A forging method for improving the morphology of manganese sulfide in free-cutting steel

Abstract

The application discloses a forging method for improving the manganese sulfide form in free-cutting steel, and comprises the following steps: uniformly heat treating and forging a free-cutting steel ingot to improve the manganese sulfide form in the free-cutting steel. The prepared free-cutting steel rod has good cutting performance, is suitable for manufacturing parts of automobile, high-speed rail, household appliances and office equipment industries to reduce machining cost, improve production efficiency and product competitiveness, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of forging processing of metal materials, and particularly relates to a forging method for improving the manganese sulfide form in free-cutting steel. BACKGROUND

[0002] Free-cutting stainless steel (hereinafter referred to as free-cutting steel) refers to an alloy steel in which a certain amount of one or more than one free-cutting element such as sulfur, phosphorus, lead, calcium, selenium and tellurium is added to improve the cutting performance. According to the different free-cutting elements contained, the free-cutting stainless steel can be divided into sulfur-based free-cutting stainless steel, lead-based free-cutting stainless steel, titanium-based free-cutting stainless steel and composite free-cutting stainless steel. The sulfur-based free-cutting stainless steel is the earliest free-cutting stainless steel in the world, and has the largest amount and the most extensive use so far, accounting for more than 70% and more than 90% of the total production of free-cutting stainless steel in the world and China respectively. The sulfur-based free-cutting stainless steel is mainly applied to bolts, nuts, pipe joints, automobile brake parts, spring seats and molds and other complex parts. These complex parts need to be cut on a numerical control machine tool. In order to prolong the service life of the tool, reduce the processing cost and improve the production efficiency, the steel material must have good cutting performance. The sulfur in the sulfur-based free-cutting stainless steel mainly exists in the form of manganese sulfide. The manganese sulfide inclusions can induce many micro-cracks in the matrix as stress concentration sources, reduce the cutting resistance and cause the steel material to easily break chips during turning.

[0003] Sims and Dahle first classified the manganese sulfide in the cast structure of steel, and divided it into three categories according to the morphology and distribution of manganese sulfide: the first category is spherical composite inclusions, randomly distributed, existing in steel without aluminum deoxidation; the second category is short rod, chain or network distribution along the grain boundary, existing in steel with a small amount of aluminum deoxidation; the third category is block, irregular distribution, existing in steel with high aluminum content and residual aluminum; later researchers added a fourth category: dendritic sulfide. Oikawa et al. studied the effect of alloying elements on the morphology of manganese sulfide in free-cutting stainless steel, and classified the manganese sulfide: the first category is spherical (category I), formed by the formation of a eutectic reaction; the second category is short rod or dendritic (category II), formed by eutectic reaction; the third category is irregular shape (category III), generated by pseudo-eutectic reaction. The size, morphology and distribution of manganese sulfide in sulfur-containing free-cutting stainless steel have a significant influence on the mechanical properties of the steel. In order to obtain the best cutting performance, it is hoped to obtain spherical or spindle-shaped sulfide inclusions with small aspect ratio, which can not be deformed due to small plasticity during rolling process, and can still maintain spindle or ellipsoidal shape after deformation of the matrix, which is very beneficial to improve the cutting performance. The elongated strip-shaped manganese sulfide with an aspect ratio of more than 4:1 not only destroys the continuity of the matrix, but also causes the adhesion of cutting chips, reducing the surface quality of the workpiece. The free-cutting stainless steel is easy to generate elongated strip-shaped manganese sulfide after forging deformation, causing anisotropy of the steel, and reducing the comprehensive mechanical properties of the steel.

[0004] Sulfide can effectively improve the cutting performance of free-cutting steel. Sulfide has good plasticity in steel and can be used as a soft phase to lubricate and reduce tool wear. There is additional stress around the sulfide, which can promote crack generation and make the cutting chip more easily broken, thereby improving the processability of the steel. However, due to the good deformation ability of sulfide, it will extend into an elongated strip along the deformation direction during rolling or forging, causing anisotropy of the steel, and seriously reducing the transverse mechanical properties of the material. The long strip-shaped sulfide also becomes a crack source in the free-cutting steel plate, seriously reducing its service life.

