CN113564476A

CN113564476A - Base plate for nitriding steel, production method, nitriding steel with excellent corrosion resistance, nitriding method and application thereof

Info

Publication number: CN113564476A
Application number: CN202110857510.0A
Authority: CN
Inventors: 俞波; 张宜; 汤亨强; 汪建威; 杨平; 王占业; 李进; 吴浩; 黄冉; 杨峥
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2021-07-28
Filing date: 2021-07-28
Publication date: 2021-10-29

Abstract

The invention provides a nitriding steel substrate and a production method thereof, nitriding steel with excellent corrosion resistance and a nitriding method and application thereof, wherein the substrate comprises the following components: c C: 0.005-0.045%, Si: less than or equal to 0.03%, Mn: 0.10-0.30%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, Als: 0.030-0.065%, more than or equal to 0.01% and less than or equal to 0.055% of Ti, more than or equal to 0.005% and less than or equal to 0.03% of Cr, and the balance of Fe and inevitable impurities. Compared with the prior art, the base plate has excellent forming performance and good nitriding property, and finally obtains nitriding steel with a nitriding layer of 20-60 mu m and excellent corrosion resistance by combining a corresponding nitriding process, has excellent corrosion resistance and wear resistance, and can not be perforated after being soaked in NaCl brine for 1000 hours.

Description

Base plate for nitriding steel, production method, nitriding steel with excellent corrosion resistance, nitriding method and application thereof

Technical Field

The invention belongs to the field of metal materials and the field of gas nitriding processes, and particularly relates to a substrate for nitriding steel, a production method, nitriding steel with excellent corrosion resistance, and a nitriding method and application thereof.

Background

At present, because the kitchen ware is mainly used in kitchens and is in a humid and dark environment, the kitchen ware is extremely easy to corrode, rust is generated, the appearance is influenced, and even the products are scrapped. Meanwhile, some pots are repeatedly corroded by the residues of heating, acidity, alkalinity and water stain. At present, pots made of various materials exist in the market, such as aluminum alloy, stainless steel, iron, aluminum, enamel and the like, but pots made of the materials such as the aluminum alloy, the stainless steel, the aluminum and the like have higher production cost, and some trace alloy elements can be absorbed by human bodies along with food when the materials are cooked, so that the health of the human bodies is seriously influenced, and iron materials are also rusty and scrapped easily in the actual use process of the traditional pot materials in China.

Chinese patent publication No. CN 106222570a, "a substrate for nitrided steel with excellent corrosion resistance and production method" published in 2016, 12, month and 14 discloses a nitrided steel substrate with excellent corrosion resistance, which comprises the following chemical components (mass fraction): c: 0.01 to 0.1%, Mn 0.1 to 1.0%, Si: 0.01-0.1%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, Als: 0.5-1.5%, N is less than or equal to 0.005%, Cr: 0.1 to 1.5%, Cu: 0.01 to 1.0%, Ni: 0.01-1.0% of Fe and inevitable impurities, and nitriding to obtain the nitriding pot with excellent corrosion resistance. The method adopts a low-C, high-ALs and high-Cr component system, and simultaneously adds elements such as Cu and Ni in steel, so that the cost of the product is increased, the method for evaluating the corrosion resistance is observed by naked eyes, the product is easily misjudged to be unqualified products by environment, abnormal points of a base material, material defects and the like, meanwhile, the structure and the appearance of a nitriding layer are not described, the nitriding period is 20-30 h, the period is longer, and the production rhythm is slow.

Chinese patent publication No. CN101649441A, "nitriding process method of austenitic stainless steel material", published 2/17/2010, discloses a nitriding treatment method for austenitic stainless steel. The method comprises the steps of adopting a two-step process for treatment, firstly carrying out pretreatment, annealing at 810 ℃ for 2 hours, then carrying out sand blowing, then carrying out nitriding treatment, carrying out heat preservation at 600 ℃ for 10-20 hours, then heating to 620-650 ℃ and carrying out heat preservation for 10-20 hours to obtain a nitriding layer with the thickness of about 20 micrometers. The nitriding process provided by the patent is a stainless steel process, and the process needs to be carried out for 20-40 hours, so that the nitriding time is long and the process is complex; and the corrosion resistance of the sample piece after nitriding is not described, and the effect is not known, but the nitriding time can be effectively shortened, a nitriding layer with excellent corrosion resistance can be obtained, the pot is further protected, the pot is prevented from being corroded in the using process, and the life cycle of the product is prolonged.

