Method for solving secondary stamping cracking of steel for deep drawing and cold rolling

Abstract

The invention relates to a method for solving secondary stamping cracking of steel for deep drawing and cold rolling, which comprises the following components in percentage by mass: 0 to 0.003 percent of C, less than or equal to 0.034 percent of Si, 0.10 to 0.30 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.0004 to 0.0008 percent of B, 0.015 to 0.070 percent of Alt, less than or equal to 0.00030 percent of H, 0.03 to 0.08 percent of Ti and the balance of iron and inevitable impurity elements, wherein B / P is more than or equal to 0.02 percent and less than or equal to 0.04 percent. On the basis of an original component system of the ultra-low carbon deep-drawing cold-rolled steel, a proper amount of B element is added, and vacuum treatment quality control parameters are optimized, so that the hydrogen content of molten steel is reduced, the grain boundary brittleness of ultra-low carbon steel is reduced, work hardening in the secondary stamping deformation process is reduced, and the forming performance is improved and stabilized.

Description

Technical Field

[0001] The invention relates to a method, in particular to a method for solving secondary stamping cracking of deep drawing and cold rolling steel, belonging to the technical field of metal materials. Background Art

[0002] Deep drawing cold rolled steel containing Ti or Nb-Ti composite addition is widely used due to its excellent deep drawing performance. However, the application of the cold rolled steel is limited by secondary stamping cracking after cold rolling, and this problem has not been well solved for a long time.

[0003] The meaning of the secondary stamping of deep-drawn cold-rolled steel is to form it in two times, the first stamping is shallow and the second stamping is deep. If it is formed by one stamping, the stamping cracking problem will be more prominent. The reasons for the secondary stamping cracking are two aspects: First, the phosphorus in the material precipitates at the grain boundary, which increases the brittleness between the grain boundaries (that is, weakens the bonding force between the grain boundaries). During deep stamping, i.e., secondary stamping, the brittleness between the grain boundaries is prominent due to the large deformation and elongation of the material, causing the material to crack. Second, during the steelmaking process, a certain amount of hydrogen is dissolved in the molten steel, causing the brittleness of the material to increase. When the material is deeply stamped, the bonding ability between the grain boundaries is insufficient, causing cracking.

[0004] The current existing patents solve the following problems:

[0005] 1. Patent No. CN01139479.X, Patent Name: Ultra-low carbon steel plate and its manufacturing method. The amount of FeO+MnO in the slag in the ladle during continuous casting is controlled to a maximum of 15%, so that the output during casting is a maximum of 5 tons / minute. When the steel plate is used for applications such as motor housings or oil filter housings that require deep stamping, it does not produce visual pinhole defects and stamping cracks caused by inclusions.

[0006] 2. Patent No. CN201210336652.3, Patent Name: A production method for improving the uniformity of mechanical properties of strip steel. The hot-rolled coil is coiled into a finished product after pickling, cold rolling, annealing and leveling. The coiling adopts a U-type coiling process to control the coiling temperature. The coiling temperature is 730±20℃ for the head 30m and the tail 40m of the steel coil, and 680±20℃ for the middle section. The method optimizes the process parameters of the hot rolling process of the steel strip to obtain high-quality steel strips with uniform size and performance, meet the user's use requirements, and prevent accidents such as breaking and stamping cracking in the subsequent production process. That is, the patent obtains a steel strip with uniform performance by controlling the hot rolling coiling temperature in sections to solve the problems of stamping cracking. None of the above solutions solve the technical difficulties existing in the prior art. Summary of the invention

[0007] The present invention is aimed at the problems existing in the prior art and provides a method for solving the secondary stamping cracking of deep drawing and cold rolling steel. The present invention adds an appropriate amount of B element on the basis of the original composition system of ultra-low carbon deep drawing and cold rolling steel, optimizes the vacuum treatment quality control parameters, so as to reduce the hydrogen content of molten steel, reduce the grain boundary brittleness of ultra-low carbon steel, reduce the work hardening in the secondary stamping deformation process, and improve and stabilize the forming performance.

[0008] In order to achieve the above-mentioned purpose, the technical scheme of the present invention is as follows: a method for solving the secondary stamping cracking of deep drawing and cold rolling steel, wherein the components adopted in the method are in accordance with the mass ratio: C: 0-0.003%, Si≤0.034%, Mn: 0.10%-0.30%, P:≤0.020%, S:≤0.020%, B: 0.0004%-0.0008%, Alt: 0.015%-0.070%, H:≤0.00030%, Ti: 0.03%-0.08%, and satisfying 0.02%≤B / P≤0.04%, and the rest are iron and unavoidable impurity elements.

