CN114058814A - Preparation method of NM400 wear-resistant steel with high hardness uniformity - Google Patents
Preparation method of NM400 wear-resistant steel with high hardness uniformity Download PDFInfo
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- CN114058814A CN114058814A CN202111200494.4A CN202111200494A CN114058814A CN 114058814 A CN114058814 A CN 114058814A CN 202111200494 A CN202111200494 A CN 202111200494A CN 114058814 A CN114058814 A CN 114058814A
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Abstract
The invention belongs to the technical field of wear-resistant steel, and mainly relates to NM400 wear-resistant steel with high hardness uniformity and a preparation method thereof, wherein the wear-resistant steel comprises the following chemical components in percentage by mass: c: 0.20 to 0.40%, Mn: 1.20-1.80%, Si: 0.20-0.50%, Cr: 0.20-0.60%, Mo: 0.20 to 0.50%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025% of Fe and inevitable impurity elements in balance; the microstructure of the wear-resistant steel is bainite and martensite, the problem that the hardness uniformity of the head, the middle and the tail of the wear-resistant steel is poor is solved, and the difference of the average hardness of the head, the middle and the tail of the wear-resistant steel is within 15HBW, so that the wear-resistant steel has more excellent hardness uniformity.
Description
Technical Field
The invention belongs to the technical field of wear-resistant steel, and mainly relates to a preparation method of NM400 wear-resistant steel with high hardness uniformity.
Background
The high-strength wear-resistant steel is a wear-resistant material widely used in various wear working conditions, widely applied to various fields such as metallurgy, mines, building materials, electric power, railways, military affairs and the like, key parts comprise excavator bucket teeth, ball mill lining plates, crusher jaw plates, crushing walls, rolling mortar walls, tractor track plates, fan mill impact plates and the like, and is mainly used on vehicles or facilities which are in contact with materials such as ore, coal slurry, silt, cement slurry and the like, such as mining electric wheels, coal mine scraper conveyors, cement mixers, bulldozers, dumpers, loaders and the like. At present, the on-line quenching process has the process advantages of short flow and greenization, and has great advantages in the field of producing high-strength steel plates. However, the production of wear-resistant steel by on-line quenching limits the large-scale popularization and application of the wear-resistant steel to a certain extent due to the performance uniformity and the fluctuation in the on-line quenching process. The main limitation link is that the early failure caused by local excessive abrasion in the service process of the steel plate caused by the hardness fluctuation of the head, the middle and the tail of the online quenching wear-resistant steel influences the wide application of the online quenching process.
The on-line quenching wear-resistant steel has a prominent problem of cooling uniformity at different parts (head, middle and tail) of the steel sheet due to the difference in the water entry temperature during the cooling process after rolling, and generally, the maximum water entry temperature of the surface of the steel sheet is taken as the water entry temperature of the whole steel sheet during the rolling process of the steel sheet, so that the influence of too low local water entry temperature is easily ignored. If the surface temperature of the steel plate on the roller way is low in the moving process of the steel plate due to the influence of the heat transfer rule, the water entering temperature of the tail part is low due to the fact that the tail part is in the air for a long time before water cooling is started, and the high-temperature ferrite transformation of the structure near the surface of the tail part is easy to happen. And the surface hardness of the wear-resistant steel is greatly influenced by the appearance of surface ferrite. Although the hardness detection is generally performed after a certain thickness of the surface of the wear-resistant steel is ground, if the temperature of water entering is low, the ferrite layer is thick, the final hardness result is greatly influenced, and a user may cause partial excessive wear of the wear-resistant steel in the use process to fail in advance, so that the user experience is influenced.
The patent refers to the field of 'methods for producing thin-gauge wear-resistant steel NM400 by on-line quenching in ultra-fast cooling', 'methods for producing thin-gauge high-Ti wear-resistant steel NM400 by on-line quenching', 'thin-gauge wear-resistant steel plates and manufacturing methods thereof', and the like, and the related methods mainly utilize on-line quenching technology to produce wear-resistant steel coils. The patent 'a method for producing Nb alloyed high-strength wear-resistant steel plate by on-line quenching', mainly adopts a small amount of Nb element to carry out fine grain strengthening and precipitation strengthening to improve the strength and toughness of low-carbon steel, and utilizes on-line quenching to reach the performance level of NM 500.
