The alloy of the element of the eighth group of the periodic table with the atomic number 26 (iron) with carbon and some other elements is commonly called steel. It has high strength and hardness, lacks ductility and viscosity due to carbon. Alloying elements increase the positive characteristics of the alloy. Nevertheless, steel is considered to be a metal material that contains at least 45% iron.
Consider an alloy such as steel P6M5, and find out what characteristics it has and in what areas it is used.
Manganese as an alloying element
Until the 19th century, ordinary steel was used to process non-ferrous metals and wood. Her cutting characteristics for this was quite enough. However, when trying to process steel parts, the tool was very quickly heated, worn out and even deformed.
The English metallurgist R. Muschett through experiments found that in order to make the alloy more durable, it is necessary to add an oxidizing agent to it, which will release excess oxygen from it. Mirror cast iron, which contained manganese, was added to cast steel . Since it is an alloying element, its percentage should not exceed 0.8%. So, P6M5 steel contains from 0.2% to 0.5% manganese.
Tungsten iron
Already in 1858, many scientists and metallurgists worked on obtaining alloys with tungsten. They knew for sure that this is one of the most refractory metals. Adding it to steel as an alloying element made it possible to obtain an alloy that could withstand high temperatures and not wear out.
Steel P6M5 contains 5.5-6.5% tungsten. Alloys with its content most often begin with the letter “P” and are called high-speed alloys. In 1858, Muschett obtained the first steel containing 9% tungsten, 2.5% manganese and 1.85 carbon. Later, adding another 0.3% C, 0.4% Cr to it and removing 1.62% Mn, 3.56% W, the metallurgist obtained an alloy called a self-propelled alloy (P6M5). In its characteristics, it is also similar to P18 steel.
Tungsten deficiency
Of course, in the 1860s, when many elements were in abundance, tungsten-added steel was considered the most durable. Over time, this element in nature becomes less and less, and the price of it increases.
From an economic point of view, adding a large amount of W to steel has become impractical. For this reason, P6M5 steel is much more popular than P18. Having looked at their chemical composition, it can be seen that the tungsten content in P18 is 17-18.5%, while in the tungsten-molybdenum alloy it is up to 6.5% maximum. In addition, up to 0.25% copper and molybdenum up to 5.3% are present in the scooter.
Other alloying elements
In addition to the above carbon, manganese, tungsten and molybdenum, P6M5 steel also contains cobalt (up to 0.5%), chromium (4.4%), copper (0.25%), vanadium (2.1%) phosphorus (0.03%), sulfur (0.025%), nickel (0.6%) silicon (0.5%). Why are they needed?
Each alloying element has its own function. For example, chromium is necessary for thermal hardening, and nickel increases viscosity. Molybdenum and vanadium virtually eliminate brittleness after tempering. Some of the alloying elements improve steel properties such as red resistance and hot hardness.
Steel P6M5, the characteristics of which we are studying, in the quenched state has a hardness of 66 HRC at a test temperature of up to 600 ° C. This means that even with strong heating, it does not lose its strength characteristics, which means that it does not wear out and does not deform.
Designation P6M5
Decoding of steel depends on how it is made, what alloying elements it includes and how much carbon it contains. Different types have their own notation. If, for example, the alloy does not contain alloying elements, then it is indicated by "St" and next to it is a number that shows the average carbon content in the steel (St20, St45).
In low-alloy alloys, first comes the percentage of carbon, and then the letters designating the chemical elements (10KHSND, 20KHN4FA). If there are no numbers near them, as in the example, it means that the content of each of them does not exceed 1%. The letter "P" in the grade of the alloy indicates that it is fast-cutting (rapid).
Next to it is a number - this is the percentage of tungsten (P9, P18), and then, letters and numbers are alloying elements and their percentage ratio. From this it follows that high-speed steel P6M5 contains up to 6% tungsten and up to 5% molybdenum.
Annealing
As a rule, the production of such an alloy is classical and will be applied to all high-speed steels. However, it should be borne in mind that in order for the tungsten-molybdenum alloy to be really strong, hard and wear-resistant, it must be annealed.
If other brands, for example, St45, lose their strength properties during annealing, then high-speed, on the contrary, improve and become stronger and harder. That is why P6M5 is annealed before quenching. How does this happen?
Rolled steel (for example, a sheet of “steel P6M5”) with a thickness of about 22 mm is heated in a special furnace to a temperature of 870 ° C, then cooled to 800 ° C, and then heated again. There can be about 10 such cycles.
In addition, after the fifth, it is necessary to gradually reduce the temperature. For example, heat again but to 850 ° C, cool to 780 ° C. And so on until it reaches the 600 ° C mark.
Such a complex annealing process is explained by the presence of austenite grains in alloyed alloys, which is extremely undesirable. Heating and cooling allows maximum dissolution of alloying elements, but austenite will not grow.
If the temperature regime is not maintained and annealed at a temperature of more than 900 ° C, then an increased amount of austenite is formed in the alloy and the hardness decreases. Cooling is recommended using oil baths, this will protect the tungsten-molybdenum alloy from cracks and punctures.
A method of manufacturing P6M5
Of course, like any other alloy, P6M5 is made in a different assortment. So, in some workshops high-speed hot steel is poured into ingots. In another production, it is rolled hot. To do this, heated ingots are pressed between the shafts of the rolling mill. Its resulting shape will depend on the shape of the shafts themselves.
Steel grade P6M5 is widely used for parts operating at high temperatures. For this reason, in recent years, a very popular method of manufacturing steel is powder.
When casting hot steel into ingots, carbides are very rapidly precipitated from the melt. In some areas, they form uneven clusters, which are subsequently the site of crack initiation.
In powder manufacturing, a special powder is used, which contains all the necessary components. It is sintered in a special vacuum container with high temperature and pressure. This helps to ensure that the material is homogeneous.
Application
P6M5 steel is widely used in various industries. Most often it is used for the manufacture of cutting tools for turning, milling and drilling machines in metallurgy. This is due to its characteristics of strength, heat resistance, hardness.
As a rule, drills, taps, dies, cutters are made from it. P6M5 steel cutting tool is excellent for cutting at high speeds, in addition, it does not require cooling with coolant. A knife made of P6M5 steel is also not uncommon.
Since the tungsten-molybdenum alloy has high hardness and high viscosity, it is often used to make knives with strong handles and beautiful patterns.
The alloying elements in the required amount allowed us to create a unique steel, which practically does not rust and has good grindability. This allows for metalworking to increase the cutting speed by 4 times.
It is also used for the production of heat-resistant ball bearings operating at high speed at a temperature of 500-600 ° C. Analogs of the R6M5 alloy are R12, R10K5F5, R14F4, R9K10, R6M3, R9F5, R9K5, R18F2, 6M5K5. If tungsten-molybdenum alloys, as a rule, are used for the manufacture of tools for roughing (drills, mills), then vanadium (P14F4) for finishing (reamers, broaches). On each cutting tool, there is always a marking that allows you to find out what alloy it is made of.