GB/T 24180-2020 English PDF (GB/T24180-2020)

GB/T 24180-2020: Cold-reduced Electrolytic Chromium / Chromium Oxide Coated Steel Sheet and Strip
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GB/T 24180-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.140.50
H 46
Replacing GB/T 24180-2009
Cold-reduced Electrolytic Chromium / Chromium
Oxide Coated Steel Sheet and Strip
ISSUED ON: JUNE 2, 2020
IMPLEMENTED ON: DECEMBER 1, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 5 
2 Normative References ... 5 
3 Terms and Definitions ... 7 
4 Classification and Codes, Designations and Labels ... 7 
5 Order Content ... 8 
6 Dimensions, Shapes and Weights ... 8 
7 Technical Requirements ... 16 
8 Test Methods ... 21 
9 Inspection Rules ... 23 
10 Packaging, Marking and Quality Certificate ... 23 
11 A Comparison of Similar Quenching and Tempering Degree Codes between
this Standard and Relevant International Standards ... 24 
Appendix A (normative) Rebound Test Method for Secondary Cold-reduced
Sheet ... 25 
Appendix B (normative) Test Method for the Amount of Metal Chromium
Coating on the Surface of Chromium Coated Sheet ... 27 
Appendix C (normative) Test Method for the Amount of Chromium Oxide
Coating on the Surface of Chromium Coated Sheet ... 35 
Appendix D (normative) Conversion Table of HR15TSm and HR30TSm ... 42 
Appendix E (informative) A Comparison of Quenching and Tempering Degree
Codes (or steel grade codes) between This Standard and Relevant
International Standards ... 43 
Bibliography ... 44 
Cold-reduced Electrolytic Chromium / Chromium
Oxide Coated Steel Sheet and Strip
1 Scope
This Standard specifies the classification and codes, designations and labels,
dimensions, shapes, weights, technical requirements, test methods, inspection rules,
packaging, marking and quality certificate of cold-reduced electrolytic chromium /
chromium oxide coated steel sheet and strip.
This Standard is applicable to primary cold-reduced electrolytic chromium / chromium
oxide coated steel sheet and strip with a nominal thickness of 0.14 mm ~ 0.80 mm, as
well as secondary cold-reduced electrolytic chromium / chromium oxide coated steel
sheet and strip with a nominal thickness of 0.12 mm ~ 0.36 mm (hereinafter referred
to as steel sheet and strip).
2 Normative References
The following documents are indispensable to the application of this document. In
terms of references with a specified date, only versions with a specified date are
applicable to this document. In terms of references without a specified date, the latest
version (including all the modifications) is applicable to this document.
GB/T 222 Permissible Tolerances for Chemical Composition of Steel Products
GB/T 223.5 Steel and Iron - Determination of Acid-soluble Silicon and Total Silicon
Content - Reduced Molybdosilicate Spectrophotometric Method
GB/T 223.9 Iron Steel and Alloy - Determination of Aluminum Content - Chrome Azurol
S Photometric Method
GB/T 223.11 Iron, Steel and Alloy - Determination of Chromium Content - Visual
Titration or Potentiometric Titration Method
GB/T 223.18 Methods for Chemical Analysis of Iron, Steel and Alloy - The Sodium
Thiosulfate Separation Iodimetric Method for the Determination of Copper Content
GB/T 223.23 Iron, Steel and Alloy - Determination of Nickel Content - The
Dimethylglyoxime Spectrophotometric Method
GB/T 223.26 Iron, Steel and Alloy - Determination of Molybdenum Content - The
Thiocyanate Spectrophotometric Method
GB/T 223.29 Iron, Steel and Alloy - Determination of Lead Content - Carrier
Precipitation-xylenol Orange Spectrophotometric Method
GB/T 223.31 Iron, Steel and Alloy - Determination of Arsenic Content - Distillation-
molybdenum Blue Spectrophotometric Method
GB/T 223.59 Iron, Steel and Alloy - Determination of Phosphorus Content - Bismuth
Phosphomolybdate Blue Spectrophotometric Method and Antimony
Phosphomolybdate Blue Spectrophotometric Method
GB/T 223.64 Iron, Steel and Alloy - Determination of Manganese Content - Flame
Atomic Absorption Spectrometric Method
GB/T 228.1-2010 Metallic Materials - Tensile Testing - Part 1: Method of Test at Room
Temperature
GB/T 230.1 Metallic Materials - Rockwell Hardness Test - Part 1: Test Method
GB/T 247 General Rule of Package Mark and Certification for Steel Plates (sheets)
and Strips
GB/T 708 Dimension, Shape, Weight and Tolerance for Cold-rolled Steel Plate
GB/T 2520 Cold-reduced Electrolytic Tinplate
GB/T 2523 Measuring Method of Surface Roughness and Peak Count for Cold-rolled
Metal Sheet (strip)
GB/T 4336 Standard Test Method for Spark Discharge Atomic Emission Spectrometric
Analysis of Carbon and Low-alloy Steel (routine method)
GB/T 6730.79 Iron Ores - Determination of Cadmium Content - Hydride Generation -
Atomic Fluorescence Spectrometric Method
GB/T 8170 Rules of Rounding off for Numerical Values and Expression and Judgement
of Limiting Values
GB/T 16597 Analytical Methods of Metallurgical Products - General Rule for X-ray
Fluorescence Spectrometric Methods
GB/T 17505 Steel and Steel Products - General Technical Delivery Requirements
GB/T 20066 Steel and Iron - Sampling and Preparation of Samples for the
Determination of Chemical Composition
GB/T 20123 Steel and Iron - Determination of Total Carbon and Sulfur Content -
Infrared Absorption Method after Combustion in an Induction Furnace (routine method)
GB/T 20125 Low-alloy Steel - Determination of Multi-element Contents - Inductively
Coupled Plasma Atomic Emission Spectrometric Method
6.1.3 In terms of steel strip, the dimensions are expressed in thickness  width in
millimeters (mm). The letter C may also be added after the number indicating the rolling
width.