At present, the patented method for producing the wear-resistant steel by on-line quenching can enable the local performance of the steel plate to meet the standard requirements, but neglects the problem that the high-temperature ferrite transformation of the tissues near the surface is caused by the difference of the water inlet temperature, the surface hardness of the wear-resistant steel is influenced, and the hardness uniformity of the head, the middle and the tail of the wear-resistant steel is poor, and the problem is not solved.
Disclosure of Invention
In view of the above problems, the present invention has been made to provide NM400 wear resistant steel with high hardness uniformity and a method for preparing the same to overcome the above problems or at least partially solve the above problems.
NM400 wear resistant steel with high hardness uniformity, the chemical composition of which comprises by mass percent: c: 0.20 to 0.40%, Mn: 1.20-1.80%, Si: 0.20-0.50%, Cr: 0.20-0.60%, Mo: 0.20 to 0.50%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025% of Fe and inevitable impurity elements in balance; the microstructure of the wear-resistant steel is bainite and martensite.
Optionally, the chemical components of the wear-resistant steel comprise, by mass: c: 0.20 to 0.30%, Mn: 1.20 to 1.50%, Si: 0.20-0.40%, Cr: 0.30-0.60%, Mo: 0.20-0.30%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025%, and the balance of Fe and inevitable impurity elements.
Optionally, the hardness difference of the head part, the middle part and the tail part of the wear-resistant steel plate is not more than 15 HBW.
Optionally, the mechanical properties of the head, the middle and the tail of the wear-resistant steel plate mother plate all satisfy: the tensile strength is 1250-1350 MPa, the elongation after fracture is not less than 10%, the impact energy at minus 20 ℃ is not less than 20J, and the surface layer Brinell hardness is HBW 370-430.
A method for preparing NM400 wear resistant steel with high hardness uniformity, the method comprising:
sequentially rolling, pre-straightening, cooling and tempering the plate blank to obtain the wear-resistant steel;
when the cooling is carried out, the temperature of the head part entering water is 790-850 ℃, and the temperature of the tail part entering water is 740-850 ℃.
Optionally, the rolling comprises heating before rolling, the temperature of the heating before rolling is 1150-1240 ℃, and the time coefficient of the heating before rolling is 200-400 min/mm; the finishing temperature of the rolling is 930-980 ℃.
Optionally, the finish temperature of the pre-straightening is 850-880 ℃.
Optionally, the cooling process of the cooling includes ultra-fast cooling or laminar cooling, and the cooling manner of the ultra-fast cooling and the laminar cooling includes any one of water cooling, fog cooling and air cooling; the final cooling temperature of the cooling is below 150 ℃, and the cooling speed of the cooling is not lower than 20 ℃/s.
Optionally, the tempering temperature is 200-400 ℃, and the tempering heating time coefficient is 1-3 min/mm.
Optionally, before or after the tempering process, the slab is subjected to flame cutting in a preheating flame cutting mode.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the wear-resistant steel provided by the embodiment of the invention does not contain ferrite structures, and is a martensite structure and a bainite structure, and the mechanical properties of the head, the middle and the tail of the wear-resistant steel plate mother plate all meet the following requirements: the tensile strength is 1250-1350 MPa, the elongation after fracture is not less than 10%, the impact energy at minus 20 ℃ is not lower than 20J, the surface brinell hardness is HBW 370-430, and the average difference of the hardness of the head, the middle and the tail of the wear-resistant steel is within 15HBW, so that the failure of the wear-resistant steel caused by local excessive wear is avoided, and the wear-resistant steel can be fully ensured to have good service stability and safety.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a surface metallographic structure of a head, a middle and a tail from left to right in example 1 of the present invention;
FIG. 2 is a view showing the metallographic structure of the surface of comparative example 1 of the present invention showing the head, middle and tail portions thereof from left to right.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, 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 invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
It should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
In order to solve the technical problems, the technical scheme in the embodiment of the invention has the following general idea:
NM400 wear resistant steel with high hardness uniformity, the chemical composition of which comprises by mass percent: c: 0.20 to 0.40%, Mn: 1.20-1.80%, Si: 0.20-0.50%, Cr: 0.20-0.60%, Mo: 0.20 to 0.50%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025% of Fe and inevitable impurity elements in balance; the microstructure of the wear-resistant steel is bainite and martensite.
