摘要:
Provided are a high-strength hot-dip galvanized steel sheet having excellent formability and a tensile strength of 440 MPa or more and a method for manufacturing the same. A steel sheet has a microstructure containing a ferrite phase having an area fraction of 60% or more, a pearlite phase having an area fraction of 20% to 30%, and a bainite phase having an area fraction of 1% to 5%, the area fraction of a cementite phase present in a grain of the ferrite phase being 5% or less. Upon manufacture, a hot-rolled sheet or a cold-rolled sheet is heated to a temperature of 650° C. or higher at an average heating rate of 10° C./s or more, is held at a temperature of 700° C. to (Ac3-5)° C. for ten seconds or more, is cooled to a temperature of 300° C. to 500° C. at an average cooling rate of 10° C./s to 200° C./s, is held at a temperature of 300° C. to 500° C. for 30 seconds to 300 seconds, and is then hot-dip galvanized.
摘要:
Provided are a high-strength hot-dip galvanized steel sheet having excellent formability and a tensile strength of 440 MPa or more and a method for manufacturing the same. A steel sheet has a microstructure containing a ferrite phase having an area fraction of 60% or more, a pearlite phase having an area fraction of 20% to 30%, and a bainite phase having an area fraction of 1% to 5%, the area fraction of a cementite phase present in a grain of the ferrite phase being 5% or less. Upon manufacture, a hot-rolled sheet or a cold-rolled sheet is heated to a temperature of 650° C. or higher at an average heating rate of 10° C./s or more, is held at a temperature of 700° C. to (Ac3-5)° C. for ten seconds or more, is cooled to a temperature of 300° C. to 500° C. at an average cooling rate of 10° C./s to 200° C./s, is held at a temperature of 300° C. to 500° C. for 30 seconds to 300 seconds, and is then hot-dip galvanized.
摘要:
A steel sheet has the chemical composition containing, by mass %, C: 0.04 to 0.13%, Si: 0.9 to 2.3%, Mn: 0.8 to 1.8%, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less, N: 0.008% or less, the remainder being Fe and the inevitable impurities and a microstructure including, in terms of area ratio, a ferrite phase of 80% or more, a bainitic ferrite phase of 1.0% or more, a pearlite phase of 1.0 to 10.0%, and a martensite phase of 1.0% or more and less than 5.0%, wherein the mean grain size of ferrite is 14 μm or less, the mean grain size of martensite is 4 μm or less, the mean free path of martensite is 3 μm or more, the Vickers hardness of ferrite is 140 or more, and the relationship area ratio of martensite/(area ratio of bainitic ferrite+area ratio of pearlite) 0.6 is satisfied.
摘要:
A high strength steel sheet including, by mass, C: 0.03% or more and 0.25% or less, Si: 0.4% or more and 2.5% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 2.5% or less, N: 0.008% or less, Si+Al: 1.0% or more, the balance being Fe and inevitable impurities. The area ratio of ferrite is 30% or more and 80% or less, the area ratio of martensite is 0% or more and 17% or less, the volume fraction of retained austenite is 8% or more, and the average grain size of retained austenite is 2 μm or less.
摘要:
A high-strength galvanized steel sheet having excellent formability and crashworthiness, including a component composition containing 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis, the remainder being Fe and unavoidable impurities, and a microstructure containing a tempered martensitic phase and a bainitic phase such that the sum of an area fraction of the tempered martensitic phase and an area fraction of the bainitic phase is 30% or more (the area fraction of the martensitic phase is 30% or more in the absence of the bainitic phase), wherein a distance of closest approach of the tempered martensitic phase is 10 μm or less and the contents of C, Mn, and B satisfy (1): (% Mn)+1000×(% B)≧35×(% C) (1).
摘要:
A high strength galvanized steel sheet with excellent workability, having a component composition containing C: 0.04% or more, and 0.15% or less, Si: 0.7% or more, and 2.3% or less, Mn: 0.8% or more, and 2.2% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less, N: 0.008% or less, and the remainder composed of iron and incidental impurities on a percent by mass basis, and a microstructure including 70% or more of ferrite phase, 2% or more, and 10% or less of bainite phase, and 0% or more, and 12% or less of pearlite phase on an area fraction basis and 1% or more, and 8% or less of retained austenite phase on a volume fraction basis, wherein an average crystal grain diameter of ferrite is 18 μm or less and an average crystal grain diameter of retained austenite is 2 μm or less.
摘要:
A high strength steel sheet including, by mass, C: 0.03% or more and 0.25% or less, Si: 0.4% or more and 2.5% or less, Mn: 3.5% or more and 10.0% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 2.5% or less, N: 0.008% or less, Si+Al: 1.0% or more, the balance being Fe and inevitable impurities. The area ratio of ferrite is 30% or more and 80% or less, the area ratio of martensite is 0% or more and 17% or less, the volume fraction of retained austenite is 8% or more, and the average grain size of retained austenite is 2 μm or less.
摘要:
A method of manufacturing a high strength galvanized steel sheet has a first heating step including heating to 400° C. to 750° C. in an atmosphere containing O2: 0.1 to 20 percent and H2O: 1 to 50 percent and heating to 600° C. to 850° C. in an atmosphere containing O2: 0.01 to less than 0.1 percent and H2O: 1 to 20 percent is applied to a steel sheet, a second heating step includes holding the steel sheet in an atmosphere containing H2: 1 to 50 percent and having a dew point of 0° C. or lower at 750° C. to 900° C. for 15 to 600 s, cooling to a temperature of 450° C. to 550° C., and holding is performed at that temperature for 10 to 200 s, and a galvanization treatment is applied.
摘要:
A galvanized steel sheet has a composition containing, by mass %, C: 0.05% or more and 0.5% or less, Si: 0.01% or more and 2.5% or less, Mn: 0.5% or more and 3.5% or less, P: 0.003% or more and 0.100% or less, S: 0.02% or less, Al: 0.010% or more and 0.5% or less, B: 0.0002% or more and 0.005% or less, Ti: 0.05% or less, a relationship of Ti>4N being satisfied, and the balance comprising Fe and inevitable impurities, and a microstructure containing 60% or more and 95% or less of tempered martensite in terms of area ratio and 5% or more and 20% or less of retained austenite in terms of area ratio.
摘要:
A high-strength galvanized steel sheet with excellent formability and shape fixability and a method for manufacturing the high-strength galvanized steel sheet.