An easily machinable steel having excellent plasticity and drillability and a method for producing the same

Abstract

The application discloses an easy-to-cut steel with excellent plasticity and drilling performance and a preparation method thereof, and the preparation method comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling and air cooling line cooling; in the continuous casting step, the water quantity of a crystallizer is 130-140 m 3 / h, and the secondary cooling water quantity is 0.8-1.0 L / kg; in the air cooling line cooling step, the cooling speed is 1-1.5 DEG C / s from the spinning temperature to greater than 650 DEG C, and the cooling speed is 2-4 DEG C / s in the range of 650 DEG C-500 DEG C; under the condition of not adding easy-to-cut elements and increasing production cost, the plasticity and drilling performance of the easy-to-cut steel are significantly improved by controlling the manganese sulfide inclusion size, hardness and structure of the rolled material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of free-cutting steel, and particularly relates to a free-cutting steel with excellent plasticity and drilling performance and a preparation method thereof. BACKGROUND

[0002] The free-cutting steel is widely used in the machining of parts of instruments, automobiles and machine tools due to its excellent cutting performance. However, the free-cutting steel is prone to produce quality problems such as drawing cracking and drilling cracking in the production and machining, resulting in product scrap and failure to use.

[0003] At present, the existing technology pays more attention to the cutting performance and sulfide form control of the free-cutting steel, and less attention to the plasticity and drilling performance of the free-cutting steel.

[0004] Chinese patent CN 101003877A discloses a low-carbon free-cutting steel with good cutting performance and chip breaking performance, which does not contain lead. Although the free-cutting steel has cutting performance and drilling performance and chip handling performance similar to or even better than other free-cutting steels, the patent adds 0.02-0.30% Se or 0.01-0.20% Te, which is high in alloy element cost and unstable in recovery rate.

[0005] Chinese patent CN 111876689A discloses a low-carbon free-cutting steel containing selenium for instruments and a manufacturing method thereof. The free-cutting steel is obtained by controlling the key process parameters of converter smelting, LF refining, continuous casting, slab heating and post-rolling slow cooling, and has low cutting resistance and low cutting heat in the cutting process, thereby protecting the cutting tool and obtaining good machining surface roughness. In the patent, LF refining needs to produce white slag, which reduces the recovery rate of ferrous sulfur alloy; the heating time requires high temperature for a long time, i.e. 1200-1300 DEG C, and heating for 2-3 hours, which reduces the production efficiency in the industrial production process and requires high heating furnace refractory. SUMMARY

[0006] The application aims to provide a free-cutting steel with excellent plasticity and drilling performance and a preparation method thereof. Without adding free-cutting elements and increasing production cost, the plasticity and drilling performance of the free-cutting steel are significantly improved by controlling the size, hardness and structure of the rolled material manganese sulfide inclusions.

[0007] The technical scheme adopted by the application is as follows:

[0008] A preparation method of a free-cutting steel with excellent plasticity and drilling performance, the preparation method comprising the following steps: converter smelting, LF refining, continuous casting, hot rolling and air cooling line cooling.

[0009] In the continuous casting step, the mold water quantity is 130-140 m3 / h, the secondary cooling water quantity is 0.8-1.0 L / kg;

[0010] In the air cooling line cooling step, the cooling is performed at a speed of 1-1.5 ℃ / s from the wire drawing temperature to a temperature greater than 650 ℃, and the cooling is performed at a speed of 2-4 ℃ / s in the range of 650 ℃-500 ℃.

[0011] In the converter smelting step, the blowing end point C content is 0.04-0.06%, and the end point temperature is 1600-1650 ℃; alloying is performed during the tapping process, and aluminum iron and lime are added during the tapping process to pre-deoxidize.

[0012] The adding amount of the aluminum iron and the lime is 1-2 kg / t of molten steel and 2-3 kg / t of molten steel, respectively.

[0013] In the LF refining step, lime, calcium carbide and silicon carbide are used for slagging; sulfur wire is supplemented according to the target value of sulfur content before the LF refining outstation, and the molten steel is poured after soft blowing for ≥15 min.

[0014] The adding amount of the lime, the calcium carbide and the silicon carbide is 1-1.5 kg / t of molten steel, 0.5-1.0 kg / t of molten steel and 0.5-1.0 kg / t of molten steel, respectively.