As an optional embodiment, the chemical composition of the wear-resistant steel comprises, by mass: c: 0.20 to 0.30%, Mn: 1.20 to 1.50%, Si: 0.20-0.40%, Cr: 0.30-0.60%, Mo: 0.20-0.30%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025% of Fe and inevitable impurity elements in balance; the microstructure of the wear-resistant steel is bainite and martensite.
The wear-resistant steel is designed by adopting a low-cost component system, and Mn-Si-Cr-Mo-Al-Ti is added, so that the wear resistance and the comprehensive mechanical property of the wear-resistant steel are improved: the Cr has the main functions of improving the hardenability and the strength and the wear resistance of the steel in the hardened and tempered structural steel; mo can improve hardenability and heat strength in steel, and ensures the thickness direction uniformity of the steel plate; ti can improve the plasticity and the toughness in the low alloy steel; mn strongly increases the hardenability of the steel and ensures that sufficient martensite is obtained after quenching; by adding a certain content of B element, the hardenability of the steel plate can be improved, the martensite and bainite structures can be ensured to be obtained, and the mechanical properties of the steel plate in the quenching and tempering states can be effectively improved by the alloy. Meanwhile, the process provided by the invention interacts with the added alloy elements, so that the wear resistance and uniform high hardness of the material are improved together.
One of the advantages of the NM400 wear-resistant steel with high hardness uniformity is low-cost component system design, the addition of Mn-Si-Cr-Mo-A1-Ti improves the wear resistance and comprehensive mechanical properties of the material, and the interaction of the Mn-Si-Cr-Mo-A1-Ti and the alloy elements added in the steel improves the wear resistance and uniform high hardness of the material.
The elements in the wear-resistant steel of the invention have the following functions:
carbon: in the invention, a relatively high C content design is adopted, C is the cheapest element for improving the strength and the wear resistance, but the high carbon content is easy to deteriorate the toughness and the weldability of the material and also has an influence on the corrosion resistance of the material. Therefore, the invention combines the addition of other alloy elements and the technical characteristics of the heat treatment process, and proposes to control the mass percentage of the carbon content to be 0.20-0.30%, the problem of overhigh hardness caused by overlarge mass fraction, and the problem of unsatisfied performance requirements caused by overlow hardness caused by undersize adverse effect.
Manganese: manganese is a solid solution strengthening element, and can improve the hardenability of the material, and the manganese is matched with the addition of C in the invention, so that the strength index and the wear resistance of the steel are ensured; the excessive addition of manganese is unfavorable for the welding performance and the toughness of the material; in addition, manganese belongs to alloy elements, and excessive addition is not beneficial to control of alloy cost. Therefore, the mass percent of the added manganese is 1.20-1.50%, the adverse effect of excessively large mass fraction is that the hardness of the wear-resistant steel is excessively large, excessively high Mn can cause the segregation problem, and the excessively small adverse effect is that the strength and hardness which are caused by insufficient hardenability can not meet the hardness requirement.
Chromium: cr is added into steel to obviously improve the strength, hardness and wear resistance, but simultaneously reduce the plasticity and toughness; can obviously improve the antioxidation of the steel and increase the corrosion resistance of the steel. Chromium can significantly increase the hardenability of the steel, but can also increase the temper brittleness tendency of the steel. And (3) raising the temperature of A3 and A1, moving the GS line to the upper left, controlling the mass percent of chromium to be 0.30-0.60%, wherein the adverse effect of excessively large mass fraction is that the ductility and toughness are reduced, and the adverse effect of excessively small mass fraction is that the strength and hardness are not good due to insufficient hardenability.