Published Chinese patent No. CN206761522U Pan and cooking utensil, 19.12.2017 discloses a cookware with multiple coatings formed on the inner surface, and an outer surface layer which is a non-stick layer and simultaneously has corrosion resistance and wear resistance. The coating is formed by plasma spraying and is made of metal oxide (Al)₂O₃、TiO₂、ZrO₂) And metal fluorides (PTFE or PFA). While the inner surface layer thereof is provided with the 3 layers, whichThe production process is complex in the preparation process and the production cost is high.

In 2019, 8, 13 th month, published chinese patent publication No. CN110117747A "a method for producing high Al nitrided steel", which discloses high Al nitrided steel having chemical components in mass percent C: 0.36-0.40%, Si: 0.22 to 0.35, Mn: 0.16-0.22, P is less than or equal to 0.015, S is less than or equal to 0.008, Cr: 1.45-1.55, Mo: 0.16 to 0.22, Al: 0.75-1.0 wt%, Ni less than or equal to 0.3 wt%, Cu less than or equal to 0.2 wt%, and Fe and inevitable impurity for the rest. The component system belongs to special steel series, the contents of Cr, Mo and Al are high, and the product is mainly used for mechanical equipment such as high-fatigue and high-wear-resistance mechanical screws, barrels, cylinders and the like; the patent mainly solves the problems of high Al on steel making, rolling and other processes, and the like, so as to obtain a plate blank with excellent surface quality and mechanical property.

Disclosure of Invention

The invention aims to provide a base plate for nitriding steel and a production method, which not only have good forming performance, but also have good permeability.

The invention also aims to provide nitriding steel with excellent corrosion resistance and a nitriding method thereof, wherein the substrate is nitrided by adopting a matched nitriding process to obtain a nitriding layer with the surface layer of about 20-60 mu m, so that a sample piece has excellent corrosion resistance.

A final object of the invention is to provide the use of nitriding steels with excellent corrosion resistance for the manufacture of utensils, in particular pots.

The specific technical scheme of the invention is as follows:

the base plate for the nitriding steel comprises the following components in percentage by mass:

c: 0.005-0.045%, Si: less than or equal to 0.03%, Mn: 0.10-0.30%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, Als: 0.030-0.065%, more than or equal to 0.01% and less than or equal to 0.055% of Ti, more than or equal to 0.005% and less than or equal to 0.03% of Cr, and the balance of Fe and inevitable impurities;

further, the substrate for nitriding steel contains less than 0.005% of Sn, N: less than or equal to 0.005 percent; as is less than 0.005 percent;

furthermore, when the C content is less than or equal to 0.01%, the Ti content is more than or equal to 0.03%, and the Mn content is more than or equal to 0.2%. The experimental steel is ensured to have certain strength and hardness, but the contents of Mn and Ti cannot be too high, otherwise MnS and Ti (C, N) precipitates are easily formed, and after the sizes of the precipitates are certain, strip-bursting defects are easily generated at the positions in the nitriding process, so that the corrosion resistance is reduced.

In order to ensure that the nitriding steel has excellent forming performance and nitriding performance, the nitriding steel is mainly based on the following principles:

c, carbon C: the steel is an economic strengthening element, which affects the strength and the formability of the steel plate, generally, the strength is increased along with the increase of the content, the formability is deteriorated when the content is too high, the content is lower, and the formability of the steel plate is better but the strength is poorer. Therefore, the steel for the cookware needs certain forming performance to prepare various shapes, and also needs certain strength to ensure safety and wear resistance. Meanwhile, C, N atomic diameter is close to each other and can be diffused in steel, so that the subsequent N-penetrating process can be influenced by solid solution of C with too high content in the substrate, and N atoms are prevented from nitriding the substrate, so that the C content in the steel is controlled to be 0.005-0.045%.

