem after nitriding, and there is no quality problem of oxidation color and rust spots in the salt spray test after nitriding. Comparative Example 1 has insufficient ferrite grain growth due to the low temperature of the soaking section of annealing, so the yield strength is high and the stamping performance is affected. Comparative Example 2 has excessive growth of ferrite grains due to the high temperature of the soaking section of annealing, so the yield strength and tensile strength are low, and it is easy to crack after nitriding and cannot meet the requirements of nitriding steel. Comparative Example 3 has a low final rolling temperature, which is easy to cause hot rolling in two phases, resulting in mixed crystal structure, and easy cracking during stamping. In comparative example 4, the final rolling temperature is too high, resulting in excessively large hot-rolled ferrite grains and low yield strength, which cannot meet the requirements of nitriding steel. In comparative example 5, the coiling temperature is too low, resulting in fine hot-rolled ferrite grains and high yield strength, which affects the stamping performance and cannot meet the requirements of nitriding steel. In comparative example 6, the coiling temperature is too high, resulting in large hot-rolled ferrite grains, which are prone to brittle cracking and cannot meet the requirements of nitriding steel.

[0170] The underlined data above do not meet the requirements of the present invention.

[0171] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A steel for a nitriding pot, characterized in that: The steel for nitriding pot includes the following components in mass percentage: C: 0.0015%~0.0035%, Mn: 0.09%~0.20%, S: ≤0.012%, P: ≤0.015%, Si: ≤0.030%, Al: 0.020%~0.040%, N: ≤0.0030%, Ti: 0.035%~0.050%, and the rest are Fe and other inevitable impurities.

2. The steel for nitriding pot according to claim 1, characterized in that: The metallographic structure of the steel for nitriding pot includes ferrite and cementite, wherein the volume proportion of the ferrite is 95-99%, the volume proportion of the cementite is 1-5%, and the grain size of the ferrite is 8.0-10.

3. The steel for nitriding pot according to claim 1 or 2, characterized in that: The yield strength of the steel for the nitriding pot is 140-175 MPa, the tensile strength is 290-310 MPa, and the elongation is A 80 ≥44%, surface roughness Ra is 0.70~1.60μm.

4. A method for producing steel for a nitriding pot according to any one of claims 1 to 3, characterized in that: The production method comprises: hot rolling of continuous casting billet, pickling and cold continuous rolling, annealing, leveling and straightening.

5. The production method according to claim 4, characterized in that: The hot rolling of the continuous casting slab includes finishing rolling, and the final rolling temperature of the finishing rolling is 860-900°C.

6. The production method according to claim 4, characterized in that: The continuous casting slab is coiled after hot rolling, and the coiling temperature is 660-700°C.

7. The production method according to claim 4, characterized in that: In the annealing, the temperature of the soaking zone is controlled to be 780-820°C.

8. The production method according to claim 4 or 7, characterized in that: For the annealing, the preheating section temperature is 140-160°C, the heating section temperature is 805-820°C, the soaking section temperature is 810-820°C, the slow cooling section temperature is 640-660°C, the fast cooling section temperature is 390-440°C, the over-aging section temperature is 300-400°C, and the final cooling section temperature is 150-180°C.

9. The production method according to claim 4, characterized in that: The flattening has a flattening elongation of 0.30 to 0.50%.

10. An application of the steel for nitriding pot according to any one of claims 1 to 3, characterized in that: Used in the manufacture of nitriding pots.

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