I came across steel 1084 for the first time on TV today.

Is there a simple guide to which steels to use for which purposes? And why they have different costs?

Setting aside steels for magnetic purposes, and setting aside thermal treatment, there seem to me to be only three parameters that control steel usefulness:

• strength
• toughness
• corrosion resistance

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

So why are there so many steel formulations?
How many different steel formulations are there anyway?

There’d be 30 or 40 variations just for knives, at a minimum. I’m actually cutting some cheese with a German 1.4116 steel. I find it an absolute mongrel to sharpen correctly but once done a quick strop and it is ready to shave.

mollwollfumble said:

I came across steel 1084 for the first time on TV today.

Is there a simple guide to which steels to use for which purposes? And why they have different costs?

Setting aside steels for magnetic purposes, and setting aside thermal treatment, there seem to me to be only three parameters that control steel usefulness:

• strength
• toughness
• corrosion resistance

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

So why are there so many steel formulations?
How many different steel formulations are there anyway?

sibeen said:

There’d be 30 or 40 variations just for knives, at a minimum. I’m actually cutting some cheese with a German 1.4116 steel. I find it an absolute mongrel to sharpen correctly but once done a quick strop and it is ready to shave.

This website seems to be a good kiddies introduction to steel types. “https://www.meadmetals.com/blog/steel-grades“https://www.meadmetals.com/blog/steel-grades Quoting from that link:

There are more than 3,500 different grades of steel Steel is often categorized into four groups—Carbon, Alloy, Stainless, and Tool.

• Carbon Steels only contain trace amounts of elements besides carbon and iron. This group is the most common, accounting for 90% of steel production. Carbon Steel is divided into three subgroups depending on the amount of carbon in the metal: Low Carbon Steels/Mild Steels (up to 0.3% carbon), Medium Carbon Steels (0.3–0.6% carbon), and High Carbon Steels (more than 0.6% carbon).
• Alloy Steels contain alloying elements like nickel, copper, chromium, and/or aluminum. These additional elements are used to influence the metal’s strength, ductility, corrosion resistance, and machinability.
• Stainless Steels contain 10–20% chromium as their alloying element and are valued for their high corrosion resistance. These steels are commonly used in medical equipment, piping, cutting tools, and food processing equipment.
• Tool Steels make excellent cutting and drilling equipment as they contain tungsten, molybdenum, cobalt, and vanadium to increase heat resistance and durability.

(That reference to heat resistance is an interesting one, how is that done?)

It’s possible for two steels with the same alloy content to have different grades based on this heat treatment process.

• The ASTM Grading System assigns each metal a letter prefix based on its overall category (“A” is the designation for iron and steel materials), as well as a sequentially-assigned number that corresponds with that metal’s specific properties.
• The SAE Grading System uses a four-digit number for classification. The first two digits denote the steel type and alloying element concentration, and the last two digits indicate the carbon concentration of the metal.

(So that 84 of 1084 represents the carbon concentration, 8.4%?)
(That different grade based on heat treatment – does that only apply to stainless?)

Of course there is also; Low-background steel.

https://www.marlinwire.com/blog/food-grade-stainless-steel-facts
https://www.marlinwire.com/blog/what-is-the-best-food-grade-stainless-steel

mollwollfumble said:

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Don’t forget Blue Steel, for maximum aesthetic.

Rule 303 said:

Don’t forget Blue Steel, for maximum aesthetic.

I know of this Blue Steel

Tamb said:

Rule 303 said:

Don’t forget Blue Steel, for maximum aesthetic.

I know of this Blue Steel

is that a scope

Tamb said:

Rule 303 said:

Don’t forget Blue Steel, for maximum aesthetic.

I know of this Blue Steel

He would have been better off using that to take out the President of Malaysia…

furious said:

Tamb said:

Rule 303 said:

Don’t forget Blue Steel, for maximum aesthetic.

I know of this Blue Steel

He would have been better off using that to take out the President Prime Minister of Malaysia…

Fixed…

The Rev Dodgson said:

mollwollfumble said:

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

Rule 303 said:

Don’t forget Blue Steel, for maximum aesthetic.

