Wear-resistant Steel Plate Testing

Wear-resistant steel plate inspection mainly conducts scientific testing and analysis on the Brinell hardness and Rockwell hardness, impact toughness, tensile properties, chemical composition analysis, metallographic structure examination and wear resistance testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Brinell hardness and Rockwell hardness: The hardness of the wear-resistant steel plate is its core performance indicator. The Brinell hardness (HBW) is applicable to the softer or medium-hardness plates, and the hardness values are calculated through the indentation diameters; the Rockwell hardness (HRC) is more suitable for the high-hardness wear-resistant steel plates (such as the materials with the hardness greater than HBW450), with the fast measurement and little damage to the surfaces. The combination of the two can comprehensively evaluate the ability of the material surface to resist the plastic deformation.

Impact toughness (Akv): The key indicator for evaluating the ability of the wear-resistant steel plate to resist the brittle fracture under the dynamic loads or low-temperature environments. Usually at the specified temperatures (such as -20 ℃ and -40 ℃), the Charpy V-notch specimens are used for the pendulum impact testing. The excellent impact toughness ensures that the plate will not produce the catastrophic fragmentation when bearing the strong impacts and wear, and is crucial for the construction machinery and mining equipment.

Tensile properties: Including the yield strength (Rp0.2), tensile strength (Rm) and elongation after fracture (A). The wear-resistant steel plates usually have the very high yield and tensile strengths, but the elongations are relatively low. The tensile property testing can verify whether the basic mechanical properties of the material meet the standard requirements, and indirectly reflect its processing forming ability and safety margins.

Chemical composition analysis: Through the means such as the spectrometers and carbon-sulphur analysers, the contents of the elements such as the carbon (C), manganese (Mn), silicon (Si), chromium (Cr), molybdenum (Mo), nickel (Ni) and boron (B) in the steel plate are precisely determined. The chemical composition is the foundation determining the final hardness, toughness, hardenability and welding performance of the steel plate, and is the primary basis for judging the consistency of the material designations and quality.

Metallographic structure examination: The microstructures of the steel plate, such as the morphologies, distributions and grain sizes of the martensite, bainite and retained austenite, are observed with the optical microscope or scanning electron microscope. The ideal wear-resistant structures are usually the uniform tempered martensite or lower bainite. This testing can reveal whether the heat treatment process is appropriate, and assist in analysing the wear mechanisms and failure causes.

Wear resistance testing: The special test simulating the actual working conditions. The common methods include the rubber wheel abrasive wear testing (ASTM G65) and pin-on-disc wear testing. By measuring the mass losses or volume losses of the specimens under the specified conditions, the relative wear resistances of the steel plates of the different materials or processes are quantitatively compared, providing the direct basis for the material selection.

Testing Scope

NM series wear-resistant steel plates: Covering the designations from NM300 to NM600 conforming to the GB/T 24186 standard, as well as the ultra-high-strength wear-resistant steels above the NM600 grade developed by the enterprises. The testing needs to cover the property uniformity of the full-thickness cross-sections, especially the hardness gradient changes from the surfaces to the cores.

High-hardness alloy wear-resistant steel plates: Such as the chromium-molybdenum alloy steels with the hardness reaching HBW500-700 and the high-carbon high-chromium cast iron clad steel plates. The testing emphasis is on the extremely high surface hardness, the bonding strength between the base plates and wear-resistant layers, and the related properties preventing the peeling during the use.

Low-alloy high-strength wear-resistant steel plates: The steel plates that have the good welding and forming properties while ensuring a certain wear resistance, commonly used as the structural parts and wear-resistant parts at the same time. The testing needs to balance the hardness, strength, plasticity and toughness indicators.

Wear-resistant surfacing clad steel plates: The clad plates made by surfacing the wear-resistant alloy layers on the low-carbon steel substrates. The testing scope includes the mechanical properties of the substrates, chemical compositions and hardnesses of the surfacing layers, bonding states of the interfaces (such as the bending testing and ultrasonic flaw detection), as well as the crack resistance of the surfacing layers.

Imported wear-resistant steel plates: Such as the Swedish HARDOX, German DILLIDUR and Japanese JFE-EH series. The testing needs to carry out the conformity verification according to their original technical conditions or the relevant international standards (such as the SSAB, DIN and JIS), and focus on the performance benchmarking with the domestic standards.

End-use application components: The testing of the formed wear-resistant components, such as the excavator bucket blade plates, crusher lining plates and mining chute lining plates. The testing needs to consider the actual stressed states of the components, possibly involving the hardness distributions of the working surfaces, impact energies of the key areas, and the performance degradation of the welding heat-affected zones.

Testing Methods

Hardness testing method: The Brinell hardness testing is carried out in accordance with GB/T 231.1, using the cemented carbide ball indenters of the specified diameters to apply the test forces; the Rockwell hardness testing is carried out in accordance with GB/T 230.1, using the diamond cones or steel ball indenters. Before the testing, the tested surfaces need to be ground to be flat and smooth, the multi-point testing is carried out and the average values are taken, and the indentation positions are recorded to evaluate the uniformity.

