阅读说明：本技术 提升高强钢冲击韧性的热加工方法 (Hot working method for improving impact toughness of high-strength steel ) 是由 王交其 冯伟 胡永平 邵忠伟 周仲成 涂明金 刘海江 陈献刚 郭运来 郭元 郭转 于 2019-10-10 设计创作，主要内容包括：本发明公开了一种提升高强钢冲击韧性的热加工方法,包括：锻造坯料和坯料高温扩散,扩散温度为1230℃-1270℃,扩散时间为20-35小时；二次变形和退火；坯料的锻造比大于等于2.5,坯料二次变形的锻造比大于等于3.0。本发明能够有效提高高强钢的冲击性能。(The invention discloses a hot working method for improving impact toughness of high-strength steel, which comprises the following steps: the forging blank and the blank are diffused at high temperature, the diffusion temperature is 1230-1270 ℃, and the diffusion time is 20-35 hours; secondary deformation and annealing; the forging ratio of the billet is 2.5 or more, and the forging ratio of the secondary deformation of the billet is 3.0 or more. The invention can effectively improve the impact property of the high-strength steel.)

1. A hot working method for improving impact toughness of high-strength steel comprises the following steps:

the forging blank and the blank are diffused at high temperature, the diffusion temperature is 1230-1270 ℃, and the diffusion time is 20-35 hours;

secondary deformation and annealing; the forging ratio of the billet is 2.5 or more, and the forging ratio of the secondary deformation of the billet is 3.0 or more.

2. The hot working method for improving the impact toughness of high-strength steel according to claim 1, wherein for crankshaft steel and high-pressure gas cylinder steel, forging is performed first, and then high-temperature diffusion is performed on the blanks; the diffusion temperature is 1230-1250 ℃, and the diffusion time is 20-25 h.

3. The hot working method for improving impact toughness of high strength steel according to claim 2, wherein the forging of the billet further comprises: smelting in an electric furnace, refining in LF + VD, casting ingots, remelting electroslag and heating; the method also comprises the following steps of before blank high-temperature diffusion: annealing the blank, preheating the blank and heating.

4. The hot working method for improving impact toughness of high strength steel according to claim 2, wherein the quenching temperature is 850 ± 15 ℃ and the tempering temperature is 580 ± 50 ℃ for the crank steel at the time of annealing, and water or oil is used for cooling.

5. The hot working method for improving impact toughness of high-strength steel according to claim 2, wherein, for the high-pressure gas cylinder steel, the temperature is kept at 890 ℃ for 2 hours during annealing, the temperature is kept at 880 ℃ for 2 hours after normalizing, and the temperature is kept at 560 ℃ for 4 hours after quenching for tempering.

6. The hot working method for improving the impact toughness of the high-strength steel according to claim 1, wherein the die steel is subjected to blank high-temperature diffusion and then forged, the diffusion temperature is 1250-1270 ℃, and the diffusion time is 25-30 hours.

7. The hot working method for improving impact toughness of high strength steel according to claim 6, further comprising, before the high temperature diffusion: smelting in an electric furnace, refining in LF + VD, casting ingots, preheating and heating; before secondary deformation, the method further comprises the following steps: and (3) blank spheroidizing annealing, blank preheating and heating.

8. The hot working method for improving the impact toughness of high strength steel according to claim 6, wherein for die steel, heat preservation at 1030 ℃ is carried out for 30 minutes during annealing, and oil quenching is carried out; 590-610 ℃ for at least 2 times.

9. The hot working method for improving impact toughness of high strength steel according to claim 1, wherein the forging ratio of the billet is 3.0 or more and the forging ratio of the secondary deformation of the billet is 2.5 or more.

10. The hot working method for improving the impact toughness of the high-strength steel according to claim 1, wherein the forging ratio of the crankshaft type and high-pressure gas cylinder steel blanks is more than or equal to 2.5, and the forging ratio of the secondary deformation is more than or equal to 3.0; the forging ratio of the die steel product blank is more than or equal to 2.5, and the forging ratio of the secondary deformation is more than or equal to 4.0.

Technical Field

The invention belongs to the field of steel hot working, and particularly relates to a hot working method for improving impact toughness of high-strength steel.

