Ultra-low carbon cold-rolled steel strip resistant to low-temperature impact

Abstract

The utility model relates to cold-rolled steel strip technical field, concretely relates to low temperature impact resistant ultralow carbon cold-rolled steel strip, including steel band body, steel band body is composite layer structure, is composed of base layer, transition layer and surface strengthening layer that are sequentially superposed and metallurgical combination, the thickness of transition layer is 2~5mu m, the side of transition layer close to base layer is equipped with dentiform boss, and the dentiform boss is embedded in base layer and realizes mechanical bite and metallurgical combination, the thickness of surface strengthening layer is 5~20mu m, and the outer surface of surface strengthening layer is equipped with the microconvex texture of uniform distribution, through the composite layer structure of base layer, transition layer, surface strengthening layer, cooperate each layer specific material selection and multiple structure optimization, the dentiform boss of transition layer forms mechanical bite and metallurgical combination with base layer, and the honeycomb groove of transition layer forms anchoring structure with surface strengthening layer, and double interface structure significantly improves the interlaminar bond strength.

Description

Technical Field

[0001] This utility model relates to the field of cold-rolled steel strip technology, specifically to low-temperature impact resistant ultra-low carbon cold-rolled steel strip. Background Technology

[0002] Ultra-low carbon cold-rolled steel strip is widely used in automobiles, home appliances, and construction machinery due to its excellent formability, weldability, and toughness. However, in low-temperature environments (such as -40°C to -60°C), the impact toughness of conventional ultra-low carbon cold-rolled steel strip will decrease significantly, making it prone to brittle fracture and unable to meet the needs of use in cold regions, polar equipment, or low-temperature operating conditions.

[0003] In existing technologies, methods to improve the low-temperature impact resistance of cold-rolled steel strips mostly focus on adjusting the alloy composition. However, these methods often suffer from problems such as unreasonable composition ratios and difficulty in balancing strengthening and toughness. Furthermore, insufficient microstructural control of the steel strip results in limited energy absorption capacity at low temperatures. In addition, some improvement schemes fail to consider the synergistic optimization of the cold rolling process and material properties, leading to poor results in improving the low-temperature impact resistance of the steel strip and high production costs, which is detrimental to large-scale production. Utility Model Content

[0004] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a low-temperature impact resistant ultra-low carbon cold-rolled steel strip, which can effectively solve the problems in the existing technology.

[0005] This utility model provides a low-temperature impact resistant ultra-low carbon cold-rolled steel strip, including a steel strip body. The steel strip body has a composite layered structure, consisting of a matrix layer, a transition layer, and a surface strengthening layer that are stacked and metallurgically bonded in sequence. The thickness of the transition layer is 2~5μm, and a toothed protrusion is provided on the side of the transition layer near the matrix layer. The toothed protrusion is embedded in the matrix layer to achieve mechanical interlocking and metallurgical bonding. The thickness of the surface strengthening layer is 5~20μm, and the outer surface of the surface strengthening layer has uniformly distributed micro-protrusion texture. The matrix layer is made of ultra-low carbon alloy material, and nano-scale TiN precipitates are uniformly distributed inside the matrix layer. The ferrite grains in the matrix layer are preferentially oriented along the rolling direction of the steel strip. The two sides of the steel strip body are provided with arc-shaped chamfers with a chamfer radius of 0.2~0.5mm and an angle of 120~150° between the chamfer surface and the surface of the steel strip.

[0006] Furthermore, the transition layer is made of Ni-Cr alloy, and the microstructure of the steel strip body is ferrite and a small amount of pearlite, wherein the grain size of ferrite is 5~10μm, and the volume fraction of pearlite is ≤3%. The transition layer has a honeycomb groove on the side near the surface strengthening layer, the groove diameter is 1~2μm and the depth is 1~1.5μm, and the surface strengthening layer material is filled in the groove to form an anchoring structure.

[0007] Furthermore, the height of the toothed boss is 0.5~1μm and the tooth pitch is 2~4μm.

[0008] Furthermore, the surface strengthening layer is made of martensitic stainless steel, wherein the depth of the micro-protrusion texture is 1~3μm and the spacing is 5~10μm. The micro-protrusion texture of the surface strengthening layer is a cross-grid, formed by vertically interwoven longitudinal and transverse textures, and the depth and spacing of the longitudinal and transverse textures are consistent.

[0009] Further, the chemical composition of the matrix layer by mass percentage is as follows: C: 0.001~0.005%, Si: 0.05~0.15%, Mn: 0.8~1.2%, P: ≤0.010%, S: ≤0.005%, Al: 0.02~0.06%, Ti: 0.01~0.03%, Nb: 0.005~0.015%, with the remainder being Fe and unavoidable impurities. The precipitated phase has a particle size of 20~50nm and a volume fraction of 0.1~0.3%. The ferrite grains in the matrix layer have an orientation degree of ≥85%, and the grains are arranged to form fiber bundles parallel to the rolling direction, with a fiber bundle diameter of 20~50μm.