[0015] In the continuous casting step, the continuous casting speed is 1.5-2.0 m / min, and the molten steel superheat is 25-35 ℃.

[0016] In the hot rolling step, the heating furnace soaking temperature is 1180-1220 ℃, the soaking time in the furnace is ≥30 min, and the in-furnace time is ≥120 min.

[0017] In the hot rolling step, the opening rolling temperature is 1180±10 ℃, the finishing rolling temperature is 950±10 ℃, and the wire drawing temperature is 840±10 ℃.

[0018] The application further provides the free-cutting steel prepared by the preparation method, which has excellent plasticity and drilling performance.

[0019] Further, the free-cuting steel comprises the following chemical components in percentage by weight: C 0.05-0.15%, Si≤0.15%, Mn≤1.50%, P 0.40-0.90%, S 0.35-0.45%, Al≤0.005%, and the balance of Fe and inevitable impurities.

[0020] The size of the manganese sulfide inclusions in the free-cutting steel is ≤200 μm, and the proportion reaches more than 90%; the hardness is 100-120 HBW; and the proportion of ferrite is 93-95%.

[0021] In view of the drawing cracking and drilling cracking problems existing in the machining process of the free-cutting steel, the application adopts the following measures: improving the continuous casting cooling intensity, controlling the size of the rolling material sulfide manganese inclusions to be less than or equal to 200 mu m, and the proportion of the size being more than 90%; and controlling the air cooling line cooling rate in stages to stabilize the disc round hardness in 100-120 HBW, and the ferrite proportion is 93-95%.

[0022] The free-cutting steel belongs to high-oxygen high-sulfur steel, and the sulfide manganese inclusions in the high-sulfur free-cutting steel are mainly generated at the end of the slab solidification, and the continuous casting cooling speed determines the original size of the sulfide manganese inclusions in the slab. With the continuous solidification, the sulfide manganese continues to grow, and the closer to the solidification end point, the faster the size of the sulfide manganese grows. The application shortens the solidification time at the end of the solidification by improving the continuous casting cooling intensity, so as to shorten the size growth time of the sulfide manganese, thereby controlling the original size of the sulfide manganese inclusions in the slab, and the size of the sulfide manganese in the rolling material is also controlled correspondingly. In the drawing or drilling tapping process of the free-cutting steel, when the part is subjected to transverse stress, the sulfide manganese size is relatively short, so as not to become a micro crack source, thereby avoiding the quality problems such as drawing cracking and drilling cracking.

[0023] The hardness of the material has a significant influence on the machining performance, and the hardness is too high or too low, which will lead to the decline of the machining performance. The high hardness will lead to poor cutting machinability, because the high hardness material will increase the cutting force, which will lead to the rapid tool wear, thereby affecting the machining quality and efficiency; and the low hardness may lead to the tool sticking phenomenon, the surface roughness of the machined part is large, the precision is poor, and the machining is also not conducive. The application controls the air cooling line cooling rate after rolling in stages, appropriately prolongs the ferrite organization formation time, so as to control the hardness of the rolling material in a moderate range, and the rolling material has excellent plasticity, and the drawing performance and drilling performance in the machining process are good.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] 1. The application overcomes the problems of drawing cracking and drilling cracking of the free-cutting steel in the machining process.

[0026] 2. The application controls the size of the rolling material sulfide manganese inclusions, the hardness and the organization without adding free-cutting elements and increasing the production cost, and significantly improves the machining performance of the product.

[0027] 3. The application is simple in operation, stable in process and strong in operability. DETAILED DESCRIPTION

[0028] Figure 1 It is the sulfide manganese size and morphology diagram of the free-cutting steel rolling material in the embodiment 1; the size of the sulfide manganese is all within 200 um, and the morphology is mainly spindle-shaped;

[0029] Figure 2The metallographic structure diagram of the free-cutting steel rolled material in Example 1 is shown in the figure; the metallographic structure is ferrite + pearlite, the distribution proportion of the graph structure is counted by using Pro-Image software, and the proportion of ferrite is 95%;

[0030] Figure 3 The hardness distribution diagram of the free-cutting steel rolled material in multiple batches obtained by the method of the present application is shown in the figure, and the hardness is stably controlled at 100-120 HBW;

[0031] Figure 4 The schematic diagram of the free-cutting steel drawing cracking in Comparative Example 1 is shown in the figure;

[0032] Figure 5 The schematic diagram of the free-cutting steel drilling cracking in Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0033] The free-cutting steel provided by the present application has excellent plasticity and drilling performance, and the chemical composition and weight percentage are as follows: C 0.05-0.15%, Si≤0.15%, Mn≤1.50%, P 0.40-0.90%, S 0.35-0.45%, Al≤0.005%, and the balance is Fe and inevitable impurities.