Background

In recent years, the market of special steel products, particularly the market of high-toughness steel, is increasingly competitive, the product requirements are higher and higher, and the requirements on the performance of materials are higher and higher along with the improvement of the performance requirements of the products. In order to meet the product requirements, for specific materials, on one hand, the level of material manufacturing equipment needs to be improved (for example, argon protection is adopted for electroslag remelting and oxygen control); on the other hand, innovation in process technology is needed, the potential performance of materials is fully exerted, and new products of high-strength and high-toughness special steel, such as high-end products of special steel such as high-pressure gas cylinders, high-quality die steel, high-strength steel and the like, are continuously developed. However, the impact toughness of some special steel products does not reach the standard or greatly fluctuates under the conditions of specified strength and hardness, and the speed of the products to market is seriously influenced.

In the production practice of special steel for many years, after the chemical components of the material are determined, the smelting purity, the solidification quality, the forming process and the heat treatment structure form of the material are all important influence factors of the performance of the forging. Therefore, under the conditions of the existing equipment capacity and purity level, technological innovation needs to be carried out through the forming and heat treatment processes, the potential of material performance is excavated, the toughness of the material is improved on the premise of ensuring the strength, the restriction on product performance is broken through, the improvement of material performance is realized, and the requirement of developing special steel products to a high end is very urgent.

Disclosure of Invention

The invention aims to provide a hot working method for improving the impact toughness of high-strength steel, which can effectively improve the impact property of the high-strength steel.

The technical scheme is as follows:

a hot working method for improving impact toughness of high-strength steel comprises the following steps:

the forging blank and the blank are diffused at high temperature, the diffusion temperature is 1230-1270 ℃, and the diffusion time is 20-35 hours;

secondary deformation and annealing; the forging ratio of the billet is 2.5 or more, and the forging ratio of the secondary deformation of the billet is 3.0 or more.

Further, for crankshaft steel and high-pressure gas cylinder steel, forging blanks and then performing high-temperature blank diffusion; the diffusion temperature is 1230-1250 ℃, and the diffusion time is 20-25 h.

Further, before forging the blank, the method also comprises the following steps: smelting in an electric furnace, refining in LF + VD, casting ingots, remelting electroslag and heating; the method also comprises the following steps of before blank high-temperature diffusion: annealing the blank, preheating the blank and heating.

Furthermore, for the crankshaft steel, the quenching temperature is 850 +/-15 ℃, the tempering temperature is 580 +/-50 ℃ and water or oil is adopted for cooling.

Further, for the high-pressure gas cylinder steel, heat preservation at 890 ℃ is carried out for 2 hours during annealing, heat preservation at 880 ℃ is carried out for 2 hours after normalizing, heat preservation at 560 ℃ is carried out for 4 hours after quenching, and tempering is carried out.

Further, the die steel is firstly subjected to blank high-temperature diffusion and then forged, wherein the diffusion temperature is 1250-1270 ℃, and the diffusion time is 25-30 h.

Further, the method also comprises the following steps before high-temperature diffusion: smelting in an electric furnace, refining in LF + VD, casting ingots, preheating and heating; before secondary deformation, the method further comprises the following steps: and (3) blank spheroidizing annealing, blank preheating and heating.

Further, for the die steel, heat preservation is carried out for 30 minutes at 1030 ℃ during annealing, and oil quenching is carried out; 590-610 ℃ for at least 2 times.

Further, the forging ratio of the billet is 3.0 or more, and the forging ratio of the secondary deformation of the billet is 2.5 or more.

Furthermore, the forging ratio of the crankshaft and high-pressure gas cylinder steel blanks is more than or equal to 2.5, and the forging ratio of the secondary deformation is more than or equal to 3.0; the forging ratio of the die steel product blank is more than or equal to 2.5, and the forging ratio of the secondary deformation is more than or equal to 4.0.

The invention has the technical effects that:

the invention has obvious effect on special steel, especially high-strength steel, in the aspect of improving the impact property. The method realizes the technical index that the impact toughness of the high-strength steel is improved by 15 percent, and has great significance for special steel products. The impact performance of the structural steel, the high-pressure gas cylinder steel, the high-quality die steel and other typical high-strength steels is improved by more than 19.25% in the modes of high-temperature diffusion and secondary deformation, the original forming mode is broken through, and a new path is opened up for the production of high-performance products. The product produced by the method has excellent comprehensive performance and stable performance.

At present, the researches on the potential of improving the purity of molten steel and excavating potential materials in heat treatment are more, but the performance improvement range is limited, and no major breakthrough exists. The research from the forging aspect is less, the single traditional process forging technology is adopted, and the impact performance is hardly improved to a large extent under the conditions of the existing equipment and materials.