Damn…on fleek popculref from the Rule

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

It’s not my clients who need to know this, it’s the people who write the standards.

But a quick search of the internet suggests that that numbers given above are way over-simplified.

For instance: https://www.steel.org.au/resources/elibrary/resource-items/fatigue-of-steel-structures-bk206/download-pdf.pdf/

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

I could add fatigue resistance to that, but for steels other than stainless the fatigue resistance is half the strength.

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

I noted a while back that steel technology, despite its antiquity, has kept advancing to the point where steel alloy is still the strongest of all known metals.

From: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiBsv_k-pbrAhUXxzgGHSruAOcQFjAKegQIBRAB&url=https%3A%2F%2Fwww.skyshop.com.au%2FMETALS.pdf&usg=AOvVaw3hIb6r-3VmMJGCZt-WbyGo

Steel, some common types. It looks as if weldability and case hardening are other very important considerations.

1010 This is one of the most widely used low carbon steels for low strength applications. It is best suited for parts whose fabrication involves moderate to severe forming and some machining. Its weldability is excellent and it can be case hardened for wear resistance by cyaniding.

1018 is a popular carburizing grade of steel. It can be strengthened by cold working or surface hardened by carburizing or cyaniding. It is relatively soft and has good weldability and formability.

1020 is a general-purpose low-carbon “mild” steel. It is easy to fabricate by the usual methods such as mild cold or hot forming and welding. It is weldable by all processes and the resulting welds are of extremely high quality.

4130 This chromium-molybdenum alloy is one of the most widely used aircraft steels because of its combination of weldability, ease of fabrication and mild hardenability. In relatively thin sections, it may be heat treated to high strength levels. In the normalized condition it has adequate strength for many applications. It may be nitrided for resistance to wear and abrasion.

4140 This chromium-molybdenum alloy is a deep hardening steel used where strength and impact toughness are required. It has high fatigue strength making it suitable for critical stressed applications. It may be nitrided for increased resistance to wear and abrasion.

4340 This chromium-nickel-molybdenum alloy is a widely used deep hardening steel. It possesses remarkable ductility and toughness. With its high alloy con tent uniform hardness is developed by heat treatment in relatively heavy sections. Its high fatigue strength makes it ideal for highly stressed parts.

6150 This chromium-vanadium alloy steel is similar to 4340. It has good hardenability, good fatigue properties and excellent resistance to impact and abrasion.

8620 This is a “triple alloy” chromium-nickel-molybdenum steel. It is readily carburized. It may be heat treated to produce a strong, tough core and high case hardness. It has excellent machinability and responds well to polishing operations. It is easily welded by any of the common welding processes, although the section should be heated and stress relieved after welding.

9310 This chromium-nickel-molybdenum alloy is a carburizing steel capable of attaining high case hardness with high core strength. It has excellent toughness and ductility.

4620 This nickel-molybdenum alloy is a carburizing steel capable of developing high case hardness and core toughness. It can be forged similarly to the other carburizing grades. Because of its relatively high nickel content, it is not as readily cold-formed.

5160 This carbon-chromium grade of spring steel has a high yield/tensile strength ratio, excellent toughness and high ductility. It is very difficult to machine in the as-rolled condition and should be annealed prior to machining. It is not readily welded, but it can be welded by either the gas or arc welding processes if the section involved is preheated and stress relieved after welding.

52100 This high carbon-high chromium alloy is produced by the electric furnace process and then vacuum degassed to meet the rigid standards of the aircraft industry for bearing applications. It develops high hardness and has exceptional resistance to wear and abrasion.

EFFECTS OF COMMON ALLOYING ELEMENTS IN STEEL
By definition, steel is a combination of iron and carbon. Steel is alloyed with various elements to improve physical properties and to produce special properties, such as resistance to corrosion or heat. Specific effects of the addition of such elements are outlined below:

CARBON ©, although not usually considered as an alloying element, is the most important constituent of steel. It raises tensile strength, hardness and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

MANGANESE (Mn) is a deoxidizer and degasifier and reacts with sulphur to improve forgeability. It in creases tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It in creases the rate of carbon-penetration in carburizing.

PHOSPHORUS (P) increases strength and hardness and improves machinability. However, it adds marked brittleness or cold-shortness to steel.