[0005] Therefore, there is an urgent need to provide a forging method for improving the morphology of manganese sulfide in free-cutting steel to overcome the above-mentioned defects. SUMMARY

[0006] In view of the above problems, the purpose of the present application is to provide a forging method for improving the morphology of manganese sulfide in free-cutting steel, which effectively controls the morphology, size and distribution state of manganese sulfide during forging process, so that the key parameters such as size, aspect ratio and maximum chord length of manganese sulfide inclusions are improved, thereby more conducive to the improvement of the cutting performance of free-cutting steel.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0008] A forging method for improving the morphology of manganese sulfide in free-cutting steel, comprising the following steps: homogenizing heat treatment and forging treatment of the free-cutting steel ingot to improve the morphology of manganese sulfide in the free-cutting steel.

[0009] Preferably, a forging method for improving the morphology of manganese sulfide in free-cutting steel, the specific steps are as follows:

[0010] (a) obtaining a free-cutting steel ingot by vacuum smelting;

[0011] (b) air cooling the free-cutting steel ingot, and after cooling to room temperature, finishing the ingot;

[0012] (c) homogenizing heat treatment of the finished ingot;

[0013] (d) obtaining a forging ingot by upsetting and elongating treatment of the homogenizing heat treated ingot;

[0014] (e) forging treatment of the forging ingot.

[0015] Preferably, in step (a), the chemical composition of the free-cutting steel ingot includes C 0.03%~0.04%; Si 0.2%~0.25%; Mn 1.8%~2.0%; P 0.01%~0.02%; S 0.15%~0.2%; Ni 7.0%~8.0%; Cr 16.0%~17.0%; Mo 0.15%~0.25%; H 0.0004%~0.0005%; O 0.007%~0.008%; N 0.01%~0.015%, the rest is Fe and inevitable impurity elements.

[0016] Preferably, the mass ratio of Mn to S in the free-cutting steel ingot is in the range of 7~10.

[0017] Preferably, in step (a), the specific process of preparing the free-cutting steel ingot is as follows:

[0018] Other raw materials except sulfur iron and carburant are loaded into the crucible according to the composition ratio, and put into the vacuum induction furnace; the vacuum induction furnace is vacuumized, and then power is turned on to melt the alloy, and the sulfur iron and carburant are added to the steel liquid in the steel liquid refining stage, the composition of the free-cutting steel is detected before tapping and adjusted slightly, and the ingot is obtained after the composition is qualified.

[0019] Preferably, in step (a), the temperature of tapping and casting is 1500℃~1580℃.

[0020] Preferably, in step (a), the vacuum degree of the vacuum induction furnace before power on is 50Pa~500Pa.

[0021] Preferably, the specific conditions of the homogenizing heat treatment in step (c) are as follows: the homogenizing heat treatment temperature is 30-50°C below the incipient melting point temperature of the free-cutting steel, and the homogenizing heat treatment time is 5-8 hours.

[0022] Preferably, the specific process of step (d) is as follows:

[0023] The cast ingot after the homogenizing heat treatment is upset, immediately after the upsetting is drawn, and then is rounded to obtain a forging ingot, the upsetting reduction is 20-50%, the drawing reduction is 10-20%, and during the upsetting, drawing and rounding, the temperature of the cast ingot is ensured to be ≥1100°C.

[0024] Preferably, the specific process of step (e) is as follows:

[0025] The forging ingot after step (d) is reheated in a furnace, the heating temperature is set to 1100-1200°C, the temperature difference between the surface temperature and the core temperature of the forging ingot is controlled to be within ±10°C, and the holding time of the forging ingot is 3-5 hours.

[0026] The above heated forging ingot is taken out of the furnace and is forged for three times, the first time the forging ingot is forged into a square billet, the second time the square billet is forged into an octagon, and the third time the octagon is forged into a round free-cutting steel bar.

[0027] Preferably, the specific conditions of the first time forging are as follows:

[0028] The time interval from the forging ingot being taken out of the furnace to the first time forging is 10-120 seconds, the feeding speed during the first time forging is controlled to be 0.3-0.5 m / s, the rotation feeding angle is 90° / hammer, the hammering frequency is controlled to be 80-100 times per minute, the surface temperature rise of the forging ingot is controlled to be 0-20°C, the core temperature rise of the forging ingot is controlled to be below 15°C, and finally the forging ingot is forged into a square billet.

