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4 development direction of special steel bearing steel

Bearings are widely used in mining machinery, precision machine tools, metallurgical equipment, heavy equipment and high-end cars and other major equipment fields, as well as wind power generation, high-speed rail motor cars and aerospace and other emerging industries. The bearings produced in China are mainly medium and low-end bearings and small and medium-sized bearings, which are characterized by low-end surplus and high-end lack. Compared with foreign countries, there is a big gap in high-end bearings and large bearings. China’s high-speed railway passenger car special supporting wheelset bearings all need to be imported from abroad. For the key bearings used in aerospace, high-speed railway, high-end cars and other industrial fields, there is a big gap between China’s bearings and the advanced level in service life, reliability, DN value and bearing capacity. For example, the service life of foreign automobile gearbox bearings is the lowest of 500000 km, while the service life of domestic similar bearings is about 100000 km, with poor reliability and stability.
Aviation
As a key basic component of aero-engine, the second generation aero-engine bearing with thrust ratio of 15-20 is being developed abroad, which is ready to be assembled into the fifth generation fighter around 2020. In the past 10 years, the United States has developed the second generation of bearing steel for aero-engine, and the representative steels are css-42l with high strength and corrosion resistance at 500 ℃ and x30 (cronidur30) with high nitrogen and rust resistance at 350 ℃. China is developing the second generation of bearing steel for aero-engine.
Automobile
For automotive hub bearings, the first and second generation of hub bearings (ball bearings) are widely used in China, while the third generation of hub bearings have been widely used in Europe. The main advantages of the third generation hub bearings are reliability, short payload spacing, easy installation, no adjustment, compact structure, etc. At present, most of the imported vehicles in China adopt this kind of lightweight and integrated hub bearing.
Railway vehicles
At present, China’s railway heavy haul train bearings are made of domestic ESR g20crni2moa carburized steel, while foreign countries have applied the vacuum degassing smelting technology, inclusion homogenization technology (IQ steel), ultra long life Steel Technology (TF steel), fine heat treatment technology, high purity bearing steel (EP steel) and other technologies Surface super hardening treatment technology and advanced sealing lubrication technology are applied to the production and manufacturing of bearings, which greatly improves the service life and reliability of bearings. The quality of ESR bearing steel in China is not only low, but also the cost is 2000-3000 yuan / ton higher than that of vacuum degassing steel. In the future, China needs to develop ultra-high purity, fine-grained, homogenized and stable quality vacuum degassing bearing steel to replace the current ESR bearing steel.
Wind power and energy
For wind turbine bearings, at present, China has not been able to produce high-tech spindle bearings and speed increaser bearings, basically relying on imports, and the localization of bearings for wind turbine units above 3MW has not been solved. In order to improve the strength, toughness and service life of wind turbine bearings abroad, a new type of special heat treatment steel SHX (40crsimo) is used. For yaw and variable pitch bearings, the depth of hardened layer, surface hardness, width of soft belt and surface crack are controlled by surface induction hardening heat treatment; Carbonitriding is used for speed increaser bearing and main shaft bearing, so that more stable volume fraction of retained austenite (30% – 35%) and a large number of fine carbides and carbonitrides can be obtained on the surface of parts, and the service life of bearing under pollution lubrication condition is improved.
In order to improve the service life and operation accuracy of rolling mill bearings, it is necessary to research and develop ultra-high purity vacuum degassing smelting of GCr15SiMn and g20cr2ni4 bearing steels for rolling mill and large austenite mass control heat treatment of bearing surface in the future. NSK and NTN have developed the surface austenite strengthening technology respectively, that is, TF bearing and WTF bearing have been developed by increasing the surface austenite content, so that the service life of bearing has been increased by 6-10 times.

The future R & D direction of bearing steel in China is mainly reflected in four aspects:
One is economic cleanliness: on the premise of considering economy, further improve the cleanliness of the steel, reduce the content of oxygen and titanium in the steel, so that the mass fraction of oxygen and titanium in the bearing steel is less than 6 × 10-6 and 15 × The content and size of inclusions in the steel are reduced and the distribution uniformity is improved.
The second is the refinement and homogenization of microstructure: through the application of alloying design and controlled rolling and cooling process, the uniformity of inclusions and carbides can be further improved, the network and band carbides can be reduced and eliminated, the average size and maximum particle size can be reduced, and the average size of carbides can be less than 1 μ The goal of M; The grain size of the matrix is further improved, and the grain size of the bearing steel is further refined.
The third is to reduce macrostructure defects: further reduce the central porosity, central shrinkage and central composition segregation in bearing steel, and improve the uniformity of macrostructure.
Fourth, high toughness of bearing steel: through new alloying, hot rolling process optimization and heat treatment process research, improve the toughness of bearing steel.