SULPHUR (S) Improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility.

SILICON (Si) is a deoxidizer and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability.

CHROMIUM (Cr) increases tensile strength, hardness, hardenability. toughness, resistance to wear and abrasion. resistance to corrosion and scaling at elevated temperatures.

NICKEL (Ni) increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high chromium (stainless) steels.

MOLYBDENUM (Mo) increases strength, hardness, hardenability and toughness, as well as creep resistance and strength at elevated temperatures. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot-work steels, it increases red-hardness properties.

TUNGSTEN (W) increases strength, hardness and toughness. Tungsten steels have superior hot-working and greater cutting efficiency at elevated temperatures.
.
VANADIUM (V) increases strength, hardness and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances the red hardness properties of high speed metal cutting tools and intensifies the individual effects of other major elements.

COBALT (Co) Increases strength and hardness and permits higher quenching temperatures. It also intensifies the individual effects of other major elements in more complex steels.

ALUMINUM (Al) is a deoxidizer and degasifier. It retards grain growth and is used to control austenitic grain size. In nitriding steels it aids in producing a uniformly hard and strong nitrided case when used in amounts 1.00% – 1.25%.

LEAD (Pb), while not strictly an alloying element, is added to improve machining characteristics. It is almost completely in soluble in steel, and minute lead particles, well dispersed, reduce friction where the cutting edge contacts the work. Addition of lead also improves chip-breaking formations.

(OK, so far so good. I’m still not where I want to be. I want to see a plot of toughness vs strength for all common steel grades, and relationships between these and other properties such as machinability).

mollwollfumble said:

mollwollfumble said:

The Rev Dodgson said:

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

I noted a while back that steel technology, despite its antiquity, has kept advancing to the point where steel alloy is still the strongest of all known metals.

From: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiBsv_k-pbrAhUXxzgGHSruAOcQFjAKegQIBRAB&url=https%3A%2F%2Fwww.skyshop.com.au%2FMETALS.pdf&usg=AOvVaw3hIb6r-3VmMJGCZt-WbyGo

Steel, some common types. It looks as if weldability and case hardening are other very important considerations.

1010 This is one of the most widely used low carbon steels for low strength applications. It is best suited for parts whose fabrication involves moderate to severe forming and some machining. Its weldability is excellent and it can be case hardened for wear resistance by cyaniding.

1018 is a popular carburizing grade of steel. It can be strengthened by cold working or surface hardened by carburizing or cyaniding. It is relatively soft and has good weldability and formability.

1020 is a general-purpose low-carbon “mild” steel. It is easy to fabricate by the usual methods such as mild cold or hot forming and welding. It is weldable by all processes and the resulting welds are of extremely high quality.

4130 This chromium-molybdenum alloy is one of the most widely used aircraft steels because of its combination of weldability, ease of fabrication and mild hardenability. In relatively thin sections, it may be heat treated to high strength levels. In the normalized condition it has adequate strength for many applications. It may be nitrided for resistance to wear and abrasion.

4140 This chromium-molybdenum alloy is a deep hardening steel used where strength and impact toughness are required. It has high fatigue strength making it suitable for critical stressed applications. It may be nitrided for increased resistance to wear and abrasion.

4340 This chromium-nickel-molybdenum alloy is a widely used deep hardening steel. It possesses remarkable ductility and toughness. With its high alloy con tent uniform hardness is developed by heat treatment in relatively heavy sections. Its high fatigue strength makes it ideal for highly stressed parts.

6150 This chromium-vanadium alloy steel is similar to 4340. It has good hardenability, good fatigue properties and excellent resistance to impact and abrasion.

8620 This is a “triple alloy” chromium-nickel-molybdenum steel. It is readily carburized. It may be heat treated to produce a strong, tough core and high case hardness. It has excellent machinability and responds well to polishing operations. It is easily welded by any of the common welding processes, although the section should be heated and stress relieved after welding.

9310 This chromium-nickel-molybdenum alloy is a carburizing steel capable of attaining high case hardness with high core strength. It has excellent toughness and ductility.