Silicon Si: the silicon element can be used as a reducing agent and a deoxidizing agent to be added into steel in the smelting process, and simultaneously, the silicon element can improve the hardenability and the tempering resistance of the steel, but the excessively high Si content can reduce the low-temperature toughness and the welding performance of the steel, and the Si content is easy to form oxides in molten steel to form inclusions, is not beneficial to forming some complex kitchenware by stamping steel plates and is easy to cause the problem of stamping cracking, so that the invention controls the Si: less than or equal to 0.03 percent.

Manganese Mn: as a common desulfurization and deoxidation element, the Mn-Mn alloy can be infinitely dissolved in ferrite and austenite to improve the strength and wear resistance of a steel plate, has small influence on the forming performance of a material, but the Mn content cannot be too high, the Mn content is too high to be easily combined with steel S to form MnS inclusion, and a defect position is formed in steel, and because the crystal structure of the defect position is distorted, atoms such as N, H and the like are easily enriched at the position in the nitriding process, so that the defects such as nitriding bulge (namely strip explosion) and the like are further caused, and the corrosion resistance is influenced, so that the Mn required by the patent is controlled to be 0.1-0.3%.

Phosphorus P: p is easily segregated, thereby reducing plasticity, low-temperature toughness, and weldability of steel.

S, sulfur: easily combine with Mn in steel to form MnS and other scale precipitates, which are unfavorable for nitriding, and simultaneously cause hot brittleness, reduce ductility and toughness of steel and cause cracks during rolling. In addition, S is also disadvantageous in welding performance, so the present invention controls S: less than or equal to 0.01 percent.

Chromium Cr: the Cr element can promote the nitriding process, and Fe (Cr, N and C) phases are easy to form in a substrate. However, when the Cr content is too high, the Cr content is an alloy element, the cost is high, and the too high Cr content is not favorable for the forming performance of the steel plate. Compared with other patents, the method adopts Cr with lower relative content, controls 0.005-0.03%, and obtains a nitriding layer with higher quality.

Titanium Ti: has stronger affinity with C, N, is very easy to combine with N in the nitriding process to promote the nitriding, and meanwhile, Ti is easy to form TiN, Ti (C, N) and Ti in the preparation process₄S₂C₂Precipitates are effective in inhibiting austenite grains from growing and promoting ferrite nucleation, and Ti forms a second phase to improve the strength and formability of the steel sheet, and Ti₄S₂C₂The precipitates can fix part of S elements, so that the influence of MnS hard brittle phase on the performance of the substrate is avoided, and the control of the invention is 0.01-0.055%.

Aluminum Al: the deoxidizer is a deoxidizer, can avoid the generation of other oxides, can prevent pore defects in molten steel, reduces steel inclusions, has strong affinity of Al to N, can play a role in nitrogen hardening, promotes a nitriding process, but forms large-size alumina inclusions with oxygen in the steel due to overhigh Al content, causes reduction of material forming performance, easily causes stamping cracking, and can simultaneously cause AL in the nitriding process₂0₃As the defect, the generation of the defect of 'strip exposure' influencing the nitriding process, the invention controls Als: 0.030-0.065%.

Arsenic As and tin Sn elements need to be strictly controlled, are toxic to human bodies, generally belong to residual elements and remain in steel, and other steel types (or products) do not require and are not controlled, so that the arsenic As and tin Sn elements need to be controlled in steelmaking, the arsenic As and tin Sn elements are prevented from being absorbed and carcinogenic by human bodies in follow-up preparation pots, when the content of As and Sn is lower than 0.005%, the elements can be effectively prevented from being diffused into food, and meanwhile, if the content of As and Sn is lower, the difficulty in controlling molten steel is increased, and the steelmaking cost is increased.

The invention provides a production method of a base plate for nitriding steel, which comprises the following steps:

1) pretreating molten iron;

2) smelting in a converter;

3) RH process;

4) continuous casting;

5) hot rolling process;

6) cold rolling;

7) annealing process;

8) and (7) flattening.

Step 1) the pretreatment of molten iron specifically comprises the following steps: pre-slagging and post-slagging are required; the target sulfur content after molten iron desulphurization is less than 0.003%.

