5 MINUTES TO UNDERSTAND HARDNESS OF ALLOY WEAR PLATE

Alloy wear plate mainly consists of base plate and wear layer. The wear-resistant layer is mainly composed of chromium alloy, and other alloy components such as manganese, molybdenum, niobium and nickel are added. The carbide in the metallographic structure is fibrous, and fiber direction is perpendicular to the surface. The microhardness of carbide can reach above HV1700-2000, and the surface hardness can reach HRC58-62. So how to understand the hardness level of alloy wear plate?

Hardness: refers to the ability of a metal surface to resist the intrusion of other harder objects. According to measurement method, it can be divided into Brinell hardness / Rockwell hardness / Vickers hardness.

Brinell hardness HB

Brinell hardness is a certain load (usually 3000kg), a hardened steel ball of a certain hardness (usually 10, 5, 2.5 mm) is pressed into the surface of the material, and then the applied load is divided by the surface area of the ball on the material. The result is the Brinell hardness value in kilograms per square millimeter, but it is customary not to be marked. According to GB231-84, the hardness measured by quenched steel ball is represented by HBS; the hardness value measured by hard alloy ball as indenter is HBW.HBS is suitable for measuring annealing/positive fire/tempering steel and cast iron/non-ferrous metal and softer materials with hardness less than 450HBS; HBW is suitable for measuring quenching materials with hardness between 450~650HBW.

Advantages: Because the metal crater area is large, the result is more accurate. At the same time, it is proved that there is a certain approximation between HB and unhardened steel tensile strength σb. For low carbon steel σb=3.53HB, medium carbon steel σb=3.5HB, high carbon steel σb=3.33HB, gray cast iron σb=0.98HB, (The σb unit is Mpa) Therefore, the tensile strength of the metal material can be approximately determined according to the Brinell hardness value of the material.

Disadvantages: It is not suitable for measuring materials with HB greater than 450, because the hardness of the material is too high, which may cause deformation of the steel ball, making the measurement results inaccurate. At the same time, due to the large embossing, it is not suitable for the determination of finished products and sheet materials.

Rockwell hardness HR

Rockwell hardness is measured by a 120 degree conical diamond indenter or a hardened steel ball with a diameter of 1.59 mm as the indenter, pressed into the surface of the material under a certain load, and the hardness of the material is calculated by the depth of the indentation. the size of. Rockwell hardness has no unit. Rockwell hardness is divided into three types according to the load used.

HRA measures high hardness or hard and thin metal with HB greater than 700, such as cemented carbide surface treated workpiece, load 60 kg and 120o gold steel cone);

HRB measures softer annealed parts and copper, aluminum and metal with HB=60~230, load of 100 kg and ф1.588mm steel balls;

HRC is generally used to measure quenched and tempered steel with HB=230~700 or workpiece after quenching and tempering, with a load of 150 kg and 120o gold steel cone;

Advantages: Easy to use, you can directly read the value directly from the dial. Due to the small embossing, it is suitable for the determination of finished and sheet materials.

Disadvantages: Because the embossing is small, it is not accurate. Generally, several points are measured, and then the average value is taken.

Among the above three Rockwell hardness, one HRC is the most widely used, and it is generally used for quenched steel.

The relationship between Rockwell hardness HRC and Brinell hardness HBS is about HRC1/10HB at high hardness;

Vickers hardness HV and microhardness

The principle of measuring the Vickers hardness is basically the same as the Brinell hardness. The difference is that the indenter adopts a diamond square pyramid with a cone angle of 136 degrees, and the unit is kg/mm, which is generally not marked.

The Vickers method uses a small load. The indentation is shallow and is suitable for measuring the hardness of the surface hardened layer, metal plating and sheet metal of the thin part, which is beyond the reach of Brinell and Rockwell. In addition, since the indenter is a diamond pyramid, the load can be adjusted in a wide range, so it is applicable to both soft and hard materials, and the measurement range is 0 to 1000 HV.

The newer national standard is GB/T4340.1-1999 “Metal Vickers hardness test Part 1: Test method”

With the hardness test method of Brinell, Rockwell and Vickers, the load is large and the indentation area is large. Only the average hardness value of the metal material mixture can be obtained. When it is necessary to measure the hardness of a certain phase or a certain grain, Microhardness is used.

The principle of the microhardness test is the same as that of Vickers and is also determined by the ratio of the load to the surface area of the indentation. The difference is that the load used is very small, generally 1~120gf (1gf=0.0098N), and the microhardness value can also be expressed by HV.

In summary, the alloy carbide of the alloy wear plate has strong stability at high temperature, maintains high hardness, and also has good oxidation resistance, and is completely used normally within 500 °C.