How to anneal spring steel

The purpose of spring steel annealing is to reduce the material stress, otherwise there will be barbed cracks during winding. During annealing, the material must be isolated from the air, otherwise surface decarburization will occur.
Annealing is a heat treatment process of heating spring steel to appropriate temperature, holding for a certain time, and then cooling slowly. Annealing is mainly used for casting, forging, welding blanks or semi-finished parts, for preparation of heat treatment. Pearlite structure was obtained after annealing.

The main purpose of annealing is to soften spring steel for cutting; Eliminate internal stress to prevent workpiece deformation; Refine the grain, improve the structure, prepare for the final heat treatment of parts. According to the composition and annealing purpose of spring steel, the common annealing methods are complete annealing, isothermal annealing, spheroidizing degradation, homogenizing annealing, stress relief annealing and recrystallization annealing.

1. Complete annealing and isothermal annealing
Complete annealing is to heat the spring steel to 30-50 ℃ for a certain period of time, cool it to below 600 ℃ with the furnace, and then air cool it out of the furnace. It is mainly used for casting and forging of hypoeutectoid spring steel, and sometimes for welding structure. The purpose of complete annealing is to refine grains, eliminate overheated fabric, reduce hardness and improve machinability. Complete annealing is not suitable for hypereutectoid spring steel in order to avoid secondary cementite precipitation along austenite grain boundary in network form, which will bring adverse effects on cutting and subsequent heat treatment. Complete annealing is time-consuming, and isothermal annealing is often used in production. The heating temperature of isothermal annealing is the same as that of complete annealing, but the cooling mode is different. Isothermal annealing is to cool rapidly to a certain temperature below, isothermal for a certain time to make austenite transform into pearlite structure, and then air cooling. For some alloy spring steels with stable austenite, the annealing cycle can be greatly shortened by isothermal annealing.

2. Spheroidizing annealing
Spheroidizing annealing is to heat the spring steel to 20-40 degrees, fully keep the temperature, and then cool it to below 600 degrees with the furnace for air cooling. When the spheroidizing annealing passes through AR1 temperature, the cooling should be slow enough to spheroidize eutectoid cementite. Spheroidizing annealing is mainly used for hypereutectoid spring steel. The purpose is to spheroidize the cementite in the spring steel, so as to reduce the hardness of the spring steel, improve the machinability, and prepare the structure for the later heat treatment process. If there is serious cementite network in the original structure of spring steel, normalizing should be carried out before spheroidizing annealing to ensure the effect of spheroidizing annealing.

3. Homogenization annealing (diffusion annealing)
Homogenization delayed ignition is to heat the spring steel to a temperature slightly lower than the solidus temperature (150-300 ℃), keep it for a long time (10h-15h), and then cool it with the furnace, so as to homogenize the chemical composition and microstructure of the spring steel. The energy consumption of homogenization annealing is high and the grain size is easy to coarsen. In order to refine the grain, complete annealing or normalizing should be carried out after homogenization annealing. This process is mainly used for alloy spring steel ingots, castings or forging billets with high quality requirements.

4. Stress relief annealing and recrystallization annealing
Stress relief annealing, also known as low temperature annealing, is to heat the spring steel to a certain temperature below AC1 (generally about 500-600 ℃) for a certain period of time, and then cool with the furnace. The purpose is to eliminate the residual stress of casting, forging, welding and cold stamping parts.
Recrystallization annealing is mainly used for spring steel after cold deformation, which can soften the hardening phenomenon caused by cold deformation.

China steel price Increasing

Since the beginning of this year, the rapid rise of steel prices has aroused social concern. What are the reasons for the rise in steel prices? What are the derivative effects of the rise in steel prices? What will be the trend of steel price in the future?

Steel price “roller coaster” led to a surge in the cost of downstream industries.