Example: 0.26  832C.
6.1.4 The inner diameter of steel coils is 406 mm, 420 mm, 450 mm or 508 mm.
6.2 Permissible Deviations for Dimensions
6.2.1 Thickness
6.2.1.1 The thickness of steel sheet and strip shall satisfy the following requirements:
a) The deviation of thickness measured at the centerline position in the width
direction from the nominal thickness shall not exceed ± 5% of the nominal
thickness.
b) The deviation of thickness measured at a position not less than 6 mm from
the side in the width direction from the nominal thickness is -8% ~ +5% of the
nominal thickness.
c) When the quantity of delivery is greater than 10,000 pieces of steel sheet (or
steel coils of equal length), the permissible deviation between the average
thickness of all steel sheets and the nominal thickness shall not exceed ± 2%
of the nominal thickness.
6.2.1.2 The measurement of thickness is carried out with a micrometer with an
accuracy of 0.001 mm. The measurement result shall be rounded off to 0.001 mm. The
thickness measurement position is any point not less than 6 mm from the side in the
width direction.
6.2.2 Thin edge
6.2.2.1 Thin edge is the thickness change of steel sheet and strip along the width
direction. It is characterized by thickness reduction occurring near the edge of steel
sheet and strip. The deviation between the thickness measured at 6 mm from both
sides of the width direction of the steel sheet and strip and the actual thickness
measured along the centerline of the width direction of the steel sheet and strip shall
not exceed 6.0% of the actual thickness measured at the centerline position.
6.2.2.2 In terms of the measurement of thin edge, use a micrometer to measure 3
points on the same straight line perpendicular to the rolling direction. The 3 measured
points are located along the straight line and respectively at the center of the width and
6 mm from the two rolling width cutting edges.
6.2.3 Width
Figure 9 -- Sampling Location
8.3 For the hardness test, a sample is usually determined at 3 points. When the range
of the 3 points (namely, the difference between the maximum value and the minimum
value) is greater than 1.0, then, 2 additional points shall be added to the determination.
Then, remove the maximum value and the minimum value of the 5 points; calculate
the average value of the 3 points as the test value. When objections are raised to the
determination result, remove the chromium-plated coating, then, re-determine it. If
objections are raised to the determined value due to the affect of surface roughness,
grind the sample surface, then, re-determine it.
8.4 When the nominal thickness of steel sheets and strips is less than 0.20 mm, the
determination of hardness shall adopt HR15TSm, then, convert it to HR30TSm in
accordance with the stipulations of Appendix D.
9 Inspection Rules
9.1 The inspection and acceptance inspection of steel sheets and strips shall be
carried out by the supply-side’s quality inspection department.
9.2 Steel sheets and strips shall be inspected in batches. Each inspection batch shall
be constituted of steel sheets or strips of the same designation, the same specification
and the same surface status. The weight of each batch shall not exceed 60 t.
9.3 The sampling size and sampling location of each batch of steel sheets and strips
shall comply with the stipulations of Table 8.
9.4 The re-inspection of steel sheets and strips shall comply with the stipulations of
GB/T 17505.
9.5 The inspection results of chemical composition and mechanical properties shall be
rounded off through the value rounding-off and comparison method. The value
rounding-off rules shall comply with the stipulations of GB/T 8170.
