Steel for brake drum and manufacturing method thereof

Abstract

The invention provides a brake drum steel and a manufacturing method thereof. The steel comprises the following components: C: 0.08%-0.10%, Si: ≤0.08%, Mn: 0.50%-0.80%, P: ≤0.015%, S: ≤0.005%, Als: 0.02%-0.05%, Nb: 0.005-0.01%, La+Ce: 0.002-0.004%, O≤25ppm, N≤40ppm, and the remainder is Fe and other inevitable impurities. The steel has a low Mn content, and only a trace amount of Nb alloy strengthening elements and rare earth elements are added, so the manufacturing cost is low. The manufacturing method has good stability, and the structure of the finally obtained finished product is uniform and fine, and the fluctuation of mechanical properties is small. The product has low yield strength ratio, high elongation, good thinning and spinning performance, high surface quality, is suitable for producing various types of brake drums, and is conducive to large-scale promotion and use by brake drum production enterprises.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material manufacturing, and in particular to the field of automobile steel manufacturing, and specifically relates to an economical brake drum steel and a manufacturing method thereof. Background Art

[0002] The brake drum is a component in the braking system that generates braking force to hinder the movement or movement trend of the vehicle. Except for various retarder devices, automobile brake drums are almost all friction brakes that use the friction between the working surface of the fixed element and the rotating element to generate braking torque. The brake drum should have sufficient strength, rigidity and heat capacity.

[0003] Traditional brake drums are cast in cast iron, with slow heat dissipation due to thick walls, and are prone to cracking due to large temperature differences. They are also heavy and fuel-consuming. In order to increase the life of brake drums and meet the requirements of lightweight vehicles, a new type of composite brake drum has emerged in recent years. This brake drum is made of steel for spinning and then produced by centrifugal casting. It has the characteristics of high strength, light weight, good thermal conductivity, excellent performance and long life. It can effectively reduce the weight of the entire vehicle, save fuel consumption during starting, braking and driving, and greatly improve the safety of vehicle driving. Therefore, it has been widely used. However, the manufacturing process of this composite brake drum involves thinning and spinning with large deformation, which places high demands on steel. Generally, steel is prone to cracking, peeling, pitting and other defects during processing.

[0004] Therefore, it is necessary to provide composite brake drum steel with low cost and good performance. Summary of the invention

[0005] The purpose of the present invention is to provide a brake drum steel and a manufacturing method thereof, wherein the manufactured product has good intrinsic quality, excellent mechanical properties, high surface quality, an elongation of more than 40%, a yield strength ratio of less than 0.74, and avoids peeling, cracking and the like during the spinning centrifugal casting process.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A steel for a brake drum, comprising the following components in percentage by mass:

[0008] C: 0.08%-0.10%, Si: ≤0.08%, Mn: 0.50%-0.80%, P: ≤0.015%, S: ≤0.005%, Als: 0.02%-0.05%, Nb: 0.005-0.01%, La+Ce: 0.002-0.004%, O≤25ppm, N≤40ppm, the rest are Fe and other unavoidable impurities.

[0009] The composition of the brake drum steel also meets the following mass ratio: Ce:La=1.5-2.5:1; the steel used is a rare earth alloy with low cost.

[0010] The structure of the brake drum steel is ferrite + pearlite, the pearlite area accounts for 8%-11%, the grain size is 10-11 levels, and the inclusion level is 1.0 level or below.

[0011] The thickness of the steel strip for the brake drum is 10-17 mm;

[0012] Performance of the brake drum steel: Rp 0.2 ≥300MPa, Rm: 420MPa-460MPa, yield strength ratio ≤0.74, A≥40.0%, good surface quality. Small fluctuation of mechanical properties, yield strength and tensile strength fluctuation controlled within 20MPa.

[0013] The method for manufacturing brake drum steel provided by the present invention comprises the following steps:

[0014] 1) Smelting and refining;

[0015] 2) Continuous casting into slab;

[0016] 3) hot rolling;

[0017] 4) Laminar cooling;

[0018] 5) Coil up.

[0019] Step 1) includes: hot metal desulfurization, converter smelting, argon blowing of the smelted steel, LF furnace refining, white slag desulfurization during the refining process and the white slag time is ≥10min, calcium wire feeding to modify inclusions and the calcium wire length is >100m, rare earth alloy is added, soft argon blowing time is ≥10min, and soft argon blowing flow rate is ≤30Nm 3 / h.