[0034] The preparation method of the free-cutting steel with excellent plasticity and drilling performance comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling, and air cooling line cooling, and specifically comprises the following steps:

[0035] In the converter smelting step, the blowing end point C content is 0.04-0.06%, and the end point temperature is 1600-1650℃; alloying is performed during tapping, and 1-2 kg / t of molten steel of aluminum iron and 2-3 kg / t of molten steel of lime are added for pre-deoxidation during tapping.

[0036] In the LF refining step, 1-1.5 kg / t of molten steel of lime, 0.5-1.0 kg / t of molten steel of calcium carbide, and 0.5-1.0 kg / t of molten steel of silicon carbide are used for slagging; before the LF refining outlet, sulfur wire is supplemented according to the target value of sulfur content, and the molten steel is poured after soft blowing for≥15 min.

[0037] In the continuous casting step, the crystallizer water quantity is 130-140 m 3 / h, the secondary cooling water quantity is 0.8-1.0 L / kg; the continuous casting speed is 1.5-2.0 m / min, and the molten steel superheat is 25-35℃.

[0038] In the hot rolling step, the heating furnace soaking temperature is 1180-1220℃, the soaking time is≥30 min, and the in-furnace time is≥120 min; the rolling temperature is 1180±10℃, the finishing rolling temperature is 950±10℃, and the wire drawing temperature is 840±10℃.

[0039] In the air cooling line cooling step, the cooling is performed at a speed of 1-1.5℃ / s from the wire rod temperature to a temperature greater than 650℃, and at a speed of 2-4℃ / s in the range of 650℃-500℃.

[0040] The application will be described in detail below with reference to the examples.

[0041] Example 1

[0042] A free-cutting steel with excellent plasticity and drilling performance, which has the following chemical components and weight percentages: C 0.08%, Si 0.05%, Mn 1.23%, P 0.55%, S 0.38%, Al 0.003%, and the balance of Fe and inevitable impurities.

[0043] The preparation method of the free-cutting steel with excellent plasticity and drilling performance comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling, and air cooling line cooling, specifically:

[0044] In the converter smelting step, the blowing end point C content is 0.05%, and the end point temperature is 1620℃; alloying is performed during tapping, and 1.5kg / t of molten steel of aluminum iron and 2.5kg / t of molten steel of lime are added for pre-deoxidation during tapping.

[0045] In the LF refining step, 1.2kg / t of molten steel of lime, 0.6kg / t of molten steel of calcium carbide, and 0.6kg / t of molten steel of silicon carbide are used for slagging; sulfur wire is fed according to the target value of sulfur content before LF refining out, and the molten steel is poured after soft blowing for 18min.

[0046] In the continuous casting step, the crystallizer water amount is 135m 3 / h, the secondary cooling specific water amount is 0.8L / kg; the continuous casting speed is 1.6m / min, and the molten steel superheat is 32℃.

[0047] In the hot rolling step, the heating furnace soaking temperature is 1200℃, the soaking section holding time is 35min, the in-furnace time is 125min; the opening rolling temperature is 1180℃, the finish rolling temperature is 950℃, and the wire rod temperature is 845℃.

[0048] In the air cooling line cooling step, the cooling is performed at a speed of 1.2℃ / s from 845℃ to a temperature greater than 650℃, and at a speed of 2.5℃ / s in the range of 650℃-500℃.

[0049] Example 2

[0050] A free-cutting steel with excellent plasticity and drilling performance, which comprises the following components in percentage by weight: C 0.011%, Si 0.08%, Mn 1.35%, P 0.62%, S 0.42%, Al 0.002%, and the balance of Fe and inevitable impurities.

[0051] The preparation method of the free-cutting steel with excellent plasticity and drilling performance comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling, air cooling line cooling, and specifically:

[0052] In the converter smelting step, the blowing end point C content is 0.055%, and the end point temperature is 1645℃; alloying is carried out during tapping, and 1.6kg / t of molten steel of aluminum iron and 3kg / t of molten steel of lime are added for pre-deoxidation during tapping.

