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Comprehensive Overview of 4140 Steel Hardness

4140 steel is a medium-carbon low-alloy steel composed of chromium, molybdenum and carbon. Its hardness is mainly determined by the carbon content. 4140 steel hardness tested under different conditions will also be different. Through correct heat treatment and hardness testing methods, the hardness of 4140 steel suitable for different application needs can be obtained. So understanding the 4140 steel hardness is critical to evaluating its application in projects. This article will provide a comprehensive overview of the knowledge points about 4140 steel hardness.

4140 Steel Hardness Testing

1.Brinell Hardness Test: It is one of the most commonly used hardness testing methods. By applying a certain predetermined load on the surface of the steel, the diameter of the indentations of different depths formed is measured. According to the indentation diameter and test Load calculation hardness value.

2.Vickers Hardness Test: This method is a commonly used microhardness testing method represented by HV (Vickers hardness). A Vickers hardness testing machine is used to apply a certain load of diamond or hard alloy indenter to the surface of 4140 steel, measure the diagonal length of the indentation, and calculate the hardness value.

3.Rockwell Hardness Test: This method is a metal hardness test method represented by the HRC symbol, which measures the depth or union depth and rebound depth of the indentation formed on the surface of 4140 steel, and reads the hardness value based on the measurement.

4.Ultrasonic Hardness Test: It is a non-contact hardness testing method that uses the propagation speed and reflection characteristics of ultrasonic waves on the surface of steel to infer hardness. The hardness value is calculated by measuring the propagation time of ultrasonic waves in the material.

4140 Steel Hardness

4140 steel hardness can be increased through different treatment processes. Due to different processing methods, the hardness range of 4140 steel will also be different under different heat treatment states.

1. Normalizing
Generally speaking, 4140 steel usually does not reach the high hardness after quenching in the normalized state. The hardness is usually 240–350HB, and some can reach 35 to 45 HRC.

2. Annealing
4140 steel undergoes an annealing process in which it is heated to a specific temperature and then slowly cooled to eliminate internal stress, giving the material a refined microstructure and higher hardness. Usually in this state, the hardness of 4140 steel reaches between 187-229HBW.

Tempering is a post-annealing process that can fine-tune the hardness of 4140 steel in this state. Depending on different tempering temperatures and times, different hardness ranges can be achieved.
– Tempered to a range of 200°C to 400°C to a hardness of 28 to 32 HRC.
– Tempered to a range of 400°C to 600°C to a hardness of 22 to 28 HRC.

The hardness of AISI 4140 steel after quenching is usually higher. The choice of quenching medium directly affects the hardness of 4140 steel. The quenching process hardens the steel by changing the microstructure of the steel. In this condition, 4140 steel typically exhibits hardness values in the range of 40 to 60 HRC.

5.Quenching and Tempering Treatment
After quenching and tempering (quenching + tempering), to balance hardness and toughness, the hardness of 4140 steel will be significantly increased, and its hardness range can usually reach between 28-34 HRC.

It should be noted that the process used by each supplier is different, and the specific hardness value depends on the choice of heat treatment process and conditions, as well as the starting state of the material.

Answers to Customer Questions About 4140 Steel Hardness

Recently, our Songshun customer from Europe asked how the hardness of our 4140 steel is tested? 4140 steel was tested on a Rockwell C hardness tester. The measurement result was 25 to 29 HRC. Is it correct? Also, is the material that reaches this hardness range quenched and tempered or natural?

To sum up, when customers need to test 4140 steel hardness, we can provide several methods. Among them, in the Rockwell hardness test, two versions, HB or HRC, are usually used. When the customer measured 4140 steel hardness, the result was 25 to 29 HRC, which is correct. This hardness range can be achieved in the natural state, but there is no guarantee that the hardness can be achieved 100%. The general hardness range is 260–270HB, or 260–300HB. As the weather gets colder, the steel is air-cooled faster, and the surface hardness may reach 100%. However, the center hardness of the steel may be slower than the surface due to air cooling, so the interior may be lower than the surface hardness.

Nowadays, with the continuous innovation and improvement of technology, the hardness range of 4140 steel can reach more ideal heights, and the versatility of its hardness makes it the first choice for many industrial applications. If you have more questions or need 4140 steel or Any other steel, Songshun Steel is ready to provide it for you!


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