[0029] Preferably, the specific conditions of the second time forging are as follows:

[0030] After the first time forging is completed, the second time forging is performed, the time interval from the end of the first time forging to the start of the second time forging is 1-15 seconds, the feeding speed during the second time forging is controlled to be 0.3-0.5 m / s, the rotation feeding angle is 45° / hammer, the hammering frequency is controlled to be 80-100 times per minute, the surface temperature rise of the forging ingot is controlled to be 0-20°C, the core temperature rise of the forging ingot is controlled to be below 15°C, and finally the square billet is forged into an octagon.

[0031] Preferably, the specific conditions of the third time forging are as follows:

[0032] After the second forging is completed, the third forging is carried out, the time interval from the end of the second forging to the start of the third forging is 1s-15s; the feeding speed during the third forging process is controlled to be 0.3m / s-0.5m / s; the rotation feeding angle is 15° / hammer; the hammering frequency is controlled to be 80 times / minute-100 times / minute; by controlling the hammering frequency, the surface temperature of the forged ingot is controlled to be 0℃-20℃, and the core temperature of the forged ingot is controlled to be below 15℃; finally, the round free-cutting steel bar is obtained after the third forging is completed.

[0033] The free-cutting steel obtained by the forging method has the following characteristics: the proportion of sulfides with a length-width ratio of less than 3 in the free-cutting steel is greater than 40%; the proportion of sulfides with a size of less than 3μm in the free-cutting steel is greater than 50%; and the proportion of sulfides with a maximum chord length of less than 3μm in the free-cutting steel is greater than 50%.

[0034] The beneficial effects of the present application are as follows:

[0035] 1. The present application improves the macroscopic segregation and microscopic segregation of the free-cutting steel ingot by homogenizing heat treatment and upsetting and elongation treatment process, greatly improves the composition uniformity, and welds the loose and shrinkage defects in the core of the ingot;

[0036] 2. The present application strictly controls the feeding speed, rotation angle, forging temperature and other parameters of each time by the three times forging process, improves the organization uniformity of the forged ingot, can ensure that the material has good grain size and quality; at the same time, the morphology, size and distribution state of manganese sulfide in the forging deformation process are effectively controlled, so that the key parameters such as the size, length-width ratio and maximum chord length of the manganese sulfide inclusions are improved, thereby more conducive to the improvement of the cutting performance of Y12Cr18Ni9 free-cutting steel;

[0037] 3. The melting and forging process of the present application is simple and the raw materials of the free-cutting steel bar are widely available, which reduces the production cost of the free-cutting steel bar;

[0038] 4. The free-cutting steel bar prepared by the present application does not contain lead element, does not pollute the environment and meets the development strategy of energy saving and emission reduction;

[0039] 5. The free-cutting steel bar prepared by the present application has good cutting performance, is suitable for manufacturing parts of automobile, high-speed rail, household appliances and office equipment industries to reduce machining cost, improve production efficiency and product competitiveness, and has good application prospect.

[0040] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or can be learned by practice of the present application. The objects and other advantages of the present application will be realized and attained by the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The strength and plasticity curve of Y12Cr18Ni9 free-cutting steel;

[0043] Figure 2 Electron micrograph of the sulfide distribution in Y12Cr18Ni9 vacuum furnace ingot;

[0044] Figure 3 Electron micrograph of sulfide distribution in Y12Cr18Ni9 bar;

[0045] Figure 4 The aspect ratio distribution of Y12Cr18Ni9 free-cutting steel is shown in the diagram.

[0046] Figure 5 This is a dimensional distribution diagram of Y12Cr18Ni9 free-cutting steel;

[0047] Figure 6 The maximum chord length distribution diagram for Y12Cr18Ni9 free-cutting steel;

[0048] Figure 7 These are cutting chips from Y12Cr18Ni9 free-cutting steel. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention discloses a forging method for improving the morphology of manganese sulfide in free-cutting steel, comprising the following steps: homogenizing heat treatment and forging treatment of free-cutting steel ingot to improve the morphology of manganese sulfide in free-cutting steel.