Molybdenum: mo can refine the crystal grains of the steel, improve hardenability and heat strength, and maintain sufficient strength and creep resistance at high temperature. The red hardness can be improved in the tool steel. The alloy steel is inhibited from being tempered and brittle, the mass percent of molybdenum is controlled to be 0.20-0.30%, the adverse effect of overlarge mass fraction is that the cost is increased and the hardness and strength are overhigh, and the requirement of hardenability cannot be met due to the undersize adverse effect.
Aluminum: aluminum is a deoxidizing element, and the quality of a casting blank and the control level of inclusions are improved by adding a certain amount of aluminum. According to the invention, the mass percentage of aluminum is 0.02-0.04%, the excessive adverse effect of the mass fraction is to reduce the cleanliness of steel, and the excessive adverse effect is to increase the level of inclusions.
Titanium: titanium is a strong precipitation strengthening element, and the main purpose of the titanium is to combine with N to form TiN, so that the adverse effect of N on the toughness of the material is weakened; TiN or TiC has the function of refining austenite grains in rolling and heat treatment and simultaneously has the function of improving the performance of a welding heat affected zone. However, Ti should not be added too much, which would result in waste of alloy cost and adversely affect the toughness of the material. Therefore, 0.01-0.02 wt% of Ti is selectively added, the adverse effect of overlarge mass fraction is to cause the appearance of large-size TiN inclusions, and the function of improving the performance of a welding heat affected zone cannot be realized due to the undersize adverse effect.
Meanwhile, the wear-resistant steel does not contain ferrite structures and is martensite and bainite structures, the mechanical properties of the head, the middle and the tail of the wear-resistant steel plate mother plate meet the requirements, the average value difference of the hardness of the head, the middle and the tail of the wear-resistant steel is within 15HBW, the partial excessive wear of the wear-resistant steel is avoided, the failure in advance is avoided, and the wear-resistant steel can be fully ensured to have good service stability and safety.
As an optional embodiment, the chemical composition of the wear-resistant steel comprises, by mass: c: 0.20 to 0.30%, Mn: 1.20 to 1.50%, Si: 0.20-0.40%, Cr: 0.30-0.60%, Mo: 0.20-0.30%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025%, and the balance of Fe and inevitable impurity elements.
The hardness mean value difference of the wear-resistant steel head, the middle and the tail is within 15HBW, so that the advanced failure caused by local excessive wear of the wear-resistant steel is avoided, and the good service stability and safety of the wear-resistant steel can be fully ensured. The reason why the specification of the wear-resistant steel plate is 12 mm-40 mm is that the application effect of the water cooling capacity of on-line quenching in the specification range is considered to be good, the adverse effect of excessively taking the value is that insufficient quenching is easily caused, and the adverse effect of excessively taking the value is that the unevenness is poor.
A method for preparing NM400 wear resistant steel with high hardness uniformity, the method comprising:
sequentially rolling, pre-straightening, cooling and tempering the plate blank to obtain the wear-resistant steel;
when the cooling is carried out, the temperature of the water entering from the head part is 790-850 ℃, and the temperature of the water entering from the tail part is 740-850 ℃.
The reason for selecting the temperature of the head part starting to enter water to be 790-850 ℃ is to ensure that an austenite structure which is fully deformed and does not generate phase transformation after being rolled is obtained, and the adverse effect of overlarge temperature value is that the adverse effect of overlong temperature value causes the appearance of a high-temperature ferrite structure.
The reason for selecting the tail water inlet temperature of 740-850 ℃ is to ensure that the tail structure does not generate high-temperature ferrite transformation, the adverse effect of overlarge temperature value is to ensure that the austenite structure which is fully deformed and does not generate phase transformation after rolling is obtained, and the adverse effect of overlarge temperature value is to cause the high-temperature ferrite structure to appear.