[0009] A method for solving secondary stamping cracking of deep drawing and cold rolling steel, wherein the components used in the method are matched by mass: C: 0.0014%, Si: 0.006%, Mn: 0.15%, P: 0.016%, S: 0.007%, B: 0.0006%, Alt: 0.04%, H: 0.0001%, Ti: 0.05%, and the rest are iron and unavoidable impurity elements.

[0010] A method for solving secondary stamping cracking of deep drawing and cold rolling steel, wherein the components used in the method are matched by mass as follows: C: 0.0015%, Si: 0.008%, Mn: 0.14%, P: 0.015%, S: 0.006%, B: 0.0007%, Alt: 0.04%, H: 0.0002%, Ti: 0.046%, and the rest are iron and unavoidable impurity elements.

[0011] A method for solving secondary stamping cracking of deep drawing and cold rolling steel, wherein the components used in the method are matched by mass: C: 0.0013%, Si: 0.008%, Mn: 0.15%, P: 0.013%, S: 0.006%, B: 0.0004%, Alt: 0.05%, H: 0.0001%, Ti: 0.049%, and the rest are iron and unavoidable impurity elements.

[0012] A method for solving secondary stamping cracking of deep drawing and cold rolling steel, the method comprising the following steps:

[0013] Step 1: In the composition design of deep drawing steel products, a boron (B) component is added, and its content is specified to be 0.0004% to 0.0008%, and the boron (B) element and the phosphorus (P) element meet the following ratio relationship: 0.02%≤B / P≤0.04%;

[0014] Step 1 Mechanism Description: The accumulation of phosphorus in steel, i.e., segregation at the grain boundaries, reduces the bonding force between crystals, which is one of the reasons for the secondary stamping cracking of deep-drawn steel. Boron can inhibit the accumulation of phosphorus at the grain boundaries, so that phosphorus remains inside the crystals without precipitation, thereby increasing the bonding force between crystals and preventing deep-drawn steel from cracking during secondary stamping. However, the boron content cannot be too much, otherwise it is easy to cause corner cracking defects in the slab produced by continuous casting of deep-drawn steel. However, too little boron will not have a significant effect on inhibiting the accumulation of phosphorus at the grain boundaries. Compared with phosphorus, the relationship between the occurrence and phosphorus content is maintained as follows: 0.02% ≤ B / P ≤ 0.04%, which can not only ensure the inhibition of phosphorus, but also ensure that the slab does not have corner cracking defects.

[0015] Step 2: Desulfurization of hot metal, adding magnesium powder and lime as desulfurizers, spraying into the hot metal, spraying time 8-12 minutes, magnesium powder 110-150 kg, lime 800-900 kg, so that the sulfur in the hot metal is reduced from 0.030%-0.040% to 0.0020%-0.0030%, reaching the desulfurization requirement (≤0.0115%), the advantage is that the magnesium powder spraying speed is increased from the original 10 kg / min to 15-18 kg / min, thereby improving the desulfurization efficiency of magnesium powder, and does not increase the consumption of magnesium powder. The target desulfurization requirement is ≤0.0115%, but it can actually be removed to ≤0.0030%, reaching the control level of deep desulfurization.

[0016] Step 3: After completing step 2, the molten iron in the ladle enters the converter process, where scrap steel, molten iron and slag-making materials are added to the converter to smelt molten steel.

[0017] Step 4: After completing step 3, the molten steel enters the vacuum (RH) treatment process after being tapped, in which decarburization is first performed, alloying is then performed, and finally the dehydrogenation vacuum degree control mode is entered. Compared with the prior art, the dehydrogenation vacuum degree control mode is highlighted. The vacuum degree required for dehydrogenation is controlled according to the decarburization vacuum degree. The specific invention is shown in the following steps 5-7.

[0018] Step 5: After completing step 4, the vacuum molten steel is subjected to oxygen blowing decarburization treatment and controlled according to the required vacuum degree standard (P). The vacuum degree standard is controlled at ≤270Pa during decarburization. At this time, the molten steel coming out of the converter has a carbon content of 0.030%, which is not ultra-low carbon molten steel. Therefore, oxygen blowing decarburization treatment must be performed in the RH vacuum furnace first. The oxygen consumption is automatically determined by the carbon-oxygen reaction system. The carbon is removed from 0.030% to below 0.002%. This process is the same as the prior art.

