Basic Information of Hardness of Castings
During the test of mechanical properties of castings, the hardness is always required by the end users or customers. Due to different materials and casting processes, the required number of hardness is covered from a wide range. In this article, we introduce the basic information of the hardness and the main types of hardness methods.
Hardness refers to the ability of a material to locally resist hard objects pressed into its surface. The local resistance of a solid to the intrusion of external objects is an index for comparing the hardness of various materials. As different test methods are specified, there are different hardness standards. Various hardness standards have different mechanical meanings and cannot be directly converted to each other, but they can be compared through experiments.
Scratch HardnessIt is mainly used to compare the softness and hardness of different minerals. The method is to select a rod with one end hard and one soft end, and the tested material is scratched along the rod, and the hardness of the tested material is determined according to the position of the scratch. Qualitatively speaking, hard objects have long scratches and soft objects have short scratches. In 1722, the French R. A. F. De Leomir first proposed a very rough scratch hardness test. This method is to make the quilt and the material scribble on a metal rod that gradually changes from one end to a soft end, and the hardness of the tested material is determined according to the position of the scratch on the rod. In 1822, F. Moss uses the scratch hardness of ten minerals as the standard and sets ten hardness grades called Mohs hardness. The Mohs hardness levels of ten minerals are: diamond (10), corundum (9), topaz (8), quartz (7), feldspar (6), apatite (5), fluorite (4), Calcite (3), gypsum (2), talc (1). Among them, diamond is the hardest and talc is the softest. The Mohs hardness standard is arbitrarily set and cannot be accurately used to determine the hardness of the material. For example, the actual hardness difference between grade 10 and grade 9 is much larger than the actual hardness difference between grade 2 and grade 1. However, this classification is very useful for fieldwork of mineralogists.
Indentation Hardness.It is mainly used for metal materials. The specified indenter is pressed into the tested material with a certain load, and the hardness of the tested material is compared according to the degree of local plastic deformation on the surface of the material. The harder the material, the smaller the plastic deformation. Due to the difference of indenter, load and load duration, there are many kinds of indentation hardness, mainly Brinell hardness, Rockwell hardness, Vickers hardness and Micro hardness. . Indentation hardness has a wide range of applications in engineering technology. There are many types of indenters, such as steel balls with a certain diameter, diamond cones, diamond pyramids and so on. The load range is from a few grams of force to several tons of force (that is, tens of millinewtons to tens of thousands of newtons). The indentation hardness also stipulates the duration of the load acting on the surface of the material to be tested.
Rebound HardnessThe rebound hardness is also called Shore hardness, referred to as HS. A standard that indicates the hardness of a material. It was proposed by the British Albert F. Shore in 1906 when he studied the hardness test method of hardened steel. The measuring principle of the Shore hardness test method is: use a small hammer with a diamond round head or a steel ball weighing 1/12 ounce force (1 ounce force is equal to 0.2780 Newton), and drop it freely from a height of 10 inches to make the small hammer Impact the surface of the specimen with a certain kinetic energy. Part of the kinetic energy of the hammer is converted into plastic deformation work on the surface of the specimen and is consumed; the other part is converted into elastic strain energy and stored by the specimen. When the specimen elastically deforms and recovers, it releases energy, causing the hammer to jump back to a certain height. The harder the test object, the higher the elastic limit, the more stored elastic strain energy, and the higher the rebound of the hammer. The symbol of rebound hardness is HS, which is indexed by the rebound height of the small hammer. The rebound hardness can only be compared between materials with the same elastic modulus, otherwise it will be concluded that rubber is harder than steel. The measurement of indentation hardness belongs to the static measurement method, and the measurement of the rebound hardness belongs to the dynamic measurement method. Mainly used for metal materials, the method is to make a special hammer fall freely from a certain height to impact the sample of the material to be tested, and how much strain energy the sample stores (and then releases) during the impact process (through the return of the hammer) Jump height measurement) to determine the hardness of the material.
|Hardness Comparison: HB-HRC-HV-HS|
|Brinell Hardness(HB)||Rockwell Hardness||Vickers Hardness (HV)||Shore Hardness (HS)||Briness Hardness (HB)||Rockwell Hardness||Vickers Hardness (HV)||Shore Hardness (HS)|