The invention is improved based on an online quenching process, and the NM400 wear-resistant steel prepared by adopting the chemical component system has the tensile strength of more than 1380MPa, the yield strength of more than 1220MPa, the elongation of more than 13 percent, the hardness of more than HBW380, the impact energy of minus 20 ℃ of more than 29J, and the difference of any mean value of the hardness of the head, the middle and the tail of the wear-resistant steel is within 15 HBW.
As an optional embodiment, the rolling comprises heating before rolling, wherein the temperature of the heating before rolling is 1150-1240 ℃, and the time coefficient of the heating before rolling is 200-400 min/mm; the finishing temperature of the rolling is 930-980 ℃.
The rolling comprises rough rolling and finish rolling, the finish rolling temperature is 930-980 ℃, and grains are refined in the rolling stage through rough rolling in a recrystallization region and finish rolling in a non-recrystallization region; the finish temperature of the plate blank is the temperature of the plate blank out of a pre-straightening machine, the temperature of the finish rolling beginning and the finish rolling temperature which are set in a key mode are higher than the temperature of a conventional rolling process, the process scheme is based on an online quenching process, the temperature difference of the head, the middle and the tail of a rolled steel plate before entering water cooling is fully considered, the temperature of the steel plate at the tail position where the water entering temperature is low is particularly required to be strictly higher than Ar3, the head, the middle and the tail tissues of the steel plate before entering the water are fully ensured to be in an untransformed austenite state, the tissues after cooling can be ensured to be in a full martensite tissue in the subsequent cooling process, and the hardness of each part of the wear-resistant steel plate can be ensured to meet the use requirements of users.
As an alternative embodiment, the end temperature of the pre-straightening of the slab is 850 ℃ to 880 ℃; the pre-straightening process can improve the head-tail warping and the wave of the rolled steel plate, but the increase of the pre-straightening process can reduce the water inlet temperature of the steel plate.
When the slab is cooled, the initial temperature of water entering from the head part is 790-850 ℃, and the water entering temperature of the tail part of the slab is 740-850 ℃.
In order to ensure that the cooling speed in the cooling process is greater than the martensite transformation critical cooling speed, the final cooling temperature must be ensured to be below the Ms point, and further, the structure is ensured to be a sufficient full martensite structure to ensure that the hardness requirement of the wear-resistant steel is met.
As an alternative embodiment, the method for preparing the wear-resistant steel comprises the following steps: heating the plate blank, and then carrying out descaling, rolling, pre-straightening, online water cooling and tempering. And a descaling step is added, and descaling is mainly used for reducing surface cracks and improving welding performance.
In an optional embodiment, the slab is heated before rolling, the temperature of the heating before rolling is 1150-1240 ℃, and the heating time is 200-400 min/mm multiplied by the thickness of the slab.
The effect of the heating temperature before rolling is to completely austenitize the plate blank by heating, so that subsequent rolling and water cooling processes are convenient to carry out tissue regulation, the adverse effect of overlarge heating temperature is that austenite grains are easily formed to be abnormal thick, the adverse effect of undersize is that sufficient austenitizing is not realized or sufficient homogenization is achieved, the adverse effect of overlong heating time is that austenite grains are easily formed to be thick and production efficiency is influenced, and the adverse effect of overlong heating time is that insufficient austenitizing and insufficient homogenization are caused.
As an alternative embodiment, the cooling comprises a cooling process of ultra-rapid cooling and/or laminar cooling;
the effect of the cooling process of ultra-rapid cooling and/or laminar cooling is to obtain the desired bainite and martensite structures by rapid cooling of the steel sheet.
As an optional embodiment, the cooling process comprises any one of water cooling, fog cooling and air cooling, the final cooling temperature is below 150 ℃, and the cooling speed is not lower than 20 ℃/s. The final cooling temperature and the cooling rate are set to ensure that the cooling rate in the cooling process is greater than the martensite transformation critical cooling rate, the final cooling temperature must be ensured below an Ms point, and further the structure is ensured to be a sufficient full martensite structure to ensure that the hardness requirement of the wear-resistant steel is met.
