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Q/BQB 420-2023: Hot-dip zinc /zinc-iron/zinc-magnesium/zinc-aluminum-magnesium alloy coated steel sheet and strip
Q/BQB 420-2023
BQB®
ENTERPRISE STANDARD OF BAOSTEEL CO., LTD.
Replacing Q/BQB 420-2021
Hot-dip zinc /zinc-iron /zinc-magnesium /zinc-aluminum-
magnesium alloy coated steel sheet and strip
ISSUED ON: APRIL 09, 2023
IMPLEMENTED ON: JULY 01, 2023
Issued by: BaoSteel Co., Ltd.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Classification and code ... 9
5 Information required for ordering ... 11
6 Dimensions, appearance, weight, allowable deviations ... 12
7 Technical requirements ... 13
8 Inspection and testing ... 26
9 Packaging, marking, inspection documents ... 28
10 Numerical rounding rules ... 28
11 Comparison of similar designation ... 28
Appendix A (Normative) Permissible deviations in thickness and unevenness of steel
sheet and strip (hot-rolled pickled substrates) ... 29
Appendix B (Normative) Weight calculation method in theoretical weighing ... 32
Appendix C (Normative) Chemical composition of steel ... 33
Appendix D (Informative) Comparison of similar designations between this document
and relevant domestic and foreign documents ... 37
Hot-dip zinc /zinc-iron /zinc-magnesium /zinc-aluminum-
magnesium alloy coated steel sheet and strip
1 Scope
This document specifies the requirements for terms and definitions, classification and
codes, dimensions, appearance, weight, technical requirements, inspection and testing,
packaging, marking and inspection documents of the hot-dip zinc /zinc-iron /zinc-
magnesium /zinc-aluminum-magnesium alloy coated steel sheet and strip (hereinafter
referred to as steel sheet and strip).
This document applies to steel sheet and strip, which has a thickness of 0.23 mm ~ 4.00
mm, as produced by Baoshan Iron and Steel Co., Ltd. They are mainly used to make
internal and external covering parts and structural parts in the automobile, construction,
home appliances and other industries.
2 Normative references
The contents of the following documents constitute essential provisions of this
document through normative references in the text. Among them, for dated reference
documents, only the version corresponding to the date applies to this document; for
undated reference documents, the latest version (including all amendments) applies to
this document.
GB/T 222 Method of sampling steel for determination of chemical composition and
permissible variations for product analysis
GB/T 223 Methods for chemical analysis of iron, steel and alloy
GB/T 228.1-2021 Metallic materials - Tensile testing - Part 1: Method of test at room
temperature
GB/T 232 Metallic materials - Bend test
GB/T 1839 Test method for gravimetric determination of the mass per unit area of
galvanized coatings on steel products
GB/T 2523 Measuring method of surface roughness, peak count and waviness for
cold-rolled metal sheet and strip
GB/T 2975 Steel and steel products - Location and preparation of samples and test
3.2 Hot-dip zinc-iron alloy coating (ZF)
On a hot-dip zinc production line, the coating which is obtained by immersing pre-
treated steel strips in molten zinc. The zinc content in the molten zinc liquid shall be no
less than 99%. Subsequently, a zinc-iron alloy layer is formed on the entire coating
through an alloying process. The iron content in the alloy coating is usually 8 ~ 15%.
3.3 Hot-dip zinc-magnesium alloy coating (ZM)
On a hot-dip zinc production line, the coating which is obtained by immersing the
pretreated steel strip in a molten zinc solution containing aluminum and magnesium.
The mass percentage of magnesium in the molten zinc-magnesium alloy solution is 1.0
~ 2.0%; the mass percentage of aluminum is 0.8 ~ 3.0%; the mass percentage of other
trace control elements is less than 1%; the remaining components are zinc.
3.4 Hot-dip zinc-aluminum-magnesium alloy coating (XM)
On a hot-dip zinc production line, the coating which is obtained by immersing the
pretreated steel strip in a molten zinc solution containing aluminum and magnesium.
The mass percentage of magnesium in the molten zinc-aluminum-magnesium alloy
solution is 2.0 ~ 4.0%; the mass percentage of aluminum is 5.0 ~ 7.0%; the mass
percentage of other trace control elements is less than 1%; the remaining components
are zinc.