Step 2) smelting in a converter: the method can adopt circulating scrap steel, the slag blocking operation is enhanced during tapping, and lime is required during tapping.

The RH process in the step 3) is specifically as follows: RH adopts hydrogen treatment process; if oxygen blowing is needed, oxygen can be blown in at the middle stage according to the temperature and the oxygen level; and the components are adjusted to the target values.

The continuous casting in the step 4) is specifically as follows: the target temperature of the tundish is controlled to be 20-35 ℃ above the liquidus temperature; the casting blank needs to be checked and cleaned, flame cutting is adopted for the surface of the casting blank, the cutting thickness is 0-5 mm, and the casting blank is easy to remain on the surface of the plate blank due to the fact that protective slag in molten steel in the continuous casting process, otherwise the residues, impurities and the like can be pressed into the steel plate in the subsequent rolling process, the surface quality and the formability of the steel plate are affected finally, and meanwhile the thickness of a nitriding layer in the nitriding process can be affected seriously by the surface of the steel plate;

step 5) the hot rolling process: tapping temperature: 1200 plus or minus 20 ℃, finishing temperature: 890 +/-20 ℃, coiling temperature: 680 +/-20 ℃.

Cold rolling in step 6): the hot rolled plate coil firstly enters a pickling tank, the surface iron scale is removed, and the hot rolled plate coil is sent to a five-stand continuous rolling mill set to be rolled into a target thickness; the total cold rolling reduction rate is 50-75 percent;

the annealing in the step 7) adopts continuous annealing or cover annealing;

the soaking temperature of the continuous annealing is as follows: 800 +/-10 ℃ and soaking time: 55-90 s, overaging temperature: 340-380 ℃, aging time: 4-10 min;

the cover annealing comprises the following specific steps: heating rate of temperature rise is 20-70 ℃/h, cold spot temperature is 630 +/-10 ℃, and cooling speed is as follows: 20-50 ℃/h.

The leveling in the step 8) specifically comprises the following steps: leveling elongation: 0.6 to 2.0 percent to eliminate a yield platform, ensure the plate shape, obtain a substrate with uniform tissue, good forming performance, certain toughness and convenience for forming a pot at the later stage.

The invention finally obtains ferrite structure with grain size of 8-10 grade. The components and the structure of the substrate provided by the invention are beneficial to the later nitriding process and the formation of a corrosion-resistant nitriding layer. The substrate disclosed by the invention has the advantages that through the design of a formula and a process, the morphology and the phase of the structure are influenced, the generation of pearlite is avoided, and the influence on the diffusion of nitrogen atoms is favorable for the formation of a corrosion-resistant nitriding layer.

The invention provides a production method of nitriding steel with excellent corrosion resistance, which utilizes the nitriding treatment of the substrate for nitriding steel, and the specific nitriding method comprises the following steps:

s1, placing the sample piece in a nitriding furnace, and heating and preserving heat;

s2, heating to nitriding temperature along with the furnace, introducing ammonia gas, and preserving heat;

and S3, continuing heating with the furnace, introducing ammonia gas, and preserving heat.

And S4, finally cooling along with the furnace.

The sample piece specifically is: after the base plate for the nitriding steel is punched and deformed, the surface is cleaned and deoiled, and the base plate for the nitriding steel cannot have the defects of rusty spots, impurities, scratches, pits and the like, and then is subjected to nitriding treatment.

The heating and heat preservation in the step S1 means that: heating to 300-400 ℃ at a speed of 5-20 ℃/min, and preserving heat for 30-60 min, wherein the process is a pre-oxidation process, so that a thinner oxide layer is formed on the surface of the substrate, and the formation of a nitriding layer can be promoted in the subsequent nitriding process.