As an alternative embodiment, the water cooling comprises on-line water cooling. The on-line water cooling means that the steel plate is cooled to a specified temperature by on-line ultra-fast cooling (also called direct quenching) after rolling, and can be delivered directly without an off-line quenching step or delivered after tempering.
The tempering temperature is 200-400 ℃, and the tempering heating time coefficient is 1-3 min/mm.
The tempering of the wear-resistant steel strictly eliminates the residual stress of the steel plate, and is beneficial to improving the plasticity and toughness level of the wear-resistant steel, thereby being beneficial to prolonging the service life of the wear-resistant steel. The heating time is 1-3 min/mm multiplied by the plate thickness, so that the steel plate can uniformly reach the set temperature in the time range and can be fully insulated, the residual stress of the wear-resistant steel plate can be fully released, carbide can be precipitated, and the wear resistance and the service stability of the wear-resistant steel can be improved. The adverse effect of too long a heating time is to reduce the production rhythm and production efficiency, and the adverse effect of too short a heating time is to not sufficiently eliminate internal stress.
The mode of carrying out flame cutting on the plate blank before or after the tempering process is preheating flame cutting.
Because the strength of the wear-resistant steel plate after on-line quenching is high, the internal stress and the structural stress of the steel plate are high, and the problem of steel plate cracking caused by direct flame cutting is solved, the steel plate needs to be subjected to flame cutting after preheating, and the wear-resistant steel before and after the tempering process needs to be subjected to preheating flame cutting.
After the tempering, the structure of the plate blank is a tempered martensite structure.
In order to ensure the hardness level of the wear-resistant steel, the steel plate structure must be ensured to be a martensite structure, and the hardness of the martensite structure is higher.
The following provides a detailed description of embodiments of the present invention in conjunction with examples and experimental data.
NM400 wear resistant steels prepared in examples and comparative examples
The NM400 wear-resistant steels of the examples 1-4 and the comparative examples 1-2 are subjected to chemical component analysis, and the obtained chemical components are shown in the following table 1 in percentage by mass:
table 1 NM400 abrasion resistant steels according to examples 1 to 4 and comparative examples 1 to 2 were prepared by the following chemical composition table (balance Fe and inevitable impurity elements).
The preparation method of the NM400 wear-resistant steel with high hardness uniformity in the embodiments 1-4 comprises the following steps: heating the plate blank, and then obtaining high-hardness uniform NM400 wear-resistant steel through rough rolling, finish rolling, pre-straightening, cooling and tempering; the finishing temperature of the finish rolling is 930-980 ℃; and in the pre-straightening, the temperature of the steel plate taken out of the pre-straightening machine is 850-880 ℃, the on-line water cooling starting temperature is 790-850 ℃, and the water inlet temperature at the tail part of the steel plate is required to be above 740 ℃. The temperature for heating the plate blank is 1150-1240 ℃, and the heating time is 200-400 min/mm. The on-line water cooling adopts a water cooling process of linkage of ultra-fast cooling and laminar cooling, the final cooling temperature is below 150 ℃, and the cooling speed is not lower than 20 ℃/s. The tempering temperature of the tempering is 200-400 ℃, and the heating time is the product of 1-3 min/mm and the plate thickness. The cooling adopts on-line water cooling, and the mode that the steel sheet carries out flame cut must be for preheating the flame cut. After the tempering, the wear resistant steel is a tempered martensite structure. Comparative examples 1-2 provide a preparation method of conventional online quenched NM400 wear-resistant steel, which comprises S1, heating, descaling, rough rolling and finish rolling a plate blank obtained by continuous casting to obtain a steel plate; and S2, carrying out online water cooling and tempering on the steel plate to obtain the online quenching wear-resistant steel. Wherein the finish rolling finishing temperature is 800-850 ℃, the temperature of the pre-straightening machine is 780-800 ℃, and the highest water inlet temperature of online water cooling is 740-770 ℃; the tempering temperature of the tempering process is 370 ℃, 400 ℃, and the heating time is 60min and 45min respectively. The other embodiments are the same. Specific process controls are shown in tables 2 and 3.