[0051] The homogenization heat treatment and the forging treatment of the present application effectively control the morphology, size and distribution state of manganese sulfide in the forging process, so that the key parameters such as the size, aspect ratio and maximum chord length of the manganese sulfide inclusions are improved, thereby being more conducive to the improvement of the cutting performance of the free-cutting steel. At the same time, the forging treatment also improves the microstructure uniformity of the free-cutting steel, so as to ensure that the material has good grain size and quality; the homogenization heat treatment improves the macrosegregation and microsegregation of the free-cutting steel ingot, and the composition uniformity is greatly improved, and the porosity and shrinkage hole defects in the core of the ingot are welded.

[0052] Preferably, a forging method for improving the morphology of manganese sulfide in a free-cutting steel, the specific steps are as follows:

[0053] (a) obtaining a free-cutting steel ingot by vacuum smelting;

[0054] Specifically, the chemical composition of the free-cutting steel ingot includes C 0.03%~0.04%; Si 0.2%~0.25%; Mn 1.8%~2.0%; P 0.01%~0.02%; S 0.15%~0.2%; Ni 7.0%~8.0%; Cr 16.0%~17.0%; Mo 0.15%~0.25%; H 0.0004%~0.0005%; O 0.007%~0.008%; N 0.01%~0.015%, and the rest is Fe and inevitable impurity elements.

[0055] Preferably, the mass ratio of Mn to S in the free-cutting steel ingot is in the range of 7~10, and the preferred value is 9~10.

[0056] Specifically, the specific process of preparing the free-cutting steel ingot is as follows:

[0057] Other raw materials (other raw materials are high-purity iron, metallic silicon, metallic manganese, phosphorus iron, nickel plate, metallic chromium, molybdenum iron and copper wire) except for sulfur iron and carbon additive are loaded into a crucible according to the component ratio, and are placed into a vacuum induction furnace; the vacuum induction furnace is pumped to 50Pa~500Pa, and then electricity is supplied to melt the alloy; the sulfur iron and the carbon additive are added to the molten steel in the steel liquid refining stage; the composition of the free-cutting steel is detected before tapping, and is adjusted slightly; after the composition is qualified, the steel is tapped and cast to obtain an ingot, and the tapping and casting temperature is 1500℃~1580℃, and the preferred value is 1550℃. Here, the preparation mainly includes smooth feeding, and the high-purity iron, the metallic silicon, the metallic manganese, the phosphorus iron, the nickel plate, the metallic chromium, the molybdenum iron and the copper wire are added first, and the sulfur iron and the carbon additive are added in the refining stage.

[0058] (b) air cooling the free-cutting steel ingot, and finishing the ingot after cooling to room temperature;

[0059] (c) homogenization heat treatment of the finished ingot;

[0060] Specifically, the specific conditions of the homogenization heat treatment are as follows: the homogenization heat treatment temperature is 30-50°C below the incipient melting point temperature of the free-cutting steel, and the homogenization heat treatment time is 5-8h, preferably 8h.

[0061] (d) performing a heading and elongating treatment on the cast ingot after the homogenization heat treatment to obtain a forging ingot;

[0062] Specifically, the cast ingot after the homogenization heat treatment is subjected to heading, elongating and rounding to obtain a forging ingot, the heading reduction is 20-50%, preferably 30%, the elongating reduction is 10-20%, preferably 15%, and the temperature of the cast ingot is ensured to be ≥1100°C during the heading, elongating and rounding.

[0063] (e) performing a forging treatment on the forging ingot.

[0064] Specifically, the specific process of the forging treatment is as follows:

[0065] The forging ingot after the treatment in step (d) is reheated in a furnace, the heating temperature is set to 1100-1200°C, the temperature difference between the surface temperature and the core temperature of the forging ingot is controlled to be within ±10°C, and the holding time of the forging ingot is 3-5h, preferably the heating temperature is 1150°C and the holding time is 5h.

[0066] The above heated forging ingot is taken out of the furnace and subjected to three times of forging, the first time of forging is to forge the forging ingot into a square billet, the second time of forging is to forge the square billet into an octagon, and the third time of forging is to forge the octagon into a round free-cutting steel bar.