Detailed Description

The following description sufficiently illustrates specific embodiments of the invention to enable those skilled in the art to practice and reproduce it.

The hot working method is based on the research on the influence of high-temperature diffusion of the steel ingot on the performance, combines forging secondary deformation processing, and is suitable for improving the impact toughness of the high-strength steel and the comprehensive mechanical property of the material. The invention aims at taking the structural and die high-strength steel as an application object, improves the comprehensive mechanical property of the material by a hot working method, starts from the structure transformation rule and the hot working deformation of the steel, combines high-temperature diffusion and secondary deformation to achieve the aim of exploring the comprehensive property of the material,

the hot working method for improving the impact toughness of the high-strength steel comprises the following specific steps:

step 1: the forging blank and the blank are diffused at high temperature, the diffusion temperature is 1230-1270 ℃, and the diffusion time is 20-35 hours;

for crankshaft steel and high-pressure gas cylinder steel, a blank is forged first and then high-temperature diffusion of the blank is carried out. The diffusion temperature is 1230-1250 ℃, and the diffusion time is 20-25 h. Before forging the blank, the method also comprises the following steps: smelting in an electric furnace, refining in LF + VD, casting ingots, remelting electroslag and heating; the method also comprises the following steps of before blank high-temperature diffusion: annealing the blank, preheating the blank and heating.

The method comprises the following steps of firstly carrying out blank high-temperature diffusion on die steel and then forging the blank, and before the high-temperature diffusion, the method also comprises the following steps: smelting in an electric furnace, LF + VD refining, ingot casting, preheating and heating. The die steel product has high carbon content and high content of carbide forming elements, so that in order to prevent carbide liquation cracks from influencing the product quality, the steel ingot is subjected to high-temperature diffusion, and liquation is eliminated in an as-cast state. The diffusion temperature of the die steel product is 1250-1270 ℃, and the diffusion time is 25-30 h.

Specific diffusion temperature and time designs are shown in table 1.

TABLE 1 diffusion temperature, time

Type of product	Diffusion temperature	Diffusion time	Timing of diffusion
				Crankshaft product	1230℃～1250℃	20h	Blank diffusion before secondary deformation
Die steel product	1250℃～1270℃	25h	High temperature diffusion of steel ingot
				Steel products of high-pressure gas cylinder	1230℃～1250℃	20h	Blank diffusion before secondary deformation

Step 2: secondary deformation and annealing; the forging ratio of the billet is 2.5 or more, and the forging ratio of the secondary deformation of the billet is 3.0 or more.

The forging ratio is a method of expressing the degree of metal deformation at the time of forging, and is generally expressed as a ratio of cross-sectional areas before and after the metal deformation. The invention improves the performance of the steel product by uniform components and uniform structure. Generally, high-temperature diffusion can improve component segregation, but the diffused steel ingot (blank) is not subjected to annealing and cooling, so that a forging is overheated, and the product has phenomena of coarse crystals, mixed crystals and nonuniform texture, thereby reducing the mechanical property of the product. In practical production, the phenomena of coarse grains, mixed grains and nonuniform structures of special steels, particularly high-strength steels containing CrNiMo, are proved to be difficult to eliminate only through heat treatment.

For die steel products, the method also comprises the following steps before secondary deformation: and (3) blank spheroidizing annealing, blank preheating and heating.

Selecting a blank forging ratio, wherein the forging ratio of a refining ingot is more than 4.0, the forging ratio of an electroslag ingot is more than 3.0, and the blank is in a fully forged structure state; the forging ratio of the secondary deformation of the blank is more than 2.5, the improvement of the dispersion distribution of the impurities is ensured, the bar blank is selected, the same deformation method is adopted before and after the forging, and the comparison conditions before and after the forging are convenient to be the same.

The forging ratio of crankshaft and high-pressure gas cylinder steel product blanks is more than or equal to 2.5, and the forging ratio of secondary deformation is more than or equal to 3.0; the forging ratio of the die steel product blank is more than or equal to 2.5, and the forging ratio of the secondary deformation is more than or equal to 4.0. The specific forging parameter design is shown in table 2.