Step S2 specifically includes: heating the mixture to a nitriding temperature of 550-650 ℃ along with the furnace, introducing ammonia gas, and controlling the flow rate to be 0.1-0.8 m³And h, preserving heat for 1-4 h, decomposing introduced ammonia gas at high temperature to form nitrogen atoms, and further enriching the nitrogen atoms on the surface of the substrate, wherein the nitrogen atoms on the outer surface have high concentration and low concentration in the substrate and can enter the surface of the steel plate through diffusion to be combined with Fe atoms to form a plurality of nitrogen-containing phases (Fe)₂N、Fe₃N、Fe₄N、Fe₁₆N₂) At the same time, the elements such as Ti and Cr in the structure promote the diffusion of N atoms into the substrate to form TiN, Ti (C, N), Fe (Cr, N, C), AlN, etc., and finally form a nitrided layer on the surface.

Step S3 specifically includes: heating the mixture to 580-700 ℃ along with the furnace, introducing ammonia gas, and controlling the flow to be 0.1-0.5 m³Keeping the temperature for 0-3 h, wherein the heat preservation time is not 0 h; the method mainly comprises the step of forming austenite containing N by adopting a high-temperature nitriding process, wherein the more the formed austenite containing N on the surface is, the more the formed austenite containing N is, the better the formation of a nitriding layer containing martensite in the later-stage cooling process is, but the content of N cannot be too high, and otherwise, the high-N structure is easy to crack in the later-stage cooling process, so that the nitriding layer is not compact.

The nitriding steel with excellent corrosion resistance provided by the invention is produced by the nitriding method by adopting the base plate for the nitriding steel.

The invention provides an application of nitriding steel with excellent corrosion resistance, which is used for preparing kitchen ware, in particular to preparing cookware.

The low-carbon nitriding steel with excellent forming and nitriding properties is obtained through the processes of steel making, hot rolling, acid pickling and cold rolling, annealing and leveling of a metal plate (strip), and after nitriding is carried out by correspondingly adopting the gas nitriding process, a workpiece has excellent corrosion resistance, and a nitriding substrate with excellent forming properties and a nitriding layer with excellent corrosion resistance of 20-60 mu m are finally obtained, so that the product is widely used for kitchenware.

Compared with the prior art, the cold-rolled steel plate with low cost, excellent forming performance and good nitriding property is obtained through reasonable chemical component matching and rolling annealing process, can be punched into pots with various shapes, and has the following base plate material yield strength: 160-250 MPa, tensile strength: 250-400 MPa, and the elongation is more than or equal to 38%; the substrate has low strength, high elongation and yield ratio less than 0.7, which shows that the substrate has better forming performance. The substrate produced by the method disclosed by the invention is simple in elements, not complex, pure and single in structure, and has a good nitriding performance, and a nitriding layer with the thickness of 20-60 mu m is easily formed on the surface layer after nitriding. Simultaneously, by combining with a corresponding nitriding process, nitriding steel with a nitriding layer of 20-60 mu m and excellent corrosion resistance is finally obtained, the nitriding layer and the Fe-N martensite characteristic of a dense BCC structure between the nitriding layer and a base body are utilized, so that a nitrided sample piece has excellent corrosion resistance, and a nitriding pot is soaked in NaCl salt water for 1000 hours without perforation. The invention controls the temperature of the furnace, the flow of the introduced ammonia gas and the time, and has simple process; the whole nitriding process of the invention is about 8-12 hours, and compared with other nitriding methods, the nitriding method of the invention can reach 20-40 hours and above. Therefore, the nitriding steel plate has good forming performance and good nitriding performance, and the corresponding nitriding process is simple, short in nitriding period, high in working efficiency and low in cost.

Drawings

FIG. 1 is a structural view of a nitriding steel of example 2-A;

FIG. 2 is a structural view of a nitriding steel of example 4-B;

FIG. 3 is a structural view of a nitriding steel of example 5;

FIG. 4 is a structural view of a nitriding steel of comparative example 1;

FIG. 5 is a structural view of a nitrided steel of comparative example 2-B;

FIG. 6 is a structural diagram of a nitrided steel in comparative example 3.

Detailed Description

c: 0.005-0.045%, Si: less than or equal to 0.03%, Mn: 0.10-0.30%, P: less than or equal to 0.020%, S: less than or equal to 0.01 percent, Als: 0.030-0.065%, N: not more than 0.005 percent, not less than 0.01 percent and not more than 0.055 percent of Ti, not less than 0.005 percent and not more than 0.03 percent of Cr, less than 0.005 percent of As, less than 0.005 percent of Sn, and the balance of Fe and inevitable impurities;

furthermore, when the C content is less than or equal to 0.01%, the Ti content is more than or equal to 0.03%, and the Mn content is more than or equal to 0.2%.