[0067] Preferably, the specific conditions of the first time of forging are as follows:

[0068] The time interval from the taking out of the furnace to the first time of forging is 10-120s, preferably 60s, the feeding speed during the first time of forging is controlled to be 0.3-0.5m / s, preferably 0.5m / s, the rotation feeding angle is 90° / hammer, the hammering frequency is controlled to be 80-100 times per minute, preferably 100 times per minute, the surface temperature rise of the forging ingot is controlled to be 0-20°C by controlling the hammering frequency, the core temperature rise of the forging ingot is controlled to be below 15°C, and the forging ingot is finally forged into a square billet after the first time of forging.

[0069] Preferably, the specific conditions of the second time of forging are as follows:

[0070] After the first forging is completed, the second forging is carried out, and the time interval from the end of the first forging to the start of the second forging is 1s-15s; the feeding speed during the second forging is controlled to be 0.3m / s-0.5m / s, preferably 0.5m / s; the rotation feeding angle is 45° / hammer; the hammering frequency is controlled to be 80 times / minute-100 times / minute, preferably 100 times / minute, by controlling the hammering frequency, the surface temperature of the forged ingot is controlled to be 0℃-20℃, and the core temperature of the forged ingot is controlled to be below 15℃; and the square billet is finally forged into an octagon by the second forging.

[0071] Preferably, the specific conditions of the third forging are as follows:

[0072] After the second forging is completed, the third forging is carried out, and the time interval from the end of the second forging to the start of the third forging is 1s-15s; the feeding speed during the third forging is controlled to be 0.3m / s-0.5m / s, preferably 0.5m / s; the rotation feeding angle is 15° / hammer; the hammering frequency is controlled to be 80 times / minute-100 times / minute, preferably 100 times / minute, by controlling the hammering frequency, the surface temperature of the forged ingot is controlled to be 0℃-20℃, and the core temperature of the forged ingot is controlled to be below 15℃; and the round free-cutting steel bar is finally obtained by the third forging.

[0073] By carrying out the three times of forging treatment and reasonably controlling the process conditions of the forging treatment, including the forging heating temperature control, the rotation angle control, the forging deformation pass control, the feeding speed control, the hammering frequency control and the like, the morphology of the manganese sulfide in the forging deformation process is effectively controlled, the key parameters such as the size, the aspect ratio and the maximum chord length of the inclusions are improved, the proportion of the sulfides with the aspect ratio ≤3 in the free-cutting steel obtained after the forging is greater than 40%, the proportion of the sulfides with the size ≤3μm in the free-cutting steel is greater than 50%, and the proportion of the sulfides with the maximum chord length ≤3μm in the free-cutting steel is greater than 50%, so that the improvement of the cutting performance of the free-cutting steel is more favorable.

[0074] The following will take Y12Cr18Ni9 free-cutting steel as an example to give Example 1 to specifically illustrate the forging method for improving the morphology of the manganese sulfide in the Y12Cr18Ni9 free-cutting steel.

[0075] Example 1

[0076] A forging method for improving the morphology of the manganese sulfide in Y12Cr18Ni9 free-cutting steel, comprising the following steps:

[0077] (a) vacuum smelting Y12Cr18Ni9 free cutting steel ingot, the components of which are, by weight, C 0.03%~0.04%; Si 0.2%~0.25%; Mn 1.8%~2.0%; P 0.01%~0.02%; S 0.15%~0.2%; Ni 7.0%~8.0%; Cr 16.0%~17.0%; Mo 0.15%~0.25%; H 0.0004%~0.0005%; O 0.007%~0.008%; N 0.01%~0.015%, the rest being Fe and inevitable impurities; the components of the final Y12Cr18Ni9 free cutting steel are shown in Table 1;

[0078] Table 1 Component content table of Y12Cr18Ni9 free cutting steel (%)

[0079]