[0020] Preferably, the refining is as follows: white slag time ≥ 12 min, calcium wire is fed to modify inclusions and the length of calcium wire is > 150 m, rare earth alloy is added, soft argon blowing time ≥ 12 min, and soft argon blowing flow rate is 10-25 Nm 3 / h. .

[0021] Step 2) is specifically as follows: dynamic soft reduction is adopted, with the reduction amount of 8-12 stages being ≥5mm; electromagnetic end stirring is adopted to reduce the segregation of the ingot; the superheat is controlled within 30°C; and the fluctuation of the liquid level in the tundish is controlled within ±5mm.

[0022] Preferably, the continuous casting is as follows: dynamic soft reduction is adopted, with the reduction amount of 8-12 stages being ≥5.5 mm; electromagnetic end stirring is adopted to reduce the segregation of the ingot; the superheat is controlled within 25°C; and the fluctuation of the liquid level in the tundish is controlled within ±3 mm.

[0023] The hot rolling described in step 3) is specifically as follows: the heating temperature is controlled at 1100-1240°C, the slab furnace temperature is controlled at below 1220°C, a full-pass descaling mode is adopted, the descaling pressure is greater than 20MPa, the initial rolling is carried out in 3+5 passes, the initial rolling outlet temperature is controlled at 960-1000°C, and the finishing rolling outlet temperature is controlled at 830-860°C.

[0024] The laminar cooling in step 4) is specifically: ultrafast cooling + laminar cooling. The ultrafast cooling speed is controlled at 30 / s-50°C / s, and the laminar cooling speed is controlled at 10-20°C / s.

[0025] The coiling in step 5) is specifically as follows: the coiling temperature is 560°C-620°C.

[0026] Preferably, the coiling in step 5) is specifically performed at a coiling temperature of 560°C-600°C.

[0027] The product manufacturing process of the present invention is as follows: first, the molten iron is desulfurized and smelted in a converter, the smelted molten steel is argon blown, and refined in an LF furnace. Then, the molten steel is continuously cast into slabs. The continuously cast slabs are hot rolled, laminar cooled and coiled into steel strips to produce hot rolled brake drum steel strips.

[0028] The process flow and steps of brake drum are as follows: blanking → punching → primary spinning → secondary spinning → rolling → casting → heat treatment → finishing. The cracking of brake drum steel is mainly reflected in the secondary spinning and rolling processes. The main reason for the cracking is that the thinning rate is too high (the maximum thinning rate of secondary spinning exceeds 53%, and the total thinning rate exceeds 71.2%), and the material performance does not meet the standard. The peeling of brake drum steel is mainly reflected in the primary spinning. The main reason is that the material steel quality is poor and there are too many inclusions. In addition, the brake drum also has certain requirements for the surface, and obvious pits, roller marks, and iron oxide scale indentation are not allowed. Therefore, the production of brake drum steel needs to consider steel quality, spinning performance and surface quality at the same time. Therefore, the overall idea of ​​the present invention is: 1. Ensure higher spinning performance: The present invention controls the C and Mn contents at a suitable level to play a role in solid solution strengthening and refinement of ferrite grains; add trace amounts of Nb and rare earth elements to improve the uniformity and toughness of the grains. 2. Improve the surface quality, especially the surface quality of the head and tail: reduce the generation of secondary and tertiary oxide scale by controlling the billet's furnace temperature, finishing rolling outlet temperature and coiling temperature.

[0029] According to the composition set in the present invention, in the subsequent smelting, refining, continuous casting and hot rolling production processes, the white slag making time is controlled to be ≥10min, the calcium wire is fed to modify the inclusions and the calcium wire length is >100m, and the soft argon blowing time is ≥10min. The composition S: ≤0.005%, La+Ce: 0.002-0.004%, O≤25ppm, N≤40ppm, to ensure the effect of rare earth element purification of molten steel and inclusion modification. Dynamic soft pressing is adopted, and the pressing amount of 8-12 stages is ≥5mm; electromagnetic end stirring is adopted to reduce the segregation of the casting; the superheat is controlled within 30℃; the fluctuation of the liquid level in the tundish is controlled within ±5mm. The heating temperature is controlled at 1100-1240℃, the slab temperature out of the furnace is controlled below 1220℃, the full-pass descaling mode is adopted, the descaling pressure is greater than 20MPa, the initial rolling is carried out in 3+5 passes, the initial rolling outlet temperature is controlled at 960-1000℃, and the finishing rolling outlet temperature is controlled at 830-860℃. The coiling temperature is 560℃-620℃. The final Rp 0.2 : ≥300MPa, Rm: 420MPa-460MPa, yield strength ratio ≤0.74, A ≥40.0%, brake drum steel with good surface quality.