According to the monitoring of China Iron and Steel Industry Association, from the beginning of this year to the middle of May, the domestic steel price went out of a wave of rising market. As of May 14 this year, the domestic steel composite price index (CSPI) was 174.81 points, up 40.4% from the end of last year; The long timber price index was 179.56 points, up 42.2% from the end of last year; The price index of sheet metal was 175.07 points, up 38.7% from the end of last year, reaching a historical high of more than 10 years.

The reason for this round of steel price rise is mainly the spillover effect brought by the expansionary quantitative easing policy of developed economies in Europe and the United States, which gave birth to the expectation and trend of raw material price rise in the world. At the same time, China’s economic development is resilient, exports are strong, manufacturing investment is supported, and consumption continues to recover marginally, which also drives the growth of steel demand and drives up steel prices.

“The rise of iron ore is larger than that of steel price, which is an important factor in the rise of steel price. The financial attribute of iron ore futures makes the market speculative, which promotes the continuous rise of steel price.”measures such as double control of production capacity and output, environmental protection and production restriction, and steel de production capacity, etc, It also increases the market’s expectation of the reduction of steel supply and the rise of steel price.
In the face of steel prices continue to hit new highs, the cost pressure of downstream steel industry is obvious, not only facing the difficulty of increasing costs, but also the more serious problem is the shortage of funds and increased occupation. Some downstream enterprises have weak ability to transfer costs. The rise of steel prices has caused a substantial reduction in profits and even losses, and the willingness to purchase steel will gradually decrease.
It is worth noting that the adverse effects of the recent rising commodity prices have attracted the attention of the relevant state departments.https://otaialloysteel.com/contact/

On May 12, the executive meeting of the State Council called for tracking and analyzing the situation and market changes at home and abroad, doing a good job in market regulation, and coping with the rapid rise of commodity prices and its associated effects. On May 19, the executive meeting of the State Council proposed that we should do a good job in ensuring the supply and stabilizing the price of bulk commodities, curb the unreasonable price rise, and strive to prevent the transmission to consumer prices. On May 26, the executive meeting of the State Council demanded that we should do a good job in ensuring the supply and stabilizing the price of bulk commodities, and crack down on hoarding and driving up prices. At the same time, on May 23, the national development and Reform Commission, the Ministry of industry and information technology, the state owned assets supervision and Administration Commission, the General Administration of market supervision and the China Securities Regulatory Commission jointly interviewed key enterprises with strong market influence in iron ore, steel, copper, aluminum and other industries. They were required to take the lead in maintaining the market price order of bulk commodities, not to collude with each other to manipulate market prices, fabricate and disseminate price increase information, and not to hoard Bid up prices.
Affected by this, since May 20, all kinds of steel products in the national steel market have decreased by more than 10%. On May 21, the domestic steel composite price index was 154.34 points, which has fallen back to the level at the beginning of May.
Steel and other commodity prices fell, mainly due to the government’s strict supervision measures. This shows that the rapid rise of commodity prices in the early stage is due to the dislocation of supply and demand, as well as the market’s follow-up speculation and even bid up prices.
Recently, the prices of raw materials, including steel, have risen sharply, and some downstream industries are under great pressure. The sharp rise in prices is likely to be accompanied by a sharp decline. The market trend in may fully illustrates this phenomenon. At present, the price of steel has fallen back to the level before the May Day holiday, but the price of raw materials has not fallen at the same time. In fact, it is unfavorable for iron and steel enterprises.
Therefore, iron and steel enterprises should take the lead in maintaining the price order of steel market, and do not engage in low price dumping and vicious competition; Do not collude with each other to manipulate the market price, fabricate and spread price information; Do not hoard and drive up prices. At the same time, it is necessary to adjust the export strategy, put the starting point and foothold on meeting the domestic demand, give play to the role of supplement and adjustment of import and export, and adapt to the new development pattern of iron and steel import and export.
At present, from the domestic market situation, there is no overall and trend change in the supply and demand of iron and steel products, and the steel price does not have the basis for continuous and substantial rise. From the supply side, the crude steel output reduction and environmental protection supervision are about to start, and it is difficult for the crude steel output to increase significantly in the later stage; From the demand side, due to the rapid rise of steel prices since April, shipbuilding, home appliances and other downstream steel industries can not bear the pressure brought by the high consolidation of steel prices, and it is difficult for steel prices to rise significantly in the later period.
Industry insiders believe that from an international perspective, the world economic recovery is still unstable and unbalanced, there is no overall and trend change in the supply and demand of bulk commodities, and their prices do not have the basis for long-term rise.
In the future, with the slowing down of macro-economy, the market demand side will return to a reasonable level. With the gradual narrowing of domestic and international price gap, the export tax rebate adjustment policy will gradually play a role, the domestic supply will increase, and the steel price will gradually return to a reasonable range.
(Source: People.cn)