[0010] Furthermore, the surface roughness Ra of the surface strengthening layer is ≤0.8μm, the surface of the steel strip body is free of oxide scale, cracks and inclusions, and the interlayer bonding strength is ≥350MPa.

[0011] Compared with existing technologies, the beneficial effects of this invention are as follows: By designing a composite layered structure of a matrix layer, transition layer, and surface strengthening layer, and with specific material selection and multiple structural optimizations for each layer, the toothed protrusions of the transition layer form a mechanical interlocking and metallurgical bond with the matrix layer. At the same time, the honeycomb grooves of the transition layer form an anchoring structure with the surface strengthening layer. This dual-interface structure significantly improves the interlayer bonding strength and avoids interlayer delamination caused by differences in the thermal expansion coefficients of the layers at low temperatures. The cross-grid micro-convex texture of the surface strengthening layer further improves the surface friction performance, and the martensitic stainless steel material enhances the surface hardness. The preferentially oriented ferrite fiber bundles and nano-scale TiN precipitation in the matrix layer work synergistically to further refine the grains and hinder crack propagation. Combined with ultra-low carbon content, it reduces carbide precipitation. The synergistic effect of multiple structures and components significantly improves the low-temperature impact resistance and structural stability of the steel strip. In addition, the arc-shaped chamfer at the edge of the steel strip can avoid brittle fracture caused by edge stress concentration at low temperatures, thus improving safety in use. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this utility model 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 only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is one of the structural schematic diagrams of this utility model; Figure 2 for Figure 1 A schematic diagram of the structure at point A in the diagram; Figure 3 This is the second structural schematic diagram of the present utility model; Figure 4 This is the third structural schematic diagram of this utility model.

[0014] The labels in the diagram represent: 1. Steel strip body; 11. Arc chamfer; 2. Substrate layer; 3. Transition layer; 31. Toothed boss; 4. Surface strengthening layer. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without creative effort are within the scope of protection of this utility model.

[0016] The present invention will be further described below with reference to the embodiments.

[0017] Example: Low-temperature impact resistant ultra-low carbon cold-rolled steel strip, see attached document. Figure 1 - Appendix Figure 4 It includes a steel strip body 1, which has a composite layered structure and is composed of a matrix layer 2, a transition layer 3 and a surface strengthening layer 4 that are stacked and metallurgically bonded in sequence. The transition layer 3 has a thickness of 2~5μm. A toothed protrusion 31 is provided on the side of the transition layer 3 closest to the substrate layer 2, and this toothed protrusion 31 is embedded in the substrate layer 2 to achieve mechanical interlocking and metallurgical bonding. The transition layer 3 is made of Ni-Cr alloy. The microstructure of the steel strip body 1 consists of ferrite and a small amount of pearlite, wherein the ferrite grain size is 5~10μm, and the pearlite volume fraction is ≤3%. A honeycomb-shaped groove is provided on the side of the transition layer 3 closest to the surface strengthening layer 4, and the groove pore size is... The surface strengthening layer 4 material is filled in the groove to form an anchoring structure with a height of 1~2μm and a depth of 1~1.5μm; the toothed boss 31 has a height of 0.5~1μm and a tooth pitch of 2~4μm; the microstructure of the steel strip controlled by this utility model is fine-grained ferrite and a small amount of pearlite. The ferrite grain size is controlled at 5~10μm. The fine grains can hinder the initiation and propagation of cracks, further improving the low-temperature impact toughness. At the same time, the presence of a small amount of pearlite ensures the strength of the steel strip.

[0018] The surface strengthening layer 4 has a thickness of 5~20μm, and its outer surface is provided with uniformly distributed micro-protrusion textures. The surface strengthening layer 4 is made of martensitic stainless steel, and the depth of the micro-protrusion textures is 1~3μm with a spacing of 5~10μm. The micro-protrusion textures of the surface strengthening layer 4 are cross-grid-like, formed by the vertical interweaving of longitudinal and transverse textures, with the depth and spacing of the longitudinal and transverse textures being consistent. The surface roughness Ra of the surface strengthening layer 4 is ≤0.8μm, and the surface of the steel strip body 1 is free of oxide scale, cracks, and inclusion defects. The interlayer bonding strength is ≥350MPa. The layered structure design of this utility model is reasonably matched with the chemical composition ratio of the base layer 2, taking into account the low-temperature impact resistance, formability, and weldability. The yield strength, tensile strength, and elongation after fracture can all meet the requirements of conventional engineering applications, and it can be widely used in automotive parts, home appliance housings, and engineering machinery structural parts under low-temperature conditions.