[0030] The steelmaking process of the present invention obtains a casting with good intrinsic quality by adding rare earth elements, controlling the soft blowing time, adopting dynamic soft pressure reduction and electromagnetic end stirring, controlling the superheat, the fluctuation of the liquid level in the tundish, etc. At the same time, the content of S and O is controlled at a low level to ensure the fluidity of the molten steel and avoid the formation of more rare earth sulfides and oxides to block the water inlet and affect the pouring.

[0031] The heating temperature of the present invention is controlled at 1100-1240°C, mainly to ensure that the alloy is fully dissolved. Too high a temperature will cause the original austenite grains to be coarse, affecting the performance of the finished product. The initial rolling outlet temperature is controlled at 960-1000°C, and the final rolling temperature is controlled at 830-860°C, mainly to ensure that the finishing rolling is rolled in the austenite region, and the fine and dispersed Nb (CN) two-phase particles are precipitated by deformation induction, promoting the refinement of austenite grains and the refinement of finished ferrite grains. If the finishing rolling start temperature is too high, it will enter the incomplete recrystallization zone, produce mixed crystal structure, and the surface iron oxide is thick, which increases the difficulty of descaling. If the final rolling temperature is high, the austenite grains after rolling are coarse, and the surface iron oxide scale is thick in the later stage, which directly affects the surface quality of the finished product. If the final rolling temperature is low, it will enter the austenite and ferrite two-phase region for rolling, produce mixed crystal structure, and reduce the strength and toughness of the finished product. The cooling method adopts ultra-fast cooling + laminar cooling, and the coiling temperature is controlled at 560-620°C. Fast cooling speed can make the surface and core of the steel plate cool evenly, forming fine and uniform ferrite grains, and improving the strength and toughness of the finished product. However, if the cooling is too fast and the coiling temperature is too low, abnormal structures such as bainite or even martensite will be produced, affecting the mechanical properties and processing properties of the finished product. If the coiling temperature is too high, the structure will be coarse and the surface quality will be poor.

[0032] The present invention ensures the strength and plasticity index of brake drum steel and improves the comprehensive performance through component design, smelting, refining, continuous casting, hot rolling and laminar cooling. Compared with the prior art, the present invention has reasonable component design, low Mn content, and only adds trace Nb alloy strengthening elements and rare earth elements, and has low manufacturing cost; and the manufacturing method has good stability, and the final product has uniform and fine structure, grain size is controlled at level 10 or above, mechanical property fluctuation is small, and yield strength and tensile strength fluctuation are controlled within 20MPa; the product has low yield strength ratio, high elongation, good thinning and spinning performance, high surface quality, and is suitable for the production of various types of brake drums, which is conducive to large-scale promotion and use by brake drum production enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the metallographic photograph of Example 1;

[0034] Figure 2 This is a photo of the strip surface of Example 1;

[0035] Figure 3 It is the metallographic photograph of Example 2;

[0036] Figure 4 It is the metallographic photograph of Example 3;

[0037] Figure 5 It is the metallographic photograph of comparative example 2;

[0038] Figure 6 This is a surface photograph of Comparative Example 3;

[0039] Figure 7 This is the metallographic photograph of Comparative Example 4. DETAILED DESCRIPTION

[0040] Example 1

[0041] A method for manufacturing steel for brake drums, comprising the following mass percentage components: as shown in Table 1, the remainder not shown in Table 1 is iron and unavoidable impurities.

[0042] Table 1 Chemical composition of steel for brake drum in various embodiments and comparative examples (mass percentage, %)

[0043] serial number C Si Mn P S Nb La+Ce Als O N Example 1 0.09 0.04 0.76 0.012 0.003 0.007 0.0035 0.030 0.0025 0.0033 Example 2 0.10 0.05 0.71 0.013 0.002 0.009 0.0032 0.032 0.0019 0.0036 Example 3 0.08 0.04 0.65 0.010 0.002 0.008 0.0036 0.038 0.0022 0.0029 Example 4 0.08 0.03 0.60 0.008 0.004 0.008 0.0029 0.031 0.0024 0.0030 Comparative Example 1 0.08 0.05 0.77 0.012 <![CDATA[ 0.006 ]]> 0.007 <![CDATA[ / ]]> 0.025 <![CDATA[ 0.0036 ]]> 0.0032 Comparative Example 2 0.09 0.06 0.72 0.011 0.002 0.009 <![CDATA[ / ]]> 0.024 <![CDATA[ 0.0028 ]]> 0.0037 Comparative Example 3 0.08 0.05 0.65 0.012 0.003 0.008 <![CDATA[ / ]]> 0.031 <![CDATA[ 0.0026 ]]> 0.0035 Comparative Example 4 0.08 0.05 <![CDATA[ 1.15 ]]> 0.011 0.005 <![CDATA[ 0.001 ]]> <![CDATA[ / ]]> 0.035 <![CDATA[ 0.0031 ]]> 0.0045

