US 5,629,099 A · Alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability and method for manufacturing same

Abstract

An alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability, having, on the surface thereof, numerous fine concavities which satisfy the following conditions: (1) that the number of fine concavities having a depth of at least 2 .mu.m is within a range of from 200 to 8,200 per mm.sup.2 of the plating layer, and (2) that the total opening area per unit area of the fine concavities in the plating layer is within a range of from 10 to 70% of the unit area. The above-mentioned plated steel sheet is manufactured by subjecting a cold-rolled steel sheet to a zinc dip-plating treatment in a zinc dip-plating bath having an aluminum content of from 0.05 to 0.30 wt. %, in which the temperature region causing an initial reaction for forming an iron-aluminum layer is limited within a range of from 500.degree. to 600.degree. C., an alloying treatment in which an alloying treatment temperature is limited within a range of from 480.degree. to 600.degree. C., and a temper-rolling treatment. It is possible to further impart an excellent image clarity after painting to the above-mentioned plated steel sheet by replacing the above-mentioned condition (2) with a condition that a bearing length ratio tp (2 .mu.m) in a profile curve is within a range of from 30 to 90%.

Claims11

Dependent claims

An alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability, which comprises:

a steel sheet;
and
an alloying-treated iron-zinc alloy dip-plating layer formed on at least one surface of said steel sheet, said alloying-treated iron-zinc alloy dip-plating layer having numerous fine concavities on the surface thereof;
characterized in that:
the number of fine concavities having a depth of at least 2 .mu.m from among said numerous fine concavities is within a range of from 200 to 8,200 per mm.sup.2 of said alloying-treated iron-zinc alloy dip-plating layer;
and
the total opening area per unit area of said fine concavities having a depth of at least 2 .mu.m in said alloying-treated iron-zinc alloy dip-plating layer, is within a range of from 10 to 70% of said unit area.

4 more elements

An alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability and image clarity after painting, which comprises:

a steel sheet;
and
an alloying-treated iron-zinc alloy dip-plating layer formed on at least one surface of said steel sheet, said alloying-treated iron-zinc alloy dip-plating layer having numerous fine concavities on the surface thereof;
characterized in that:
the number of fine concavities having a depth of at least 2 .mu.m from among said numerous fine concavities is within a range of from 200 to 8,200 per mm.sup.2 of said alloying-treated iron-zinc alloy dip-plating layer;
and
said fine concavities having a depth of at least 2 .mu.m further satisfy the following condition:
a bearing length ratio tp (2 .mu.m) is within a range of from 30 to 90%, said bearing length ratio tp (2 .mu.m) being expressed, when cutting a profile curve over a prescribed length thereof by means of a straight line parallel to a mean line and located below the highest peak in said profile curve by 2 .mu.m, by a ratio in percentage of a total length of cut portions thus determined of said alloying-treated iron-zinc alloy dip-plating layer having a surface profile which corresponds to said profile curve, relative to said prescribed length of said profile curve.

5 more elements

A method for manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability, which comprises the steps of:

subjecting a hot-rolled steel sheet to a cold-rolling treatment to prepare a cold-rolled steel sheet;
passing said cold-rolled steel sheet through a zinc dip-plating bath having a chemical composition comprising zinc, aluminum and incidental impurities to apply a zinc dip-plating treatment to said cold-rolled steel sheet, thereby forming a zinc dip-plating layer on at least one surface of said cold-rolled steel sheet;
subjecting said cold-rolled steel sheet having said zinc dip-plating layer thus formed on the surface thereof to an alloying treatment at a prescribed temperature, thereby forming an alloying-treated iron-zinc alloy dip-plating layer on said at least one surface of said cold-rolled steel sheet, said alloying-treated iron-zinc alloy dip-plating layer having numerous fine concavities;
and then
subjecting said cold-rolled steel sheet having said alloying-treated iron-zinc alloy dip-plating layer having said numerous fine concavities thus formed on the surface thereof to a temper-rolling, thereby manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability;
characterized by:
limiting the content of said aluminum in said zinc dip-plating bath within a range of from 0.05 to 0.30 wt. %;
limiting the temperature region causing an initial reaction for forming an iron-aluminum alloy layer in said zinc dip-plating treatment within a range of from 500.degree. to 600.degree. C.;
and
limiting said prescribed temperature in said alloying treatment within a range of from 480.degree. to 600.degree. C.

7 more elements

A method for manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability, which comprises the steps of:

subjecting a hot-rolled steel sheet to a cold-rolling treatment to prepare a cold-rolled steel sheet;
passing said cold-rolled steel sheet through a zinc dip-plating bath having a chemical composition comprising zinc, aluminum and incidental impurities to apply a zinc dip-plating treatment to said cold-rolled steel sheet, thereby forming a zinc dip-plating layer on at least one surface of said cold-rolled steel sheet;
subjecting said cold-rolled steel sheet having said zinc dip-plating layer thus formed on the surface thereof to an alloying treatment at a prescribed temperature, thereby forming an alloying-treated iron-zinc alloy dip-plating layer on said at least one surface of said cold-rolled steel sheet, said alloying-treated iron-zinc alloy dip-plating layer having numerous fine concavities;
and then,
subjecting said cold-rolled steel sheet having said alloying-treated iron-zinc alloy dip-plating layer having said numerous fine concavities thus formed on the surface thereof to a temper-rolling, thereby manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability;
characterized by:
using, as said cold-rolled steel sheet, a cold-rolled steel sheet into which at least one element selected from the group consisting of carbon, nitrogen and boron is dissolved in the form of solid-solution in an amount within a range of from 1 to 20 ppm;
limiting the content of said aluminum in said zinc dip-plating bath within a range of from 0.05 to 0.30 wt. %;
and
limiting said prescribed temperature in said alloying treatment within a range of from 480.degree. to 600.degree. C.

7 more elements

A method for manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability, which comprises the steps of:

subjecting a hot-rolled steel sheet to a cold-rolling treatment to prepare a cold-rolled steel sheet;
passing said cold-rolled steel sheet through a zinc dip-plating bath having a chemical composition comprising zinc, aluminum and incidental impurities to apply a zinc dip-plating treatment to said cold-rolled steel sheet, thereby forming a zinc dip-plating layer on at least one surface of said cold-rolled steel sheet;
subjecting said cold-rolled steel sheet having said zinc dip-plating layer thus formed on the surface thereof to an alloying treatment at a prescribed temperature, thereby forming an alloying-treated iron-zinc alloy dip-plating layer on at least one surface of said cold-rolled steel sheet, said alloying-treated iron-zinc alloy dip-plating layer having numerous fine concavities;
and then
subjecting said cold-rolled steel sheet having said alloying-treated iron-zinc alloy dip-plating layer having said numerous fine concavities thus formed on the surface thereof to a temper-rolling, thereby manufacturing an alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability;
characterized by:
limiting the content of said aluminum in said zinc dip-plating bath within a range of from 0.10 to 0.25 wt. %;
and
carrying out said alloying treatment at a temperature T(.degree.C.) satisfying the following formula:
440+400.times.[Al wt. %].ltoreq.T.ltoreq.500+400.times.[Al wt. %]
where, [Al wt. %] is the aluminum content in said zinc dip-plating bath.

8 more elements

Dependencies are inferred from the claim text.

Alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability and method for manufacturing same

Life of this patent

Alloying-treated iron-zinc alloy dip-plated steel sheet excellent in press-formability and method for manufacturing same

Life of this patent

Abstract

Claims11