Table 2 example specific process control parameters.
Table 3 examples and comparative examples specific process control parameters.
The properties of the wear-resistant steels prepared in examples 1 to 4 and comparative examples 1 and 2 were measured, and the results are shown in table 4.
Table 4, the properties of NM400 wear resistant steels were examined.
In table 1, the influence of the process parameters on the mechanical properties of the wear-resistant steels is determined by measuring the chemical components of the NM400 wear-resistant steels of the same examples 1 to 4 and comparative examples 1 to 2 and controlling the process parameters on the basis.
In table 2-3, different process parameters are controlled from examples 1 to 4 and comparative examples 1 to 2, the rolling start temperature and the rolling finish temperature that are set to be important are higher than those of the conventional rolling process, and the influence of the process parameters on the mechanical properties of the wear-resistant steel is finally judged according to the temperature difference of the head, the middle and the tail of the rolled steel plate before entering water cooling, especially the temperature of the steel plate at the tail position with lower water entering temperature.
As can be seen from the data in Table 4, the properties of the wear resistant steels of 4 groups of examples and 2 groups in the application are tested, and the tensile strength, yield strength, elongation and-20 ℃ impact energy and hardness are all qualified from the standard point of view.
From the data in examples 1 to 4, it is understood that the tensile strength, yield strength, elongation, and-20 ℃ impact power and hardness of the wear-resistant steel can be ensured by controlling the finish temperature of finish rolling to 930 ℃ to 980 ℃, the temperature of the finish rolling to be taken out of the pre-straightener to 850 ℃, the starting temperature of the water inlet at the head of the plate blank to be 790 ℃ to 850 ℃, and the temperature of the water inlet at the tail of the plate blank to be 740 ℃ to 850 ℃.
Under the components and the process of the example 2, the wear-resistant steel has the most excellent performance, the tensile strength is 1390Mpa, the elongation after fracture is 13, the impact energy at minus 20 ℃ is 42J, the Brinell hardness of the surface layer is HBW403, and the average difference of the hardness of the head, the middle and the tail of the wear-resistant steel is within +/-3 HBW. The technical internal control requirement that the average difference of the hardness of the wear-resistant steel head, the wear-resistant steel middle and the wear-resistant steel tail is within 15HBW is met.
As can be seen from the data in comparative examples 1-2, the finish rolling temperature is 800-850 ℃, the temperature of the pre-straightening machine is 780-800 ℃, the maximum water-entry temperature of the on-line water cooling is 740-770 ℃, the tensile strength, the yield strength, the elongation and the impact energy at minus 20 ℃ are qualified, but the average difference of the hardness of the head, the middle and the tail reaches 40HBW and 36HBW, and the hardness is not uniform.
In summary, regarding the mechanical properties, the difference between the average values of the hardness of the head, the middle and the tail of the embodiment is within 15HBW, and the hardness of the head, the middle and the tail of the wear-resistant steel is uniform, so that the use requirements of users can be met.
Detailed description of the drawings figures 1 and 2:
in the embodiment 1 shown in fig. 1, the metallographic composition of the surface of the head, the middle and the tail mainly comprises a martensite structure, and part of bainite, no ferrite and high-temperature ferrite are not transformed, so that the surface hardness of the wear-resistant steel is not influenced, and the head, the middle and the tail of the wear-resistant steel are all martensite structures and have uniform hardness.
The structure in the middle of the head structure of the comparative example 1 in fig. 2 contains a small amount of ferrite, and the surface position of the tail part contains a large proportion (5% -15%) of ferrite, and the structure easily causes serious problems of reduced surface hardness, local softening and the like of the wear-resistant steel, so that the hardness of the head, the middle and the tail of the wear-resistant steel is uneven.