TABLE 2 forging parameters

And after secondary deformation, adopting the same annealing process as the blank. In order to realize the same comparison conditions, the performance detection is carried out on small samples under the same heat treatment system conditions before and after the secondary deformation, the crankshaft adopts a longitudinal sample, the die steel and the gun steel adopt a transverse sample, and the heat treatment parameter design of the samples is shown in Table 3.

TABLE 3 Heat treatment parameters for small samples

High temperature diffusion + secondary deformation post test conditions.

1. Crankshaft test conditions

1.1 technical index item detection results before and after crankshaft secondary deformation.

Measuring a 1000mm cut test piece 150mm from the imprinting end on the forge piece before secondary deformation for tissue and performance detection, cutting a 150mm cut piece on a diameter phi 200 table of the forge piece after secondary deformation for tissue and performance detection, and obtaining a detection result shown in table 4.

TABLE 4 detection results of the structure and performance of the crankshaft forgings

1.2 technical index item detection results after re-annealing

The forging after secondary deformation is only annealed at low temperature, the structure is bainite, and the grain size is 4.0 grade. The impact performance of the small sample is improved by 8.06 percent under the same heat treatment condition as that before the secondary deformation, which shows that the high-temperature diffusion and the secondary deformation play a role, therefore, the annealing is carried out again, and the detection result of the impact performance is shown in table 5.

TABLE 5 results of re-annealing Performance test

1.3 comparison of impact Properties before and after Secondary deformation forging

The SAE4140 crankshaft steel forging is subjected to high-temperature diffusion and secondary deformation, the forging ratio of the secondary deformation is more than 2.5, the primary forging is annealed under the same conditions after the secondary deformation, the sample is subjected to the same heat treatment system, the average impact increase amplitude reaches 21.3 percent, the requirement of the expected index of 15 percent is met, the single increase value is 8.24J-21.1J, the increase amplitude is 12.16-31.2 percent, and the specific result is shown in Table 6.

TABLE 6 comparison of impact before and after secondary deformation

2. Test conditions of die Steel

1. Detection condition of technical indexes before and after secondary deformation

Cutting 150mm ends before and after secondary deformation, cutting a transverse test piece, and performing grain size, annealing structure and impact performance on the central part of the test piece, wherein the detection results of the technical indexes before and after secondary deformation are shown in table 7.

TABLE 7 results of technical index detection before and after secondary deformation

2. Comparison of impact properties before and after secondary deformation

Under the condition that the actual grain size is similar to the annealing structure, the impact performance value is greatly improved, the average impact power of the V-shaped notch before secondary deformation is 18.3J, the average impact power of the V-shaped notch after secondary deformation is 28.67J, the average impact power is 10.37J, the improvement amplitude is 56.7 percent, and the specific comparison result is 8.

TABLE 8 comparison of impact before and after Secondary deformation

3. Steel test conditions for high pressure gas cylinders

1. Mechanical properties of high-pressure gas cylinder steel before and after secondary deformation

Transverse samples (20mm by 20mm) were taken at a radius of 1/2 points of the sample before and after the secondary deformation, and the results of the performance test were shown in Table 9.

TABLE 9 results of Performance measurements before and after secondary deformation

2. Comparison of impact Properties before and after Secondary deformation

Under the condition of equal strength before and after secondary deformation, the impact performance before secondary deformation is average 51.97J, which is 8.39J higher than 43.58J in secondary deformation, and the increase amplitude reaches 19.25%, so that the expected effect is achieved, and the specific results are shown in Table 10.

TABLE 10 comparison of impact Properties before and after Secondary deformation

In summary, the invention has significant effect on special steel, especially high-strength steel, in the aspect of improving impact performance, and adopts a high-temperature diffusion and secondary deformation combined forming integrated technology process, and the determination of technical parameters of each forming point and the connection relationship among the forming points in the process flow are not available in the prior art, and the method specifically comprises the following steps:

firstly, the influence of the size of the forming ratio of primary forging forming and secondary deformation forming and the mutual arrangement on the product structure state;

secondly, eliminating the influence of segregation on impact performance by high-temperature diffusion time, diffusion temperature and diffusion time;

and thirdly, annealing treatment is carried out after the primary forging, so that the gas content in the forging is reduced, and the dispersion distribution and the refinement of the inclusions in the secondary deformation are facilitated. From the product performance detection result, the impact performance of the treated material is improved by 19.25-56.7 percent on the basis of the original product, and a production approach and technical reserve are provided for the development of high-performance products.

The terminology used herein is for the purpose of description and illustration, rather than of limitation. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.