Q/BQB 420-2023 PDF English
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Q/BQB 420-2023: PDF in English (QBQB 420-2023) 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
responsible for the corresponding product quality.
7.9.9 The available surface treatments are as follows:
7.9.9.1 Chromic acid passivation (C) and chromium-free passivation (organic) (C5)
This surface treatment reduces white rust on the surface of the product during
transportation and storage. During chromium-free passivation treatment, the hexavalent
chromium substances in the passivation film that are harmful to human health are
restricted.
7.9.9.2 Chromic acid passivation + oil coating (CO) and chromium-free
passivation (organic) + oil coating (CO5)
This surface treatment can further reduce the formation of white rust on the surface of
the product during transportation and storage. During chromium-free passivation
treatment, the hexavalent chromium substances in the passivation film that are harmful
to human health are restricted.
7.9.9.3 Chrome-free and fingerprint-resistant (N5)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage, while the fingerprint-resistant film can improve the
resistance of electronic or electrical products to sweat stains. The chromium-free
fingerprint-resistant film limits hexavalent chromium substances that are harmful to
human health.
7.9.9.4 Self-lubricating (SL)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage, meanwhile the self-lubricating film can better improve the
formability of the steel sheet.
7.9.9.5 Inorganic solid lubrication (T)
The solid lubricating film produced by this surface treatment can better improve the
formability of the steel sheet.
7.9.9.6 Chrome-free, highly conductive, fingerprint-resistant (NE)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage, meanwhile limits chromium elements that are harmful to
human health. At the same time, the highly conductive and fingerprint-resistant film
can further improve the grounding performance of parts, thereby improving the EMC
performance of electronic or electrical products (electromagnetic compatibility).
7.9.9.7 Chrome-free self-lubricating (SL2)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage, meanwhile limits chromium elements that are harmful to
human health. At the same time, the self-lubricating film can better improve the
formability of the steel sheet and further enhance the corrosion resistance of the parts.
7.9.9.8 Chromium-free inorganic passivation (IC)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage, meanwhile limits chromium elements that are harmful to
human health. At the same time, the inorganic treatment film can further improve the
processing blackening resistance and coating performance of the steel sheet.
7.9.9.9 Chrome-free inorganic passivation + oiling (ICO)
This surface treatment can further reduce the white rust produced on the surface of the
product during transportation and storage, meanwhile limits chromium elements that
are harmful to human health. At the same time, the inorganic treatment film can further
improve the processing blackening resistance and coating performance of the steel sheet.
7.9.9.10 Inorganic self-lubricating (SW)
This surface treatment can reduce white rust on the surface of zinc, aluminum,
magnesium products during transportation and storage, meanwhile limits chromium
elements that are harmful to human health. At the same time, the inorganic self-
lubricating film can improve the forming performance of steel sheets and enhance the
appearance quality of formed parts.
7.9.9.11 Easy to process self-lubricating (EW)
This surface treatment is an easy-to-process surface nano-modification treatment with
the characteristics of high lubrication, good adhesion, and good coating. It can
effectively match the application of efficient and environmentally friendly processing
technology for molding, connection, coating.
7.9.9.12 Oiling (O)
This surface treatment can reduce white rust on the surface of the product during
transportation and storage. The anti-rust oil applied is generally not used as rolling oil
and stamping lubricant for subsequent processing.
7.9.9.13 Untreatment (U)
There is no surface treatment such as chemical passivation, oiling, fingerprint-resistant
film; this type of product is prone to surface defects such as white rust, scratches,
friction marks during handling, storage, and use.
7.10 Surface quality
7.10.1 Steel sheet and strip shall comply with the requirements in Table 20, according
to surface quality.
Table 20
Grade Characteristics
FB Small corrosion spots, dark spots, band marks, small chemical passivation treatment defects, small zinc particles are allowed.
FC The better side must not have corrosion spots, but slight indentations, scratches, zinc waves, slight surface passivation defects are allowed in a small area. The other side shall maintain at least the FB surface.
FN
On the better side, on the basis of FC, visual defects such as zinc dust, zinc slag, bright spots, stains, color
differences, dirt, stripes, roller marks, scratches, etc. are further restricted without affecting the use of bare
sheets. The other side shall maintain at least FC surface.
FD
The better side further limits defects on the basis of FC, that is, the better side only allows slight indentations,
scratches, zinc waves, slight surface passivation defects in a small range, meanwhile it does not affect the
use of bare sheets or general coating appearance quality. The other side shall maintain at least FB surface.
7.10.2 The edges of untrimmed steel strips are allowed to have tiny cracks in the zinc
layer and white edges that do not affect the user's blanking and stamping use.
7.10.3 For steel strips, since there is no chance to cut off the defective part of the strip,
the steel strip is allowed to be delivered with defects; however, the defective part shall
not exceed 3% of the total length of each roll. If the user has special requirements, they
can be negotiated when ordering.
7.10.4 For ZM and XM products, when the coating weight is more than 140/140 g/m2,
the surface quality may not be in accordance with Table 20, but determined through
negotiation between the supplier and the buyer when ordering.
7.11 Corrosion resistance test
7.11.1 The corrosion resistance test is evaluated by the neutral salt spray resistance test.
The neutral salt spray resistance time and judgment criteria of different surface
treatment products shall comply with Table 21. If there are special requirements for the
8.4 The r value is calculated at 15% strain. When the maximum force plastic elongation
(Ag) is less than 15%, the calculation is based on the strain value corresponding to Ag.
The n value is calculated within the strain range of 10% ~ 20%. When Ag is less than
20% but not less than 12%, the calculated strain range is 10% to Ag. When Ag is less
than 12%, the strain hardening index shall be reported (nAgt = εp, Agt) as the true strain
value (εp, Agt), which is calculated in accordance with the maximum force total
elongation rate (Agt).
8.5 The weight of the coating can be detected by gravimetric method, offline X-ray
fluorescence method, online X-ray fluorescence method. In case of dispute, the
gravimetric method shall be used. When using the gravimetric method, sampling shall
be carried out according to the position shown in Figure 1, meanwhile the area of a
single specimen shall not be less than 1200 mm2. When using the offline X-ray
fluorescence method, sampling shall be carried out according to the position shown in
Figure 1, meanwhile the area of a single specimen shall not be less than 314 mm2. When
the online X-ray fluorescence method is used, the coating weight detection is performed
on the production line, without sampling.
8.6 Steel sheet and strip shall be inspected in batches. Each inspection batch consists of
steel products of the same designation, the same zinc layer weight, the same
specifications, the same surface structure and surface treatment, not exceeding 30 tons.
For steel strips weighing more than 30 tons, each steel coil forms an inspection batch.
8.7 The inspection items, number of specimens, sampling methods, test methods for
each batch of steel sheet and strip shall comply with the provisions of Table 22.
8.8 The supplier may use different inspection and test methods for acceptance testing.
In the event of a dispute, the inspection and test methods and relevant technical
requirements specified in this document shall be used for testing.
8.9 If a certain test result does not meet the requirements of this document, double the
number of specimens will be taken from the same batch for reinspection of the
unqualified item. If the reinspection results (including all indicators required for the
item test) are qualified, the entire batch will be qualified. If even one index in the
reinspection results (including all indicators required for the test of the item) fails, the
reinspection will fail. If the reinspection fails, the individual pieces that have been tested
and have inconsistent test results cannot be accepted; however, the individual pieces in
the batch of materials that have not been tested can be resubmitted for testing and
acceptance one by one.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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