By combining the table 4 and the fig. 1-2, compared with the indexes of the comparative example, the tensile property, the impact property and the like of the example are basically at the same level, meanwhile, the example mainly comprises a martensite structure, and also comprises a part of bainite, the hardness uniformity of the head, the middle and the tail is kept at a higher level, on the premise of ensuring that all indexes are qualified, the Brinell hardness difference of the head, the middle and the tail of the wear-resistant steel produced by the technical scheme of the example is controlled within 15HBW, and the comparative example contains a small amount of ferrite, has larger Brinell hardness difference of the head, the middle and the tail of the wear-resistant steel, has uneven hardness, has good application and popularization potential, can fully meet the use requirements of users, avoids quality objections caused by low local hardness and reduces the risk of the wear-resistant steel in the service process.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. NM400 wear resistant steel with high hardness uniformity, characterized in that the chemical composition of the wear resistant steel comprises by mass percent: c: 0.20 to 0.40%, Mn: 1.20-1.80%, Si: 0.20-0.50%, Cr: 0.20-0.60%, Mo: 0.20 to 0.50%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025% of Fe and inevitable impurity elements in balance; the microstructure of the wear-resistant steel is bainite and martensite.
2. The high hardness uniformity NM400 wear resistant steel according to claim 1, characterized in that the chemical composition of said wear resistant steel comprises, in mass percent: c: 0.20 to 0.30%, Mn: 1.20 to 1.50%, Si: 0.20-0.40%, Cr: 0.30-0.60%, Mo: 0.20-0.30%, Al: 0.02 to 0.04%, Ti: 0.01-0.02%, P: less than or equal to 0.02 percent, S: less than or equal to 0.02 percent; b: 0.0001-0.0025%, and the balance of Fe and inevitable impurity elements.
3. The high hardness uniformity NM400 wear resistant steel according to claim 1, wherein the hardness difference of the head, middle and tail of said wear resistant steel plate is not more than 15 HBW.
4. The high hardness uniformity NM400 wear resistant steel according to claim 1, wherein the mechanical properties of the head, middle and tail of the wear resistant steel plate mother plate all satisfy: the tensile strength is 1250-1350 MPa, the elongation after fracture is not less than 10%, the impact energy at minus 20 ℃ is not less than 20J, and the surface layer Brinell hardness is HBW 370-430.
5. A method of preparing NM400 abrasion resistant steel with high hardness uniformity according to any of claims 1-4, comprising:
sequentially rolling, pre-straightening, cooling and tempering the plate blank to obtain the wear-resistant steel;
when the cooling is carried out, the temperature of the head part entering water is 790-850 ℃, and the temperature of the tail part entering water is 740-850 ℃.
6. The high hardness uniformity NM400 wear resistant steel according to claim 5, wherein said rolling comprises pre-rolling heating at a temperature of 1150 ℃ to 1240 ℃ with a time coefficient of 200 to 400 min/mm; the finishing temperature of the rolling is 930-980 ℃.
7. The method for preparing NM400 wear resistant steel with high hardness uniformity according to claim 5, wherein the finish temperature of pre-straightening is 850-880 ℃.
8. The method for preparing NM400 wear-resistant steel with high hardness uniformity according to claim 5, wherein the cooling process comprises ultra-fast cooling or laminar cooling, and the cooling manner of the ultra-fast cooling and the laminar cooling comprises any one of water cooling, fog cooling and air cooling; the final cooling temperature of the cooling is below 150 ℃, and the cooling speed of the cooling is not lower than 20 ℃/s.
9. The method of preparing NM400 wear resistant steel with high hardness uniformity according to claim 5, wherein the tempering temperature is 200 ℃ to 400 ℃, and the tempering heating time coefficient is 1 to 3 min/mm.
10. The method for preparing NM400 wear-resistant steel with high hardness uniformity according to claim 5, wherein the manner of performing the flame cutting treatment on the slab before or after the tempering process is preheating flame cutting.
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