Kic lottery analysis
The selection of spring material should be determined according to the nature of spring load, stress state, stress, working temperature, environmental medium, service life, requirements for electrical conductivity and magnetic conductivity, technological performance, material source and price.
When determining the cross-sectional shape and size of materials, priority should be given to the series sizes specified in national standards and ministerial standards, and materials with non-standard series specifications should be avoided as far as possible.
Small and medium-sized springs, especially spiral tension springs, should give priority to reinforced steel wire, lead bath isothermal cold-drawn steel wire and oil-quenched tempered steel wire, which have high strength, good surface quality, higher fatigue performance than ordinary quenched and tempered steel wire, simple processing, good manufacturability and stable quality.
The carbon spring steel wire and piano steel wire produce large residual stress after cold drawing. The residual stress of spring after machining is large, and the dimension changes greatly after tempering, so the dimension accuracy is difficult to control. The oil-quenched tempered steel wire is prepared and strengthened after the steel wire is drawn to the specified size, and there is basically no residual stress. After tempering at low temperature, the dimension of the formed spring has little change, and its thermal stability is better than that of cold-drawn strengthened steel wire.
For large and medium-sized springs, cold-drawn materials or polished steel after cold-drawing should be selected for high load accuracy and stress. For springs with low load accuracy and stress, hot rolled steel can be selected.
Generally, flat steel of brands such as 55Si2Mn, 60Si2MnA, 55SiMnVB, 55SiMnMoV, 60crmmn and 60CrMnB is selected for leaf springs.
The material section of spiral spring should be mainly circular. Square and rectangular cross-section materials have strong bearing capacity, good impact resistance and miniaturization of springs, but there are few sources of materials. And the price is high, except for special needs, generally try not to choose this material. In recent years, round steel wire has been developed, and trapezoidal steel wire has been replaced by flat rolling, which has achieved good results.
Spring materials working at high temperature require good thermal stability, relaxation or creep resistance, oxidation resistance and certain medium corrosion resistance.
When the working temperature of the spring increases, the elastic modulus of the spring material decreases, which leads to the decrease of stiffness and bearing capacity. Therefore, the spring working at high temperature must know the change rate (value) of elastic modulus and calculate the influence of the decline of spring bearing capacity on service performance. According to GB 1239, when the working temperature of ordinary spiral springs exceeds 60℃, the shear modulus should be corrected, and the formula is: Gt=KtG, where g is the elastic modulus at room temperature; Gt- shear modulus at working temperature t; KT- temperature correction coefficient is selected according to Table 2-98.
The spring material used at low temperature should have good low temperature toughness. Carbon spring steel wire, piano steel wire and austenitic stainless steel spring steel wire such as 1Cr 18Ni9, copper alloy and nickel alloy have good low-temperature toughness and strength.
Table 2-98 Temperature Correction Coefficient Kt
trademark
Operating temperature/℃
≤60
150
200
250
dunlin
50CrVA
60Si2Mn
1Cr 18Ni9Ti
0Cr 17Ni7A 1
QBe2
1
1
1
1
1
0.96
0.99
0.98
0.95
0.95
0.95
0.98
0.94
0.94
0.94
0.94
0.98
0.90
0.92
0.92
At low temperature, the brittleness of materials is very sensitive to surface defects, so there are strict requirements for the surface quality of materials.
At low temperature, the corrosion degree of environmental media to materials is much smaller than that in greenhouse, while cadmium plating and zinc plating are easy to cause cold brittleness.
At low temperature, the elastic modulus and expansion coefficient of the material change little, which can be ignored in design.
The hardness (i.e. strength) of the spring made of spring steel should be selected according to the bearing nature and stress of the spring. However, hardness has a great relationship with plane strain fracture toughness.
It can be seen from the curve relationship that with the increase of hardness, the value of plane strain fracture toughness (KIC) decreased significantly. That is to say, when determining the hardness value of the spring, the lower the hardness value, the better, on the premise of meeting the requirements of the spring characteristics.
When selecting spring materials, attention should be paid to the hardenability of steel. Whether the cross section of the spring material is hardened or not has a great relationship with the quality of the spring.
Generally, copper and gold materials are used as the conductor of the spring itself or the spring that works in the environment of water (including seawater) and steam and under the condition of variable humidity.
Springs working in acid contact and other corrosive media are generally made of corrosion-resistant materials, such as stainless acid-resistant steel or nickel alloy. The spring used in general environmental medium conditions is made of ordinary spring steel, and the surface of the spring is coated with antirust coating or electroplated (galvanized, cadmium plated and copper plated) to prevent corrosion.
In order to ensure that the accuracy of the spring used in weighing instruments is not affected by temperature changes, a constant elastic alloy with little change in elastic modulus and expansion coefficient is generally selected.
Reinforced plastics can be used for springs with light weight, insulation, anti-collision and anti-corrosion. At present, the suitable plastic spring is thermosetting reinforced plastic GFRP with epoxy resin and phenolic resin as matrix and glass fiber as reinforcement. Vibration-proof rubber can also be used to manufacture various types of rubber springs.
Examples of grades and uses of spring steel
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Examples of using license plates
Coil springs in the carriages of trains 60 and 70, round and square coil springs in general machines, and springs in small machines.
Circular helical springs and leaf springs that are subjected to vibration on railway vehicles, automobiles and tractors.
65Mn is used for all kinds of large-sized flat springs, such as buffer leaf springs, spring coils, valve springs, clutch springs, brake springs, etc. of light vehicles and cars.
The leaf spring, spiral spring and vehicle check valve spring in 55Si2M automobiles, tractors and railway vehicles are important springs working under high stress.
Front and rear springs and auxiliary springs of 55Si2MnB automobile.
60Si2Mn and
60Si2MnA leaf springs, spiral springs and check valves of safety valves on automobiles, tractors and railway vehicles are used to manufacture large and important spiral springs and parts that bear alternating loads and work under high stress.
10.50 steel is used to manufacture parts with high wear resistance, low dynamic load and impact, such as cast gears, pull rods and rollers. Manufacture small springs, digging plows on agricultural machinery, heavy mandrels and shafts, etc. , and can make castings.
1 1.55 steel is used to manufacture connecting rods, rollers, gears, leaf springs, rims, etc. It can also be used as a casting.
12.60-65 steel is used to manufacture springs, spring coils, various washers and clutches, as well as shafts, rollers and eccentric shafts in general machinery.
13.70-85 steel is used to manufacture springs and clockwork devices, steel wires for wire ropes and high-hardness parts such as plows, plowshares and rollers.
14. 15Mn-25Mn steel is used to manufacture parts with high mechanical properties in the center and need carburizing.
15.30Mn-35Mn steel is mainly used to manufacture bolts, nuts, screw rods and brake pedals. It can also be used to manufacture small parts that work under high stress, such as hooks, rings and chains on agricultural machinery.
40 Mn-45 Mn steel (16) is used to manufacture parts bearing fatigue loads, such as crankshafts and connecting rods. It can also be used as screws and nuts working under high stress.
17.50Mn-55Mn steel is used to manufacture gears, gear shafts, friction plates, rollers, springs and other parts with high wear resistance and heat treatment under high load.
18.60Mn-70Mn steel is used to make springs and plowshares.