High-strength cold-rolled steel sheet and method for producing same

Abstract

Provided are a high strength cold rolled steel sheet for press forming that is used in, for example, automobiles through a press forming process and a method for manufacturing such a steel sheet. A multiphase steel sheet has a steel composition containing, in percent by mass, more than 0.015% to less than 0.100% of carbon, less than 0.40% of silicon, 1.0% to 1.9% of manganese, more than 0.015% to 0.05% of phosphorus, 0.03% or less of sulfur, 0.01% to 0.3% of soluble aluminum, 0.005% or less of nitrogen, less than 0.30% of chromium, 0.0050% or less of boron, less than 0.15% of molybdenum, 0.4% or less of vanadium, 0.02% or less of titanium, and optionally at least one of niobium, tungsten, zirconium, copper, nickel, tin, antimony, calcium, cerium, lanthanum, and magnesium, wherein [Mneq] is 2.0 to 2.8, the balance being iron and incidental impurities. The steel composition satisfies a plurality of parameter formulas of particular elements. The steel sheet has a microstructure containing ferrite and a particular volume fraction of a second phase containing martensite and retained ³.

Description

technical field [0001] The present invention relates to a high-strength steel sheet for press forming used in automobiles, home appliances, etc. through a press forming process, and a method for producing the same. Background technique [0002] In the past, TS: 340MPa grade BH steel plate (sinter hardened steel plate, hereinafter referred to as 340BH ). [0003] 340BH is a single-phase ferrite that controls the amount of solid-solution C by adding carbonitride-forming elements such as Nb and Ti to ultra-low carbon steel with C less than 0.01 mass%, and uses Mn and P for solid-solution strengthening steel. In recent years, the demand for lightweight car bodies has further increased, and research is being carried out: thinning the steel plate by making the outer plate of these 340BH applications further high-strength; reducing R / F (reinforcement: inner Reinforced parts); and reduce the temperature and shorten the time of the sintering coating process. [0004] However, if ...

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Problems solved by technology

[0006] In addition, for steel with higher strength than 340BH, material changes such as YP, TS, and E1 are easy to occur, and surface deformation and stamping cracks are easy to occur

For a steel plate with high YP, when the change in material is small, it is possible to reduce the surface deformation of the design surface by adjusting the shape of the stamping die. However, YP and TS change in the length direction or width direction of the coil, and further Extremely difficult to reduce face distortion when changing from roll to roll

This is because it is impossible to adjust the surface shape of each coil by cutting the stamping die in mass production, and even if the stamping conditions such as forming pressure are adjusted, the effect of suppressing surface deformation is small

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