Hardness Test 1. Describe the differences between Rockwell B and Rockwell C hard

Question

Hardness Test

1.         Describe the differences between Rockwell B and Rockwell C hardness tests.

2.         Which scale (Rockwell B or C) is used to measure the hardness of pure Al and non-          ferrous alloys?

3.         Both tensile strength and hardness are indicators of metal's resistance to plastic      deformation. For steels, the tensile strength is roughly proportional to their Brinell hardness number (HB). Based on this information and on the notes provided in class,            estimate the tensile strength of steel with 500 HB.

4.         When making hardness measurements, what is the effect of making an indentation very    close to a pre-existing indentation?

5.         Which hardness test can be used to measure the hardness of both metals and ceramic         materials?

Explanation / Answer

The given text solve all your questions:read carefully

Difference between rockwell B and rockwell C hardnesstest:The Rockwell scale characterizes the indentation hardness of materials through the depth of penetration of an indenter, loaded on a material sample and compared to the penetration in some reference material. It is one of several definitions of hardness in materials science. It involves the application of a minor load followed by a major load, and then noting the hardness value directly from a dial. Its chief advantage is its ability to display hardness values directly, thus obviating tedious calculations involved in other hardness measurement techniques. Also, the relatively simple and inexpensive set-up enables its installation in college laboratories.

It is typically used in engineering and metallurgy and is most common in the USA. Its commercial popularity arises from its speed, reliability, robustness, resolution and small area of indentation.

There are several alternative scales, the most commonly used being the "B", and "C" scales. Both express hardness as an arbitrary dimensionless number.

The B-scale is used for softer materials (such as aluminum, brass, and softer steels). It employs a hardened steel ball as the indenter and a 100kg weight to obtain a value expressed as "HRB".

The C-scale, for harder materials, uses a diamond cone, known as a Brale indenter and a 150kg weight to obtain a value expressed as "HRC".

The depth of penetration is converted to a scale in which the harder the material the higher the number.
Answer2) The B-scale is used for softer materials (such as aluminum, brass, and softer steels). It employs a hardened steel ball as the indenter and a 100kg weight to obtain a value expressed as "HRB"
Common values

Very hard steel (e.g. a good knife blade) HRC 55 to HRC 62 or so
Axes, chisels, etc. HRC 40 - 45
Readings below HRC 20 are generally considered unreliable, as are readings much above HRB 100.

Several other scales, including the extensive A-scale, are used for specialised applications. There are special scales for measuring case-hardened specimens.

Good practice includes:

Cleaning indenter and test-piece to be clear of dirt, grease, rust or paint;
Measuring on a perpendicular, flat surface ("round work correction factors" are invoked to adjust for test-piece curvature);
Ensuring that the thickness of the test-piece is at least 10 times the depth of the indentation;
Maintaining an adequate spacing between multiple indentations; and
Controlling the speed of the indentation.

The Brinell scale characterises the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.

Brinelling refers to surface fatigue caused by repeated impact or overloading. It is a common cause of roller bearing failures, and loss of preload in bolted joints when a hardened washer is not used. Engineers will use the Brinell hardness of materials in their calculations to avoid this mode of failure. Fretting corrosion can cause a similar-looking kind of damage and is called false brinelling since the mechanism is different.

Proposed by Swedish engineer Johan August Brinell in 1900, it was the first widely used and standardised hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness.

The typical test uses a 10 mm diameter steel ball as an indenter with a 3,000 kgf (29 kN) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:
BHN=2P/3.14D(D-Sq.Root(D2-d2)

where:

P = applied force (kgf)
D = diameter of indenter (mm)
d = diameter of indentation (mm)

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.