[0080] In step (a), the vacuum smelting method is to put the other raw materials (the other raw materials are high-purity iron, metallic silicon, metallic manganese, ferrophosphorus, nickel plate, metallic chromium, ferromolybdenum and copper wire) except ferrous sulphur and carbon additive into a crucible according to the component ratio, and put them into a vacuum induction furnace; the vacuum induction furnace is pumped to 100 Pa, then the alloy is melted by power supply, ferrous sulphur and carbon additive are added to the molten steel in the steel refining stage, the components of the Y12Cr18Ni9 free cutting steel are detected before tapping and are adjusted slightly, the steel is tapped after the components are qualified, the tapping and casting temperature is 1550℃, and the ingot with a diameter of 230 mm is cast. Here, the main point is to add the materials smoothly, the high-purity iron, metallic silicon, metallic manganese, ferrophosphorus, nickel plate, metallic chromium, ferromolybdenum and copper wire are added first, and the ferrous sulphur and carbon additive are added in the refining stage. Here, the ferrous sulphur alloy and carbon additive are added in the refining stage, which makes it easier to control the S and C content in the free cutting steel.

[0081] (b) air cooling the ingot cast in step (a) until it cools to room temperature, and then finishing the diameter of the ingot to 200 mm;

[0082] (c) first homogenizing heat treatment is performed on the finished ingot, the homogenizing heat treatment temperature is 1370℃ for the Y12Cr18Ni9 free cutting steel, and the homogenizing time is 8h;

[0083] (d) the ingot in step (c) is subjected to upsetting and elongation treatment to obtain a forged ingot, the upsetting is performed by using a 10t press, the elongation is performed immediately after the upsetting is completed, then the forged ingot with a diameter of 200 mm is rolled, the upsetting reduction is 30%, the elongation reduction is 15%, and the temperature of the forged ingot is ensured to be ≥1100℃ during the forging process;

[0084] (e) forging treatment is performed on the forged ingot;

[0085] First, the forged ingot, after upsetting and drawing, is reheated in a regenerative walking beam furnace. This furnace offers good temperature control and minimal temperature error. The heating process is based on the strength-plasticity curve of Y12Cr18Ni9 free-cutting steel (e.g., ...). Figure 1 (As shown) The heating temperature is set to between 1150℃, and the surface temperature and core temperature of the forging ingot are controlled within ±10℃. The holding time of the forging ingot is 5h.

[0086] Secondly, the heated forged ingot is taken out of the furnace and forged three times to finally obtain a Y12Cr18Ni9 free-cutting steel bar with a diameter of 60mm.

[0087] Specifically, the three forging processes are as follows:

[0088] First forging:

[0089] The time interval between the reheated forged ingot and the first forging is 60 seconds. The feeding speed during the first forging process is 0.5 m / s; the rotational feeding angle is 90° / hammer; the forging hammer frequency is controlled at 100 times / minute. By controlling the hammer frequency, the surface temperature rise of the forged ingot is controlled between 0℃ and 20℃, and the temperature rise of the core of the forged ingot is controlled below 15℃. After the first forging, the forged ingot is finally forged into a 100mm square billet.

[0090] Second forging:

[0091] After the first forging is completed, the second forging is carried out. The time interval between the end of the first forging and the start of the second forging is 10 seconds. The feeding speed of the second forging process is 0.5 m / s. The rotational feeding angle is 45° / hammer. The forging hammer frequency is 100 times / minute. By controlling the hammer frequency, the surface temperature rise of the forged ingot is controlled between 0℃ and 20℃, and the temperature rise of the core of the forged ingot is controlled below 15℃. After the second forging is completed, the square billet is finally forged into a regular octagon with an outer circle of 80 mm.

[0092] Third forging:

[0093] After the second forging is completed, a third forging is carried out. The time interval between the end of the second forging and the start of the third forging is 10 seconds. The feeding speed of the third forging process is 0.5 m / s. The rotational feeding angle is 15° / hammer. The forging hammer frequency is 100 times / minute. By controlling the hammer frequency, the surface temperature rise of the forged ingot is controlled between 0℃ and 20℃, and the temperature rise of the core of the forged ingot is controlled below 15℃. After the third forging, a Y12Cr18Ni9 free-cutting steel bar (round) with a diameter of 60 mm is finally obtained.

[0094] In the Y12Cr18Ni9 free-cutting steel bars obtained by the method of the present invention, the proportion of sulfides with an aspect ratio ≤3 is greater than 40%, the proportion of sulfides with a size ≤3μm is greater than 50%, and the proportion of sulfides with a maximum chord length ≤3μm is greater than 50%.