[0019] Step 6: After completing step 5, add ferroboron alloy and ferrotitanium alloy to the vacuum molten steel for alloying treatment. After the carbon is removed to the standard requirements, add ferroboron alloy and ferrotitanium alloy respectively through the alloy feeding port next to the vacuum furnace. The vacuum control standard at this time is the same as the decarburization mode. After the alloy is melted into the molten steel, dehydrogenation treatment is carried out.

[0020] Step 7: After completing step 6, the molten steel is subjected to vacuum dehydrogenation treatment. At this time, the vacuum degree standard of the vacuum furnace for decarburization and alloying is adjusted to half or less than half, that is, the vacuum degree in the vacuum furnace is p≤(1 / 2)*P, where p is the vacuum degree during dehydrogenation, and P is the vacuum degree standard during decarburization and alloying, then p≤135Pa, so that the molten steel enters the dehydrogenation vacuum degree control mode;

[0021] Step 7 Mechanism Description: The vacuum standard P must be met during the entire vacuum treatment process in order to meet the needs of decarburization. However, in order to solve the secondary stamping cracking problem, dehydrogenation is necessary, and the vacuum requirement for dehydrogenation is higher than that for decarburization. It has been found through experiments that it can be kept below half of the normal vacuum standard P.

[0022] Step 8: After completing step 7, enter the continuous casting process to produce slabs.

[0023] Step 9: After completing step 8, enter the hot rolling process and send the slab into the hot rolling mill heating furnace.

[0024] Step 10: After completing step 9, the slab is taken out of the furnace, and rough rolling, finish rolling, and coiling are performed.

[0025] Compared with the prior art, the present invention has the following advantages: (1) During the desulfurization of molten iron, the magnesium powder blowing speed is optimized, thereby improving the desulfurization efficiency of the magnesium powder. (2) A restrictive relationship between the boron element and the phosphorus element is established, so that the boron element can eliminate the problem of stamping cracking caused by the phosphorus element and will not cause cracks in the slab, and the content of the boron element is determined very cleverly. The prior art does not have this idea. (3) During the vacuum treatment stage, the dehydrogenation vacuum control mode is highlighted. The prior art adopts the same mode for the vacuum degree of the dehydrogenation mode and the vacuum degree during decarburization (and alloying), that is, when the prior art treats molten steel in a vacuum furnace, the vacuum degree requirements of decarburization and alloying are followed throughout the process, resulting in no breakthrough in the degree of dehydrogenation. However, after the dehydrogenation vacuum mode is added to this patent, the hydrogen in the molten steel can be dehydrogenated to a level below 3ppm. (4) This patent has strong practicality, significant effects, and is easy to promote and apply. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, a detailed description is given below in conjunction with embodiments.

[0027] Embodiment: A method for solving secondary stamping cracking of deep drawing and cold rolling steel, the specific steps are as follows:

[0028] Step 1: Five Ingredients Example:

[0029]

[0030] Step 2: Desulfurization of the molten iron of the above five components:

[0031]

[0032] Step 3: The molten iron in the ladle enters the converter process, where scrap steel, molten iron and slag-making materials are added to the converter to smelt molten steel:

[0033]

[0034] Step 4: vacuum oxygen blowing decarburization treatment is performed on the molten steel smelted in step 3:

[0035]

[0036] Step 5: After completing step 4, alloy the molten steel in the vacuum furnace by adding ferroboron alloy and ferrotitanium alloy:

[0037]

[0038] Step 6: After completing step 5, the vacuum furnace molten steel is dehydrogenated:

[0039]

[0040] In this step, the vacuum degree is made less than half of the standard requirement so that the hydrogen content in molten steel can be controlled within the standard requirement.

[0041] Step 7: After completing step 6, five furnaces of molten steel are continuously cast to produce slabs.

[0042] Step 8: After completing step 7, the slab is sent to the heating furnace of the hot rolling process for heating, and the heating time and heating temperature are controlled:

[0043]

[0044] Step 9: After completing step 8, the slab is rolled, and the relevant rolling parameters are as follows:

[0045]

[0046] Step 10: Take samples of the coils rolled in step 9 for performance testing:

[0047]

[0048] Problem solving and effectiveness of use

[0049] According to the composition of the deep-drawn cold-rolled steel designed by the present invention, the steel does not crack after secondary stamping and meets the use requirements.

[0050] Before using the present invention, the properties of deep-drawn cold-rolled steel are: yield strength 120-210MPa; tensile strength ≥260MPa; elongation ≥36%; grain size ≥8.0 grade. The metallographic structure is ferrite.