[0019] The substrate layer 2 is made of ultra-low carbon alloy material, and nano-sized TiN precipitates are uniformly distributed inside the substrate layer 2. The ferrite grains in the substrate layer 2 are preferentially oriented along the rolling direction of the steel strip. The two sides of the steel strip body 1 are provided with arc-shaped chamfers 11, the chamfer radius is 0.2~0.5mm, and the angle between the chamfer surface and the surface of the steel strip is 120~150°. The chemical composition of the substrate layer 2 by mass percentage is: C: 0.001~0.005%, Si: 0.05~0.15%, Mn: 0. 8~1.2%, P: ≤0.010%, S: ≤0.005%, Al: 0.02~0.06%, Ti: 0.01~0.03%, Nb: 0.005~0.015%, with the remainder being Fe and unavoidable impurities. The precipitated phase has a particle size of 20~50nm and a volume fraction of 0.1~0.3%. The ferrite grains in the matrix layer 2 have an orientation degree of ≥85%, and the grains are arranged to form fiber bundles parallel to the rolling direction with a fiber bundle diameter of 20~50μm.

[0020] By designing a composite layered structure of matrix layer 2, transition layer 3, and surface strengthening layer 4, and with specific material selection and multiple structural optimizations for each layer, the toothed protrusions 31 of transition layer 3 form a mechanical interlocking and metallurgical bond with matrix layer 2. At the same time, the honeycomb grooves of transition layer 3 form an anchoring structure with surface strengthening layer 4. This dual-interface structure significantly improves the interlayer bonding strength and avoids interlayer delamination caused by differences in the thermal expansion coefficients of the layers at low temperatures. The cross-grid micro-convex texture of surface strengthening layer 4 further improves surface friction performance, while the martensitic stainless steel material enhances surface hardness. The preferentially oriented ferrite fiber bundles and nano-scale TiN precipitation in matrix layer 2 work synergistically to further refine grains and hinder crack propagation. Combined with ultra-low carbon content to reduce carbide precipitation, the synergistic effect of multiple structures and compositions significantly improves the low-temperature impact resistance and structural stability of the steel strip. In addition, the arc-shaped chamfer 11 at the edge of the steel strip can avoid brittle fracture caused by edge stress concentration at low temperatures, improving safety in use.

[0021] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of this utility model.

Claims

1. Low-temperature impact resistant ultra-low carbon cold-rolled steel strip, characterized in that, The system includes a steel strip body (1), which has a composite layered structure consisting of a matrix layer (2), a transition layer (3), and a surface strengthening layer (4) that are stacked and metallurgically bonded in sequence. The thickness of the transition layer (3) is 2-5 μm, and a toothed boss (31) is provided on the side of the transition layer (3) near the matrix layer (2), and the toothed boss (31) is embedded in the matrix layer (2) to achieve mechanical interlocking and metallurgical bonding. The thickness of the surface strengthening layer (4) is 5-20 μm. μm, and the outer surface of the surface strengthening layer (4) is provided with uniformly distributed micro-convex texture. The substrate layer (2) is made of ultra-low carbon alloy material, and nano-scale TiN precipitates are uniformly distributed inside the substrate layer (2). The ferrite grains in the substrate layer (2) are preferentially oriented along the rolling direction of the steel strip. The two sides of the steel strip body (1) are provided with arc-shaped chamfers (11), the chamfer radius is 0.2~0.5mm, and the angle between the chamfer surface and the surface of the steel strip is 120~150°.

2. The low-temperature impact-resistant ultra-low carbon cold-rolled steel strip according to claim 1, characterized in that, The toothed boss (31) has a height of 0.5~1μm and a tooth pitch of 2~4μm.

3. The low-temperature impact-resistant ultra-low carbon cold-rolled steel strip according to claim 1, characterized in that, The surface strengthening layer (4) is made of martensitic stainless steel, and the depth of the micro-protrusion texture is 1~3μm and the spacing is 5~10μm. The micro-protrusion texture of the surface strengthening layer (4) is a cross-grid, which is formed by vertically interwoven longitudinal and transverse textures. The depth and spacing of the longitudinal and transverse textures are consistent.

4. The low-temperature impact-resistant ultra-low carbon cold-rolled steel strip according to claim 1, characterized in that, The surface roughness Ra of the surface strengthening layer (4) is ≤0.8μm, the surface of the steel strip body (1) is free of oxide scale, cracks and inclusion defects, and the interlayer bonding strength is ≥350MPa.

Images