[0095] Performance analysis of Y12Cr18Ni9 free-cutting steel:

[0096] Quantitative analysis of sulfides in Y12Cr18Ni9 free-cutting steel was performed using a Phenom Partical X-ray tabletop scanning electron microscope-energy dispersive spectroscopy (EDS). The area scanned by the Phenom Partical X-ray tabletop scanning electron microscope-EDS was 8.991093 mm². 2 ; Figure 2 Electron micrograph of sulfide distribution in Y12Cr18Ni9 vacuum furnace ingot (as-cast state). Figure 3 This is an electron micrograph of the sulfide distribution in the Y12Cr18Ni9 bar (forged state) obtained in Example 1. Figure 2 It can be seen that the sulfides in the as-cast state are mostly precipitated along the grain boundaries, forming clusters, which is detrimental to the machinability of the steel. Figure 3 It can be seen that the sulfides after forging are more uniformly distributed and the sulfides are fine, which is beneficial to improving the machinability of steel.

[0097] The aspect ratio distribution of Y12Cr18Ni9 free-cutting steel is as follows: Figure 4 As shown, by Figure 4 It can be seen that the proportion of sulfides with an aspect ratio ≤3 in Y12Cr18Ni9 free-cutting steel reaches 44.89%; the size distribution of Y12Cr18Ni9 free-cutting steel is as follows: Figure 5 As shown, by Figure 5 It can be seen that the proportion of sulfides with dimensions ≤3 in Y12Cr18Ni9 free-cutting steel reaches 58.16%; the maximum chord length distribution of Y12Cr18Ni9 free-cutting steel is as follows: Figure 6 As shown, by Figure 6 It can be seen that the proportion of sulfides with a maximum chord length ≤ 3 in Y12Cr18Ni9 free-cutting steel reaches 54.31%; this indicates that spindle-shaped and elliptical sulfides account for a relatively large proportion, which is beneficial to improving the machinability of Y12Cr18Ni9 free-cutting steel. From Figures 4-6 The conclusion shows that the method of the present invention yields Y12Cr18Ni9 free-cutting steel bars with a length-to-width ratio ≤3, dimensions ≤3, and a maximum chord length ≤3, resulting in a higher proportion of sulfides, which is beneficial for improving the cutting performance of Y12Cr18Ni9 free-cutting steel.

[0098] Figure 7The cutting chip of Y12Cr18Ni9 free cutting steel (cutting condition: 500 r / min, feed 0.06 mm) is obtained from Figure 7 It can be seen that the cutting chip is uniformly and finely distributed, and the Y12Cr18Ni9 free cutting steel has good cutting performance.