The production method of the base plate for the nitriding steel comprises the following steps:

1) pretreating molten iron: pre-slagging and post-slagging are required; the target sulfur content after molten iron desulphurization is less than 0.003%;

2) smelting in a converter: the method can adopt circulating scrap steel, the slag blocking operation is enhanced during tapping, and lime is required during tapping.

3) RH: wherein RH adopts hydrogen treatment process; if oxygen blowing is needed, oxygen can be blown in at the middle stage according to the temperature and the oxygen level; and the components are adjusted to the target values.

4) Continuous casting: the target temperature of the tundish is controlled to be 20-35 ℃ above the liquidus temperature; the casting blank needs to be checked and cleaned, flame cutting is adopted for the surface of the casting blank, the cutting thickness is 0-5 mm, the covering slag in molten steel is easy to remain on the surface of the plate blank in the continuous casting process, otherwise, the residues, impurities and the like can be pressed into the steel plate in the subsequent rolling process, the surface quality and the formability of the steel plate are finally influenced, and meanwhile, the thickness of a nitriding layer in the nitriding process can be seriously influenced by the surface of the steel plate.

5) Controlling a hot rolling process: tapping temperature: 1200 plus or minus 20 ℃, finishing temperature: 890 +/-20 ℃, coiling temperature: 680 +/-20 ℃.

6) The hot rolled coil firstly enters a pickling tank to remove surface iron oxide scales, and is sent to a five-stand continuous rolling unit to be rolled into a target thickness, and the total cold rolling reduction rate is 50-75%.

7) Annealing process: soaking temperature of continuous annealing: 800 +/-10 ℃ and soaking time: 55-90 s, overaging temperature: 340-380 ℃, aging time: 4-10 min; or, cover annealing: heating rate of temperature rise is 20-70 ℃/h, cold spot temperature is 630 +/-10 ℃, and cooling speed is as follows: 20-50 ℃/h.

8) Leveling: leveling elongation: 0.6% -2.0% to eliminate yield platform and ensure plate shape.

The nitriding steel with excellent corrosion resistance is prepared by nitriding treatment of the base plate for nitriding steel, and is used for producing kitchenware and cookware, and the specific nitriding method comprises the following steps:

and S1, cleaning the surface of the steel plate after stamping deformation, removing oil, and avoiding the defects of rusty spots, impurities, scratches, pits and the like.

S2, placing the sample piece in a nitriding furnace, heating to 300-400 ℃ at a speed of 5-20 ℃/min, and preserving heat for 30-60 min.

S3, heating the mixture to a nitriding temperature of 550-650 ℃ along with the furnace, introducing ammonia gas, and controlling the flow of ammonia gas to be 0.1-0.8 m³And h, preserving the heat for 1-4 h to enable the ammonia gas to be decomposed into nitrogen atoms which enter the surface of the steel plate through diffusion.

S4, heating the mixture in a furnace to 580-700 ℃, introducing ammonia gas, and controlling the flow to be 0.1-0.5 m³And h, preserving heat for 0-3 h, wherein the heat preservation time is not 0 h.

And S5, finally cooling along with the furnace.

The specific embodiment is as follows:

the substrate for nitrided steel of each example and comparative example contained the components in mass percentage shown in table 1, and the balance not shown in table 1 was Fe and inevitable impurities.

TABLE 1 composition (wt%) of base plate for nitriding steel in each of examples and comparative examples

Table 1 process for producing substrates for nitrided steels of the examples and comparative examples having the composition comprising the steps of:

The production process parameters of the substrates for nitriding steel of each example and comparative example are shown in table 2.

TABLE 2 production Process parameters

The strip a after the example in table 2 was produced using the composition of the example, and the annealing process was a continuous annealing process; example post strip B was produced using the composition of this example, with a hood annealing process. As in example 2-A, the composition of example 2 of Table 1 was used for production, and during production, a continuous annealing process was used for annealing; example 2-B was produced using the composition of example 2 of table 1, and the annealing process used was a hood-type annealing process.