[0053] In the LF refining step, 1.4kg / t of molten steel of lime, 0.8kg / t of molten steel of calcium carbide and 0.7kg / t of molten steel of silicon carbide are used for slagging; sulfur wire is supplemented before the LF refining outlet according to the sulfur content target value, and the molten steel is poured after soft blowing for 16min.

[0054] In the continuous casting step, the crystallizer water quantity is 140m 3 / h, the secondary cooling specific water quantity is 0.9L / kg; the continuous casting speed is 1.8m / min, and the molten steel superheat degree is 26℃.

[0055] In the hot rolling step, the heating furnace soaking temperature is 1220℃, the soaking section holding time is 40min, the in-furnace time is 140min; the opening rolling temperature is 1170℃, the finish rolling temperature is 940℃, and the wire drawing temperature is 830℃.

[0056] In the air cooling line cooling step, the cooling speed is 1.4℃ / s from 830℃ to more than 650℃, and the cooling speed is 3℃ / s in the range of 650℃-500℃.

[0057] Comparative Example 1

[0058] Other than Example 1, in the continuous casting step, the crystallizer water quantity is 120m 3 / h, and the secondary cooling specific water quantity is 0.5L / kg. In the air cooling line cooling step, the cooling speed is 0.8℃ / s from 845℃ to 500℃.

[0059] Comparative Example 2

[0060] Other than Example 1, in the air cooling line cooling step, the cooling speed is 4.5℃ / s from 845℃ to 500℃.

[0061] The hardness, the ratio of sulfide inclusions having a size of 200 μm or less, and the ferrite ratio of the free-cutting steels produced in each of the above examples and comparative examples are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] The above detailed description of the free-cutting steel having excellent ductility and drillability and the method for producing the same according to the above reference examples is illustrative rather than restrictive, and several examples can be enumerated within the scope of the defined range, and thus variations and modifications without departing from the general concept of the present application should be included in the scope of the present application.

Claims

1. A method of producing a free-cutting steel excellent in plasticity and drillability, characterized by, The preparation method comprises the following steps: converter smelting, LF refining, continuous casting, hot rolling, air cooling line cooling; In the converter smelting step, the blowing end point C content is 0.04-0.06%, and the end point temperature is 1600-1650℃; alloying is carried out during tapping, and aluminum iron and lime are added during tapping to pre-deoxidize; In the LF refining step, lime, carbide and silicon carbide are used for slagging; sulfur wire is fed according to the target value of sulfur content before LF refining, and the steel is poured after soft blowing for ≥15min; In the continuous casting step, the amount of water in the crystallizer 130-140 m 3 / h, and the amount of water in the secondary cooling 0.8-1.0 L / kg. In the hot rolling step, the heating furnace soaking temperature is 1180-1220℃, the soaking time is ≥30min, and the in-furnace time is ≥120min; the opening rolling temperature is 1180±10℃, the finish rolling temperature is 950±10℃, and the wire drawing temperature is 840±10℃; In the air cooling line cooling step, the cooling speed is 1-1.5℃ / s from the wire drawing temperature to greater than 650℃, and the cooling speed is 2-4℃ / s in the range of 650℃-500℃; The size of the manganese sulfide inclusions in the free-cutting steel is ≤200um, and the proportion of the size reaching 90% or more; the hardness is 100-120HBW; the ferrite proportion is 93-95%.

2. The production method according to claim 1, characterized by, The addition amount of aluminum iron and lime is 1-2kg / t molten steel and 2-3kg / t molten steel, respectively.

3. The preparation method according to claim 1, characterized in that, The addition amount of lime, carbide and silicon carbide is 1-1.5kg / t molten steel, 0.5-1.0kg / t molten steel and 0.5-1.0kg / t molten steel, respectively.

4. The method of claim 1, wherein, In the continuous casting step, the continuous casting speed is 1.5-2.0m / min, and the molten steel superheat is 25-35℃.

5. The free-cutting steel prepared by the preparation method of any one of claims 1-4 has excellent plasticity and drilling performance.

6. The free-cutting steel excellent in plasticity and drillability according to claim 5, characterized by, The free-cutting steel comprises the following chemical components in weight percentage: C 0.05~0.15%, Si≤0.15%, Mn≤1.50%, P 0.40-0.90%, S 0.35-0.45%, Al≤0.005%, and the balance is Fe and inevitable impurities.

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