Shipment to South Africa

3 steel grades suitable for making gear

Gear steel is the general name of steel used in gear manufacturing. Gear is one of the most widely used mechanical components, and is widely used in mechanical transmission. There are many types of gears, such as spur gear, chain gear, synchronous pulley, helical gear, internal gear, rack, straight bevel gear, arc bevel gear, zero bevel gear, staggered spiral gear, worm gear, etc.

Gear steel is a key material with high requirements for special alloy steel used in automobile, railway, ship and engineering machinery. Gear material needs strong bending fatigue strength and contact fatigue strength, and the tooth surface should have enough hardness and wear resistance, and the tooth core should have certain strength and toughness. Gears are usually made of forged steel, except for foundry plants with too large size (Dia > 400-600mm) or suitable for complex structures and shapes.
Carbon steel or alloy steel with carbon content of 0.15-0.6% is usually used in gear applications. The Microalloy Elements in gear steel can improve the toughness, impact resistance, wear resistance and adhesion of the material, and the mechanical properties of the material can also be improved by heat treatment or chemical heat treatment. Alloy gear steel usually does not include low carbon alloy steel, such as 15CrMo, 20Cr, etc. and medium carbon alloy steel: 40Cr, 42CrMo, 35CrMo, etc.

15CrMo
Carburizing surface quenching treatment is generally used to pay attention to the strength or toughness of parts or parts that need to bear a lot of friction, such as cylinder piston, spindle, gear, bolt, shaft, etc. It is used to make profile less than 30mm under high speed, medium load or heavy load, impact and friction of important parts; for example, crosshead of gear, ring gear and gear shaft.
In the automotive industry, the cross-section used is less than 30mm; important carburizing parts bear high speed or heavy load and impact; for example, gears, shaft gear rings, gear shafts, sliding bearing spindles, crossheads, claw clutches, worm, etc

25CrMo4
The alloy structural steel 25crmo4 (ASTM 4118) has high hardenability, no temper brittleness, good weldability, little cold crack tendency, good machinability and cold strain plasticity.
25CrMo4 gear steel is used in general conditions or under carburizing quenching conditions, which is used for manufacturing corrosive medium with working temperature lower than 250 ℃, high pressure pipe and various fasteners working with medium containing hydrogen nitrogen mixture, higher carburizing parts and automobile gears, various special wear-resistant parts, such as aircraft, shaft, high pressure pipe and various fasteners.

42CrMo4
42CrMo4 (ASTM 4140) is a medium carbon chromium molybdenum alloy steel. Chromium content provides good hardness permeability, molybdenum element provides hardness uniformity and high strength. The alloy well balances strength, toughness and wear resistance. It has the following advantages: stable composition, less harmful elements, high purity of steel, small decarbonization layer, less surface defects, etc., and easy to process under heat treatment conditions, with good ductility and high temperature stress resistance. This material is widely used in the production of high-strength steel fasteners, such as engine, mould, motor, gear, transmission parts, shaft, gear, arm, cold forging, screw products.

In addition, ASTM 4320, 4340, 8615, 8617, 8620, 8622, 9840 (https://otaialloysteel.com/products/alloy-steel/)and so on can also be used for gear purposes. As common alloy carburizing and bearing steel, they are mainly used as materials for automobile bearings, transmission shafts, gears, screws, tool parts and other impact resistant and wear-resistant parts. The surface after carburization has high hardness, wear resistance and contact fatigue strength, while the core still maintains good toughness and can bear high impact load.

86CrMoV7 cold work steel

86CrMoV7 steel belongs to cold work alloy tool steel. 86CrMoV7 features for its high strength and hardness, good weldability, toughness, machinability and so on.

86CrMoV7 material equivalent steel grades:

86CrMoV7 mechanical properties:

Yield Strength  (MPa):≥446

Tensile Strength (MPa):≥329

Impact KV/Ku (J):32

Elongation A (%): 41

Reduction Z (%):24

The consequences of buying inferior Cr12MoV

Cr12MoV tool steel has high hardenability. The cross section is 300 ~ 400mm. It can harden completely. It can keep good hardness and wear resistance at 300 ~ 400 ℃.