The properties of the substrates for nitriding steel produced in the above examples and comparative examples are shown in Table 3.

TABLE 3 mechanical Properties of the substrates for nitriding steels of examples and comparative examples

Categories	Thickness of	R_p0.2/MPa	R_m/MPa	A₅₀/％	Yield ratio
						Example 1	1.2	204	331	40	0.62
Example 2A	1.5	202	331	43	0.61
						Example 3	1.2	199	332	43	0.60
Example 4A	1.8	168	307	43	0.55
						Example 5	2.0	178	318	41	0.56
Example 6A	0.8	220	345	38	0.64
						Example 7	2.0	250	365	38	0.68
Example 2-B	1.2	207	328	39	0.63
						Example 4-B	1.8	175	285	44	0.61
Example 6-B	1.0	180	300	43	0.60
						Comparative example 1-A	1.0	158	265	36	0.60
Comparative example 1-B	2.0	145	333	36	0.44
						Comparative example 2-A	1.2	255	435	32	0.59
Comparative example 2-B	1.8	248	375	36	0.66

The nitriding steel substrates produced in the above examples and comparative examples were nitrided by the following method to obtain nitriding steel with excellent corrosion resistance, which comprises the following specific steps:

s1, after the base plate for the nitriding steel is punched and deformed, the surface is cleaned and deoiled, and the base plate cannot have the defects of rusty spots, impurities, scratches, pits and the like.

S3, heating the steel plate to the nitriding temperature of 550-650 ℃ in a furnace, introducing ammonia gas, and controlling the flow: 0.1 to 0.8m³And h, preserving the heat for 1-4 h to enable the ammonia gas to be decomposed into nitrogen atoms which enter the surface of the steel plate through diffusion.

S4, heating the mixture along with a furnace to 580-700 ℃, introducing ammonia gas, and controlling the flow: 0.1 to 0.5m³And keeping the temperature for 0-3 h.

And S5, finally, rapidly cooling along with the furnace.

The nitriding process parameters and the nitrided layer thickness for each example and comparative example are shown in table 4.

TABLE 4 nitriding Process and nitriding layer thickness for each example and comparative example

As can be seen from the above examples, the steel sheet having good nitriding properties and formability satisfies the designed composition, and at the same time, when the C content is not more than 0.01, Ti is not less than 0.03%, Mn is not less than 0.2%, so that the substrate can obtain the material yield strength: 160-250 MPa, tensile strength: 250-400 MPa, the elongation rate is more than or equal to 38 percent, and the nitriding layer with the thickness of 20-60 mu m can be finally obtained according to the substrate and the nitriding process provided by the patent, the nitriding layer has good corrosion resistance, and a FeN black martensite structure exists between the nitriding layer and the matrix, so that the prepared pot can be soaked in NaCl for 1000h without perforation (24 h under the normal temperature condition, soaking in 3.5 percent NaCl solution, standing for 1000h, and no perforation, liquid leakage and other phenomena occur).

In addition, compared with the prior art, the invention has the following advantages:

compared with the technical scheme disclosed in patent publication No. CN 106222570A substrate for nitriding steel with excellent corrosion resistance and a production method thereof, the invention is obviously different from the steel component system; the patent adopts a low C, high ALs and high Cr component system, and simultaneously adds elements such as Cu, Ni and the like in steel, which inevitably increases the cost of products; meanwhile, the nitriding method described in the patent is substantially different from the nitriding method provided by the invention, the method for evaluating the corrosion resistance is easily judged to be unqualified products by error due to the environment, abnormal points of a base material, material defects and the like through visual observation, the structure appearance of the nitriding layer is not described, but the nitriding layer with extremely strong corrosion resistance is obtained through the material and the nitriding method disclosed by the patent, and the material, the structure of the nitriding layer and the corrosion resistance are scientifically described and explained.