4620 This nickel-molybdenum alloy is a carburizing steel capable of developing high case hardness and core toughness. It can be forged similarly to the other carburizing grades. Because of its relatively high nickel content, it is not as readily cold-formed.

5160 This carbon-chromium grade of spring steel has a high yield/tensile strength ratio, excellent toughness and high ductility. It is very difficult to machine in the as-rolled condition and should be annealed prior to machining. It is not readily welded, but it can be welded by either the gas or arc welding processes if the section involved is preheated and stress relieved after welding.

52100 This high carbon-high chromium alloy is produced by the electric furnace process and then vacuum degassed to meet the rigid standards of the aircraft industry for bearing applications. It develops high hardness and has exceptional resistance to wear and abrasion.

EFFECTS OF COMMON ALLOYING ELEMENTS IN STEEL
By definition, steel is a combination of iron and carbon. Steel is alloyed with various elements to improve physical properties and to produce special properties, such as resistance to corrosion or heat. Specific effects of the addition of such elements are outlined below:

CARBON ©, although not usually considered as an alloying element, is the most important constituent of steel. It raises tensile strength, hardness and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

MANGANESE (Mn) is a deoxidizer and degasifier and reacts with sulphur to improve forgeability. It in creases tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It in creases the rate of carbon-penetration in carburizing.

PHOSPHORUS (P) increases strength and hardness and improves machinability. However, it adds marked brittleness or cold-shortness to steel.

SULPHUR (S) Improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility.

SILICON (Si) is a deoxidizer and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability.

CHROMIUM (Cr) increases tensile strength, hardness, hardenability. toughness, resistance to wear and abrasion. resistance to corrosion and scaling at elevated temperatures.

NICKEL (Ni) increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high chromium (stainless) steels.

MOLYBDENUM (Mo) increases strength, hardness, hardenability and toughness, as well as creep resistance and strength at elevated temperatures. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot-work steels, it increases red-hardness properties.

TUNGSTEN (W) increases strength, hardness and toughness. Tungsten steels have superior hot-working and greater cutting efficiency at elevated temperatures.
.
VANADIUM (V) increases strength, hardness and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances the red hardness properties of high speed metal cutting tools and intensifies the individual effects of other major elements.

COBALT (Co) Increases strength and hardness and permits higher quenching temperatures. It also intensifies the individual effects of other major elements in more complex steels.

ALUMINUM (Al) is a deoxidizer and degasifier. It retards grain growth and is used to control austenitic grain size. In nitriding steels it aids in producing a uniformly hard and strong nitrided case when used in amounts 1.00% – 1.25%.

LEAD (Pb), while not strictly an alloying element, is added to improve machining characteristics. It is almost completely in soluble in steel, and minute lead particles, well dispersed, reduce friction where the cutting edge contacts the work. Addition of lead also improves chip-breaking formations.

(OK, so far so good. I’m still not where I want to be. I want to see a plot of toughness vs strength for all common steel grades, and relationships between these and other properties such as machinability).

You’ll need to study metallurgy.

roughbarked said:

mollwollfumble said:

You’ll need to study metallurgy.

Gold is not steel and alloys all do different things but there is also more to it all than just that.
https://mb.nawcc.org/threads/comparative-value-of-14k-and-18k-gold.166781/#post-1392583

roughbarked said:

roughbarked said:

mollwollfumble said:

You’ll need to study metallurgy.

Gold is not steel and alloys all do different things but there is also more to it all than just that.
https://mb.nawcc.org/threads/comparative-value-of-14k-and-18k-gold.166781/#post-1392583

oops. I want you to read the whole thread. https://mb.nawcc.org/threads/comparative-value-of-14k-and-18k-gold.166781/

The Rev Dodgson said:

mollwollfumble said:

The Rev Dodgson said:

Can you let the people as Standards Australia know that?

It will save me a lot of time, and save my clients a lot of steel.

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

It’s not my clients who need to know this, it’s the people who write the standards.

But a quick search of the internet suggests that that numbers given above are way over-simplified.

For instance: https://www.steel.org.au/resources/elibrary/resource-items/fatigue-of-steel-structures-bk206/download-pdf.pdf/

Thanks. Reading that now.
“Tests on smooth samples of ferritic steels exhibit a fatigue limit of roughly half the yield strength as is shown in Figure 23”.