Charpy pendulum impact testing method: In accordance with GB/T 229, the standard V-notch specimen is placed on the supports of the impact testing machine, and the pendulum is released to break it, reading the absorbed energy (KV2). The test temperatures are strictly controlled, and the low-temperature baths are usually needed to cool the specimens. This method is the standard method of evaluating the ductile-brittle transition characteristics of the material.

Room-temperature tensile testing method: In accordance with GB/T 228.1, the standard tensile specimens are prepared, and the axial tensile forces are applied at the specified rates on a universal material testing machine until the fracture. Through the stress-strain curves or extensometers, the yield strength, tensile strength and elongation after fracture are precisely determined, and the gauge lengths of the specimens need to strictly conform to the standards.

Spectrometry analysis method: The spark discharge atomic emission spectrometry (OES) is used for the fast non-destructive analysis of the multi-element compositions except C and S in the steel plate; the infrared absorption method is used for the precise determination of the carbon and sulphur contents. Before the analysis, the instrument needs to be calibrated with the standard samples, and the testing is carried out on the clean and flat metal excitation surfaces.

Macro and micro metallographic examination method: In accordance with GB/T 13298. The macro examination can observe whether there are the defects such as the blowholes, slag inclusions and cracks on the steel plate cross-sections; the micro examination needs to cut the specimens, and after the mounting, grinding, polishing and etching (commonly using the 4% nitric acid alcohol solution), observe the structure morphologies, measure the grain sizes and non-metallic inclusion grades under a metallographic microscope.

Wear testing simulation method: In the rubber wheel abrasive wear testing (ASTM G65), the specimen is pressed on the rotating rubber wheel, while the artificial quartz sand of the specified grain sizes is fed into the contact area, and the wear amount is calculated through the specimen weight losses. In the pin-on-disc wear testing (ASTM G99), the stationary pin specimen rubs against the rotating wear disc, and the different abrasives and media can be selected, with the higher flexibility.

Testing Standards

Domestic Standards:

1. GB/T 24186, NM series high strength abrasion resistant steel plates

2. GB/T 231.1, Metallic materials — Brinell hardness test — Part 1: Test method

3. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

4. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

5. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

6. GB/T 13298, Inspection methods of microstructure for metals

7. GB/T 232-2010, Metallic materials — Bend test method

International Standards:

1. ASTM G65, Standard test method for measuring abrasion using the dry sand/rubber wheel apparatus

2. ASTM G99, Standard test method for wear testing with a pin-on-disk apparatus

3. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

4. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Brinell/Rockwell/Vickers hardness tester: The core equipment of the hardness testing. The modern hardness testers mostly adopt the electronic loading and automatic measurement of the indentation diagonals or depths, and the data can be directly output and stored. Some models are equipped with the camera systems, which can automatically locate and measure the indentations, greatly improving the testing efficiency and accuracy, especially suitable for the batch testing.

Pendulum impact testing machine: Used to carry out the Charpy impact testing. The equipment needs to be regularly verified for its energy losses and the zero-return precision of the pendulum idling. The models equipped with the automatic sample feeding devices and low-temperature baths can realize the automatic low-temperature cooling, transfer and testing of the specimens, minimizing the human errors and temperature fluctuation effects.

Microcomputer-controlled electro-hydraulic servo universal testing machine: The main equipment for the mechanical property tests such as the tensile, bending and compression. The electro-hydraulic servo closed-loop control systems are adopted, realizing the high-precision control and measurement of the loads and displacements. Equipped with the high and low temperature environmental chambers, the mechanical property testing of the material at the different temperatures can also be carried out.

Direct-reading spectrometer and carbon-sulphur analyser: The direct-reading spectrometer (OES) excites the sample through the electric arcs to generate the characteristic spectra for the multi-element quantitative analysis, with the fast speed and high precision. The carbon-sulphur analyser usually adopts the high-frequency induction combustion-infrared absorption principle, specially used for the precise determination of the contents of the two key elements carbon and sulphur in the steel.

Optical/digital metallographic microscope and scanning electron microscope (SEM): The optical metallographic microscope is the basic tool for observing the microstructures, and the digital models are convenient for the image acquisition and measurement. The scanning electron microscope can carry out the observation at the higher magnifications (tens of thousands to hundreds of thousands of times), and combined with the energy dispersive spectrometers (EDS), carry out the qualitative and semi-quantitative analysis of the micro-area compositions, used for the in-depth research of the wear mechanisms.

Abrasive wear testing machine: The dedicated dry sand/rubber wheel wear testing machine is strictly designed according to the standards, ensuring the stable and controllable parameters such as the abrasive flow rates, rubber wheel hardness and loading pressures. The pin-on-disc wear testing machines usually have the more integrated functions, and can replace the friction pairs, adjust the rotational speeds and loads, and monitor the friction coefficients in real time, suitable for the simulation of the various wear working conditions.