Compared with the technology disclosed in the publication No. CN101649441B nitriding process method for austenitic stainless steel materials, the invention can effectively shorten the nitriding time, obtain the nitriding layer with excellent corrosion resistance, further protect the cookware, prevent the cookware from being rusted in the using process and increase the life cycle of the product.

The technical scheme disclosed in publication No. CN110117747A production method of high Al nitriding steel is that the component system belongs to special steel series, the contents of Cr, Mo and Al are high, the product is mainly used for mechanical equipment such as high fatigue and high wear resistance mechanical screw, machine barrel, cylinder and the like, the pot described in the patent is not a product at all, and the used base plate, nitriding process and nitriding performance are different at all. The patent mainly solves the problems of high Al on steel making, rolling and other processes, and the like, so as to obtain a plate blank with excellent surface quality and mechanical property. The nitriding pot tool and the nitriding process have different base plate component structures and nitriding processes and problems to be solved.

The base plate provided by the invention has good forming performance and good permeability, the nitriding layer with the surface layer about 20-60 mu m is obtained by the nitriding method provided by the invention, a sample piece has excellent corrosion resistance, the nitriding layer is obviously different from a common gas nitriding layer in structure, a BCC-structured Fe-N martensite phase is formed between a white bright layer of the nitriding layer and the base plate, and a nitrided pot has strong corrosion resistance and wear resistance by virtue of the good compactness and corrosion resistance of the nitriding layer. The nitriding kitchen ware prepared by utilizing the characteristics of compactness and corrosion resistance can reach 1000h in NaCl salt water without perforation.

The above description is only for specific exemplary description of the present invention, and it should be noted that the specific implementation of the present invention is not limited by the above manner, and it is within the protection scope of the present invention as long as various insubstantial modifications are made by using the technical idea and technical solution of the present invention, or the technical idea and technical solution of the present invention are directly applied to other occasions without modifications.

Claims

1. The base plate for the nitriding steel is characterized by comprising the following components in percentage by mass:

c: 0.005-0.045%, Si: less than or equal to 0.03%, Mn: 0.10-0.30%, P is less than or equal to 0.020%, S is less than or equal to 0.01%, Als: 0.030-0.065%, more than or equal to 0.01% and less than or equal to 0.055% of Ti, more than or equal to 0.005% and less than or equal to 0.03% of Cr, and the balance of Fe and inevitable impurities.

2. The substrate for nitriding steel according to claim 1, wherein when C is 0.01% or less, Ti is 0.03% or more and Mn is 0.2% or more.

3. The substrate for nitriding steel according to claim 1, wherein the substrate for nitriding steel has a structure of ferrite having a grain size of 8 to 10 grades.

4. A method for producing a substrate for nitriding steel according to any one of claims 1 to 3, characterized in that the method comprises the steps of:

1) pretreating molten iron;

2) smelting in a converter;

3) RH process;

4) continuous casting;

5) hot rolling process;

6) cold rolling;

7) annealing process;

8) and (7) flattening.

5. The production method according to claim 4, wherein the annealing in step 7) employs continuous annealing or hood annealing;

6. A method for producing a nitrided steel having excellent corrosion resistance using the substrate for a nitrided steel according to any one of claims 1 to 3, comprising the steps of:

s3, continuing heating with the furnace, introducing ammonia gas, and preserving heat;

and S4, finally, rapidly cooling along with the furnace.

7. The method according to claim 6, wherein step S2 specifically comprises: heating the mixture to a nitriding temperature of 550-650 ℃ along with the furnace, introducing ammonia gas, and controlling the flow rate to be 0.1-0.8 m³And h, preserving the heat for 1-4 h.

8. The method according to claim 6 or 7, wherein step S3 specifically includes: heating the mixture to 580-700 ℃ along with the furnace, introducing ammonia gas, and controlling the flow to be 0.1-0.5 m³And h, preserving heat for 0-3 h, wherein the heat preservation time is not 0 h.

9. A nitriding steel with excellent corrosion resistance produced by the method according to any one of claims 6-8, wherein the nitriding layer of the nitriding steel with excellent corrosion resistance is 20-60 μm.

10. Use of a nitriding steel with excellent corrosion resistance produced by the method according to any one of claims 6-8 for kitchen appliances.