10 Packaging, Marking and Quality Certificate
The packaging, marking and quality certificate of steel sheets and strips shall comply
with the stipulations of GB/T 247.
Appendix A
(normative)
Rebound Test Method for Secondary Cold-reduced Sheet
A.1 Principle
Firstly, measure the thickness of the rectangular test piece. Make a 180° bend around
the cylindrical mandrel, then, loosen it to measure the rebound angle. It provides a
simple and convenient method for the evaluation of the yield strength of secondary
cold-reduced sheet.
A.2 Sample
From each piece of sample steel sheet of secondary cold-reduced electrolytic
chromium coated sheet, along the rolling direction at the edge and in the middle, take
two 200 mm  25 mm samples. The distance between the edge sample and the edge
of the steel sheet is not less than 25 mm.
A.3 Test
A.3.1 Test instrument
Rebound tester.
A.3.2 Test Procedures
A.3.2.1 Measure the thickness of the sample, accurate to 0.001 mm.
A.3.2.2 Insert the sample into the rebound tester. Use moderate pressure to tighten
the clamping screw; fix the sample in the test position.
A.3.2.3 Stably swing the builder arm, so that the sample is bent 180° around the axis.
A.3.2.4 Return the builder arm to the starting position. Along the sample, directly
observe, read and record the rebound angle. Then, remove the sample.
A.3.2.5 In accordance with the measured value of the sample thickness and the
rebound angle, on the nomogram matched with the rebound tester, measure the
rebound index (SBI).
A.3.2.6 In order to ensure the accuracy of the test results, a standard sample or
another reference rebound tester shall be used to calibrate the rebound tester being
used.
A.4 Test Result Report
dissolve it in 100 mL of deionized water.
B.4.1.2.8 NaNO2 solution (2 g/L): weigh-take 0.2 g of analytically pure sodium nitrite;
dissolve it in 100 mL of deionized water.
B.4.1.2.9 Urea solution (200 g/L): weigh-take 20 g of analytically pure urea; use
deionized water to dissolve it and reach a constant volume of 100 mL.
B.4.1.2.10 Diphenylcarbazide solution (2.5 g/L): weigh-take 0.25 g of
diphenylcarbazide; dissolve it in 100 mL of analytically pure acetone. This reagent
should be prepared for immediate use.
B.4.1.2.11 Hexavalent chromium standard solution (1,000 mg/L): a commercially
available national standard solution.
B.4.1.2.12 Hexavalent chromium standard solution (10 mg/L): use a transfer pipette to
accurately dispense 10.0 mL of hexavalent chromium standard solution (1,000 mg/L);
reach a constant volume in a 1,000 mL volumetric flask.
B.4.1.3 Operating procedures
B.4.1.3.1 Add 25 mL of NaOH solution (40 g/L) to a conical flask. Add 1 drop of
phenolphthalein (1%) indicator; use H2SO4 solution (1+3) to titrate it, until the red color
of the indicator just fades. Then, record the volume of the consumed sulfuric acid
VH2SO4 (mL).
B.4.1.3.2 Take an appropriate amount of NaOH solution (300 g/L); on an electric
heating plate or electric furnace, heat it up to 90 °C. Then, put the sample into it.
Maintain it immersed and heated for 5 min ~ 10 min. Dissolve it to remove the
chromium oxide coating on the surface of the sample.
B.4.1.3.3 Take out the sample which has the chromium oxide coating peeled off. Put it
into the electrolysis device as shown in Figure B.1. Take the sample as an anode. Add
25 mL of NaOH solution (40 g/L) as the electrolytic solution. At the current density of
0.4 mA/cm2 ~ 2.5 mA/cm2, carry out electrolysis at room temperature. When small
bubbles emerge from the sample, stop the electrolysis.
B.4.1.3.4 Transfer all the electrolyte to a 100 mL volumetric flask. Rinse the sample,
the electrode and electrolytic cell. Incorporate all the rinsing fluid into the volumetric
flask. Add the H2SO4 solution (1+3) VH2SO4 (mL) obtained through the test in B.4.1.3.1.
Use deionized water to reach a constant volume to the scale, then, shake it well.
NOTE: since alkali will corrode glass container, and the dispensed test solution consumes
about 0.5 mL of H2SO4 solution (1+3), it is quite difficult to adjust the acidity.
Meanwhile, neutral solution makes it easy for dispensing and rinsing.
B.4.1.3.5 From the above-mentioned constant-volume electrolyte, dispense 20.0 mL
The test result shall be calculated in accordance with Formula (B.2).
Where,
WCr---the content of metal chromium, expressed in (mg/m2);
t---the electrolysis time, expressed in (s);
I---the electrolysis current, expressed in (mA);
A---the area of electrolytic stripping, expressed in (cm2)...