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relation between strength and hardness of material 1
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In general, strength and indentation hardness are proportional to each other. There are variations based on the specific material and the hardness test method. The most common relationship is between the ultimate tensile strength and indentation hardness for steels, which is summarized in ISO 18265 Metallic materials -- Conversion of hardness values and ASTM A370 Standard Test Methods and Definitions for Mechanical Testing of Steel Products.
To get a good answer to this question, you need to define what you mean by strength (as well as hardness). Between tensile strength and indentation hardness, as CoryPad has stated, there are fairly well defined correlations. These tend to be material-specific, so you need to make sure you are looking at the right correlation.
On the other hand, there are different types of strength (other than tensile strength) and hardness (other than indention hardness). For example, there is impact strength, compressive strength, chemical strength, magnetic strength, and so on. The correlation between these other types of strength to the indention hardness is much less than that for tensile strength (for some, there is no correlation).
As far as hardness goes, many a machinist has told me that 321 stainless is difficult to machine because it is so hard. 321 SS has relatively low indentation hardness (and correspondingly, tensile strength), however. The machinists know what they are talking about, however, they just do not mean indention hardness when they say that 321 is hard, they mean that it dulls their tools more quickly and gives them more pushback than low-allloy steels. The correlation between this type of hardness and those other types of strength is even more nebulous.
On the other hand, there are different types of strength (other than tensile strength) and hardness (other than indention hardness). For example, there is impact strength, compressive strength, chemical strength, magnetic strength, and so on. The correlation between these other types of strength to the indention hardness is much less than that for tensile strength (for some, there is no correlation).
As far as hardness goes, many a machinist has told me that 321 stainless is difficult to machine because it is so hard. 321 SS has relatively low indentation hardness (and correspondingly, tensile strength), however. The machinists know what they are talking about, however, they just do not mean indention hardness when they say that 321 is hard, they mean that it dulls their tools more quickly and gives them more pushback than low-allloy steels. The correlation between this type of hardness and those other types of strength is even more nebulous.
[as long as you're not just talking about "surface hardness" etc]
It is a big area of research in most industries. How do you increase hardness (wear life) and toughness (strength)?
Thomas J. Walz
Carbide Processors, Inc.
Good engineering starts with a Grainger Catalog.
Thomas J. Walz
Carbide Processors, Inc.
Good engineering starts with a Grainger Catalog.
In traditional metallurgy 'strength' is normally considered to mean tensile strength and hardness to be a measure of resistance to indentation and it is clear that in the vast majority of circumstances there is a valid correlation between these two values.
'Impact Strength' is also a common expression but can be misleading as most Impact test measure the energy absorbed and the results of these tests is a much better guide to a materials's toughness rather than strength.
In many cases toughness and strength are mutually exclusive properties and this is when more data is needed to make the correct choices.
I don't understand the idea that there are different types of hardness. I have always thought that hardness is just hardness.
Stainless Steels such as 321 can be difficult to machine but this is due the manner in which they work harden and using the correct machining conditions and lubricants is important to ensure good results. When set up correctly 321 machines well.
For the vast majority of families of metallic materials hardness correlates very well to tensile strength.
'Impact Strength' is also a common expression but can be misleading as most Impact test measure the energy absorbed and the results of these tests is a much better guide to a materials's toughness rather than strength.
In many cases toughness and strength are mutually exclusive properties and this is when more data is needed to make the correct choices.
I don't understand the idea that there are different types of hardness. I have always thought that hardness is just hardness.
Stainless Steels such as 321 can be difficult to machine but this is due the manner in which they work harden and using the correct machining conditions and lubricants is important to ensure good results. When set up correctly 321 machines well.
For the vast majority of families of metallic materials hardness correlates very well to tensile strength.
many parts would be consider to have failed if they bend or deform permanently That "failure" is related to yield strength.
Yield strength does not follow hardness or tensile strength very closely.
UTS / Yield strength / UTS/YS
1015 HR 61 45.5 1.34
N 61.5 47 1.31
Annealed 56 41.25 1.36
1040 HR 90 60 1.50
N 85.5 54.25 1.58
Annealed 75.25 51.25 1.47
1340 N 121.25 81 1.50
Annealed 102 63.25 1.61
4130 N 97 63.25 1.53
Annealed 81.25 52.5 1.55
4140 N 148 95 1.56
Annealed 95 60.5 1.57
mil spec 23284
class 1 95 75 1.27
class 2 80 55 1.45
class 3 75 45 1.67
class 4 60 35 1.71
class 5 105 75 1.40
class 6 110 90 1.22
Yield strength does not follow hardness or tensile strength very closely.
UTS / Yield strength / UTS/YS
1015 HR 61 45.5 1.34
N 61.5 47 1.31
Annealed 56 41.25 1.36
1040 HR 90 60 1.50
N 85.5 54.25 1.58
Annealed 75.25 51.25 1.47
1340 N 121.25 81 1.50
Annealed 102 63.25 1.61
4130 N 97 63.25 1.53
Annealed 81.25 52.5 1.55
4140 N 148 95 1.56
Annealed 95 60.5 1.57
mil spec 23284
class 1 95 75 1.27
class 2 80 55 1.45
class 3 75 45 1.67
class 4 60 35 1.71
class 5 105 75 1.40
class 6 110 90 1.22
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