You’re right, the people who write the standards should be told this.

“Firstly the limit disappears in corrosive conditions, and even brief exposure to corrosive conditions can cause its removal. Secondly, the fatigue limit is dependent on the size of the initial flaw that propagates to failure. Thirdly, failure at stress ranges below the limit has been observed beyond 10^8 cycles.”

This has to be quantified. Especially the “can cause”. For what steels, heat treatments and corrosion conditions?

“wide scatter of the data, samples with a Class—C detail subjected to a 150 MPa stress range would have a mean life of 2.6 million cycles. However, the test results will be scattered over a range of 1 million to 6.7 million cycles”

That’s not necessarily a wide scatter. eg. It’s not a wide scatter if 150 MPa is very close to the fatigue limit.

The following graph is in total disagreement with the notion of a fatigue limit for steel. What is happening here? PS, the lack of a scatter here says that the data points plotted are not actual measurements but based on a theoretical model of questionably validity.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

It’s not my clients who need to know this, it’s the people who write the standards.

But a quick search of the internet suggests that that numbers given above are way over-simplified.

For instance: https://www.steel.org.au/resources/elibrary/resource-items/fatigue-of-steel-structures-bk206/download-pdf.pdf/

Thanks. Reading that now.
“Tests on smooth samples of ferritic steels exhibit a fatigue limit of roughly half the yield strength as is shown in Figure 23”.

You’re right, the people who write the standards should be told this.

“Firstly the limit disappears in corrosive conditions, and even brief exposure to corrosive conditions can cause its removal. Secondly, the fatigue limit is dependent on the size of the initial flaw that propagates to failure. Thirdly, failure at stress ranges below the limit has been observed beyond 10^8 cycles.”

This has to be quantified. Especially the “can cause”. For what steels, heat treatments and corrosion conditions?

“wide scatter of the data, samples with a Class—C detail subjected to a 150 MPa stress range would have a mean life of 2.6 million cycles. However, the test results will be scattered over a range of 1 million to 6.7 million cycles”

That’s not necessarily a wide scatter. eg. It’s not a wide scatter if 150 MPa is very close to the fatigue limit.

The following graph is in total disagreement with the notion of a fatigue limit for steel. What is happening here? PS, the lack of a scatter here says that the data points plotted are not actual measurements but based on a theoretical model of questionably validity.

In the context of steel that is highly likely to have some corrosion, I think:

“Firstly the limit disappears in corrosive conditions, and even brief exposure to corrosive conditions can cause its removal. Secondly, the fatigue limit is dependent on the size of the initial flaw that propagates to failure.”

is the relevant comment.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

Really?
Your clients need to know the fatigue resistance of steel?

Column 6 in the table on Engineering toolbox. https://www.engineeringtoolbox.com/steel-endurance-limit-d_1781.html

It’s not my clients who need to know this, it’s the people who write the standards.

But a quick search of the internet suggests that that numbers given above are way over-simplified.

For instance: https://www.steel.org.au/resources/elibrary/resource-items/fatigue-of-steel-structures-bk206/download-pdf.pdf/

Thanks. Reading that now.
“Tests on smooth samples of ferritic steels exhibit a fatigue limit of roughly half the yield strength as is shown in Figure 23”.

You’re right, the people who write the standards should be told this.

“Firstly the limit disappears in corrosive conditions, and even brief exposure to corrosive conditions can cause its removal. Secondly, the fatigue limit is dependent on the size of the initial flaw that propagates to failure. Thirdly, failure at stress ranges below the limit has been observed beyond 10^8 cycles.”

This has to be quantified. Especially the “can cause”. For what steels, heat treatments and corrosion conditions?

“wide scatter of the data, samples with a Class—C detail subjected to a 150 MPa stress range would have a mean life of 2.6 million cycles. However, the test results will be scattered over a range of 1 million to 6.7 million cycles”

That’s not necessarily a wide scatter. eg. It’s not a wide scatter if 150 MPa is very close to the fatigue limit.

The following graph is in total disagreement with the notion of a fatigue limit for steel. What is happening here? PS, the lack of a scatter here says that the data points plotted are not actual measurements but based on a theoretical model of questionably validity.