[0099] Although the present application is described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and the modification or replacement does not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A forging method for improving the morphology of manganese sulfide in free-cutting steel, characterized in that, The process includes the following steps: homogenizing heat treatment and forging treatment of free-cutting steel ingots to improve the morphology of manganese sulfide in free-cutting steel; The specific steps are as follows: (a) Obtaining free-cutting steel ingots through vacuum smelting; (b) Air-cool the free-cutting steel ingot and then finish the ingot after it has cooled to room temperature; (c) The refined ingot is subjected to homogenization heat treatment; (d) The homogenized heat-treated ingot is upsetting and drawing to obtain a forged ingot; (e) Forging the forged ingot; In step (a), the chemical composition of the free-cutting steel ingot, by mass percentage, includes C 0.03%~0.04%; Si 0.2%~0.25%; Mn 1.8%~2.0%; P 0.01%~0.02%; S 0.15%~0.2%; Ni 7.0%~8.0%; Cr 16.0%~17.0%; Mo 0.15%~0.25%; H 0.0004%~0.0005%; O 0.007%~0.008%; N 0.01%~0.015%, with the remainder being Fe and unavoidable impurity elements; The specific conditions for homogenization heat treatment in step (c) are as follows: the homogenization heat treatment temperature is 30 ℃~ 50 ℃ below the initial melting point temperature of the free-cutting steel, and the homogenization heat treatment time is 5 h~ 8 h; The specific process of step (e) is as follows: The forged ingot processed in step (d) is reheated in the furnace. The heating temperature is set to 1100 ℃~1200 ℃. The temperature difference between the surface temperature and the core temperature of the forged ingot is controlled within ±10 ℃. The holding time of the forged ingot is 3 h~5 h. The heated forged ingot is then subjected to three forging processes. The first forging process shapes the ingot into a square billet; the second forging process shapes the square billet into a regular octagon; and the third forging process shapes the regular octagon into a round, free-cutting steel bar. The specific conditions for the first forging are as follows: The time interval between the forging ingot exiting the furnace and the first forging is 10 s to 120 s. The feeding speed during the first forging process is controlled at 0.3 m / s to 0.5 m / s; the rotational feeding angle is 90° per hammer; the forging hammer frequency is controlled at 80 to 100 times per minute. By controlling the hammer frequency, the surface temperature rise of the forging ingot is controlled at 0 ℃ to 20 ℃, and the temperature rise of the core of the forging ingot is controlled below 15 ℃. After the first forging, the forging ingot is finally forged into a square billet. The specific conditions for the second forging are as follows: After the first forging is completed, a second forging is performed. The time interval between the end of the first forging and the start of the second forging is 1 to 15 seconds. The feeding speed during the second forging process is controlled at 0.3 m / s to 0.5 m / s; the rotational feeding angle is 45° per hammer; the forging hammer frequency is controlled at 80 to 100 times per minute. By controlling the hammer frequency, the surface temperature rise of the forged ingot is controlled at 0 to 20 ℃, and the temperature rise of the core of the forged ingot is controlled below 15 ℃. After the second forging, the square billet is finally forged into a regular octagon. The specific conditions for the third forging are as follows: After the second forging is completed, a third forging is carried out. The time interval between the end of the second forging and the start of the third forging is 1 s to 15 s. The feeding speed during the third forging process is controlled at 0.3 m / s to 0.5 m / s. The rotational feeding angle is 15° per hammer. The forging hammer frequency is controlled at 80 to 100 times per minute. By controlling the hammer frequency, the surface temperature rise of the forged ingot is controlled at 0 ℃ to 20 ℃, and the temperature rise of the core of the forged ingot is controlled below 15 ℃. After the third forging, a round free-cutting steel bar is finally obtained.

2. The forging method for improving the manganese sulfide morphology in free-cutting steel according to claim 1, characterized in that, The mass ratio of Mn to S in free-cutting steel ingots ranges from 7 to 10.

3. The forging method for improving the manganese sulfide morphology in free-cutting steel according to claim 1, characterized in that, In step (a), the specific process for preparing the free-cutting steel ingot is as follows: All raw materials except ferrous sulfate and carbon raiser are loaded into a crucible according to the composition ratio and placed in a vacuum induction furnace. The vacuum induction furnace is evacuated and then energized to melt the alloy. During the steel refining stage, ferrous sulfate and carbon raiser are added to the molten steel. Before tapping the steel, the composition of the free-cutting steel is tested and fine-tuned. Once the composition is qualified, the steel can be tapped and cast into an ingot.

4. The forging method for improving the morphology of manganese sulfide in free-cutting steel according to claim 3, characterized in that, In step (a), the steel casting temperature is 1500℃~1580℃.

5. A forging method for improving the morphology of manganese sulfide in free-cutting steel according to claim 3, characterized in that, Before powering on in step (a), the vacuum degree of the vacuum induction furnace is 50Pa~500Pa.

6. The forging method for improving the morphology of manganese sulfide in free-cutting steel according to claim 1, characterized in that, The specific process of step (d) is as follows: The ingot after homogenization heat treatment is upset, and immediately after upset, it is drawn and then rolled to obtain a forged ingot. The upset reduction rate is 20%~50%, and the drawing reduction rate is 10%~20%. During the upset, drawing and rolling process, the temperature of the ingot is ensured to be ≥1100 ℃.

7. A free-cutting steel obtained by the forging method according to any one of claims 1-6, characterized in that, The proportion of sulfides with an aspect ratio ≤3 in the free-cutting steel obtained after forging is greater than 40%, the proportion of sulfides with a size ≤3μm in the free-cutting steel is greater than 50%, and the proportion of sulfides with a maximum chord length ≤3μm in the free-cutting steel is greater than 50%.

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