Cr12MoV can be used to make various moulds and tools with large cross section, complex shape and bearing large impact load. It has the characteristics of wear resistance, hardenability, micro deformation, high thermal stability and high bending strength. It is second only to high speed steel. Cr12MoV is an important material for die cold heading. The consumption of cold working die steel(https://otaialloysteel.com/products/tool-steel/)ranks first.

In fact, some unreliable suppliers may, regardless of the interest of the customers, cheat customers with inferior products. These dishonest actions not only disrupt the market. At the same time, it also has a serious impact on customers.

The consequences for end users who purchase these crude Cr12MoV cold work tool steels are as follows:
1) The microstructure of inferior Cr12MoV die steel is seriously segregated. Because of the poor processing performance, drilling and tapping difficulties are often encountered.
2) The deformation of heat treatment is large and the risk of cracking and bending is high. It can’t guarantee the stability of the mold size, affect the appearance of the mold and even scrap.
3) There are many impurities in Cr12MoV die steel after scrap renovation. It makes the mold produce poor red hardness at high temperature. The hardness of the die decreases quickly and the knife edge is easy to wear.
4) The purity of die steel is poor and there are many non-metallic inclusions. The impact toughness of the die is poor, and the knife edge is easy to collapse and fall.

1.3537 bearing steel

1.3537 steel is bearing steel. Small amount of Chromium and trace amounts of Molybdenum provides for some carbide formation, and it can hold decent polished edge.It has characteristics similar to 100Cr6 steel(1.3537 vs 100Cr6). The addition of molybdenum guarantees toughness for diameters up to 200mm.it has good wear resistance, with good non-deformability.

1.3537 Steel equivalent standards:

1.3537 steel  mechanical properties:
Hardness in spheroidized annealing condition +AC: < 217 HB
Hardness in spheroidized annealing condition after drawing +AC+C: < 251 HB
Hardness of tubes and sleeves <321 HB
Density ρ 7,79 g/cm3

1.3537 steel Application

1.3537 works better  for small to medium knives, after appropriate heat treatment might do well in a larger blade. It’s suitable for the construction of bearings,cylinders, small rolling mills, knives, etc.

1.7131 carburized steel

EN 1.7131 steel (16MnCr5 material) is an European standard carburized steel (case hardening steel) with good hardenability and machinability. For larger cross-section parts, high surface hardness and wear resistance can be obtained after heat treatment, and low-temperature impact toughness is also high.

1.7131 steel – Equivalent Materials:

1.7131 steel Mechanical Properties:

Yield Strength Rp0.2 (MPa):≥461
Tensile Strength Rm (MPa):882
Impact KV/Ku (J):21
Elongation A (%):24
Reduction Z (%):41
Brinell hardness (HBW):413

46Mn7 alloy structural steel

46Mn7 is a kind of moderate strength alloy structural steel, as a carbon quenched and tempered steel, its strength, abrasion resistance and hardenability are high. After quenching and has good mechanical properties, machinability is still good.

46Mn7 equivalent steel grades:

46Mn7 Mechanical Properties:

Tensile strength σb (MPa): ≥885

Yield strength σs (MPa): ≥735

Elongation δ5 (%): ≥10

Impact energy Akv (J): ≥47

32NiCrMo14-5 Alloy steel

32NiCrMo14-5 has good corrosion resistance and high strength. It is often used as thin plate and has good welding performance.

32NiCrMo14-5  Equivalent Steel Grades:

32NiCrMo14-5 Mechanical property:

Yield Strength R_p0.2 (MPa):649

Tensile Strength R_m (MPa):814

Impact KV/Ku (J):13

Elongation A (%):32

Reduction Z (%):11

52CrMoV4 spring steel

52CrMoV4 spring steel,its strength and hardenability is strengthened not only by chromium and vanadium – as in the case of 51CrV4 / AISI 6150, but also by molybdenum. Molybdenum strengthens the solution during heat treatment, while chromium and vanadium form carbides that improve the hardness of the material during tempering.

Equivalent Materials to  52CrMoV4 steel:

52CrMoV4 Physical properties:

• Density: 7,79 g/cm³
• Specific heat capacity: 470 J/kg-K
• Melting temperature: 1420-1460 °C
• Thermal conductivity: 44 W/m-K