Hold on a moment. I may be misinterpreting this. The graph uses “stress range”.

But a stress range of 150 MPa may mean ±75 MPa, or it may mean 200 to 350 MPa. I don’t see any reason for supposing that the fatigue conditions for the two different types of stress cycles should lead to the same fatigue properties. So what exactly do they mean by “stress range”?

mollwollfumble said:

Hold on a moment. I may be misinterpreting this. The graph uses “stress range”.

But a stress range of 150 MPa may mean ±75 MPa, or it may mean 200 to 350 MPa. I don’t see any reason for supposing that the fatigue conditions for the two different types of stress cycles should lead to the same fatigue properties. So what exactly do they mean by “stress range”?

In the context of reinforced concrete, the stress range at the critical section is likely to be entirely tensile.

The Rev Dodgson said:

mollwollfumble said:

Hold on a moment. I may be misinterpreting this. The graph uses “stress range”.

But a stress range of 150 MPa may mean ±75 MPa, or it may mean 200 to 350 MPa. I don’t see any reason for supposing that the fatigue conditions for the two different types of stress cycles should lead to the same fatigue properties. So what exactly do they mean by “stress range”?

In the context of reinforced concrete, the stress range at the critical section is likely to be entirely tensile.

And do the standards take this into account? By using only data measured under entirely tensile conditions in a laboratory?

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

Hold on a moment. I may be misinterpreting this. The graph uses “stress range”.

But a stress range of 150 MPa may mean ±75 MPa, or it may mean 200 to 350 MPa. I don’t see any reason for supposing that the fatigue conditions for the two different types of stress cycles should lead to the same fatigue properties. So what exactly do they mean by “stress range”?

In the context of reinforced concrete, the stress range at the critical section is likely to be entirely tensile.

And do the standards take this into account? By using only data measured under entirely tensile conditions in a laboratory?

I no idea what testing they used, but the stress range limit for a high number of repetitions is about 100 MPa for steel with a yield strength of 500 MPa.

The Rev Dodgson said:

mollwollfumble said:

The Rev Dodgson said:

In the context of reinforced concrete, the stress range at the critical section is likely to be entirely tensile.

And do the standards take this into account? By using only data measured under entirely tensile conditions in a laboratory?

I no idea what testing they used, but the stress range limit for a high number of repetitions is about 100 MPa for steel with a yield strength of 500 MPa.

That seems to my naive expectations to be awfully low.

It might be worth tracking down the original references for this. Ideally, the testing was done under real world conditions:

• The reinforcing encased in concrete during fatigue testing. Ideally in cracked concrete.
• The reinforcing subjected to corrosion before encasing it in concrete. For several severities of prior corrosion.
• Realistic minimum and peak stresses in the steel.

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

And do the standards take this into account? By using only data measured under entirely tensile conditions in a laboratory?

I no idea what testing they used, but the stress range limit for a high number of repetitions is about 100 MPa for steel with a yield strength of 500 MPa.

That seems to my naive expectations to be awfully low.

It might be worth tracking down the original references for this. Ideally, the testing was done under real world conditions:

• The reinforcing encased in concrete during fatigue testing. Ideally in cracked concrete.
• The reinforcing subjected to corrosion before encasing it in concrete. For several severities of prior corrosion.
• Realistic minimum and peak stresses in the steel.
  

I imagine someone somewhere did all that. It’s probably based on European work, but I don’t know. The fatigue check has been in the bridge code for a long time, but has only recently been added to the code for buildings, and people don’t talk about it much yet.

Let’s have a look at one of the most recent papers on steel reinforcement fatigue. From 2016.

https://www.researchgate.net/profile/Lenka_Jakubovicova/publication/293043975_Fatigue_Resistance_of_Reinforcing_Steel_Bars/links/56bb19de08aeb271632b6967.pdf

“Designs of highway bridges are assessed for lives of 120 years during which time up to 7.10^7 cycles of traffic induced
stress may be applied. To date there have been no fatigue fractures reported for concrete highway bridges in normal
service.”

Well, that’s encouraging. But it also points to the possibility of standards that are too strict.