3.5 Interstitial free steels
Interstitial-free steel is a type of steel in which an appropriate amount of titanium or
niobium is added to ultra-low carbon steel, so that the carbon and nitrogen interstitial
atoms in the steel are completely fixed into carbon and nitride, meanwhile there are no
interstitial atoms in the steel.
3.6 High strength interstitial free steels (Y)
The plastic strain ratio (r value) and strain hardening index (n value) of steel are
improved, by controlling the chemical composition of the steel. Due to the solid
solution strengthening of the elements in the steel and the interstitial-free microstructure,
this steel has both high strength and very good cold forming properties, so it is often
used to make complex parts that require deep drawing.
3.7 Bake hardening steels (B)
A certain amount of solid solution carbon and nitrogen atoms are retained in low carbon
steel or ultra-low carbon steel, meanwhile solid solution strengthening elements such
as phosphorus and manganese may be added, to improve the strength. After processing
and forming, after baking at a certain temperature, the yield strength of the steel further
increases due to age hardening.
3.8 High strength low alloy steels (LA)
In low carbon steel or ultra-low carbon steel, micro-alloying elements such as niobium,
titanium, vanadium are added singly or in combination, to form carbonitride particles
and precipitate for strengthening. At the same time, higher strength is obtained through
the refinement of grains by micro-alloying elements.
3.9 Dual phase steels (DP)
The microstructure of steel is mainly ferrite and martensite, wherein the martensite
structure is dispersed in an island shape on the ferrite matrix. Duplex steel has a low
yield-to-strength ratio, high work hardening index, bake hardening value, which is one
of the preferred materials for structural parts.
3.10 Transformation induced plasticity steels (TR)
The microstructure of steel is ferrite, bainite, retained austenite, of which the content of
retained austenite is at least 5%. During the forming process, retained austenite can
transform into martensite structure, which has high work hardening rate, uniform
elongation, tensile strength. Compared with dual-phase steel with the same tensile
strength, it has higher elongation.
3.11 Complex phase steels (CP)
The microstructure of steel is mainly ferrite and/or bainite. On the ferrite and/or bainite
matrix, a small amount of martensite, retained austenite and pearlite are usually
distributed. By adding micro-alloying elements Ti or Nb, the effect of grain refinement
or precipitation strengthening is achieved. This steel has very high tensile strength.
Compared with dual-phase steel with the same tensile strength, its yield strength is
significantly higher. This steel has a high energy absorption capacity and a high residual
strain capacity.
3.12 Quenching and partitioning steel (QP)
Steel is a type of ultra-high-strength steel with high formability, as produced using the
quenching-partitioning process. The microstructure of steel is composed of a multi-
phase composite of martensite + ferrite + retained austenite. By utilizing the ultra-high
strength brought by martensite and the transformation-induced plasticity (TRIP) effect
of retained austenite, it can obtain better formability than traditional ultra-high-strength
steel. QP steel is age-free, which has a medium yield-to-strength ratio and high work-
hardening properties; it is suitable for vehicle frame parts and safety parts, which have
relatively complex shapes and high strength requirements.
3.13 Dual phase high ductility steels (DH)
The microstructure of steel is mainly composed of ferrite, martensite, a small amount
of retained austenite and bainite. Compared with DP steel of the same strength level, it
6.2 The allowable deviations in size and shape of steel sheet and strip, which is
produced from cold-rolled substrates, shall comply with the provisions of Q/BQB 401.
The thickness tolerance of steel sheet and strip which has a designation of
S550GD+Z/ZM/XM shall comply with the requirements of Table 4 in Q/BQB 401-
2023 (specifying minimum yield strength 260 MPa ~ < 360 MPa); the maximum
allowable deviation of unevenness shall comply with the requirements of Table 11 in
Q/BQB 401-2023 (specifying minimum yield strength 260 MPa ~ < 360 MPa). The
allowable deviations of thickness and unevenness of steel sheet and strip, which is
produced from hot-rolled pickled substrates, shall comply with the provisions of
Appendix A (Normative); the allowable deviations of width, length and other shapes
shall comply with the provisions of Q/BQB 401.
6.3 Steel sheets are usually delivered according to theoretical weight. However, they
may also be delivered according to actual weight. The calculation method of the
theoretical weight of steel sheets shall comply with the provisions of Appendix B
(Normative). Steel strips are usually delivered according to actual weight.