[0051] After using the present invention, the performance, grain size grade and metallographic structure of deep-drawn cold-rolled steel are improved. The performance of deep-drawn cold-rolled steel is: yield strength 150-210MPa; tensile strength ≥280MPa; elongation ≥36%; grain size ≥8.5. The metallographic structure is ferrite + dispersed two-phase boride (BN, BC, etc.) particles. Since the structure contains dispersed two-phase boride, the dislocation between the grains in the structure is increased, and the bonding force between the grains is enhanced, thereby solving the problem of secondary stamping cracking.

[0052] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A method for solving secondary stamping cracking of deep drawing and cold rolling steel, characterized in that: The components used in the method are matched by mass ratio: C: 0-0.003%, Si≤0.034%, Mn: 0.10%-0.30%, P: ≤0.020%, S: ≤0.020%, B: 0.0004%-0.0008%, Alt: 0.015%-0.070%, H: ≤0.00030%, Ti: 0.03%-0.08%, and satisfy 0.02%≤B / P≤0.04%, and the rest are iron and unavoidable impurity elements.

2. The method for solving secondary stamping cracking of deep drawing and cold rolling steel according to claim 1, characterized in that: The components used in this method are in the following mass ratios: C: 0.0014%, Si: 0.006%, Mn: 0.15%, P: 0.016%, S: 0.007%, B: 0.0006%, Alt: 0.04%, H: 0.0001%, Ti: 0.05%, and the rest are iron and unavoidable impurity elements.

3. The method for solving secondary stamping cracking of deep drawing and cold rolling steel according to claim 1, characterized in that: The components used in this method are arranged in the following mass ratios: C: 0.0015%, Si: 0.008%, Mn: 0.14%, P: 0.015%, S: 0.006%, B: 0.0007%, Alt: 0.04%, H: 0.0002%, Ti: 0.046%, and the rest are iron and unavoidable impurity elements.

4. The method for solving secondary stamping cracking of deep drawing and cold rolling steel according to claim 1, characterized in that: The components used in this method are in the following mass ratios: C: 0.0013%, Si: 0.008%, Mn: 0.15%, P: 0.013%, S: 0.006%, B: 0.0004%, Alt: 0.05%, H: 0.0001%, Ti: 0.049%, and the rest are iron and unavoidable impurity elements.

5. The method for solving secondary stamping cracking of deep drawing and cold rolling steel according to claim 1, characterized in that: The method comprises the following steps: Step 1: In the composition design of deep drawing steel products, a boron (B) component is added, and its content is specified to be 0.0004% to 0.0008%, and the boron (B) element and the phosphorus (P) element meet the following ratio relationship: 0.02%≤B / P≤0.04%; Step 2: Desulfurization of molten iron: add magnesium powder and lime as desulfurizers, spray them into the molten iron for 8-12 minutes, 110-150 kg of magnesium powder and 800-900 kg of lime, so that the sulfur in the molten iron is reduced from 0.030%-0.040% to 0.0020%-0.0030%, meeting the desulfurization requirements (≤0.0115%). Step 3: After completing step 2, the molten iron in the ladle enters the converter process, where scrap steel, molten iron and slag-making materials are added to the converter to smelt molten steel. Step 4: After completing step 3, the molten steel enters the vacuum (RH) treatment process after being tapped, in which decarburization is first performed, alloying is then performed, and finally the dehydrogenation vacuum control mode is entered. Step 5: After completing step 4, the vacuum molten steel is subjected to oxygen blowing decarburization treatment and controlled according to the required vacuum standard (P). The vacuum standard during decarburization is controlled at ≤270Pa. At this time, the carbon content of the molten steel coming out of the converter is 0.030%. Step 6: After completing step 5, add ferroboron alloy and ferrotitanium alloy to the vacuum molten steel for alloying treatment. After the carbon is removed to the standard requirements, add ferroboron alloy and ferrotitanium alloy through the alloy feeding port next to the vacuum furnace. After the alloy is melted into the molten steel, dehydrogenation treatment is carried out. Step 7: After completing step 6, the molten steel is subjected to vacuum dehydrogenation treatment. At this time, the vacuum degree standard of the vacuum furnace for decarburization and alloying is adjusted to half or less than half, that is, the vacuum degree in the vacuum furnace is p≤(1 / 2)*P, where p is the vacuum degree during dehydrogenation, and P is the vacuum degree standard during decarburization and alloying, then p≤135Pa, so that the molten steel enters the dehydrogenation vacuum degree control mode; Step 8: After completing step 7, enter the continuous casting process to produce slabs. Step 9: After completing step 8, enter the hot rolling process and send the slab into the hot rolling mill heating furnace. Step 10: After completing step 9, the slab is taken out of the furnace, and rough rolling, finish rolling, and coiling are performed.

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