“current practice is … the elastic stresses should not exceed 80% of the characteristic strength defined as the 0.2%
proof stress. Stress ranges can be higher if there is a compressive element in the dynamic load-cycle.”

Am I misinterpreting this? Stress ranges permitted to be larger than 80% of the limit state stress. That can’t be right, can it.

“tests were performed under cyclic loading with the zero mean value” on a bar not encased in concrete or pre-corroded.

Yuckety yuck yuk. Three deviations from real conditions.

Results:

Well, there’s certainly no fatigue limit of 50% in these tests. Why not? The geometry of the rebar? Or the composition?

mollwollfumble said:

Let’s have a look at one of the most recent papers on steel reinforcement fatigue. From 2016.

https://www.researchgate.net/profile/Lenka_Jakubovicova/publication/293043975_Fatigue_Resistance_of_Reinforcing_Steel_Bars/links/56bb19de08aeb271632b6967.pdf

“Designs of highway bridges are assessed for lives of 120 years during which time up to 7.10^7 cycles of traffic induced
stress may be applied. To date there have been no fatigue fractures reported for concrete highway bridges in normal
service.”

Well, that’s encouraging. But it also points to the possibility of standards that are too strict.

“current practice is … the elastic stresses should not exceed 80% of the characteristic strength defined as the 0.2%
proof stress. Stress ranges can be higher if there is a compressive element in the dynamic load-cycle.”

Am I misinterpreting this? Stress ranges permitted to be larger than 80% of the limit state stress. That can’t be right, can it.

“tests were performed under cyclic loading with the zero mean value” on a bar not encased in concrete or pre-corroded.

Yuckety yuck yuk. Three deviations from real conditions.

Results:

Well, there’s certainly no fatigue limit of 50% in these tests. Why not? The geometry of the rebar? Or the composition?

Thanks for the link, I’ll read it properly later, but a few comments:

- I think the wording is misleading. For strength design the maximum live load (which already allows for future increase in heavy vehicle weights) is factored up (by 1.8 in the Australian code), and the design capacity assumes plastic behaviour of both the steel and the concrete. There are also checks under unfactored loading, which typically limit the stress to about 250 MPa (about 50% of the yield stress). The loading for the fatigue check uses a factored down loading (70% in Australia), on the basis that the calculation should be for actual frequent loads, not one-off extremes, and that’s the loading where the 100 MPa stress range limit applies. I don’t know what the number is in the Eurocode, but it certainly wouldn’t be 80% of the yield, or anywhere close to that.

- The reason for the 50% limit not applying may be the rolled in ribs, which are pretty well universal these days. Also reinforcement is almost always has a surface layer of rust at the time of installation (at least in non-desert reasons), so they really should have checked for the effect of that.

- I’m pretty skeptical that there have been no cases of fatigue failure, although they may have been reported as corrosion failures rather than fatigue.

You can see from this chart that steels are still considered the strongest metals.

Toughness and strength seem to be anti-correlated for high alloy steels, see above. I’d like to see individual steel compositions plotted on a chart like this.

Maraging steels are clearly the strongest (bulk steel) from the chart below, but have low toughness.

What’s the relationship between kJ/m^2 on the top chart and MPa m^0.5 on the bottom chart? They are different units, differing by a factor of m^0.5.

According to Wikipedia, units of toughness are MPa or kJ/m^3, not in agreement with either of the units used on the charts.
Units of “fracture toughness” on the other hand are given by wikipedia as MPa m^0.5 or kJ/m^2.5.

So what’s with the units kJ/m^2 on the top chart? They should not be used, although I see it used in a publication by CERN. I have a materials science textbook here that has similar charts to the top chart, even to the same colouring scheme, but it uses MPa m^1/2 for fracture toughness.

LOL. I just realised. The materials science textbook I have is by Ashby. Which was the original source of the “Ashby plot”, which includes all charts of this type.

Databases for fracture toughness of steels seem to be off web, in places such as “Structural alloys handbook” (1985) and “The ASM Metals Handbook”. Volume 1 (‘Irons, steels and high-performance alloys’) and Volume 3 (“Stainless steels, tool materials and special-purpose metals’).