7 Technical requirements
7.1 Chemical composition
The chemical composition (smelting analysis) of steel shall comply with the provisions
of Appendix C. The allowable deviation of the chemical composition of finished steel
sheet and strip shall comply with the provisions of GB/T 222. If the buyer has special
requirements for chemical composition, these shall be negotiated when ordering.
7.2 Smelting methods
The steel used for steel sheet and strip is smelted in an oxygen converter.
7.3 Delivery status
Normally, steel sheet and strip are delivered after being hot-dip galvanized and
smoothed.
7.4 Mechanical properties
7.4.1 Tables 5 ~ 15 specify the shapes and directions of tensile specimens applicable to
steel sheet and strip. Unless otherwise specified, tensile specimens shall be coated
specimens.
7.4.2 For steel sheet and strip with designations of DC51D+Z, DC51D+ZF,
DC51D+ZM, DC51D+XM, DD51D+Z, DD51D+ZF, DC52D+Z, DC52D+ZF,
DC52D+ZM, DC52D+XM in Table 5, it shall be guaranteed that within 1 month from
the date of completion of manufacturing, the mechanical properties of the steel sheet
and strip comply with the provisions of Table 5. For other designations of steel sheet
and strip in Table 5, it shall be guaranteed that within 6 months from the date of
completion of manufacturing, the mechanical properties of steel sheet and strip shall
comply with the requirements in Table 5.
Note: The issuance date in the product inspection document is usually specified as the
manufacturing completion date of the product.
7.4.3 For the steel sheet and strip of the designations specified in Table 6, it shall be
ensured that the mechanical properties of the steel sheet and strip comply with the
requirements of Table 6, within 3 months from the date of completion of manufacturing.
7.4.4 For the steel sheet and strip of the designations specified in Table 7 and Table 8,
it shall be ensured that the mechanical properties of the steel sheet and strip comply
with the requirements in the corresponding tables, within 6 months from the date of
completion of manufacturing.
7.4.5 For the steel sheet and strip of the designations specified in Table 9, as for the hot-
dip zinc products (Z, ZM, XM), it shall ensure that within 6 months from the date of
completion of product manufacturing, the mechanical properties of the steel sheet and
strip comply with the requirements of Table 9; as for hot-dip zinc iron alloy products
(ZF), it shall ensure that within 3 months from the date of completion of product
manufacturing, the mechanical properties of steel sheet and strip meet the requirements
of Table 9.
7.4.6 For the steel sheet and strip of the designations specified in Table 10, it shall be
ensured that the mechanical properties of the steel sheet and strip comply with the
provisions of Table 10, within 6 months from the date of completion of manufacturing.
7.4.7 For the steel sheet and strip of the designations specified in Table 11, Table 12,
Table 13, Table 14, Table 15, it shall be ensured that the mechanical properties of the
steel sheet and strip comply with the requirements of corresponding tables, within 6
months from the date of completion of manufacturing.
7.4.8 When steel sheet and strip are supplied as specified parts, the supplier and the
buyer can agree on a mechanical property range, that meets the processing requirements
of the parts, as the acceptance criterion. At this time, the mechanical properties specified
in Tables 5 ~ 15 will no longer be used as the basis for goods delivery.
7.4.9 Due to the influence of aging, the mechanical properties of steel sheet and strip
will deteriorate with the extension of storage time. For example, the yield strength and
tensile strength will increase, the elongation after fracture will decrease, the formability
will deteriorate, tensile strain marks will appear, etc.; therefore, it is recommended that
users use it as soon as possible.
7.5 Tensile strain marks
7.5.1 The requirements for tensile strain marks only apply to steel sheet and strip, which
improve the adhesion of the paint layer during subsequent processing and protect the
coating.
7.9.6 If subsequent processing requires phosphating, ceramicizing, zirconating or
painting, it is not recommended to adopt passivation treatment.
7.9.7 For surface treatment methods involving oil coating, the purchaser shall ensure
that the cleaning agent used in its degreasing equipment will not damage the coating
quality.
7.9.8 If the user specifies the non-surface treatment method (U), it shall be clearly stated
in the contract. If this type of product produces surface defects such as white rust,
scratches, friction marks during handling, storage, use, the supplier will not be