[0044] The method for manufacturing the steel strip for brake drum of embodiment 1 comprises the following steps:

[0045] 1) Desulfurization of molten iron, converter smelting, blowing argon into the molten steel, LF furnace refining, controlling the white slag making time ≥10min, feeding calcium wire to modify inclusions and the length of calcium wire>100m, adding rare earth elements La+Ce, soft blowing argon time ≥10min, soft blowing argon flow ≤30Nm3 / h.

[0046] 2) Dynamic soft reduction is adopted in the continuous casting process, and the reduction amount in the 8-12 stage is ≥5mm; electromagnetic end stirring is adopted to reduce the segregation of the cast slab; the superheat is controlled within 30°C; and the fluctuation of the liquid level in the tundish is controlled within ±5mm. Example 1 The composition of the slab is shown in Table 1, and the specific steelmaking process parameters are shown in Table 2.

[0047] 3) The continuous casting slab is hot rolled into a steel strip. In the hot rolling process, the slab is heated, the target hot rolling thickness is 16.0 mm, the billet is heated, rough rolled, finished rolled and coiled to obtain a hot rolled steel strip, the heating temperature is controlled at 1100-1240°C, the slab furnace temperature is controlled below 1220°C, the full pass descaling mode is adopted, the descaling pressure is greater than 20 MPa, the initial rolling is rolled in 3+5 passes, the initial rolling outlet temperature is controlled at 960-1000°C, and the finishing rolling outlet temperature is controlled at 830-860°C. Example 1 Specific hot rolling process parameters are shown in Table 3.

[0048] 4) Laminar cooling is specifically: ultrafast cooling + laminar cooling, the ultrafast cooling speed is controlled at 30 / s-50℃ / s, and the laminar cooling rate is controlled at 10-20℃ / s.

[0049] 5) Coiling is specifically: coiling temperature 560℃-620℃.

[0050] Figure 1 This is a microstructure photograph of the brake drum steel of Example 1, which is ferrite + pearlite, with a pearlite area ratio of 9% and a grain size of 10.5. The inclusion level of the brake drum steel of Example 1 is all at level 1.0 or below. Figure 2 This is a surface photo of the brake drum steel of Example 1, and it can be seen that the surface quality is good.

[0051] Table 2 Steelmaking process parameters for each embodiment and comparative example

[0052]

[0053] Table 3 Hot rolling process parameters of various embodiments and comparative examples

[0054]

[0055]

[0056] Example 2

[0057] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 14.6 mm. Figure 3This is a microstructure photograph of the brake drum steel of Example 2, which is ferrite + pearlite, with the pearlite area ratio being 11% and the grain size being 10.5.

[0058] Example 3

[0059] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 13.5 mm. Figure 4 This is a microstructure photograph of the brake drum steel of Example 3, which is ferrite + pearlite, with the pearlite area ratio of 8% and the grain size of 10.0.

[0060] Example 4

[0061] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 10.0 mm.

[0062] Comparative Example 1

[0063] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 16.0 mm.

[0064] Comparative Example 2

[0065] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 14.6 mm. Figure 5 This is a microstructure photograph of the brake drum steel of comparative example 2, which is ferrite + pearlite, with a pearlite area ratio of 9%, a grain size of 8.5, and relatively coarse grains.

[0066] Comparative Example 3

[0067] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 13.5 mm. Figure 6 This is a surface photo of the brake drum steel in comparative example 3, where it can be clearly seen that there is a lot of oxide scale.

[0068] Comparative Example 4

[0069] A method for manufacturing a steel strip for a brake drum is according to the method of Example 1, except for the composition, steelmaking and hot rolling process parameters listed in Table 1, Table 2 and Table 3. The thickness of the steel strip is 10.0 mm. Figure 7This is a microstructure photograph of the brake drum steel of comparative example 4, which is ferrite + pearlite, with the pearlite area ratio of 8%, the grain size of 9.0, and the grains are relatively coarse and uneven.

[0070] The final properties of the hot rolled coils obtained in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 4.

[0071] Table 4 Hot rolled coil properties of examples and comparative examples

[0072]

[0073] The underlined data in the above table are data that do not meet the requirements of the present invention and are not produced according to the requirements of the present invention.

[0074] The results show that the brake drum steel manufactured according to the composition and key process parameters designed by the present invention has a ferrite + pearlite structure, a grain size of 10-10.5, and inclusions of 1.0 or below. The yield strength (303-320MPa) and yield strength ratio (0.72-0.74) are relatively low, while the tensile strength (420-435MPa) and elongation (>40%) are relatively high.

[0075] No rare earth elements were added to all the comparative examples, so the overall elongation was low. For comparative example 1, the white slag making time and soft blowing time in the steelmaking process were short, and the liquid level fluctuated greatly, resulting in the inclusion grade of the final product exceeding the standard and the elongation was also low. For comparative example 2, the coiling temperature was high, the grains were coarse, the performance was low, and the tensile strength did not meet the requirements. For comparative example 3, the heating temperature, the initial rolling outlet temperature, and the finishing rolling outlet temperature were high, the surface of the finished product had too much iron oxide scale, and the appearance quality after processing was not up to standard. For comparative example 4, the composition was changed by increasing the Mn content to replace the microalloying element Nb. The final product had uneven grain size, high yield strength, and high yield strength ratio. At the same time, the white slag making time was less than 10 minutes, resulting in a high oxygen content in the steel grade, and the inclusion class B was level 1.5, which significantly reduced the processing performance.

[0076] The embodiment of the present invention has low inclusion level and high surface quality while meeting the requirements of mechanical properties, greatly improving the application range and utilization rate of parts. The brake drum produced by the present invention has no cracking and peeling during processing and has a good appearance. The steel strip for brake drums of the present invention has a wide process window and stable performance, and is suitable for industrialized mass production of traditional 1580 hot rolling production lines, and has good promotion and applicability.

[0077] Finally, it should be noted that the above specific implementations are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to examples, a person skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A steel for a brake drum, characterized in that: The brake drum steel comprises the following components in percentage by mass: C: 0.08%-0.10%, Si: ≤0.08%, Mn: 0.50%-0.80%, P: ≤0.015%, S: ≤0.005%, Als: 0.02%-0.05%, Nb: 0.005-0.01%, La+Ce: 0.002-0.004%, O≤25ppm, N≤40ppm, the rest is Fe and other unavoidable impurities; The structure of the brake drum steel is ferrite + pearlite, the pearlite area accounts for 8%-11%; the grain size is 10-11, and the inclusion level is 1.0 or below; Performance of the brake drum steel: Rp 0.2 ≥300MPa, Rm: 420MPa-460MPa, yield strength ratio ≤0.74, A ≥40.0%; yield strength and tensile strength fluctuations are controlled within 20MPa.

2. A method for manufacturing the brake drum steel according to claim 1, characterized in that: The manufacturing method comprises the following steps: 1) Smelting and refining; 2) Continuous casting into slab; 3) hot rolling; 4) Laminar cooling; 5) Coil up.

3. The manufacturing method according to claim 2, characterized in that: Step 1) includes: desulfurization of white slag during the refining process with a white slag making time of ≥10min, modification of inclusions by calcium wire feeding with a calcium wire length of >100m, addition of rare earth alloy, and soft argon blowing time of ≥10min.

4. The manufacturing method according to claim 2, characterized in that: Step 2) is specifically as follows: dynamic soft reduction is adopted, with the reduction amount of 8-12 stages being ≥5mm; electromagnetic end stirring is adopted to reduce the segregation of the ingot; the superheat is controlled within 30°C; and the fluctuation of the liquid level in the tundish is controlled within ±5mm.

5. The manufacturing method according to claim 2, characterized in that: The hot rolling in step 3) is specifically as follows: the heating temperature is controlled at 1100-1240°C, the slab furnace temperature is controlled below 1220°C, a full-pass descaling mode is adopted, the descaling pressure is greater than 20MPa, the initial rolling outlet temperature is controlled at 960-1000°C, and the finishing rolling outlet temperature is controlled at 830-860°C.

6. The manufacturing method according to claim 2, characterized in that: The laminar cooling described in step 4) is specifically: ultrafast cooling + laminar cooling; the ultrafast cooling speed is controlled at 30 / s-50°C / s, and the laminar cooling rate is controlled at 10-20°C / s.

7. The manufacturing method according to claim 2, characterized in that: The coiling described in step 5) is specifically: the coiling temperature is 560°C-620°C.

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